Condensed Matter

19 pages, 3452 KiB

Open AccessArticle

Investigating the Individual Performances of Coupled Superconducting Transmon Qubits

by Halima Giovanna Ahmad, Caleb Jordan, Roald van den Boogaart, Daan Waardenburg, Christos Zachariadis, Pasquale Mastrovito, Asen Lyubenov Georgiev, Domenico Montemurro, Giovanni Piero Pepe, Marten Arthers, Alessandro Bruno, Francesco Tafuri, Oleg Mukhanov, Marco Arzeo and Davide Massarotti

Condens. Matter 2023, 8(1), 29; https://doi.org/10.3390/condmat8010029 - 21 Mar 2023

Cited by 2 | Viewed by 2154

Abstract

The strong requirement for high-performing quantum computing led to intensive research on novel quantum platforms in the last decades. The circuital nature of Josephson-based quantum superconducting systems powerfully supports massive circuital freedom, which allowed for the implementation of a wide range of qubit [...] Read more.

The strong requirement for high-performing quantum computing led to intensive research on novel quantum platforms in the last decades. The circuital nature of Josephson-based quantum superconducting systems powerfully supports massive circuital freedom, which allowed for the implementation of a wide range of qubit designs, and an easy interface with the quantum processing unit. However, this unavoidably introduces a coupling with the environment, and thus to extra decoherence sources. Moreover, at the time of writing, control and readout protocols mainly use analogue microwave electronics, which limit the otherwise reasonable scalability in superconducting quantum circuits. Within the future perspective to improve scalability by integrating novel control energy-efficient superconducting electronics at the quantum stage in a multi-chip module, we report on an all-microwave characterization of a planar two-transmon qubits device, which involves state-of-the-art control pulses optimization. We demonstrate that the single-qubit average gate fidelity is mainly limited by the gate pulse duration and the quality of the optimization, and thus does not preclude the integration in novel hybrid quantum-classical superconducting devices. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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15 pages, 2932 KiB

Open AccessArticle

Electrical Manipulation of Spin-Dependent Anisotropy of a Dirac Cone in a Graphene Superlattice with Alternating Periodic Electrostatic and Exchange Fields

by Pattana Somroob and Watchara Liewrian

Condens. Matter 2023, 8(1), 28; https://doi.org/10.3390/condmat8010028 - 18 Mar 2023

Cited by 1 | Viewed by 1112

Abstract

We studied the spin-dependent behavior of the electronic properties of alternating periodic potentials applied to finite and infinite graphene superlattices coupled with tunable electrostatic and exchange fields. The band structures were evaluated using the transfer matrix approach. The results of tuning the coupled [...] Read more.

We studied the spin-dependent behavior of the electronic properties of alternating periodic potentials applied to finite and infinite graphene superlattices coupled with tunable electrostatic and exchange fields. The band structures were evaluated using the transfer matrix approach. The results of tuning the coupled electrostatic potential and exchange field showed that the spin-dependent anisotropy of a Dirac cone depends on the difference between the amplitude of periodically modulated coupling. Spin-dependent collimation occurs when the modulations become zero-average potentials with the ratio of both periodically modulated strengths equals one, in which one spin can be moved freely, but the other one is highly collimated. In addition, we find that the number of extra Dirac points in the infinite superlattice is spin-dependent. In terms of spin-ups, their number increases with an increase in the strength of both modulated fields. To ensure this calculation, we also compute the conductance of finite periodic modulation at zero energy. It is shown that the peaks of the conductance occur when the extra Dirac point emerges. This result may be utilized to design graphene-based devices with highly spin-polarized collimators. Full article

(This article belongs to the Section Quantum Materials)

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13 pages, 5762 KiB

Open AccessArticle

Complex Functions, Multipoles and Light Polarization in a Ferrocell

by Alberto Tufaile and Adriana Pedrosa Biscaia Tufaile

Condens. Matter 2023, 8(1), 27; https://doi.org/10.3390/condmat8010027 - 15 Mar 2023

Viewed by 1493

Abstract

Ferrofluid is a magnetic fluid that undergoes structural changes when subjected to a magnetic field, with the formation of arrays of nanoparticles aligned with the field. Using polarized light passing through the ferrofluid, we can observe the formation of light patterns for different [...] Read more.

Ferrofluid is a magnetic fluid that undergoes structural changes when subjected to a magnetic field, with the formation of arrays of nanoparticles aligned with the field. Using polarized light passing through the ferrofluid, we can observe the formation of light patterns for different magnetic field configurations. Using a device known as a Ferrocell, we present a study relating magnetic fields and complex functions. Our main issue here is to know what the relationship is between fundamental multipole expressions and light polarization patterns obtained with the ferrofluid. We have applied multipole fields to the Ferrocell, observed the light patterns, and compared them with multipoles of complex functions. We interpreted other luminous polarization patterns as the sum of these fundamental multipoles. Full article

(This article belongs to the Section Magnetism)

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8 pages, 518 KiB

Open AccessArticle

Effect of Transverse Confinement on a Quasi-One-Dimensional Dipolar Bose Gas

by Stefania De Palo, Edmond Orignac, Roberta Citro and Luca Salasnich

Condens. Matter 2023, 8(1), 26; https://doi.org/10.3390/condmat8010026 - 05 Mar 2023

Cited by 1 | Viewed by 1008

Abstract

We study a gas of bosonic dipolar atoms in the presence of a transverse harmonic trapping potential by using an improved variational Bethe ansatz, which includes the transverse width of the atomic cloud as a variational parameter. Our calculations show that the system [...] Read more.

We study a gas of bosonic dipolar atoms in the presence of a transverse harmonic trapping potential by using an improved variational Bethe ansatz, which includes the transverse width of the atomic cloud as a variational parameter. Our calculations show that the system behavior evolves from quasi-one dimensional to a strictly one-dimensional one by changing the atom–atom interaction, or the axial density, or the frequency of the transverse confinement. Quite remarkably, in the droplet phase induced by the attractive dipolar interaction the system becomes sub-one dimensional when the transverse width is smaller than the characteristic length of the transverse harmonic confinement. Full article

(This article belongs to the Special Issue Fluctuations and Highly Non-linear Phenomena in Superfluids and Superconductors VII)

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9 pages, 1939 KiB

Open AccessArticle

Exploring the Ultrafast Charge-Transfer and Redox Dynamics in Layered Transition Metal Oxides

by Guannan Qian, Xiaobiao Huang, Jun-Sik Lee, Piero Pianetta and Yijin Liu

Condens. Matter 2023, 8(1), 25; https://doi.org/10.3390/condmat8010025 - 05 Mar 2023

Viewed by 1557

Abstract

The rapid development and broad deployment of rechargeable batteries have fundamentally transformed modern society by revolutionizing the sectors of consumer electronics, transportation, and grid energy storage. Redox reactions in active battery cathode materials are ubiquitous, complicated, and functionally very important. While a lot [...] Read more.

The rapid development and broad deployment of rechargeable batteries have fundamentally transformed modern society by revolutionizing the sectors of consumer electronics, transportation, and grid energy storage. Redox reactions in active battery cathode materials are ubiquitous, complicated, and functionally very important. While a lot of effort has been devoted to investigating redox heterogeneity and its progressive evolution upon prolonged battery cycling, the ultrafast dynamics in these systems are largely unexplored. In this article, we discuss the potential significance of understanding redox dynamics in battery cathodes in the ultrafast time regime. Here, we outline a conceptual experimental design for investigating the ultrafast electron transport in an industry-relevant layered transition metal oxide battery cathode using a plasma-acceleration-based X-ray free-electron laser (FEL) facility. Going beyond the proposed experiment, we provide our perspectives on the use of compact FEL sources for applied research, which, in our view, is an area of tremendous potential. Full article

(This article belongs to the Special Issue Experimental Ideas for Novel FEL Facilities Based on Plasma Acceleration)

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9 pages, 443 KiB

Open AccessArticle

Using Quantum Nodes Connected via the Quantum Cloud to Perform IoT Quantum Network

by Doaa Subhi and Laszlo Bacsardi

Condens. Matter 2023, 8(1), 24; https://doi.org/10.3390/condmat8010024 - 23 Feb 2023

Viewed by 1628

Abstract

Computer networks consist of millions of nodes that need constant protection because of their continued vulnerability to attacks. Classical security methods for protecting such networks will not be effective enough if quantum computers become widespread. On the other hand, we can exploit the [...] Read more.

Computer networks consist of millions of nodes that need constant protection because of their continued vulnerability to attacks. Classical security methods for protecting such networks will not be effective enough if quantum computers become widespread. On the other hand, we can exploit the capabilities of quantum computing and communications to build a new quantum communication network. In this paper, we focused on enhancing the performance of the classical client–server Internet application. For this sake, we introduced a novel Internet of Things (IoT) quantum network that provides high security and Quality of Service (QoS) compared with the traditional IoT network. This can be achieved by adding quantum components to the traditional IoT network. Quantum counterpart nodes, channels, and servers are used. In order to establish a secure communication between the quantum nodes and the quantum server, we defined a new Communication Procedure (CP) for the suggested IoT quantum network. The currently available quantum computer has a small qubit size (from 50 to 433 qubits). The proposed IoT quantum network allows us to overcome this problem by concatenating the computation efforts of multiple quantum nodes (quantum processors). Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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10 pages, 1382 KiB

Open AccessArticle

The Origin of the Magnetic and Electric Dipole Moments of Ni²⁺ in NiCr₂O₄

by Mikhail Eremin and Kirill Vasin

Condens. Matter 2023, 8(1), 23; https://doi.org/10.3390/condmat8010023 - 18 Feb 2023

Viewed by 1167

Abstract

The energy level schema of the ground term of the nickel ion in NiCr

_{2}

O

_{4}

was calculated. The parameters of the interaction with the electric field were determined, and the distribution pattern of the electric dipole moments over different positions of [...] Read more.

The energy level schema of the ground term of the nickel ion in NiCr

_{2}

O

_{4}

was calculated. The parameters of the interaction with the electric field were determined, and the distribution pattern of the electric dipole moments over different positions of nickel in the unit cell was calculated. The model of the NiCr

_{2}

O

_{4}

magnetoelectric structure at T < T

_{c}

was constructed taking into account the data on neutron scattering and the results of the electric polarization measurements. The origin of the magnetodielectric effect was attributed to the peculiarities of the ground state of the nickel ion. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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39 pages, 11260 KiB

Open AccessArticle

A Novel Approach for Modeling the Non-Newtonian Behavior of Simple Liquids: Application to Liquid Water Viscosity from Low to High Shear Rates

by Frédéric Aitken and Ferdinand Volino

Condens. Matter 2023, 8(1), 22; https://doi.org/10.3390/condmat8010022 - 13 Feb 2023

Cited by 1 | Viewed by 2218

Abstract

The aim of this paper is to present a model for the rheological behavior of simple liquids as a function of the amplitude of the imposed shear stress or strain. The elastic mode theory is first generalized to take into account the fact [...] Read more.

The aim of this paper is to present a model for the rheological behavior of simple liquids as a function of the amplitude of the imposed shear stress or strain. The elastic mode theory is first generalized to take into account the fact that, during a flow experiment, mechanical energy is injected in a system initially at thermodynamic equilibrium. This generalized theory can be seen as a particular aspect of the general problem of perturbation by the measurement, associated with that of the coupling between fluctuation and dissipation. This generalization leads to a “finitary” character of the model. It is then combined with the inertial mode theory. The formalism thus obtained allows us to model the rheological behavior of liquids over a wide range of velocity gradients, including the intermediate narrow range corresponding to the Newtonian regime. As experimental tests, viscosity measurements with two kinds of moving rotor rheometers were performed. Only data obtained with liquid water at room temperature are presented and quantitatively analyzed here. It is also shown that liquid n-octane exhibits the same qualitative behaviors as those of liquid water. In the appendices, connection of this theory with quantum mechanics and turbulence phenomena are discussed, and the notion of viscous mass is introduced. Full article

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12 pages, 3461 KiB

Open AccessArticle

A Method to Probe the Interfaces in La_2−xSr_xCuO₄-LaSrAlO₄-La_2−xSr_xCuO₄ Trilayer Junctions

by Xiaotao Xu, Xi He, Anthony T. Bollinger, Myung-Geun Han, Yimei Zhu, Xiaoyan Shi and Ivan Božović

Condens. Matter 2023, 8(1), 21; https://doi.org/10.3390/condmat8010021 - 10 Feb 2023

Cited by 2 | Viewed by 1214

Abstract

C-axis trilayer cuprate Josephson junctions are essential for basic science and digital circuit applications of high-temperature superconductors. We present a method for probing the interface perfection in La_2−xSr_xCuO₄ (LSCO)-LaSrAlO₄ (LSAO)-La_2−xSr_xCuO [...] Read more.

C-axis trilayer cuprate Josephson junctions are essential for basic science and digital circuit applications of high-temperature superconductors. We present a method for probing the interface perfection in La_2−xSr_xCuO₄ (LSCO)-LaSrAlO₄ (LSAO)-La_2−xSr_xCuO₄ trilayer junctions. A series of LSCO-LSAO superlattices with atomically smooth surfaces and sharp interfaces were grown by the atomic-layer-by-layer molecular beam epitaxy (ALL-MBE) technique. We have systematically varied the thickness of LSCO and LSAO layers with monolayer precision. By studying the mutual inductance and electrical transport in these superlattices, we detect the non-superconducting (“dead”) layers at the interfaces and quantify their thicknesses. Our results indicate that two optimally doped LSCO monolayers just above and below the one monolayer LSAO barrier are no longer superconducting, rendering the actual barrier thickness of five monolayers. Next, we have shown that introducing a protective highly-overdoped LSCO layer reduces the thickness of dead layers by one or two monolayers. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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7 pages, 1234 KiB

Open AccessArticle

Influence of Anharmonic and Frustration Effects on Josephson Phase Qubit Characteristics

by Iman N. Askerzade

Condens. Matter 2023, 8(1), 20; https://doi.org/10.3390/condmat8010020 - 09 Feb 2023

Cited by 1 | Viewed by 1052

Abstract

This study is devoted to the investigation of the Josephson phase qubit spectrum considering the anharmonic current-phase relation of the junction. The change in energy difference in the spectrum of phase qubits based on single-band/multiband Josephson junctions is also analyzed. It was shown [...] Read more.

This study is devoted to the investigation of the Josephson phase qubit spectrum considering the anharmonic current-phase relation of the junction. The change in energy difference in the spectrum of phase qubits based on single-band/multiband Josephson junctions is also analyzed. It was shown that the presence of the anharmonic term in the current-phase relation and frustration effects in the junction electrodes leads to changing effective plasma frequencies in the different cases and results in an energy spectrum. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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10 pages, 2312 KiB

Open AccessArticle

Influence of f Electrons on the Electronic Band Structure of Rare-Earth Nickelates

by Andrzej Ptok, Surajit Basak, Przemysław Piekarz and Andrzej M. Oleś

Condens. Matter 2023, 8(1), 19; https://doi.org/10.3390/condmat8010019 - 08 Feb 2023

Cited by 3 | Viewed by 1834

Abstract

Recently, superconductivity was discovered in the infinite layer of hole-doped nickelates NdNiO₂. Contrary to this, superconductivity in LaNiO₂ is still under debate. This indicates the crucial role played by the f electrons on the electronic structure and the pairing mechanism [...] Read more.

Recently, superconductivity was discovered in the infinite layer of hole-doped nickelates NdNiO₂. Contrary to this, superconductivity in LaNiO₂ is still under debate. This indicates the crucial role played by the f electrons on the electronic structure and the pairing mechanism of infinite-layer nickelates. Here, we discuss the role of the electron correlations in the f electron states and their influence on the electronic structure. We show that the lattice parameters are in good agreement with the experimental values, independent of the chosen parameters within the DFT+U approach. Increasing Coulomb interaction U tends to shift the f states away from the Fermi level. Surprisingly, independently of the position of f states with respect to the Fermi energy, these states play an important role in the electronic band structure, which can be reflected in the modification of the NdNiO₂ effective models. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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29 pages, 8839 KiB

Open AccessArticle

Ground States of Heisenberg Spin Clusters from a Cluster-Based Projected Hartree–Fock Approach

by Shadan Ghassemi Tabrizi and Carlos A. Jiménez-Hoyos

Condens. Matter 2023, 8(1), 18; https://doi.org/10.3390/condmat8010018 - 03 Feb 2023

Cited by 2 | Viewed by 1388

Abstract

Recent work on approximating ground states of Heisenberg spin clusters by projected Hartree–Fock theory (PHF) is extended to a cluster-based ansatz (cPHF). Whereas PHF variationally optimizes a site–spin product state for the restoration of spin- and point-group symmetry, cPHF groups sites into discrete [...] Read more.

Recent work on approximating ground states of Heisenberg spin clusters by projected Hartree–Fock theory (PHF) is extended to a cluster-based ansatz (cPHF). Whereas PHF variationally optimizes a site–spin product state for the restoration of spin- and point-group symmetry, cPHF groups sites into discrete clusters and uses a cluster-product state as the broken-symmetry reference. Intracluster correlation is thus already included at the mean-field level, and intercluster correlation is introduced through symmetry projection. Variants of cPHF differing in the broken and restored symmetries are evaluated for ground states and singlet-triplet gaps of antiferromagnetic spin rings for various cluster sizes, where cPHF in general affords a significant improvement over ordinary PHF, although the division into clusters lowers the cyclical symmetry. In contrast, certain two- or three-dimensional spin arrangements permit cluster groupings compatible with the full spatial symmetry. We accordingly demonstrate that cPHF yields approximate ground states with correct spin- and point-group quantum numbers for honeycomb lattice fragments and symmetric polyhedra. Full article

(This article belongs to the Section Magnetism)

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13 pages, 577 KiB

Open AccessArticle

Study of Interacting Heisenberg Antiferromagnet Spin-1/2 and 1 Chains

by Debasmita Maiti, Dayasindhu Dey and Manoranjan Kumar

Condens. Matter 2023, 8(1), 17; https://doi.org/10.3390/condmat8010017 - 29 Jan 2023

Viewed by 1702

Abstract

Haldane conjectures the fundamental difference in the energy spectrum of the Heisenberg antiferromagnetic (HAF) of the spin S chain is that the half-integer and the integer S chain have gapless and gapped energy spectrums, respectively. The ground state (gs) of the HAF spin-1/2 [...] Read more.

Haldane conjectures the fundamental difference in the energy spectrum of the Heisenberg antiferromagnetic (HAF) of the spin S chain is that the half-integer and the integer S chain have gapless and gapped energy spectrums, respectively. The ground state (gs) of the HAF spin-1/2 and spin-1 chains have a quasi-long-range and short-range correlation, respectively. We study the effect of the exchange interaction between an HAF spin-1/2 and an HAF spin-1 chain forming a normal ladder system and its gs properties. The inter-chain exchange interaction

J_{⊥}

can be either ferromagnetic (FM) or antiferromagnetic (AFM). Using the density matrix renormalization group method, we show that in the weak AFM/FM coupling limit of

J_{⊥}

, the system behaves like two decoupled chains. However, in the large AFM

J_{⊥}

limit, the whole system can be visualized as weakly coupled spin-1/2 and spin-1 pairs which behave like an effective spin-1/2 HAF chain. In the large FM

J_{⊥}

limit, coupled spin-1/2 and spin-1 pairs can form pseudo spin-3/2 and the whole system behaves like an effective spin-3/2 HAF chain. We also derive the effective model Hamiltonian in both strong FM and AFM rung exchange coupling limits. Full article

(This article belongs to the Special Issue New Advances in Condensed Matter Physics)

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10 pages, 712 KiB

Open AccessArticle

Possible Manifestation of Q-Ball Mechanism of High-T_c Superconductivity in X-ray Diffraction

by Sergei Mukhin

Condens. Matter 2023, 8(1), 16; https://doi.org/10.3390/condmat8010016 - 28 Jan 2023

Cited by 3 | Viewed by 1259

Abstract

It is demonstrated, that recently proposed by the author Q-ball mechanism of the pseudogap state and high-Tc superconductivity in cuprates may be detected in micro X-ray diffraction, since it imposes inverse correlations between the size and scattering intensities of the Q-ball charge-density-wave (CDW) [...] Read more.

It is demonstrated, that recently proposed by the author Q-ball mechanism of the pseudogap state and high-Tc superconductivity in cuprates may be detected in micro X-ray diffraction, since it imposes inverse correlations between the size and scattering intensities of the Q-ball charge-density-wave (CDW) fluctuations in these compounds. The Q-ball charge Q gives the number of condensed elementary bosonic excitations in a CDW fluctuation of finite amplitude. The attraction between these excitations inside Euclidean Q-balls is self-consistently triggered by the simultaneous condensation of Cooper/local pairs. Euclidean Q-ball solutions, analogous to the famous Q-balls of squarks in the supersymmetric standard model, arise due to the global invariance of the effective theory under the

U (1)

phase rotation of the Fourier amplitudes of the short-range CDW fluctuations. A conserved ‘Noether charge’ Q along the Matsubara time axis equals

Q \propto T M^{2} V

, where the temperature T, Q-ball’s volume V, and fluctuation amplitude M enter. Several predictions are derived in an analytic form that follow from this picture. The conservation of the charge Q leads to an inverse proportionality between the volume V and X-ray scattering intensity ∼

M^{2}

of the CDW puddles found in micro X-ray scattering experiments. The theoretical temperature dependences of the most probable Q value of superconducting Q-balls and their size and scattering amplitudes fit well the recent X-ray diffraction data in the pseudogap phase of high-Tc cuprates. Full article

(This article belongs to the Special Issue Superstripes Physics)

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10 pages, 1777 KiB

Open AccessArticle

Q-Balls in the Pseudogap Phase of Superconducting HgBa₂CuO_4+y

by Gaetano Campi, Luisa Barba, Nikolai D. Zhigadlo, Andrey A. Ivanov, Alexey P. Menushenkov and Antonio Bianconi

Condens. Matter 2023, 8(1), 15; https://doi.org/10.3390/condmat8010015 - 28 Jan 2023

Cited by 4 | Viewed by 1812

Abstract

Fast and local probes, such as X-ray spectroscopy, X-ray diffraction (XRD), and X-ray microscopy, have provided direct evidence for nanoscale phase separation in high temperature perovskite superconductors composed of (i) free particles coexisting with (ii) Jahn Teller polarons (i.e., charges associated with local [...] Read more.

Fast and local probes, such as X-ray spectroscopy, X-ray diffraction (XRD), and X-ray microscopy, have provided direct evidence for nanoscale phase separation in high temperature perovskite superconductors composed of (i) free particles coexisting with (ii) Jahn Teller polarons (i.e., charges associated with local lattice distortions) not detected by slow experimental methods probing only delocalized states. Moreover, these experimental probes have shown the formation of a superstripes phase in the pseudogap regime below T* in cuprates. Here, we focus on the anomalous temperature dependence of short range X-ray diffraction CDW reflection satellites with high momentum transfer, probing both charge and lattice fluctuations in superconducting HgBa₂CuO_4+y (Hg1201) in the pseudogap regime below T* and above T_c. We report compelling evidence of the anomalous anticorrelation of the coherence volume with the peak maximum amplitude of the CDW XRD satellite by cooling below T*. This anomalous temperature trend of the short-range striped Jahn Teller polaronic CDW puddles is in agreement with predictions of the Q-ball theory of the quark gluon plasma extended to cuprates, providing compelling evidence for non topological soliton puddles of striped condensate of pairs in the pseudogap phase. Full article

(This article belongs to the Special Issue Superstripes Physics)

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12 pages, 1834 KiB

Open AccessTechnical Note

Methods to Create Novel La_2−xSr_xCuO₄ Devices with Multiple Atomically Sharp Interfaces

by Anthony T. Bollinger, Xi He, Roberta Caruso, Xiaotao Xu, Xiaoyan Shi and Ivan Božović

Condens. Matter 2023, 8(1), 14; https://doi.org/10.3390/condmat8010014 - 20 Jan 2023

Cited by 1 | Viewed by 1429

Abstract

We present methods to create devices that utilize the high-temperature superconductor La_2-xSr_xCuO₄ grown by atomic layer-by-layer molecular beam epitaxy (ALL-MBE). The ALL-MBE synthesis technique provides atomically precise interfaces necessary for the tunnel junctions, Josephson junctions, and dyon [...] Read more.

We present methods to create devices that utilize the high-temperature superconductor La_2-xSr_xCuO₄ grown by atomic layer-by-layer molecular beam epitaxy (ALL-MBE). The ALL-MBE synthesis technique provides atomically precise interfaces necessary for the tunnel junctions, Josephson junctions, and dyon detection devices that will be considered. A series of microfabrication processing steps using established techniques are given for each device, and their details are discussed. These procedures are easily extended to generate more complex designs and could be suitable for a wider variety of materials. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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14 pages, 2915 KiB

Open AccessProtocol

Optimization of La_2−xSr_xCuO₄ Single Crystal Film Growth via Molecular Beam Epitaxy

by Xi He, Xiaotao Xu, Xiaoyan Shi and Ivan Božović

Condens. Matter 2023, 8(1), 13; https://doi.org/10.3390/condmat8010013 - 20 Jan 2023

Cited by 2 | Viewed by 1406

Abstract

Atomic layer-by-layer molecular beam epitaxy (ALL-MBE) combined with ozone is one of the best methods to fabricate single-crystal thin films of complex oxides. Cuprate such as La_2−xSr_xCuO₄ (LSCO) is a representative complex-oxide high-temperature superconductor (HTS) material. Our group [...] Read more.

Atomic layer-by-layer molecular beam epitaxy (ALL-MBE) combined with ozone is one of the best methods to fabricate single-crystal thin films of complex oxides. Cuprate such as La_2−xSr_xCuO₄ (LSCO) is a representative complex-oxide high-temperature superconductor (HTS) material. Our group utilizes this method to produce high-quality single-crystal HTS films with atomically smooth surfaces and interfaces. In addition, ALL-MBE enables us to engineer multilayer heterostructures with atomic precision. This allows the fabrication of tunnel junctions, various nanostructures, and other HTS devices of interest for superconducting electronics. We have synthesized over three thousand LSCO thin films in the past two decades. These films’ structural and electronic properties have been studied and characterized by various methods. Here, we distill the extensive experience we accumulated into a step-by-step protocol to fabricate atomically perfect LSCO films. The recipe includes substrate preparation, ozone generation and distillation, source calibration, the in situ monitoring of the film synthesis, post-growth annealing, and ex situ characterization. It discloses a reproducible way to fabricate single-crystal LSCO films for basic research and HTS electronic applications. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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23 pages, 8102 KiB

Open AccessArticle

A Method for the Dynamics of Vortices in a Bose-Einstein Condensate: Analytical Equations of the Trajectories of Phase Singularities

by Sergi De María-García, Albert Ferrando, J. Alberto Conejero, Pedro Fernández De Córdoba and Miguel Ángel García-March

Condens. Matter 2023, 8(1), 12; https://doi.org/10.3390/condmat8010012 - 17 Jan 2023

Cited by 1 | Viewed by 1569

Abstract

We present a method to study the dynamics of a quasi-two dimensional Bose-Einstein condensate which initially contains several vortices at arbitrary locations. The method allows one to find the analytical solution for the dynamics of the Bose-Einstein condensate in a homogeneous medium and [...] Read more.

We present a method to study the dynamics of a quasi-two dimensional Bose-Einstein condensate which initially contains several vortices at arbitrary locations. The method allows one to find the analytical solution for the dynamics of the Bose-Einstein condensate in a homogeneous medium and in a parabolic trap, for the ideal non-interacting case. Secondly, the method allows one to obtain algebraic equations for the trajectories of the position of phase singularities present in the initial condensate along with time (the vortex lines). With these equations, one can predict quantities of interest, such as the time at which a vortex and an antivortex contained in the initial condensate will merge. For the homogeneous case, this method was introduced in the context of photonics. Here, we adapt it to the context of Bose-Einstein condensates, and we extend it to the trapped case for the first time. Also, we offer numerical simulations in the non-linear case, for repulsive and attractive interactions. We use a numerical split-step simulation of the non-linear Gross-Pitaevskii equation to determine how these trajectories and quantities of interest are changed by the interactions. We illustrate the method with several simple cases of interest, both in the homogeneous and parabolically trapped systems. Full article

(This article belongs to the Special Issue Computational Methods for Quantum Matter)

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7 pages, 326 KiB

Open AccessArticle

Second-Neighbor Hopping Effects in the Two-Dimensional Attractive Hubbard Model

by Rodrigo Alves Fontenele, Nathan Vasconcelos, Natanael Carvalho Costa, Thereza Paiva and Raimundo Rocha dos Santos

Condens. Matter 2023, 8(1), 11; https://doi.org/10.3390/condmat8010011 - 17 Jan 2023

Viewed by 1427

Abstract

The emergence of superconductivity (SC) in lattice models, such as the attractive Hubbard one, has renewed interest since the realization of cold-atom experiments. However, reducing the temperature in these experiments is a bottleneck; therefore, investigating how to increase the energy scale for SC [...] Read more.

The emergence of superconductivity (SC) in lattice models, such as the attractive Hubbard one, has renewed interest since the realization of cold-atom experiments. However, reducing the temperature in these experiments is a bottleneck; therefore, investigating how to increase the energy scale for SC is crucial to cold atoms. In view of this, we examine the effects of next-nearest-neighbor hoppings (

t^{'}

) on the pairing properties of the attractive Hubbard model in a square lattice. To this end, we analyze the model through unbiased Quantum Monte Carlo simulations for fixed density

n = 0.87

, and perform finite-size scaling analysis to the thermodynamic limit. As our main result, we notice that the existence of further hopping channels leads to an enhancement of the pairing correlations, which, in turn, increases the ground-state order parameter

Δ

. Finally, at finite temperatures, for

t^{'} / t \neq 0

, this enhancement of pairing correlations leads to an increase in the critical temperature

T_{c}

. That is, the fine-tuning of second-neighbor hoppings increases the energy scales for SC, and may be a route by which cold-atom experiments can achieve such a phase and to help us further understand the nature of this phenomenon. Full article

(This article belongs to the Special Issue Fluctuations and Highly Non-linear Phenomena in Superfluids and Superconductors VII)

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2 pages, 183 KiB

Open AccessEditorial

Acknowledgment to the Reviewers of Condensed Matter in 2022

by Condensed Matter Editorial Office

Condens. Matter 2023, 8(1), 10; https://doi.org/10.3390/condmat8010010 - 17 Jan 2023

Viewed by 932

Abstract

High-quality academic publishing is built on rigorous peer review [...] Full article

12 pages, 7991 KiB

Open AccessArticle

Detection of Surface States in Quantum Materials ZrTe₂ and TmB₄ by Scanning Tunneling Microscopy

by Maria Victoria Ale Crivillero, Jean C. Souza, Vicky Hasse, Marcus Schmidt, Natalya Shitsevalova, Slavomir Gabáni, Konrad Siemensmeyer, Karol Flachbart and Steffen Wirth

Condens. Matter 2023, 8(1), 9; https://doi.org/10.3390/condmat8010009 - 16 Jan 2023

Viewed by 2042

Abstract

Scanning Tunneling Microscopy and Spectroscopy (STM/S), with its exceptional surface sensitivity and exquisite energy resolution, is well suited for the investigation of surface states down to atomic length scales. As such, it became an essential tool to probe the surface states of materials, [...] Read more.

Scanning Tunneling Microscopy and Spectroscopy (STM/S), with its exceptional surface sensitivity and exquisite energy resolution, is well suited for the investigation of surface states down to atomic length scales. As such, it became an essential tool to probe the surface states of materials, including those with non-trivial topology. One challenge, however, can be the preparation of clean surfaces which allow the study of preferably unchanged surface properties with respect to the bulk amount. Here, we report on the STM/S of two materials, ZrTe

_{2}

and TmB

_{4}

. The former cleaves easily and defects can be examined in detail. However, our STS data can only qualitatively be compared to the results of band structure calculations. In the case of TmB

_{4}

, the preparation of suitable surfaces is highly challenging, and atomically flat surfaces (likely of B-termination) were only encountered rarely. We found a large density of states (DOS) at the Fermi level

E_{F}

and a mostly featureless differential conductance near

E_{F}

. Further efforts are required to relate our results to the electronic structure predicted by ab initio calculations. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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10 pages, 2725 KiB

Open AccessArticle

Experimental and Theoretical Investigation of High-Resolution X-ray Absorption Spectroscopy (HR-XAS) at the Cu K-Edge for Cu₂ZnSnSe₄

by Wei Xu, Yujun Zhang, Kenji Ishii, Hiroki Wadati, Yingcai Zhu, Zhiying Guo, Qianshun Diao, Zhen Hong, Haijiao Han and Lidong Zhao

Condens. Matter 2023, 8(1), 8; https://doi.org/10.3390/condmat8010008 - 13 Jan 2023

Viewed by 1853

Abstract

Energy sustainability is critical for social activities in the human world. The quaternary compound Cu₂ZnSnSe₄ (CZTSe), as a promising candidate for thin-film solar cell absorption with medium-level thermoelectric performance, is of interest for the purpose of utilizing solar energy. The [...] Read more.

Energy sustainability is critical for social activities in the human world. The quaternary compound Cu₂ZnSnSe₄ (CZTSe), as a promising candidate for thin-film solar cell absorption with medium-level thermoelectric performance, is of interest for the purpose of utilizing solar energy. The defect chemistry and atomic ordering in this particular compound also triggers interests in understanding its crystallographic structure as well as defects. Hereby, high energy resolution X-ray absorption spectroscopy is employed to investigate the electronic and geometric structural complexity in pristine and cobalt-doped Cu₂ZnSnSe₄. The occupational atomic sites of Cu are found to be mixed with the Zn atoms, forming Cu_Zn anti-defects, which serve as a knob to tune local electronic structures. With proper doping, the band structure can be manipulated to improve the optical and thermoelectric properties of the CZTSe compounds. Full article

(This article belongs to the Special Issue Superstripes Physics)

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26 pages, 9897 KiB

Open AccessReview

Is Nematicity in Cuprates Real?

by Ivan Božović, Xi He, Anthony T. Bollinger and Roberta Caruso

Condens. Matter 2023, 8(1), 7; https://doi.org/10.3390/condmat8010007 - 10 Jan 2023

Cited by 3 | Viewed by 1861

Abstract

In La₂-_xSr_xCuO₄ (LSCO), a prototype high-temperature superconductor (HTS) cuprate, a nonzero transverse voltage is observed in zero magnetic fields. This is important since it points to the breaking of the rotational symmetry in the electron fluid, [...] Read more.

In La₂-_xSr_xCuO₄ (LSCO), a prototype high-temperature superconductor (HTS) cuprate, a nonzero transverse voltage is observed in zero magnetic fields. This is important since it points to the breaking of the rotational symmetry in the electron fluid, the so-called electronic nematicity, presumably intrinsic to LSCO (and other cuprates). An alternative explanation is that it arises from extrinsic factors such as the film’s inhomogeneity or some experimental artifacts. We confront this hypothesis with published and new experimental data, focusing on the most direct and sensitive probe—the angle-resolved measurements of transverse resistivity (ARTR). The aggregate experimental evidence overwhelmingly refutes the extrinsic scenarios and points to an exciting new effect—intrinsic electronic nematicity. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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12 pages, 3417 KiB

Open AccessArticle

Magnetic Studies of Iron-Doped Probable Weyl Semimetal WTe₂

by Andranik S. Khachatryan, Elena V. Charnaya, Marina V. Likholetova, Evgeniy V. Shevchenko, Min Kai Lee, Lieh-Jeng Chang, Sergey V. Naumov, Alexandra N. Perevalova, Elena B. Marchenkova and Vyacheslav V. Marchenkov

Condens. Matter 2023, 8(1), 6; https://doi.org/10.3390/condmat8010006 - 06 Jan 2023

Viewed by 2033

Abstract

The non-trivial topology of electronic bands in Weyl semimetals originates from band inversion due to strong spin–orbit coupling. The Weyl semimetals have pairs of Weyl gap-less nodes in the bulk Brillouin zone. The tungsten ditelluride WTe₂ likely belongs to type II Weyl [...] Read more.

The non-trivial topology of electronic bands in Weyl semimetals originates from band inversion due to strong spin–orbit coupling. The Weyl semimetals have pairs of Weyl gap-less nodes in the bulk Brillouin zone. The tungsten ditelluride WTe₂ likely belongs to type II Weyl semimetals. Doping WTe₂ with magnetic ions could induce magnetic ordering in this crystal, which provides prospects for practical applications. We studied the magnetic properties of the iron-doped single crystals Fe_0.03W_0.97Te₂, annealed and unannealed, in comparison with the undoped WTe₂. Measurements of the dc magnetization were carried out from 1.8 to 400 K. We revealed pronounced ferromagnetic ordering that was affected by annealing. Anomalies associated with antiferromagnetism and paramagnetism were also found. The magnetic order was suppressed by a field of 60 kOe. The rise in susceptibility with increasing temperature was observed at high temperatures in all samples and was treated using a model developed for Weyl semimetals. The Curie–Weiss law fit at 60 kOe showed that the effective magnetic moment was close to that of Fe²⁺. Metamagnetism was demonstrated for the unannealed doped WTe₂ crystal. The data for the heat capacity of the iron-doped sample agreed with results for the undoped WTe₂. Full article

(This article belongs to the Section Magnetism)

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8 pages, 2149 KiB

Open AccessArticle

Charge–Phase Duality and Cotunneling of Fluxons in SQUID-like Nanorings

by Alex Latyshev, Andrew G. Semenov and Andrei D. Zaikin

Condens. Matter 2023, 8(1), 5; https://doi.org/10.3390/condmat8010005 - 31 Dec 2022

Viewed by 1275

Abstract

Employing charge–flux duality for Josephson junctions and superconducting nanowires, we predict a novel effect of fluxon cotunneling in SQUID-like nanorings. This process is strictly dual to that of Cooper pair cotunneling in superconducting transistors formed by a pairs of Josephson tunnel junctions connected [...] Read more.

Employing charge–flux duality for Josephson junctions and superconducting nanowires, we predict a novel effect of fluxon cotunneling in SQUID-like nanorings. This process is strictly dual to that of Cooper pair cotunneling in superconducting transistors formed by a pairs of Josephson tunnel junctions connected in series. Cooper pair cotunneling is known to lift Coulomb blockade in these structures at low temperatures. Likewise, fluxon cotunneling may eliminate the magnetic blockade of superconducting phase fluctuations in SQUID-like nanorings, driving them into an insulating state. Full article

(This article belongs to the Special Issue Superstripes Physics)

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18 pages, 2719 KiB

Open AccessArticle

Destructive Interference of the Superconducting Subband Condensates in the Quasi-1D Multigap Material Nanostructures

by Wojciech Julian Pasek, Marcos Henrique Degani and Marcelo Zoéga Maialle

Condens. Matter 2023, 8(1), 4; https://doi.org/10.3390/condmat8010004 - 28 Dec 2022

Viewed by 1563

Abstract

This modelling work concerns the effects of the interference between two partial subband condensates in a quasi-one-dimensional superconducting superlattice. The iterative under-relaxation with phase control method is used to solve Bogoliubov–de Gennes equations in the envelope ansatz. This method—easily generalisable to a wide [...] Read more.

This modelling work concerns the effects of the interference between two partial subband condensates in a quasi-one-dimensional superconducting superlattice. The iterative under-relaxation with phase control method is used to solve Bogoliubov–de Gennes equations in the envelope ansatz. This method—easily generalisable to a wide class of multiband superconducting systems—allows us to obtain both the constructive and the destructive interference solution. The discussion is centred on the latter case, with one of the condensates collapsing with increased inter-subband coupling strength, due to the other—the dominating one—imposing its symmetry on the overall order parameter. The in-depth qualitative analysis is made of underlying intra-subband and inter-subband dynamics, such as the possible factors determining the dominant subband condensate or the ones determining the region where the destructive solution coexists with the constructive one. A comprehensive discussion with the recent works concerning inter-band coupling effects follows, pointing that the destructive solution is nearly universally omitted. Full article

(This article belongs to the Special Issue Superstripes Physics)

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22 pages, 2283 KiB

Open AccessReview

Spin Transport in Magnetically Ordered Systems: Ferromagnets, Antiferromagnets and Frustrated Systems

by Danh-Tai Hoang and Hung T. Diep

Condens. Matter 2023, 8(1), 3; https://doi.org/10.3390/condmat8010003 - 27 Dec 2022

Cited by 1 | Viewed by 1376

Abstract

In this review, we outline the important results on the resistivity encountered by an electron in magnetically ordered materials. The mechanism of the collision between the electron and the lattice spins is shown. Experiments on the spin resistivity in various magnetic materials as [...] Read more.

In this review, we outline the important results on the resistivity encountered by an electron in magnetically ordered materials. The mechanism of the collision between the electron and the lattice spins is shown. Experiments on the spin resistivity in various magnetic materials as well as the theoretical background are recalled. We focus on our works of 15 years of principally using Monte Carlo simulations. In these works, we have studied the spin resistivity in various kinds of magnetic systems ranging from ferromagnets and antiferromagnets to frustrated spin systems. It is found that the spin resistivity shows a broad peak at the transition temperature in systems with a second-order phase transition, while it undergoes a discontinuous jump at the transition temperature of a first-order transition. New results on the hexagonal-close-packed (HCP) antiferromagnet are also shown in extended detail for the Ising case in both the frustrated and non-frustrated parameter regions. Full article

(This article belongs to the Special Issue Spin Dynamics in Magnetic Materials: Spin Resistivity, Spin Waves, Spin-Orbit Coupling, Phase Transition)

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15 pages, 1613 KiB

Open AccessArticle

Magnetic Monopoles, Dyons and Confinement in Quantum Matter

by Carlo A. Trugenberger

Condens. Matter 2023, 8(1), 2; https://doi.org/10.3390/condmat8010002 - 27 Dec 2022

Cited by 1 | Viewed by 1786

Abstract

We show that magnetic monopoles appear naturally in granular quantum matter. Their condensation leads to a new state of matter, superinsulation, in which Cooper pairs are bound into purely electric pions by strings of electric flux. These electric flux tubes, the dual of [...] Read more.

We show that magnetic monopoles appear naturally in granular quantum matter. Their condensation leads to a new state of matter, superinsulation, in which Cooper pairs are bound into purely electric pions by strings of electric flux. These electric flux tubes, the dual of Abrikosov vortices, prevent the separation of charge–hole pairs, thereby causing an infinite resistance, even at finite temperatures, the dual behaviour of superconductors. We will discuss the electric Meissner effect, asymptotic freedom and their measurements and describe the recent direct detection of a linear, confining potential by dynamic relaxation experiments. Finally, we consider dyons, excitations carrying both a magnetic and an electric charge, and show that a condensate of such dyons leads to a possible solution of the mysteries of the pseudogap state of high-

T_{c}

cuprates. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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8 pages, 468 KiB

Open AccessFeature PaperArticle

Conductivity Sum Rule in the Nearly Free Two-Dimensional Electron Gas in an Uniaxial Potential

by Zoran Rukelj and Danko Radić

Condens. Matter 2023, 8(1), 1; https://doi.org/10.3390/condmat8010001 - 23 Dec 2022

Cited by 1 | Viewed by 1525

Abstract

We report an investigation of the conductivity sum rule in the two-dimensional system of free electrons in a weak uniaxial potential. The sum rule is defined through the integration of a real part of a multiband conductivity tensor and separates between the intraband [...] Read more.

We report an investigation of the conductivity sum rule in the two-dimensional system of free electrons in a weak uniaxial potential. The sum rule is defined through the integration of a real part of a multiband conductivity tensor and separates between the intraband and interband charge transport concentrations. It is shown how the relative direction of the electric field and the uniaxial potential defines the transport concentrations of the nearly free electron system and why the sum rule is obeyed. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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Condens. Matter, Volume 8, Issue 1 (March 2023) – 29 articles

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