Research

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13 pages, 674 KiB

Open AccessFeature PaperArticle

The Shrinking Fermi Liquid Scenario for Strange-Metal Behavior from Overdamped Optical Phonons

by Giovanni Mirarchi, Marco Grilli, Götz Seibold and Sergio Caprara

Condens. Matter 2024, 9(1), 14; https://doi.org/10.3390/condmat9010014 - 06 Feb 2024

Viewed by 951

We discuss how the interaction of electrons with an overdamped optical phonon can give rise to a strange-metal behavior over extended temperature and frequency ranges. Although the mode has a finite frequency, an increasing damping shifts spectral weight to progressively lower energies so [...] Read more.

We discuss how the interaction of electrons with an overdamped optical phonon can give rise to a strange-metal behavior over extended temperature and frequency ranges. Although the mode has a finite frequency, an increasing damping shifts spectral weight to progressively lower energies so that despite the ultimate Fermi liquid character of the system at the lowest temperatures and frequencies, the transport and optical properties of the electron system mimic a marginal Fermi liquid behavior. Within this shrinking Fermi liquid scenario, we extensively investigate the electron self-energy in all frequency and temperature ranges, emphasizing similarities and differences with respect to the marginal Fermi liquid scenario. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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11 pages, 543 KiB

Open AccessArticle

A Theoretical Study of Doping Evolution of Phonons in High-Temperature Cuprate Superconductors

by Saheli Sarkar

Condens. Matter 2024, 9(1), 13; https://doi.org/10.3390/condmat9010013 - 06 Feb 2024

Cited by 1 | Viewed by 1158

Abstract

Hole-doped high-temperature copper oxide-based superconductors (cuprates) exhibit complex phase diagrams where electronic orders like a charge density wave (CDW) and superconductivity (SC) appear at low temperatures. The origins of these electronic orders are still open questions due to their complex interplay and correlated [...] Read more.

Hole-doped high-temperature copper oxide-based superconductors (cuprates) exhibit complex phase diagrams where electronic orders like a charge density wave (CDW) and superconductivity (SC) appear at low temperatures. The origins of these electronic orders are still open questions due to their complex interplay and correlated nature. These electronic orders can modify the phonons in the system, which has also been experimentally found in several cuprates as a softening in the phonon frequency at the CDW vector. Recent experiments have revealed that the softening in phonons in cuprates due to CDW shows intriguing behavior with increasing hole doping. Hole doping can also change the underlying Fermi surface. Therefore, it is an interesting question whether the doping-induced change in the Fermi surface can affect the softening of phonons, which in turn can reveal the nature of the electronic orders present in the system. In this work, we investigate this question by studying the softening of phonons in the presence of CDW and SC within a perturbative approach developed in an earlier work. We compare the results obtained within the working model to some experiments. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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11 pages, 1687 KiB

Open AccessFeature PaperArticle

Dynamic Correlations in Disordered Systems: Implications for High-Temperature Superconductivity

by Takeshi Egami

Condens. Matter 2024, 9(1), 12; https://doi.org/10.3390/condmat9010012 - 03 Feb 2024

Viewed by 1109

Abstract

Liquids and gases are distinct in their extent of dynamic atomic correlations; in gases, atoms are almost uncorrelated, whereas they are strongly correlated in liquids. This distinction applies also to electronic systems. Fermi liquids are actually gas-like, whereas strongly correlated electrons are liquid-like. [...] Read more.

Liquids and gases are distinct in their extent of dynamic atomic correlations; in gases, atoms are almost uncorrelated, whereas they are strongly correlated in liquids. This distinction applies also to electronic systems. Fermi liquids are actually gas-like, whereas strongly correlated electrons are liquid-like. Doped Mott insulators share characteristics with supercooled liquids. Such distinctions have important implications for superconductivity. We discuss the nature of dynamic atomic correlations in liquids and a possible effect of strong electron correlations and Bose–Einstein condensation on the high-temperature superconductivity of the cuprates. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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9 pages, 874 KiB

Open AccessArticle

Single-Band versus Two-Band Description of Magnetism in Infinite-Layer Nickelates

by Tharathep Plienbumrung, Maria Daghofer, Jean-Baptiste Morée and Andrzej M. Oleś

Condens. Matter 2023, 8(4), 107; https://doi.org/10.3390/condmat8040107 - 06 Dec 2023

Viewed by 1185

Abstract

We present a weak-coupling analysis of magnetism in infinite-layer nickelates, where we compare a single-band description with a two-band model. Both models predict that (i) hybridization due to hopping is negligible, and (

i i

) the magnetic properties are characterized [...] Read more.

We present a weak-coupling analysis of magnetism in infinite-layer nickelates, where we compare a single-band description with a two-band model. Both models predict that (i) hybridization due to hopping is negligible, and (

i i

) the magnetic properties are characterized by very similar dynamic structure factors,

S (\vec{k}, ω)

, at the points

(π, π, 0)

and

(π, π, π)

. This gives effectively a two-dimensional description of the magnetic properties. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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15 pages, 1416 KiB

Open AccessArticle

Two-Dimensional Discommensurations: An Extension to McMillan’s Ginzburg–Landau Theory

by Lotte Mertens, Jeroen van den Brink and Jasper van Wezel

Condens. Matter 2023, 8(4), 100; https://doi.org/10.3390/condmat8040100 - 17 Nov 2023

Viewed by 1309

Abstract

Charge density waves (CDWs) profoundly affect the electronic properties of materials and have an intricate interplay with other collective states, like superconductivity and magnetism. The well-known macroscopic Ginzburg–Landau theory stands out as a theoretical method for describing CDW phenomenology without requiring a microscopic [...] Read more.

Charge density waves (CDWs) profoundly affect the electronic properties of materials and have an intricate interplay with other collective states, like superconductivity and magnetism. The well-known macroscopic Ginzburg–Landau theory stands out as a theoretical method for describing CDW phenomenology without requiring a microscopic description. In particular, it has been instrumental in understanding the emergence of domain structures in several CDW compounds, as well as the influence of critical fluctuations and the evolution towards or across lock-in transitions. In this context, McMillan’s foundational work introduced discommensurations as the objects mediating the transition from commensurate to incommensurate CDWs, through an intermediate nearly commensurate phase characterised by an ordered array of phase slips. Here, we extended the simplified, effectively one-dimensional, setting of the original model to a fully two-dimensional analysis. We found exact and numerical solutions for several types of discommensuration patterns and provide a framework for consistently describing multi-component CDWs embedded in quasi-two-dimensional atomic lattices. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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14 pages, 396 KiB

Open AccessArticle

On the Evaluation of Higher-Harmonic-Current Responses for High-Field Spectroscopies in Disordered Superconductors

by Götz Seibold

Condens. Matter 2023, 8(4), 95; https://doi.org/10.3390/condmat8040095 - 13 Nov 2023

Viewed by 1100

Abstract

We discuss a formalism that allows for the calculation of a higher-harmonic-current response to a strong applied electric field for disordered superconducting systems described on the basis of tight-binding models with on- and/or intersite interactions. The theory is based on an expansion of [...] Read more.

We discuss a formalism that allows for the calculation of a higher-harmonic-current response to a strong applied electric field for disordered superconducting systems described on the basis of tight-binding models with on- and/or intersite interactions. The theory is based on an expansion of the density matrix in powers of the field amplitudes, where we solve the equation of motion for the individual components. This allows the evaluation of higher-order response functions on significantly larger lattices than one can achieve with a previously used approach, which is based on a direct temporal integration of the equation of motion for the complete density matrix. In the case of small lattices, where both methods can be applied by including also the contribution of collective modes, we demonstrate the agreement of the corresponding results. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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8 pages, 2820 KiB

Open AccessArticle

Suppression of Stacking Order with Doping in 1T-TaS_2−xSe_x

by Sharon S. Philip, Despina Louca, Matthew B. Stone and Alexander I. Kolesnikov

Condens. Matter 2023, 8(4), 89; https://doi.org/10.3390/condmat8040089 - 10 Oct 2023

Cited by 1 | Viewed by 1310

Abstract

In 1T-TaS

_{2 - x}

Se

_{x}

, the charge density wave (CDW) state features a star of David lattice that expands across layers as the system becomes commensurate upon cooling. The layers can also order along the c-axis, and different stacking orders [...] Read more.

In 1T-TaS

_{2 - x}

Se

_{x}

, the charge density wave (CDW) state features a star of David lattice that expands across layers as the system becomes commensurate upon cooling. The layers can also order along the c-axis, and different stacking orders have been proposed. Using neutron scattering on powder samples, we compared the stacking order previously observed in 1T-TaS

_{2}

when the system is doped with Se. While at low temperature, a 13c layer sequence stacking was observed in TaS

_{2}

; this type of ordering was not evident with doping. Doping with Se results in a metallic state in which the Mott transition is suppressed, which may be linked to the absence of layer stacking. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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7 pages, 506 KiB

Open AccessArticle

Ultrafast Pump–Probe Spectroscopy in Organic Dirac Electron Candidate α-(BETS)₂I₃

by Satoshi Tsuchiya, Masato Katsumi, Ryuhei Oka, Toshio Naito and Yasunori Toda

Condens. Matter 2023, 8(4), 88; https://doi.org/10.3390/condmat8040088 - 10 Oct 2023

Viewed by 1035

Abstract

Photo-induced carrier dynamics were measured in the organic Dirac electron candidate

α

-(BETS)

_{2}

I

_{3}

to investigate why resistivity increases below

T_{MI}

= 50 K. We found a change in carrier dynamics due to an insulating gap formation below

T^{'}

[...] Read more.

Photo-induced carrier dynamics were measured in the organic Dirac electron candidate

α

-(BETS)

_{2}

I

_{3}

to investigate why resistivity increases below

T_{MI}

= 50 K. We found a change in carrier dynamics due to an insulating gap formation below

T^{'}

= 50 K. On the other hand, the relaxation time and polarization anisotropy of the observed dynamics differ from those in the charge-ordering (CO) state of the isostructural salt

α

-(ET)

_{2}

I

_{3}

. Based on the difference, it can be concluded that the insulating phase has a different origin than the CO state. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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11 pages, 669 KiB

Open AccessArticle

Gauge Theories of Josephson Junction Arrays: Why Disorder Is Irrelevant for the Electric Response of Disordered Superconducting Films

by Carlo A. Trugenberger

Condens. Matter 2023, 8(3), 85; https://doi.org/10.3390/condmat8030085 - 19 Sep 2023

Cited by 1 | Viewed by 1217

Abstract

We review the topological gauge theory of Josephson junction arrays and thin film superconductors, stressing the role of the usually forgotten quantum phase slips, and we derive their quantum phase structure. A quantum phase transition from a superconducting to the dual, superinsulating phase [...] Read more.

We review the topological gauge theory of Josephson junction arrays and thin film superconductors, stressing the role of the usually forgotten quantum phase slips, and we derive their quantum phase structure. A quantum phase transition from a superconducting to the dual, superinsulating phase with infinite resistance (even at finite temperatures) is either direct or goes through an intermediate bosonic topological insulator phase, which is typically also called Bose metal. We show how, contrary to a widely held opinion, disorder is not relevant for the electric response in these quantum phases because excitations in the spectrum are either symmetry-protected or neutral due to confinement. The quantum phase transitions are driven only by the electric interaction growing ever stronger. First, this prevents Bose condensation, upon which out-of-condensate charges and vortices form a topological quantum state owing to mutual statistics interactions. Then, at even stronger couplings, an electric flux tube dual to Abrikosov vortices induces a linearly confining potential between charges, giving rise to superinsulation. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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13 pages, 2742 KiB

Open AccessArticle

Superlattices, Bonding-Antibonding, Fermi Surface Nesting, and Superconductivity

by Jose A. Alarco and Ian D. R. Mackinnon

Condens. Matter 2023, 8(3), 72; https://doi.org/10.3390/condmat8030072 - 15 Aug 2023

Viewed by 1287

Abstract

Raman and synchrotron THz absorption spectral measurements on MgB₂ provide experimental evidence for electron orbital superlattices. In earlier work, we have detected THz spectra that show superlattice absorption peaks with low wavenumbers, for which spectral density evolves and intensifies after cooling below [...] Read more.

Raman and synchrotron THz absorption spectral measurements on MgB₂ provide experimental evidence for electron orbital superlattices. In earlier work, we have detected THz spectra that show superlattice absorption peaks with low wavenumbers, for which spectral density evolves and intensifies after cooling below the superconducting transition temperature for MgB₂. In this work, we show how these observations indicate a direct connection to superconducting properties and mechanisms. Bonding–antibonding orbital character is identified in calculated electronic band structures and Fermi surfaces consistent with superlattice structures along the c-axis. DFT calculations show that superlattice folding of reciprocal space generates Brillouin zone boundary reflections, Umklapp processes, and substantially enhances nesting relationships. Tight binding equations are compared with expected charge density waves from nesting relationships and adjusted to explicitly accommodate these linked processes. Systematic analysis of electronic band structures and Fermi surfaces allows for direct identification of Cooper pairing and the superconducting gap, particularly when the k-grid resolution of a calculation is suitably calibrated to structural parameters. Thus, we detail a robust and accurate DFT re-interpretation of BCS superconductivity for MgB₂. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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9 pages, 3846 KiB

Open AccessFeature PaperArticle

Multiband Superconductivity in High-Pressure Sulfur Hydrides

by Giovanni Alberto Ummarino and Antonio Bianconi

Condens. Matter 2023, 8(3), 69; https://doi.org/10.3390/condmat8030069 - 09 Aug 2023

Viewed by 921

Abstract

The temperature dependence of the two superconducting gaps in pressurised

H_{3} S

at 155 GPa with a critical temperature of 203 K has been determined using a data analysis of the experimental curve of the upper critical magnetic field as a function [...] Read more.

The temperature dependence of the two superconducting gaps in pressurised

H_{3} S

at 155 GPa with a critical temperature of 203 K has been determined using a data analysis of the experimental curve of the upper critical magnetic field as a function of temperature in the framework of the two-band s-wave Eliashberg theory. Two different phonon-mediated intra-band Cooper pairing channels in a regime of moderate strong couplings have the key role of the pair-exchange interaction between the two gaps, giving the two non-diagonal terms of the coupling tensor, which are missing in the single-band s-wave Eliashberg theory. The results provide a prediction of the different temperature dependence of the small and large gaps as a function of temperature, which provides evidence of multigap superconductivity in

H_{3} S

. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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Review

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9 pages, 449 KiB

Open AccessReview

Superconductors without Symmetry Breaking

by Maria Cristina Diamantini

Condens. Matter 2024, 9(2), 21; https://doi.org/10.3390/condmat9020021 - 02 Apr 2024

Viewed by 625

Abstract

We review the main features of type-III superconductivity. This is a new type of superconductivity that exists in both 2 and 3 spatial dimensions. The main characteristics are emergent granularity and the superconducting gap being opened by a topological mechanism, with no Higgs [...] Read more.

We review the main features of type-III superconductivity. This is a new type of superconductivity that exists in both 2 and 3 spatial dimensions. The main characteristics are emergent granularity and the superconducting gap being opened by a topological mechanism, with no Higgs field involved. Superconductivity is destroyed by the proliferation of vortices and not by the breaking of Cooper pairs, which survive above the critical temperature. The hallmark of this superconductivity mechanism, in 3 spatial dimensions (3D), is the Vogel–Fulcher–Taman scaling of the resistance with temperature. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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