Symmetry and New Advances in Unconventional Superconductors

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Physics".

Deadline for manuscript submissions: closed (31 December 2023) | Viewed by 2048

Special Issue Editors

School of Microelectronics, Tianjin University, Tianjin 300384, China
Interests: superconductivity; combinatorial material science; neuromorphic computing
Physics Department, University College Cork, Cork, Ireland
Interests: superconductivity; STM; Raman

Special Issue Information

Dear Colleagues,

Since the discovery of high-temperature superconductivity in La2-xBaxCuO4, many high-Tc superconductors have been reported. Meanwhile, the need for a quantitative understanding of the nature of the superconducting state itself has also been proposed in these unconventional superconductors. However, some issues remain unsolved, such as the complexity of the phase diagram, and the various forms of pronounced collective fluctuations. This Special Issue aims to highlight experimental studies on recent advances in unconventional superconductors, including, but not limited to: superconductor exploration, competing orders, collective fluctuations, pseudogaps, strange metals, quantum criticality and the proximity effect.

Dr. Heshan Yu
Dr. Ge He
Guest Editors

Manuscript Submission Information

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Keywords

  • unconventional superconductors
  • phase diagram
  • material synthesis
  • collective fluctuations
  • quantum criticality
  • competing orders

Published Papers (1 paper)

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Research

20 pages, 4567 KiB  
Article
D-Wave Superconducting Gap Symmetry as a Model for Nb1−xMoxB2 (x = 0.25; 1.0) and WB2 Diborides
by Evgeny F. Talantsev
Symmetry 2023, 15(4), 812; https://doi.org/10.3390/sym15040812 - 27 Mar 2023
Cited by 2 | Viewed by 1770
Abstract
Recently, Pei et al. (National Science Review2023, nwad034, 10.1093/nsr/nwad034) reported that ambient pressure β-MoB2 (space group: R3¯m) exhibits a phase transition to α-MoB2 (space group: P6/mmm [...] Read more.
Recently, Pei et al. (National Science Review2023, nwad034, 10.1093/nsr/nwad034) reported that ambient pressure β-MoB2 (space group: R3¯m) exhibits a phase transition to α-MoB2 (space group: P6/mmm) at pressure P~70 GPa, which is a high-temperature superconductor exhibiting Tc=32 K at P~110 GPa. Although α-MoB2 has the same crystalline structure as ambient-pressure MgB2 and the superconducting critical temperatures of α-MoB2 and MgB2 are very close, the first-principles calculations show that in α-MoB2, the states near the Fermi level, εF, are dominated by the d-electrons of Mo atoms, while in MgB2, the p-orbitals of boron atomic sheets dominantly contribute to the states near the εF. Recently, Hire et al. (Phys. Rev. B2022, 106, 174515) reported that the P6/mmm-phase can be stabilized at ambient pressure in Nb1−xMoxB2 solid solutions, and that these ternary alloys exhibit Tc~8 K. Additionally, Pei et al. (Sci. China-Phys. Mech. Astron. 2022, 65, 287412) showed that compressed WB2 exhibited Tc~15 K at P~121 GPa. Here, we aimed to reveal primary differences/similarities in superconducting state in MgB2 and in its recently discovered diboride counterparts, Nb1−xMoxB2 and highly-compressed WB2. By analyzing experimental data reported for P6/mmm-phases of Nb1−xMoxB2 (x = 0.25; 1.0) and highly compressed WB2, we showed that these three phases exhibit d-wave superconductivity. We deduced 2Δm(0)kBTc=4.1±0.2 for α-MoB2, 2Δm(0)kBTc=5.3±0.1 for Nb0.75Mo0.25B2, and 2Δm(0)kBTc=4.9±0.2 for WB2. We also found that Nb0.75Mo0.25B2 exhibited high strength of nonadiabaticity, which was quantified by the ratio of TθTF=3.5, whereas MgB2, α-MoB2, and WB2 exhibited TθTF~0.3, which is similar to the TθTF in pnictides, A15 alloys, Heusler alloys, Laves phase compounds, cuprates, and highly compressed hydrides. Full article
(This article belongs to the Special Issue Symmetry and New Advances in Unconventional Superconductors)
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