非中心对称NbReSi中的超导电性：超越谐波与绝热极限
Superconductivity in Noncentrosymmetric NbReSi: Beyond Harmonic and Adiabatic Limits
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中文总结 AI 辅助
本研究通过第一性原理计算揭示非中心对称超导体NbReSi的超导机制，发现谐波理论高估Tc，需引入非谐波效应和顶点修正才能与实验吻合。
中文摘要 AI 辅助
非中心对称超导体NbReSi（Tc=6.5 K）因其破缺的反演对称性所允许的非传统配对而受到积极研究。尽管实验上广泛关注，但其超导电性的驱动机制仍是一个未解之谜。我们表明费米能级处的电子态主要由Nb和Re的d态主导。同一重金属框架的振动贡献了超过95%的电子-声子耦合，其中最强耦合源于涉及强键合Re原子的亚晶格选择性呼吸模式。谐波Migdal-Eliashberg理论高估了Tc超过60%。这些模式的零点非谐波硬化将耦合降低了20%。尽管声子能量较低，但由于空间局域的Re-d轨道对费米能级附近电子能带结构的贡献，领先的顶点修正也变得重要。综合来看，非谐波效应和顶点修正使计算得到的Tc和超导能隙与实验接近一致，确立了NbReSi为中等耦合、声子介导的超导体，其定量描述需要超越谐波Migdal-Eliashberg理论。
英文摘要
The noncentrosymmetric superconductor NbReSi (Tc=6.5 K) is being actively explored for unconventional pairing that is allowed by its broken inversion symmetry. Despite broad experimental interest, what drives its superconductivity remains an open question. We show that the electronic states at the Fermi level are dominated by Nb and Re $d$-states. Vibrations of the same heavy-metal framework contribute more than 95% of the electron-phonon coupling, with the strongest coupling arising from the sublattice-selective breathing mode involving strongly bonded Re atoms. Harmonic Migdal-Eliashberg theory overestimates Tc by more than 60%. The zero-point anharmonic hardening of these modes reduces the coupling by 20%. The leading vertex correction becomes important as well despite low phonon energies due to the contribution of spatially localized Re-d orbitals to the electronic band structure near the Fermi level. Together, anharmonicity and vertex corrections bring the calculated Tc and superconducting gap into close agreement with experiment, establishing NbReSi as a moderately coupled, phonon-mediated superconductor whose quantitative description requires going beyond harmonic Migdal--Eliashberg theory.
发表机构
- Laboratory for Physical Sciences, University of Maryland（马里兰大学物理科学实验室）
- Department of Physics, Virginia Tech（弗吉尼亚理工大学物理系）
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