Jiang Cunyuan, Beneduce Enrico, Baggioli Matteo, Setty Chandan, Zaccone Alessio
School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China.
Department of Physics "A. Pontremoli", University of Milan, via Celoria 16, 20133 Milan, Italy.
J Phys Condens Matter. 2023 Feb 24;35(16). doi: 10.1088/1361-648X/acbd0a.
Phonon softening is a ubiquitous phenomenon in condensed matter systems which is often associated with charge density wave (CDW) instabilities and anharmonicity. The interplay between phonon softening, CDW and superconductivity is a topic of intense debate. In this work, the effects of anomalous soft phonon instabilities on superconductivity are studied based on a recently developed theoretical framework that accounts for phonon damping and softening within the Migdal-Eliashberg theory. Model calculations show that the phonon softening in the form of a sharp dip in the phonon dispersion relation, either acoustic or optical (including the case of Kohn-type anomalies typically associated with CDW), can cause a manifold increase of the electron-phonon coupling constant. This, under certain conditions, which are consistent with the concept of optimal frequency introduced by Bergmann and Rainer, can produce a large increase of the superconducting transition temperatureTc. In summary, our results suggest the possibility of reaching high-temperature superconductivity by exploiting soft phonon anomalies restricted in momentum space.
声子软化是凝聚态物质系统中普遍存在的现象，它通常与电荷密度波（CDW）不稳定性及非简谐性相关。声子软化、CDW与超导性之间的相互作用是一个激烈争论的话题。在这项工作中，基于最近发展的一个理论框架，研究了反常软声子不稳定性对超导性的影响，该框架在Migdal - Eliashberg理论中考虑了声子阻尼和软化。模型计算表明，以声子色散关系中的尖锐凹陷形式出现的声子软化，无论是声学声子还是光学声子（包括通常与CDW相关的Kohn型反常情况），都能导致电子 - 声子耦合常数大幅增加。在与Bergmann和Rainer引入的最佳频率概念相一致的某些条件下，这会使超导转变温度Tc大幅升高。总之，我们的结果表明，通过利用动量空间中受限的软声子反常来实现高温超导是有可能的。
