Acharya Swagata, Pashov Dimitar, Jamet Francois, van Schilfgaarde Mark
King's College London, Theory and Simulation of Condensed Matter, The Strand, WC2R 2LS London, United Kingdom.
National Renewable Energy Laboratories, Golden, Colorado 80401, USA.
Phys Rev Lett. 2020 Jun 12;124(23):237001. doi: 10.1103/PhysRevLett.124.237001.
Recent observations of selective emergence (suppression) of superconductivity in the uncollapsed (collapsed) tetragonal phase of LaFe_{2}As_{2} has rekindled interest in understanding what features of the band structure control the superconducting T_{c}. We show that the proximity of the narrow Fe-d_{xy} state to the Fermi energy emerges as the primary factor. In the uncollapsed phase this state is at the Fermi energy, and is most strongly correlated and a source of enhanced scattering in both single and two particle channels. The resulting intense and broad low energy spin fluctuations suppress magnetic ordering and simultaneously provide glue for Cooper pair formation. In the collapsed tetragonal phase, the d_{xy} state is driven far below the Fermi energy, which suppresses the low-energy scattering and blocks superconductivity. A similar source of broad spin excitation appears in uncollapsed and collapsed phases of CaFe_{2}As_{2}. This suggests controlling coherence provides a way to engineer T_{c} in unconventional superconductors primarily mediated through spin fluctuations.
最近对LaFe₂As₂未塌缩（塌缩）四方相中超导性的选择性出现（抑制）的观察，重新激发了人们对理解能带结构的哪些特征控制超导转变温度（Tc）的兴趣。我们表明，窄的Fe-dxy态与费米能的接近程度成为主要因素。在未塌缩相中，这个态处于费米能处，具有最强的关联性，并且是单粒子和双粒子通道中增强散射的来源。由此产生的强烈且宽泛的低能自旋涨落抑制了磁有序，同时为库珀对的形成提供了“胶水”。在塌缩四方相中，dxy态被驱动到远低于费米能的位置，这抑制了低能散射并阻碍了超导性。类似的宽泛自旋激发源出现在CaFe₂As₂的未塌缩和塌缩相中。这表明控制相干性为在主要通过自旋涨落介导的非常规超导体中调控Tc提供了一种方法。
