Nonadiabatic coupling effects in MgB$_2$ reexamined

高阶非绝热性决定声子谱的温度依赖关系

Higher-order nonadiabaticity governs the temperature dependence of the phonon spectrum

该研究针对现有非绝热声子自能计算的缺陷，以MgB₂为对象，发现高阶非绝热声子修正可缓解问题，得到更吻合实验的线宽与圆顶状耦合强度温度依赖，揭示高阶非绝热性决定声子谱的温度依赖。

Ultrafast Hot Phonon Dynamics in MgB$_2$ Driven by Anisotropic Electron-Phonon Coupling

The zone-center $E_{2g}$ modes play a crucial role in MgB$_2$, controlling the scattering mechanisms in the normal state as well the superconducting pairing. Here, we demonstrate via first-principles quantum-field theory calculations that, due to the anisotropic electron-phonon interaction, a $hot$-$phonon$ regime where the $E_{2g}$ phonons can achieve significantly larger effective populations than other modes, is triggered in MgB$_2$ by the interaction with an ultra-short laser pulse. Spectral signatures of this scenario in ultrafast pump-probe Raman spectroscopy are discussed in detail, rev…

Small Fermi energy and phonon anharmonicity in MgB_2 and related compounds

The remarkable anharmonicity of the E_{2g} phonon in MgB_2 has been suggested in literature to play a primary role in its superconducting pairing. We investigate, by means of LDA calculations, the microscopic origin of such an anharmonicity in MgB_2, AlB_2, and in hole-doped graphite. We find that the anharmonic character of the E_{2g} phonon is essentially driven by the small Fermi energy of the sigma holes. We present a simple analytic model which allows us to understand in microscopic terms the role of the small Fermi energy and of the electronic structure. The relation between anharmonicit…