Phonon enhancement of electronic order and negative isotope effect in the Hubbard-Holstein model on a square lattice

Article

关键词: FUNCTIONAL RENORMALIZATION-GROUP;    HIGH-TC SUPERCONDUCTORS;    TRANSITION-TEMPERATURE;    DENSITY-WAVE;    SYSTEMS;    LA2-XSRXCUO4;    INSTABILITY;    VIBRATIONS;    DYNAMICS;    COPPER;   

DOI  :  10.1103/PhysRevB.92.195102

来源: SCIE

【 摘 要 】

In phonon mediated conventional s-wave superconductors, higher-frequency phonon (or smaller atomic mass) leads to a higher superconducting transition temperature, known as the isotope effect. However, in correlated systems, various competing electronic order (such as spin-density-wave, charge-density-wave, and unconventional superconductivity) arises and the effect of electron-phonon coupling on these orders is a long-standing problem. Using the functional renormalization group, here we investigated the interplay between the electron correlation and electron-phonon coupling in the Hubbard-Holstein model on a square lattice. At half-filling, we found spin-density-wave and charge-density-wave phases and the transition between them, while no superconducting phase arises. Upon finite doping, d-wave/s-wave superconductivity emerges in proximity to the spin-density-wave/charge-density-wave phase. Surprisingly, lower-frequency Holstein phonons are either less destructive or even beneficial to the various phases, resulting in a negative isotope effect. For the superconducting phases, such an effect is apparently beyond the Bardeen-Cooper-Schrieffer theory.

【 授权许可】

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