Electron-phonon coupling: a key component for high-temperature superconductivity?

Since the discovery of high-temperature superconductivity (SC) in 1986, the microscopic origin of high-temperature SC has remained one of the most important and challenging problems in physics. Despite significant experimental and theoretical advances over nearly four decades, a complete theoretical mechanism of high-temperature SC remains elusive. The Hubbard model has long been regarded as a minimal model for explaining high-Tc SC. However, increasing numerical studies showed that the simplest Hubbard model on the square lattice may not exhibit high-temperature superconductivity. Exploring mechanisms beyond the minimal Hubbard model has become a critical research frontier.

Addressing this fundamental challenge, a collaborative team from Tsinghua University and ShanghaiTech University proposed a novel theoretical framework: the Su-Schrieffer-Heeger-Hubbard (SSHH) model which integrates Su-Schrieffer-Heeger (SSH) electron-phonon coupling with Hubbard electronic interactions. Their research demonstrates interplay between the electron-phonon coupling and Hubbard interaction enables robust d-wave high-Tc superconductivity in the SSHH model. Using state-of-the-art density matrix renormalization group (DMRG) methods accelerated by GPU, the researchers obtained the ground-state phase diagram of the SSHH model, which reveals intricate competition among s-wave superconductivity, d-wave superconductivity, and stripe charge-density order. Crucially, the study identified that SSH-induced effective antiferromagnetic exchange interactions are pivotal for stabilizing d-wave SC—offering new theoretical insights into high-Tc mechanisms.

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