Polaronic high-temperature superconductivity in optimally doped bismuthate Ba0:63K0:37BiO3

TL;DR

This paper demonstrates that polaronic effects significantly enhance electron-phonon coupling in Ba0.63K0.37BiO3, explaining its high-temperature superconductivity around 32 K, which surpasses conventional predictions.

Contribution

It reveals the crucial role of polaronic effects in boosting electron-phonon coupling, leading to high-temperature superconductivity in bismuthates, supported by experimental and first-principles calculations.

Findings

Polaronic effects increase the electron-phonon coupling constant from 0.3-0.4 to about 1.4.

Enhanced coupling explains superconductivity at 32 K.

Experimental data supports the polaronic enhancement mechanism.

Abstract

Magnetic measurements have been carried out in the superconducting and normal states of the optimally doped nonmagnetic bismuthate superconductor Ba0.63K0.37BiO3. The magnetic data along with previous muSR, resistivity, and tunneling data consistently show that there is a large polaronic enhancement in the density of states and effective electron-phonon coupling constant. The first-principle calculation within the density-functional theory indicates a small electron-phonon coupling constant of about 0.3-0.4, which can only lead to about 1 K superconductivity within the conventional phonon-mediated mechanism. Remarkably, the polaronic effect increases the electron-phonon coupling constant to about 1.4, which is large enough to leads to 32 K superconductivity. The present work thus uncovers the mystery of high-temperature superconductivity in bismuthate superconductors, which will also provide important insight into the pairing mechanism of other high-temperature superconductors.