Enhancement of maximum superconducting temperature by applying pressure and reducing the charge transfer gap

TL;DR

This paper investigates how applying pressure and reducing the charge transfer gap can enhance the maximum superconducting temperature in cuprates, using a 3-band Hubbard model and variational Monte Carlo simulations.

Contribution

It introduces a charge fluctuation mechanism based on the 3-band Hubbard model to explain pressure effects on superconductivity in cuprates, addressing previously unexplained experimental puzzles.

Findings

Charge fluctuation enhances $T_c$ in underdoped and optimally doped cuprates.

Pressure effects on $T_c$ are explained by charge fluctuation dynamics.

The model accounts for the suppression of $T_c$ in overdoped samples.

Abstract

Recent Scanning Tunneling Spectra(STS) measurement on underdoped cuprate discovers the increase of the maximum superconducting transition temperature $T_c$ when the size of charge transfer gap (CTG) is reduced. Applying pressure is another well known method to increase maximum $T_c$. However, these pressure experiments also found another puzzle that $T_c$ is enhanced in underdoped and optimal doped samples but suppressed in overdoped. Here we present a possible mechanism based on the charge fluctuation to explain both these two effects simultaneously. Starting from 3-band Hubbard model, we retrieve the charge fluctuation(CF) between oxygen 2$p^6$ band and copper 3$d^{10}$ band which is ignored in the $t-J$ model. This model is studied via variational Monte Carlo method(VMC).