Pressure-induced phase transition and superconductivity in YBa2Cu4O8

TL;DR

This study explores how pressure influences the structural phase transition and superconductivity in YBa2Cu4O8, revealing a collapse of superconductivity above 10 GPa due to changes in phonon-electron interactions.

Contribution

It provides combined experimental and theoretical insights into pressure-induced structural changes and their impact on superconductivity in YBa2Cu4O8.

Findings

Pressure induces a reversible structural phase transition around 10 GPa.

Superconductivity-related phonon renormalization is suppressed above 10 GPa.

Superconductivity in YBa2Cu4O8 is greatly weakened or destroyed at high pressure.

Abstract

We investigate the pressure and temperature dependence of the lattice dynamics of the underdoped, stoichiometric, high temperature superconductor YBa2Cu4O8 by means of Raman spectroscopy and ab initio calculations. This system undergoes a reversible pressure-induced structural phase transition around 10 GPa to a collapsed orthorhombic structure, that is well reproduced by the calculation. The coupling of the B1g-like buckling phonon mode to the electronic continuum is used to probe superconductivity. In the low pressure phase, self-energy effects through the superconducting transition renormalize this phonon, and the amplitude of this renormalization strongly increases with pressure. Whereas our calculation indicates that this mode's coupling to the electronic system is only marginally affected by the structural phase transition, the aforementioned renormalization is completely suppressed in the high pressure phase, demonstrating that under hydrostatic pressures higher than 10 GPa, superconductivity in YBa2Cu4O8 is greatly weakened or obliterated.