NMR study of charge density waves under hydrostatic pressure in YBa2Cu3Oy

TL;DR

This study uses NMR to investigate how hydrostatic pressure affects charge density waves in YBa2Cu3Oy, revealing that CDWs are only slightly weakened at 1.9 GPa and possibly suppressed at higher pressures, which may relate to increased superconducting transition temperatures.

Contribution

The paper provides new NMR evidence showing that charge density waves are not fully suppressed at moderate pressures, challenging previous x-ray scattering results and proposing a model linking pressure, doping, and Tc enhancement.

Findings

CDW is slightly weakened at 1.9 GPa

Possible suppression of CDW at 10-20 GPa

Pressure-induced decrease in CDW may increase Tc

Abstract

The effect of hydrostatic pressure (P) on charge density waves (CDW) in YBa2Cu3Oy has recently been controversial. Using NMR, we find that both the short-range CDW in the normal state and the long-range CDW in high fields are, at most, slightly weakened at P=1.9 GPa. This result is in contradiction with x-ray scattering results finding complete suppression of the CDW at ~1 GPa and we discuss possible explanations of this discrepancy. Quantitative analysis, however, shows that the NMR data is not inconsistent with a disappearance of the CDW on a larger pressure scale, typically ~10-20 GPa. We also propose a simple model reconciling transport data with such a hypothesis, provided the pressure-induced change in doping is taken into account. We conclude that it is therefore possible that most of the spectacular increase in Tc upon increasing pressure up to ~15~GPa arises from a concomitant decrease of CDW strength.