Unusual interplay between superconductivity and field-induced charge order in YBa2Cu3Oy

TL;DR

This study investigates how superconductivity and charge order interact in underdoped YBa2Cu3Oy, revealing an unusual field-dependent density of states behavior and suggesting a possible pair-density wave state at low temperatures.

Contribution

It uncovers a novel interplay between superconductivity and charge order, highlighting an unusual field dependence of the density of states and proposing a new theoretical framework involving pair-density waves.

Findings

Density of states becomes field-independent above H_{DOS}

H_{DOS}(T) shows an inflection near charge-density wave onset

Evidence suggests coexistence of mutually-exclusive orders at low T

Abstract

We present a detailed study of the temperature (T) and magnetic field (H) dependence of the electronic density of states (DOS) at the Fermi level, as deduced from specific heat and Knight shift measurements in underdoped YBa2Cu3Oy. We find that the DOS becomes field-independent above a characteristic field H_{DOS} and that the H_{DOS}(T) line displays an unusual inflection near the onset of the long range 3D charge-density wave order. The unusual S-shape of H_{DOS}(T) is suggestive of two mutually-exclusive orders that eventually establish a form of cooperation in order to coexist at low T. On theoretical grounds, such a collaboration could result from the stabilisation of a pair-density wave state, which calls for further investigations in this region of the phase diagram