Doping dependence of the upper critical field in untwinned YBa$_2$Cu$_3$O$_{7-\delta}$ thin films

TL;DR

This study investigates how the upper critical magnetic field varies with doping in untwinned YBa₂Cu₃O₇−δ thin films, revealing a significant decrease in underdoped regimes and highlighting the role of charge density waves.

Contribution

First measurement of doping dependence of $H_{c,2}$ in untwinned YBa₂Cu₃O₇−δ thin films, showing the impact of strain and charge density wave competition.

Findings

$H_{c,2}$ decreases in underdoped region

Strain influences phase diagram of high-$T_c$ superconductors

Charge density waves compete with superconductivity

Abstract

We report on measurements of the doping dependence of the upper critical field $H_{c,2}$ in 50 nm thick YBa$_2$Cu$_3$O$_{7-\delta}$ films. The films are untwinned and are characterized by a small in-plane compressive strain. We find that the $H_{c,2}$ shows a strong decrease in the underdoped region of the phase diagram, in agreement with what has been measured in relaxed single crystals. The origin of the decrease of $H_{c,2}$ in the underdoped regime is discussed within a scenario where charge density wave order competes with superconductivity. This demonstrates the potential of using thin films for studying the phase diagram of high-$T_c$ materials under strain.