Effect of pseudogap on electronic anisotropy in the strain dependence of the superconducting $T_c$ of underdoped YBa$_2$Cu$_3$O$_y$

TL;DR

This study investigates how the pseudogap influences electronic anisotropy and the strain dependence of the superconducting transition temperature in underdoped YBa2Cu3O7, revealing an electronic origin of anisotropy enhancement.

Contribution

It demonstrates that the pseudogap potential enhances electronic anisotropy in underdoped YBCO, linking it to local energy scales and strain effects, which was not previously understood.

Findings

Thermodynamic anisotropy N peaks at intermediate doping levels.

Pseudogap potential increases as the Mott insulator is approached.

Strain can be used to tune the pseudogap and potentially enhance Tc.

Abstract

For orthorhombic superconductors we define thermodynamic anisotropy $N \equiv d T_c/d \epsilon_{22} - dT_c/d \epsilon_{11}$ as the difference in how superconducting $T_c$ varies with strains $\epsilon_{ii}$, $i=(1, 2)$, along the in-plane directions. We study the hole doping ($p$) dependence of $N$ on detwinned single crystals of underdoped YBa$_2$Cu$_3$O$_y$ (YBCO) using ultrasound technique. While the structural orthorhombicity of YBCO reduces monotonically with decreasing doping over $0.065 <p<0.16$, we find that the thermodynamic anisotropy shows an intriguing enhancement at intermediate doping level, which is of electronic origin. Our theoretical analysis shows that the enhancement of the electronic anisotropy can be related to the pseudogap potential in the electronic specturm that itself increases when the Mott insulating state is approached. Our results imply that the pseudogap is controlled by a local energy scale that can be tuned by varying the nearest neighbor Cu-Cu bond length. Our work opens the possibility to strain engineer the pseudogap potential to enhance the superconducting \Tc.