Magnetic field controlled charge density wave coupling in underdoped YBa$_2$Cu$_3$O$_{6+x}$

TL;DR

This study reveals how high magnetic fields induce a three-dimensional charge density wave order in underdoped YBa$_2$Cu$_3$O$_{6+x}$, highlighting the magnetic field's role in modifying electronic correlations and symmetry breaking.

Contribution

It demonstrates that magnetic fields induce a 3D charge density wave order in underdoped YBCO by altering interlayer coupling and breaking mirror symmetry, providing insights into high-field electronic states.

Findings

High magnetic fields induce 3D CDW order along the CuO chain direction.

Field modifies coupling between CuO$_2$ bilayers, leading to symmetry breaking.

Field enhances CDW correlations along the $a$-direction without creating new correlation patterns.

Abstract

The application of large magnetic fields ($B \sim B_{c2}$) to layered cuprates suppresses their high temperature superconducting behaviour and reveals competing ground states. In the widely-studied material YBa$_2$Cu$_3$O$_{6+x}$ (YBCO), underdoped ($p \sim 1/8$) samples show signatures of field-induced electronic and structural changes at low temperatures. However, the microscopic nature of the field-induced reconstruction and the high-field state are unclear. Here we report an x-ray study of the high-field charge density wave (CDW) in YBCO, for doping, $0.1 \lesssim p \lesssim 0.13$. For $p \sim 0.123$, we find that a field ($B \sim 10$~T) induces new CDW correlations along the CuO chain ($b$) direction only, leading to a 3-D ordered state along this direction at $B \sim 15$~T. The CDW signal along the $a$-direction is also enhanced by field, but does not develop a new pattern of correlations. We find that field modifies the coupling between the CuO$_2$ bilayers in the YBCO structure, and causes the sudden appearance of 3D CDW order. The mirror symmetry of individual bilayers is broken by the CDW at low and high fields, allowing recently suggested Fermi surface reconstruction.