Intra-Unit-Cell magnetic correlations near optimal doping in $\rm YBa_2Cu_3O_{6.85}$

TL;DR

This study reveals the presence of intra-unit-cell magnetic correlations in nearly optimally doped YBa2Cu3O6.85, showing distinct temperature-dependent regimes that are closely linked to pseudogap phenomena in high-temperature superconductors.

Contribution

It provides new polarized neutron scattering evidence of magnetic intra-unit-cell order with temperature-dependent characteristics near optimal doping.

Findings

Finite size planar magnetic domains with weak c-axis correlation.

High-temperature out-of-plane magnetic correlations indicating Ising anisotropy.

Development of in-plane magnetic response below pseudogap temperature T*.

Abstract

Understanding high-temperature superconductivity requires a prior knowledge of the nature of the enigmatic pseudogap metallic state, out of which the superconducting state condenses. In addition to the electronic orders involving charge degrees of freedoms recently reported inside the pseudogap state, a magnetic intra-unit-cell (IUC) order was discovered in various cuprates to set in just at the pseudogap temperature, T*. In nearly optimally doped YBa$_2$Cu$_3$O$_{6.85}$, polarized neutron scattering measurements, carried out on two different spectrometers, reveal new features. The order is made of finite size planar domains, hardly correlated along the c-axis. At high temperature, only the out-of-plane magnetic components correlate, revealing a strong Ising anistropy, as originally predicted in the loop current model. Below T*, a correlated in-plane response develops, giving rise the apparent tilt of the magnetic moment at low temperature. The discovery of these two regimes put stringent constraints on the intrinsict nature of IUC order, tightly bound to the pseudogap physics.