Unconventional electronic order in a codoped high-Tc superconductor

TL;DR

This study uncovers an unconventional charge nematic phase in a cuprate superconductor, revealing its emergence between charge stripe order and metallic states through multiple experimental techniques.

Contribution

It identifies a charge nematic phase in a cuprate superconductor, clarifying its relation to charge stripe order and pseudogap phenomena, supported by comprehensive experiments.

Findings

Discovery of a nematic phase without broken translational symmetry.

The nematic phase appears through a sharp phase transition.

The phase exists within a dome-shaped region of the phase diagram.

Abstract

Charge stripe order has recently been established as an important ingredient of the physics of cuprate high-T$_c$ superconductors. However, due to the complex interplay between competing phases and the influence of disorder, it is unclear how it emerges from the parent metallic state. Here we report on the discovery of an unconventional electronic ordered phase between charge-stripe order and (pseudogapped) metal in the cuprate La$_{2-x-y}$Eu$_{y}$Sr$_x$CuO$_4$ with $y = 0.2$ (LESCO). The peculiar properties of the intermediate phase are revealed through three complementary experiments: nuclear quadrupole resonance, nonlinear conductivity, and specific heat. We demonstrate that the order appears through a sharp phase transition, and exists in a dome-shaped region of the phase diagram, similar to charge stripes. A comparison to recent theoretical work shows that the order is a state without broken translational symmetry -- a charge nematic. We thus resolve the complex process of charge stripe development in cuprates, show that the nematic phase is unrelated to high-temperature pseudogap physics, and establish a link with other strongly correlated electronic materials where nematic order is prominent.