Intra-unit-cell electronic nematicity of the high-Tc copper-oxide pseudogap states

TL;DR

This study identifies intra-unit-cell electronic nematicity in high-Tc cuprates' pseudogap phase, revealing broken rotational symmetry within CuO2 units and linking it to electronic differences at oxygen sites, advancing understanding of pseudogap phenomena.

Contribution

It provides the first quantitative measure of intra-unit-cell nematicity in the pseudogap phase of cuprates, connecting electronic symmetry breaking to oxygen site differences.

Findings

Evidence for electronic nematicity near the pseudogap energy.

Broken 90-degree rotational symmetry within CuO2 unit cells.

Electronic differences at oxygen sites drive nematicity.

Abstract

In the high-transition-temperature (high-Tc) superconductors the pseudogap phase becomes predominant when the density of doped holes is reduced1. Within this phase it has been unclear which electronic symmetries (if any) are broken, what the identity of any associated order parameter might be, and which microscopic electronic degrees of freedom are active. Here we report the determination of a quantitative order parameter representing intra-unit-cell nematicity: the breaking of rotational symmetry by the electronic structure within CuO2 unit cell. We analyze spectroscopic-imaging scanning tunneling microscope images of the intra-unit-cell states in underdoped Bi2Sr2CaCu2O8+{\delta} and, using two independent evaluation techniques, find evidence for electronic nematicity of the states close to the pseudogap energy. Moreover, we demonstrate directly that these phenomena arise from electronic differences at the two oxygen sites within each unit cell. If the characteristics of the pseudogap seen here and by other techniques all have the same microscopic origin, this phase involves weak magnetic states at the O sites that break 90o -rotational symmetry within every CuO2 unit cell.