STM imaging of symmetry-breaking structural distortion in the Bi-based cuprate superconductors

TL;DR

This study uses STM to identify a structural distortion in Bi-based cuprates that breaks inversion symmetry, clarifying its distinction from the pseudogap state and introducing a new analysis algorithm.

Contribution

The paper reports the first observation of a structural distortion breaking inversion symmetry in cuprates and introduces a novel algorithm for detecting lattice variations.

Findings

Structural distortion breaks inversion symmetry in Bi-based cuprates.

The distortion is insensitive to temperature, magnetic field, and doping.

A new algorithm for detecting lattice variations is developed.

Abstract

A complicating factor in unraveling the theory of high-temperature (high-Tc) superconductivity is the presence of a "pseudogap" in the density of states, whose origin has been debated since its discovery [1]. Some believe the pseudogap is a broken symmetry state distinct from superconductivity [2-4], while others believe it arises from short-range correlations without symmetry breaking [5,6]. A number of broken symmetries have been imaged and identified with the pseudogap state [7,8], but it remains crucial to disentangle any electronic symmetry breaking from pre-existing structural symmetry of the crystal. We use scanning tunneling microscopy (STM) to observe an orthorhombic structural distortion across the cuprate superconducting Bi2Sr2Can-1CunO2n+4+x (BSCCO) family tree, which breaks two-dimensional inversion symmetry in the surface BiO layer. Although this inversion symmetry breaking structure can impact electronic measurements, we show from its insensitivity to temperature, magnetic field, and doping, that it cannot be the long-sought pseudogap state. To detect this picometer-scale variation in lattice structure, we have implemented a new algorithm which will serve as a powerful tool in the search for broken symmetry electronic states in cuprates, as well as in other materials.