Spectroscopic Imaging STM Studies of Electronic Structure in the Superconducting and Pseudogap Phases of Cuprate High-Tc Superconductors

TL;DR

This study uses spectroscopic imaging STM to analyze the electronic structure of cuprate high-Tc superconductors, revealing two distinct classes of electronic states with different symmetry properties and energy scales in both superconducting and pseudogap phases.

Contribution

It identifies and characterizes two classes of electronic states with different symmetry breaking behaviors and energy scales, advancing understanding of cuprate electronic phases.

Findings

Dispersive Bogoliubov quasiparticles detected below |E|={}0

C4 symmetry breaking occurs at energies near the pseudogap scale |E| {}1

States at |E| {}1 exhibit intra-unit-cell nematic and smectic symmetry breaking

Abstract

One of the key motivations for the development of atomically resolved spectroscopic imaging STM (SI-STM) has been to probe the electronic structure of cuprate high temperature superconductors. In both the d-wave superconducting (dSC) and the pseudogap (PG) phases of underdoped cuprates, two distinct classes of electronic states are observed using SI-STM. The first class consists of the dispersive Bogoliubov quasiparticles of a homogeneous d-wave superconductor. These are detected below a lower energy scale |E|={\Delta}0 and only upon a momentum space (k-space) arc which terminates near the lines connecting k=\pm({\pi}/a0,0) to k=\pm(0, {\pi}/a0). In both the dSC and PG phases, the only broken symmetries detected in the |E|\leq {\Delta}0 states are those of a d-wave superconductor. The second class of states occurs at energies near the pseudogap energy scale |E| {\Delta}1 which is associated conventionally with the 'antinodal' states near k=\pm({\pi}/a0,0) and k=\pm(0, {\pi}/a0). We find that these states break the 90o-rotational (C4) symmetry of electronic structure within CuO2 unit cells, at least down to 180o rotational (C2) symmetry (nematic) but in a spatially disordered fashion. This intra-unit-cell C4 symmetry breaking coexists at |E| {\Delta}1 with incommensurate conductance modulations locally breaking both rotational and translational symmetries (smectic). The properties of these two classes of |E| {\Delta}1 states are indistinguishable in the dSC and PG phases. To explain this segregation of k-space into the two regimes distinguished by the symmetries of their electronic states and their energy scales |E| {\Delta}1 and |E|\leq{\Delta}0, and to understand how this impacts the electronic phase diagram and the mechanism of high-Tc superconductivity, represents one of a key challenges for cuprate studies.