From a single-band metal to a high-temperature superconductor via two thermal phase transitions

TL;DR

This study investigates the pseudogap phase in cuprate high-temperature superconductors, revealing a phase transition at T* and the coexistence of pseudogap and superconducting states through multiple experimental techniques.

Contribution

It provides a comprehensive multi-technique analysis of the pseudogap onset and its relation to superconductivity in cuprates, highlighting phase transition signatures.

Findings

Abrupt onset of a particle-hole asymmetric gap at T*

Detection of Kerr rotation indicating a phase transition

Superconducting features emerge near Tc, coexisting with pseudogap

Abstract

The nature of the pseudogap phase of cuprate high-temperature superconductors is a major unsolved problem in condensed matter physics. We studied the commencement of the pseudogap state at temperature T* using three different techniques (angle-resolved photoemission spectroscopy, polar Kerr effect, and time-resolved reflectivity) on the same optimally-doped Bi2201 crystals. We observed the coincident, abrupt onset at T* of a particle-hole asymmetric antinodal gap in the electronic spectrum, a Kerr rotation in the reflected light polarization, and a change in the ultrafast relaxational dynamics, consistent with a phase transition. Upon further cooling, spectroscopic signatures of superconductivity begin to grow close to the superconducting transition temperature (Tc), entangled in an energy-momentum-dependent fashion with the pre-existing pseudogap features, ushering in a ground state with coexisting orders.