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

He, R.-H.*; Hashimoto, Makoto*; Karapetyan, H.*; Koralek, J. D.*; Hinton, J. P.*; Testaud, J. P.*; Nathan, V.*; Yoshida, Yoshiyuki*; Yao, H.*; Tanaka, Kiyohisa*; et al.

Science, 331(6024), p.1579 - 1583, 2011/03

https://doi.org/10.1126/science.1198415

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 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 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 (), entangled in an energy-momentum dependent manner with the preexisting pseudogap features, ushering in a ground state with coexisting orders.