Calendar of Events

CM WEB SEMINAR

Electronic Phase diagram of the Cuprate Superconductors - a Balancing Act

Zhi-Xun Shen

Departments of Physics and Applied Physics

Stanford University

Stanford Institute for Materials and Energy Sciences

SLAC National Accelerator Laboratory

 

WEB SEMINAR LINK:

 https://zoom.us/j/802273402

 

High-temperature superconductivity in copper based materials, with critical temperature well above what was anticipated by the BCS theory, remains a major unsolved physics problem more than 30 years after its discovery. The problem is fascinating because it is simultaneously simple - being a single band and ½ spin system, yet extremely rich - boasting d-wave superconductivity, pseudogap, spin and charge orders, and strange metal phenomenology. For this reason, cuprates emerge as the most important model system for correlated electrons – stimulating conversations on the physics of Hubbard model, quantum critical point, Planckian metal and others.

 

At the heart of this challenge is the complex electronic phase diagram consisting of intertwined states with unusual properties. Angle-resolved photoemission spectroscopy has emerged as the leading experimental tool to understand the electronic structure of these states and their relationships [1]. In this talk, I will describe our results on band structures and Fermi surfaces [2-3]; d-wave superconducting state[4, 5]; the birth of a metal from a Mott insulator [7-10]; the two energy scales of the pseudogap [7,8,11-12]; the temperature, doping and symmetry properties of the low energy pseudogap and its competition with superconductivity [13-17]; the missing quasiparticle and the chemical potential puzzle [18-19], the interplay of electron-electron and electron-phonon interactions and the enhanced superconductivity [20-23]; the incoherent metal sharply bounded by a critical doping and quantum critical point[24-25]. The rich phenomenology suggests that a delicate balance between local Coulomb interaction and electron-phonon interaction holds the key to cuprate physics.

 

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[20] KM Shen et al., Science 307, 901 (2005)

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[23] Yu He et al., Science, 362, 62 (Oct. 2018)

[24] I.M. Vishik et al., PNAS 109/45, 18332-18337 (2012)

[25] S. Chen et al. ; Science 2019