Quantum Cafe: Zhi-Xun Shen

Quantum Café is CCQ’s ongoing seminar series: open to all bona fide members of the greater NYC scientific community and held every second week, Quantum Café presents a series of informal, highly interactive talks, typically by external speakers, which present the most interesting recent developments and open questions in our field.

Title: Cooperative Interactions as a Pathway to High Temperature Superconductivity

Abstract: High-temperature superconductivity in copper and iron based materials, with critical temperature well above what was anticipated by the BCS theory, remains a major unsolved physics problem today. The challenge of this problem is symbolized by a complex phase diagram consisting of intertwined states with extreme properties in addition to unconventional superconductivity. None of them can be described by conventional theory, thus compounding the difficulty to understand high-temperature superconductivity itself as these states are different manifestations of the same underlying physical system, making an integrated understanding a necessity.

We discuss experimental evidence for a general theme of high temperature superconductivity – cooperative enhancement and positive feedback loop of different interactions exemplified by electron-electron and electron-phonon interactions. The accumulated evidence comes from an expanded version of angle-resolved photoemission spectroscopy and its match to in-situ material synthesis. In such experiments, the precision measurements of electron’s energy, momentum and time dynamics provide evidence for cooperative interactions as a pathway to increase the superconducting transition temperature.