Prof. Phillip Phillips

University of Illinois Urbana-Champaign

Host:  Murthy

Title: Beyond BCS: An Exact Model for Superconductivity and Mottness\

Abstract: The Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity described all superconductors until the 1986 discovery of the high-temperature counterpart in the cuprate ceramic materials.  This discovery has challenged conventional wisdom as these materials are well known to violate the basic tenets of the  Landau Fermi liquid theory of metals, crucial to the BCS solution.   Precisely what should be used to replace Landau's theory remains an open question.   The natural question arises: What is the simplest model for a non-Fermi liquid that yields tractable results.  Our work builds[1] on an overlooked symmetry that is broken in the normal state of generic models for the cuprates and hence serves as a fixed point.  A surprise is that this fixed point also exhibits Cooper's instability[2,3].  However, the resultant superconducting state differs drastically[3] from that of the standard BCS theory.  For example the famous Hebel-Slichter peak is absent and the elementary excitations are no longer linear combinations of particles and holes but rather are superpositions of composite excitations.  Our analysis here points a way forward in computing the superconducting properties of strongly correlated electron matter.

[1] E. Huang, G. La Nave, P. Phillips, Nat. Phys., 18, pages511–516 (2022).

[2] PWP, L. Yeo, E. Huang, Nature Physics, 16, 1175-1180 (2020).

[3]J. Zhao, L. Yeo, E. Huang, PWP, PRB, Phys. Rev. B 105, 184509 (2022).