School of Physics Spring Colloquium Series- Dr. Subir Sachdev

Speaker: Dr. Subir Sachdev

Host: Zhu-Xi Luo

Title: Detecting a quantum spin liquid in the cuprate superconductors

Abstract: Soon after the discovery of the cuprate high-temperature superconductors, P. W. Anderson presciently suggested in 1987 that their physics is connected to highly entangled many-body states now known as quantum spin liquids. However, the development of this idea over subsequent decades encountered significant tensions with experimental observations. I address these difficulties using the fractionalized Fermi liquid (FL*) state, proposed in 2002, which describes the doping of a quantum spin liquid with electron-like quasiparticles.

Recent angle-dependent magnetoresistance measurements in lightly hole-doped cuprates are consistent with key predictions of the FL* theory. The non-symmetry-breaking quantum phase transition between the FL* state and a conventional Fermi liquid, in the presence of impurities, can be described by a two-spatial-dimensional extension of the Sachdev–Ye–Kitaev (SYK) model. This framework is then applied to the strange-metal regime at intermediate temperatures and dopings. I will also briefly mention how the SYK model has led to recent progress in understanding the density of quantum states of charged black holes.

Bio: Subir Sachdev is Herchel Smith Professor of Physics at Harvard University. He has been elected to national academies of science in India and the US, and the Royal Society in the U.K. He is a recipient of several awards, including the Dirac Medal from the International Centre for Theoretical Physics, and the Lars Onsager Prize from the American Physical Society.

Sachdev has made extensive contributions to the theory of the diverse varieties of states of quantum matter, and of their behavior near quantum phase transitions.