Research Accomplishments

Research areas: Strongly correlated systems, quantum matter, esp. superfluidity and superconductivity, from high temperature superconductors to ultracold atomic gases; quantum simulations and quantum engineering.

Developed a pairing fluctuation theory that self-consistently includes the contribution of pairing fluctuations in fermion self energy. It can address the wide-spread abnormal pseudogap phenomena in high Tc superconductors, and has been one of several major schools of high Tc theories, since it was published in Phys. Rev. Lett. Based on a BCS-BEC crossover scenario, this theory is a natural generalization of BCS theory to short coherence length superconductors. It is one (of very few theories) that can generate a quantitative cuprate phase diagram, in (semi-)quantitative agreement with experiment. It provides a natural explanation for the mysterious quasi-universal behavior of the temperature dependence of the penetration depth for different doping concentrations in cuprate superconductors. It also provides a unified picture for the anomalous diamagnetic response, Nernst effect, and unusual behavior of the Hall coefficient throughout the entire cuprate phase diagrams. Recent works feature a review article in Reviews of Modern Physics on recently discovered superconductors pertaining to BCS-BEC crossover.

Applied successfully the pairing fluctuation theory to address quantitatively experiments in ultracold Fermi gases, including the phase diagram, thermodynamic phase transitions, density profile, rf spectroscopy, final state effect, population imbalance, impurity effect, Lieb lattice, dipolar Fermi gas, the intrinsic instability of FFLO superfluids, etc. First introduced the pseudogap concept into the atomic Fermi gas field, which has now been established experimentally. 

Explored and predicted exotic new quantum phenomena associated with pairing and superfluidity with unusual parameters or configurations, including physics in mixed dimensionality, in lattice-continuum mixed systems, and in flat/multi-band systems.

Published about 100 SCI papers, with H-index = 31 and an overall SCI citation of over 3310 (or Google scholar citations > 4710, H-index = 36), including high-profile journals such as Science, Nature, Reviews of Modern Physics, Physics Reports, Reports on Progress in Physics, Physical Review Letters, etc.

My current research activities span the two fields of condensed matter theory and cold atoms physics, with focuses in the following areas:

1. Strongly correlated electrons, including theory of high Tc superconductivity, especially phenomena associated with the widespread anormalous pseudogap phenomena. This include cuprate, iron-based, nickel-based, graphene-based, surface and interface superconductors. I am particularly interested in the pseudogap, strange metal behavior, pair density wave, photo radiation induced superconducting phenomena.

2. Quantum simulations based on cold atoms, including the superfluidity and pairing physics of atomic gases in a trap and in an optical lattice with various different geometries, such as square and cubic lattices, Lieb lattice, and Kagome lattice, at different filling factors and population imbalances. In particular, we are focusing on the low temperature quantum phases of the Fermi Hubbard model, in the hope to uncover the mechanism of high Tc superconductivity.  In addition to quantum simulations of existing condensed matter models that are difficult to solve, by utilizing the multiple experimentally tunable parameters of a cold atom system, we do quantum engineering by constructing exotic, presently unknown systems, in the hope to find new quantum physics.