报告人：严佳伟 青年研究员，中科院上海微系统所

邀请人：王健 教授

时 间：3月25日上午9:30

地 点：致原楼1007室

摘要：

The quantum many-body  problem encompasses key physical phenomena such as high-temperature  superconductivity, exciton condensation, and magnetism, etc. Due to  exponentially growth of the Hilbert space, solving these many-body  systems requires advanced numerical approaches. Among them, dynamical  mean-field theory (DMFT) stands out as one of the few methods capable of  simulating real materials. However, conventional single-site DMFT  neglects nonlocal fluctuations, making it difficult to obtain  qualitatively accurate results for low-dimensional materials.

To overcome this  limitation, I will present our recently developed two-particle  self-consistent (TPSC) theory, which treats both local and nonlocal  electron correlations on equal footing by incorporating a renormalized  local two-particle vertex. This approach respects the Mermin-Wagner  theorem and satisfies various sum rules. By introducing a novel  Hartree-Fock Ansatz, our multi-orbital TPSC resolves issues in the  previous formulation, which fails when Hund’s coupling J = 0. Benchmark  results demonstrate that TPSC successfully captures the AFM-induced  pseudogap in the 2D Hubbard model—a feature conventional DMFT fails to  describe. Furthermore, numerical simulations of the bilayer Hubbard  model show excellent agreement with recent ultracold atom experiments.  Notably, we have also observed an AFM-to-FM transition in the bilayer  system under a perpendicular electric field. Finally, to extend TPSC to  strongly coupled systems, we are developing a TPSC+DMFT framework, which  is expected to achieve accuracy comparable to DΓA but at a  significantly lower computational cost.

报告人简介：

     　严佳伟，2013本科毕业于上海交通大学，2019年博士毕业于上海科技大学。之后，他先后赴捷克科学院物理研究所以及瑞士弗里堡大学从事博士后研究工作。他于2024年9月加入中科院上海微系统所2020前沿实验室任青年研究员。截至目前，他在《Physical Review B》，《SciPost Physics》等国际期刊上发表论文15篇。他目前的主要研究方向为发展非平衡态量子多体理论以及第一性原理电子结构计算方法。