Time: Jan. 03 (Wednesday), 10:00

Place: Rm M830, IOP-CAS

Speaker: Dr. Haoyu Guo (Cornell University)

Abstract:

The model of a Fermi surface coupled to gapless bosonic fluctuation (critical Fermi surface) plays a central role in modern condensed matter physics. The model appears in the descriptions of various quantum phases of matter, such as quantum spin liquid, half-filled Landau level, fermionic quantum criticality and strange metal. In this talk, I will present some recent progress on this subject based on the Yukawa-SYK formulation of the model. Historically, the Migdal-Eliashberg (ME) theory of non-Fermi liquids has been phenomenologically successful but is not analytically controlled. By promoting the Yukawa coupling to a Gaussian random variable like Sachdev-Ye-Kitaev models, we obtain the first large-N theory that admits the Migdal-Eliashberg (ME) theory as the saddle point. The Yukawa-SYK formulation enables us to systematically study the fluctuation spectrum of the theory around the ME saddle point. Surprisingly, the ME saddle point is only stable in the weak coupling regime, and instability appears in the strong coupling regime. I will discuss the transport consequences of the fluctuation spectrum, such as optical conductivity and hydrodynamics. If time permitting, I will also discuss the role of disorder and how it leads to a universal theory of strange metal.

Short bio: Haoyu Guo(郭浩宇) is a Bethe postdoctoral fellow at Cornell University. He received his PhD from Harvard University in 2023 under Prof. Subir Sachdev and BS from MIT in 2018 under Prof. Leonid Levitov. He is interested in various novel transport phenomena in strongly correlated systems, such as strange metallicity, thermal Hall effect and electron hydrodynamics.

More details can be found in http://seminar.cpsjournals.cn/