Title: Fractional Anomalous Hall effect: Theory of Ideal Flatband and Experimental Implications

Spearker: Jie Wang (王捷), Harvard University

Time: 2 pm, Jun 08 (Thursday), 2023

Location: 理科楼C302

Abstract: Fractional anomalous Hall effect (FAH) in the zero-field analogy of fractional quantum Hall effect. How to stabilize FAH in real material is important to both theory and experiment. Conventional wisdom is based on the so-called “Landau level mimicry”: looking into materials with flat single-particle dispersion and uniform Berry curvature. This talk proves its incompleteness and discusses new implications.

We propose a new concept call “ideal flatbands” [1,2] what emphasis not only Berry curvature but also quantum metric --- another intrinsic geometric degree of freedom of wavefunction. We prove ideal flatbands exhibits uniform wavefunction form and stabilizes FAH exactly regardless of Berry curvature’s non-uniformness. As a result, ideal bands point out an exact and new criterion about the stability of FAH.

I will also discuss how to apply the theory to real materials and experimental implications. I will focus on twisted MoTe2 material. Very recent two independent experiments [one from University of Washington and another from Cornell University] reported signature of FAH at -2/3 and -3/5 filling at zero field of such material. Theory shows such material exhibits nearly ideal flatbands in a wide range of parameter space [3]. Our recent work further predict it is an ideal platform for composite Fermi liquid phase too [3], an interaction driven gapless state that is also the “parent” of many Abelian and non-Abelian gapped FAH states [4,5].

Refs:

[1] Exact Landau level description of geometry and interaction in a flatband (2021). JW, J Cano, A. Millis, Z. Liu, B. Yang (PRL 127, 246403)

[2] Hierarchy of ideal flatbands in chiral twisted multilayer graphene models (2022). JW and Zhao Liu (PRL 128, 176403)

[3] Composite Fermi liquids at zero magnetic field in twisted MoTe2 (2023). JW with Ashvin Vishwanath et al (arXiv: 2306.01719)

[4] Berry phase and model wavefunction in the half-filled Landau level (2018). JW with Duncan Haldane, et al (PRL 121.147202)

[5] Dirac fermion hierarchy of composite Fermi liquids (2019). JW (PRL 122, 257203)

BIO: 王捷于2009-2013本科就读于中国科学技术大学。2013-2019于普林斯顿大学攻读物理学博士学位。2019-2022于Flatiron Institute从事博士后研究。2022至今于哈佛大学从事博士后研究。