LASSP & AEP Seminar: Zhiqiang Mao (Penn State)

Description

Nonlinear Hall Effect from Spin-Valley Locking and Nonreciprocal Hall Effect via Asymmetric Scattering at Room Temperature

Spin-valley locking in the band structure of monolayers of MoS₂ and other group-VI transition metal dichalcogenides (TMDCs) has garnered significant interest due to its potential for valleytronic and optoelectronic applications. This exotic electronic state is rarely observed in bulk materials. In this talk, I will present the discovery of a bulk spin-valley locked electronic state in the 3D non-centrosymmetric Dirac material BaMnSb₂ [1]. This state has been uncovered through a combination of first-principles calculations, tight-binding and effective model analyses, and angle-resolved photoemission spectroscopy measurements. Moreover, BaMnSb₂ exhibits a stacked quantum Hall effect (QHE), with the spin-valley degeneracy, derived from the QHE, being close to 2. This, along with Landau level spin splitting, further corroborates the presence of spin-valley locking in BaMnSb₂. Recently, we also discovered that this spin-valley locked state induces an intrinsic nonlinear Hall effect at room temperature. This is characterized by a second-harmonic and rectified Hall voltage response, driven by alternating current, under time-reversal symmetry [2]. These findings extend the understanding of coupled spin and valley physics from 2D systems into 3D systems. In addition, I will report on a colossal nonreciprocal Hall effect, driven by an exceptionally strong extrinsic nonlinear Hall effect, which arises from geometrically asymmetric scattering of textured Pt nanoparticles [3].

References:
[1] Liu et al., Nature Communications 12, 4062(2021).
[2] Min et al., Nature Communications 14, 364(2023).
[3] Min et al., Nature Materials, (2024) https://www.nature.com/articles/s41563-024-02015-7
 

Bio: Zhiqiang Mao received his B.S. in physics from Nanjing Normal University in China, and his Ph.D. in physics from University of Science and Technology of China in 1992. After his postdoc training at Kyoto University in Japan and The Pennsylvania State University, he was recruited as an assistant professor in 2002 to Tulane University, where he rose to the rank of full professor in physics in 2009 and held an endowed professorship from 2011-2018. He served as the chair of the Department of Physics and Engineering Physics from 2011-2014. He joined Penn State as a full professor in July 2018.

He has been awarded the Tulane University School of Science and Engineering Outstanding Researcher Award in 2017, the NSF Career Award in 2007, the Cottrell Scholar Award in 2005, and the Tulane President Early Career Development Award in 2005. He is a Fellow of the American Physical Society since 2015. Currently he is the bulk growth lead of the 2D Crystal Consortium (2DCC)-Materials Innovation Platform funded by the NSF. Dr. Mao has published 380 peer-reviewed papers, including 57 papers in high impact journals such as Nature, Science, Nature Materials, Nature Nanotechnology, Nature Physics, Nature Communications, Physical Review X, Physical Review Letters, etc. His published papers have been widely cited, with the citation h-index of 58.