Emergent Phenomena Seminar 290S/QM Seminar Speaker Binghai Yan (Weizmann Institute) Wednesday, October 27 at 2:00 pm

Time/Venue Wednesday, October 27 at 2 pm in 402 Physics South and Zoom: https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09 Meeting ID: 995 2349 9113 Passcode: 600704
Host Ehud Altman
 Band structure topology and nonlinear effects in quantum materials
 Topological quantum materials provide fascinating platforms to investigate band structure topology and explore its impacts on material properties. They also triggered renewed interest in the bulk photovoltaic effect (BPVE), where a homogenous material (instead of a p-n junction) rectifies light into a dc current. For example, nonmagnetic Weyl semimetals (e.g., TaAs and WTe2) are found to exhibit giant photocurrent and second harmonic generation. Recently, we proposed that magnetism can lead to unexpected, even stronger nonlinear effects [1]. For example, linearly polarized light can generate an injection current in a magnet [2], which is forbidden by symmetry in ordinary materials. Surprisingly, the magnetic indued photocurrent does not vanish even in the subgap regime (hν < Eg) [3]. In the dc electric field limit, related nonlinear transport remains and results in the unidirectional magnetoresistance, i.e., a diode controlled by magnetism or magnetic field. The diode rectification can be significantly enhanced by flat bands for example in magic angle twisted bilayer graphene [4,5].
References: [1] Phys. Rev. Research 2, 033100 (2020). [2] Nature Commun. 10,3783 (2019). [3] Phys. Rev. Lett. 125, 227401(2020). [4] The Innovation 2 (1), 100085(2021). [5] arXiv:2101.07539

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