Talk by professor Dr Mario Amado Montero

Wednesday 16 Nov 22

Talk: Lifted valley degeneracy in single layer graphene from orbital valley Hall effects (Zoom)

When: November 17 at 10.00.

In this work we report on electrical measurements on single layer graphene Hall-bars encapsulated within hexagonal boron nitride thin films with controlled twisting angle between the layers. The samples have been fabricated by means of a cryo-etching method [1], permitting an unprecedented control of the roughness of the edges. The whole structure was placed onto a thin graphite back gate, preventing dopants or trapped charges arising from the standard semiconductor substrates [2]. 

We have carried out an exhaustive study of the electrical response at different temperatures when an in-to-out-of-plane external magnetic field has been exerted with special attention to the possible effects arising due to the Moiré pattern. Local and non-local signals are presented and a striking chiral behaviour at low magnetic fields of the nonlocal currents resulting from a charge carrier-valley coupling is found, in stark contrast with previous results of similar structures at different twisting angles [3]. Orbital valley Hall effect [4,5] has been found responsible for the presented chiral response with thorough theoretical calculations supporting the experimental results [6].

[1]    V. Clericò, J. A. Delgado-Notario, M. Saiz-Bretín, A. V. Malyshev, Y. M. Meziani, P. Hidalgo, B. Méndez, M. Amado, F. Domínguez-Adame, and E. Diez, Scientific Reports, 9 (2019) 13572
[2]    A.A. Zibrov, C. Kometter, H. Zhou, E. M. Spanton, T.  Taniguchi, K. Watanabe, M. P. Zaletel and A. F. Young, Nature. 549 (2017) 360
[3]    A. Aharon-Steinberg, A. Marguerite, D. J. Perello, K. Bagani, T. Holder, Y. Myasoedov, L. S. Levitov. A. K. Geim, and E. Zeldoz, Nature 593 (2021) 528
[4]    S. Bhowal and G. Vignale, Physical Review B. 103 (2021) 195309
[5]    S. Roche, S. R. Power, B. K. Nikolić, J. H. García, and A.-P. Jauho, Journal of Physics: Materials 5 (2022) 021001
[6]    J. Salvador-Sánchez et al. ArXiv:2206.04565.

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