Orbital and valley transport in two-dimensional materials


The orbital-Hall effect (OHE) refers to the transverse flow of orbital angular momentum due to a longitudinally applied electric field [1]. Most of the theoretical understanding of this phenomenon has been consolidated by studying three dimensional (3D) metallic systems with promising results [2,3,4]. Only recently, the OHE has acquired a consistent interest of the community interested in two dimensional (2D) materials. The interplay between the low-dimensionality and the particular geometry of the band structure of 2D systems allow the occurrence of orbital phenomena up to now absent in 3D materials, such as orbital Hall insulating phases [5].
In my talk, I will discuss the fundamentals of orbital angular momentum transport in 2D insulating systems. I will discuss the characterisation of the orbital Hall insulating phases in terms of the orbital Chern numbers [6]. Also, based on the reinterpretation of the valley Hall effect in terms of the orbital valley Hall effect [7], I will extend the analysis to discuss possible experimental signatures of orbital angular momentum transport in 2D systems and in particular, I will revisit the origin of non-local resistance signals in Gr/hBN heterostructures.

[1] Bernevig, B. A., Hughes, T. L., & Zhang, S. C. (2005). Orbitronics: The intrinsic orbital current in p-doped silicon. Physical Review Letters, 95(6), 066601.
[2] Kontani, H., Tanaka, T., Hirashima, D. S., Yamada, K., & Inoue, J. (2009). Giant orbital Hall effect in transition metals: Origin of large spin and anomalous Hall effects. Physical review letters, 102(1), 016601.
[3] Go, D., Jo, D., Kim, C., & Lee, H. W. (2018). Intrinsic spin and orbital Hall effects from orbital texture. Physical Review Letters, 121(8), 086602.
[4] Ding, S., Liang, Z., Go, D., Yun, C., Xue, M., Liu, Z., ... & Yang, J. (2022). Observation of the orbital Rashba-Edelstein magnetoresistance. Physical Review Letters, 128(6), 067201.
[5] Canonico, L. M., Cysne, T. P., Rappoport, T. G., & Muniz, R. B. (2020). Two-dimensional orbital Hall insulators. Physical Review B, 101(7), 075429.
[6] Cysne, T. P., Costa, M., Canonico, L. M., Nardelli, M. B., Muniz, R. B., & Rappoport, T. G. (2021). Disentangling orbital and valley Hall effects in bilayers of transition metal dichalcogenides. Physical Review Letters, 126(5), 056601.
[7] Bhowal, S., & Vignale, G. (2021). Orbital Hall effect as an alternative to valley Hall effect in gapped graphene. Physical Review B, 103(19), 195309.