Paul M. HANEY
Berry curvature plays an essential role in determining material properties. In time-reversal symmetric systems which break inversion symmetry, the total Berry curvature vanishes while the crystal momentum-resolved Berry curvature may be nonzero. In this talk, we consider two nonmagnetic systems in which the compensated Berry curvature in different valleys leads to unique observable effects. We first consider MoS2, which exhibits an orbital Hall effect. We show that an applied electric field induces a change in the charge density distribution, and utilize first principles calculations to show that the distorted charge density profile may be used to determine to the energy-resolved orbital Hall conductivity [1]. We next consider twisted double bilayer graphene. This system develops valley contrasting Berry curvature and orbital magnetization as a function of vertical displacement field [2]. We use semi-classical analysis together with calculations of the Hofstadter spectrum to show how the valley-dependent orbital magnetization is reflected in the magnetic field-dependent spectrum [3]. We compare our results on the twisted double bilayer graphene system with scanning tunneling microscopy data.
[1] F. Xue, V. Amin, and P. M. Haney, Phys. Rev. B 102, 161103(R) (2020).[2] N. R. Chebrolu, B. L. Chittari, and J. Jung, Phys. Rev. B 99, 235417 (2019).
[3] Y. Gao and C. Niu, Proc. Natl. Acad. Sci., 114, 7295 (2017).