报告题目（Title）：Deformations in single layer two-dimensional materials 单层二维材料的形变及规范场
报 告 人（Speaker）：Reena Gupta (Friedrich-Alexander-University)
报告时间（Time）：2019年3月18日（周一）18:00
报告地点（Place）：校本部E106
邀请人（inviter）：任伟
报告摘要（Abstract）：
Two dimensional (2d) materials not only possess an intrinsic tendency to deformation not found in 3d materials, but also a geometry that more naturally allows for imposed deformations, for example via a vicinal substrate. In graphene, state-of-the-art theory based on encoding deformation through gauge potentials in the Dirac-Weyl equation neglects the role of the sub-lattice degrees of freedom, and thus only considers homogeneous (Cauchy-Born) deformation. We have generalized this theory to account for both acoustic and optical deformation fields [1], finding that non-Cauchy-Born gauges behave very differently and, in principle, allow for the long distance transport of valley charge. Our approach is based on formulating a general operator equivalence between the Slater-Koster tight-binding method and a general continuum effective Hamiltonian [2], an approach which captures both perturbative and non-perturbative deformation (such as interlayer twists). This methodology allows for the treatment of deformation via effective Hamiltonians in general 2d materials, and we demonstrate this via a discussion of deformations in the semi-metallic graphynes and stanene. Despite of their complex structure, the graphynes show a remarkable closeness to the physics of deformation in graphene. Stanene, on the other hand, due to its intrinsic buckling and hence broken mirror symmetry behaves rather differently, with very different gauge fields generated by in-plane versus out-of-plane deformations, and also an interesting valley-spin polarization in real space as a result of coupling between deformation induced polarized pseudospin and real spin, created by intrinsic spin-orbit-coupling. While studying deformation in 2d materials, the Hermiticity of the Hamiltonian is carefully examined as deformations can generate real as well as imaginary gauge fields [3].
§ [1] R. Gupta, F. Rost, M. Fleischmann, S. Sharma, and S. Shallcross, "Straintronics beyond homogeneous deformation" – Phys. Rev. B 99, 125407 (2019).
§ [2] F. Rost, R. Gupta, M. Fleischmann, D. Weckbecker, N. Ray, J. Olivares, M. Vogl, S. Sharma, O. Pankratov, S. Shallcross, "A non-perturbative theory of effective Hamiltonians: example of moiré materials" – submitted to Phys. Rev. B (arXiv:1901.04535).
§ [3] Amorim et al., "Novel effects of strains in graphene and other two dimensional materials" Physics Reports 617, 1 (2016).
