Jonathan Sabota, Stanford University and SLAC National Accelerator Laboratory

"Influence of Local Symmetry on Lattice Dynamics and Spin Texture of Surface States"

Abstract: While global symmetries are decisive for determining bulk material properties, local symmetries can have a propound impact on confined electronic states, particularly those at surfaces. In this talk, we will examine the consequences on the lattice dynamics and spin-texture of topological surface states. Our experimental methodology spans time-resolved and spin-resolved photoemission spectroscopies.

First, we employ time- and angle- resolved photoemission spectroscopy (trARPES) to study coherent phonons in the topological insulator Bi2Te3. We find that the surface state couples to coherent modes that cannot be photoexcited in the bulk [1]. Our models show that these behaviors arise naturally due to the translational and inversion symmetries broken at the surface. By leveraging these locally broken symmetries, these effects expand the phase space for tailoring material properties on-demand, and they may provide a necessary ingredient for driving topological phase transitions via optical excitation.

Next, we will present our first steps towards measuring the spin degree-of-freedom associated with these dynamics. We select the Rashba semiconductor BiTeCl as a model system to investigate strong spin-orbit coupling using spin-resolved ARPES. Our measurements reveal a strongly momentum-dependent spin texture in the surface states which can only be described by incorporating higher-order terms into the canonical Rashba Hamiltonian [2]. These terms are determined by local symmetries, and should have a strong impact on the spin-dependent transport of charge carriers at the surface.

References

[1] J.A. Sobota et al, Phys. Rev. B 107, 014305 (2023)
[2] J. Qu et al, npj Quant. Mat. 8, 13 (2023)