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arXiv · 1706.05776

Chiral Spin Mode on the Surface of a Topological Insulator

H. -H. Kung·S. Maiti·X. Wang·S. -W. Cheong·D. L. Maslov·G. Blumberg
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Abstract

Using polarization-resolved resonant Raman spectroscopy, we explore collective spin excitations of the chiral surface states in a three dimensional topological insulator, Bi$_2$Se$_3$. We observe a sharp peak at 150 meV in the pseudovector $A_2$ symmetry channel of the Raman spectra. By comparing the data with calculations, we identify this peak as the transverse collective spin mode of surface Dirac fermions. This mode, unlike a Dirac plasmon or a surface plasmon in the charge sector of excitations, is analogous to a spin wave in a partially polarized Fermi liquid, with spin-orbit coupling playing the role of an effective magnetic field.

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H. -H. Kung, S. Maiti, X. Wang, S. -W. Cheong, D. L. Maslov, G. Blumberg. 2017-08-31. Chiral Spin Mode on the Surface of a Topological Insulator. https://doi.org/10.1103/physrevlett.119.136802

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