Blair Connelly^1*, Patrick Taylor¹, George de Coster^1*

1 US Army DEVCOM Army Research Laboratory, Adelphi, MD, 20783

* Corresponding authors emails: blair.c.connelly.civ@army.mil, george.j.decoster.civ@army.mil

DOI10.24435/materialscloud:4p-f2 [version v1]

Publication date: Jan 05, 2024

How to cite this record

Blair Connelly, Patrick Taylor, George de Coster, Emergence of threefold symmetric helical photocurrents in epitaxial low twinned Bi₂Se₃, Materials Cloud Archive 2024.4 (2024), https://doi.org/10.24435/materialscloud:4p-f2

Description

We present evidence of a strong circular photon drag effect (PDE) in topological insulators (TIs) through the observation of threefold rotationally symmetric helicity-dependent topological photocurrents using THz spectroscopy in epitaxially-grown Bi₂Se₃ with reduced crystallographic twinning. We establish how twinned domains introduce competing nonlinear optical (NLO) responses inherent to the crystal structure that obscure geometry-sensitive optical processes through the introduction of a spurious mirror symmetry. Minimizing the twinning defect reveals strong NLO response currents whose magnitude and direction depend on the alignment of the excitation to the crystal axes and follow the threefold rotational symmetry of the crystal. Notably, photocurrents arising from helical light reverse direction for left/right circular polarizations and maintain a strong azimuthal dependence—a result uniquely attributable to the circular PDE, where the photon momentum acts as an applied in-plane field stationary in the laboratory frame. Our results demonstrate new levels of control over the magnitude and direction of photocurrents in TIs and that the study of single-domain films is crucial to reveal hidden phenomena that couple topological order and crystal symmetries.

Materials Cloud sections using this data

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File name	Size	Description
THZ_Data.zip MD5md5:3aaa1f560d3e36dee927b0b70d4aa1e1	67.0 KiB	Data discussed in paper.

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Keywords

topological materials electronic structure spectroscopy terahertz photon drag effect Experimental