Emergence of threefold symmetric helical photocurrents in low twinned

• 成果类型: Article
• 署名作者: Connelly, Blair C.; Taylor, Patrick J.; de Coster, George J.
• 署名单位: United States Department of Defense; US Army Research, Development & Engineering Command (RDECOM); US Army Research Laboratory (ARL); United States Army
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-13082
• DOI: 10.1073/pnas.2307425121
• 发表日期: 2024-01-30
• 关键词: 3-dimensional topological insulator; surface

摘要

We present evidence of a strong circular photon drag effect (PDE) in topological insulators (TIs) through the observation of helicity- dependent topological photocurrents with threefold rotational symmetry 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.