Ultrafast Spin-To-Charge Conversion at the Surface of Topological Insulator Thin Films

Abstract

Strong spin-orbit coupling, resulting in the formation of spin-momentum-locked surface states, endows topological insulators with superior spin-to-charge conversion characteristics, though the dynamics that govern it have remained elusive. Here, we present an all-optical method that enables unprecedented tracking of the ultrafast dynamics of spin-to-charge conversion in a prototypical topological insulator Bi${}_2$Se${}_3$/ferromagnetic Co heterostructure, down to the sub-picosecond timescale. Compared to pure Bi${}_2$Se${}_3$ or Co, we observe a giant terahertz emission in the heterostructure than originates from spin-to-charge conversion, in which the topological surface states play a crucial role. We identify a 0.12-picosecond timescale that sets a technological speed limit of spin-to-charge conversion processes in topological insulators. In addition, we show that the spin-to-charge conversion efficiency is temperature independent in Bi${}_2$Se${}_3$ as expected from the nature of the surface states, paving the way for designing next-generation high-speed opto-spintronic devices based on topological insulators at room temperature.

19 pages, 4 figures

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Cited by in corpus (14)

• Roadmap of spin-orbit torques
• Spintronic Sources of Ultrashort Terahertz Electromagnetic Pulses
• Ultrafast spin-currents and charge conversion at 3d-5d interfaces probed by time-domain terahertz spectroscopy
• Principles of spintronic THz emitters
• Large spin-to-charge conversion at room temperature in extended epitaxial Sb2Te3 topological insulator chemically grown on Silicon
• Ultrafast spin-charge conversion at SnBi${}_2$Te${}_4$/Co topological insulator interfaces probed by terahertz emission spectroscopy
• Transition of laser-induced terahertz spin currents from torque- to conduction-electron-mediated transport
• Emerging spintronics phenomena and applications
• Spin-orbit readout using thin films of topological insulator Sb2Te3 deposited by industrial magnetron sputtering
• Removal of spectral distortion due to echo for ultrashort pulses propagating through multilayer structures with thick substrate
• Excitation wavelength-dependent ultrafast THz emission from surface and bulk of three-dimensional topological insulators
• Theory of spin and orbital charge conversion at the surface states of Bi_{1-x}Sb_x topological insulator
• Terahertz time-domain signatures of the inverse Edelstein effect in topological-insulator|ferromagnet heterostructures
• Generation and manipulation of chiral terahertz waves emitted from the three-dimensional topological insulator Bi2Te3