Resonance-type thickness dependence of optical second harmonic generation in thin-films of the topological insulator Bi2Se3

Abstract

Optical second harmonic generation (SHG) has been measured for the first time in reflection from the nanometer-thick films (6 to 40 nm) of the topological insulator Bi2Se3 using 1.51 eV (820 nm) Ti:Sapphire laser photons and revealed a strong dependence of the integral SHG intensity on the film thickness. The integral SHG intensity was determined by area integration of the SHG rotational anisotropy patterns measured for different input-output light polarization geometries. A ~100-fold enhancement of the integral SHG intensity with decreasing film thickness has been suggested to result from the DC-electric-field-induced SHG (EFISHG) effects. Two sources of dynamically created DC electric field were proposed: (i) the capacitor-type DC electric field that gradually increases with decreasing film thickness from 40 to 6 nm due to a dynamical imbalance of photoexcited long-lived carriers between the opposite-surface Dirac surface states and (ii) an DC electric field associated with a nonlinearly excited Dirac plasmon, which is responsible for the resonant enhancement of the integral SHG intensity for the 10 nm thick film with a Lorentz-shaped resonance of ~1.6 nm full width at half maximum. Additionally to the general SHG enhancement trends with decreasing film thickness, a relative decrease of the out-of-plane contribution with respect to the in-plane contribution was observed. Using a theoretical treatment of the measured SHG rotational anisotropy patterns, this effect has been suggested to result from the joint contributions of the linear and quadratic DC electric field effects to the EFISHG response.

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• Clarifying ultrafast carrier dynamics in ultrathin films of the topological insulator Bi2Se3 using transient absorption spectroscopy
• Nonlinear Optical Observation of Coherent Acoustic Dirac Plasmons in Thin-Film Topological Insulators
• Plasmon-enhanced electron-phonon coupling in Dirac surface states of the thin-film topological insulator Bi2Se3
• Fundamentally fastest optical processes at the surface of a topological insulator
• Effect of Mn doping on ultrafast carrier dynamics in thin films of the topological insulator Bi2Se3
• A cascading nonlinear magneto-optical effect in topological insulators
• Second harmonic generation by strongly coupled exciton-plasmons: the role of polaritonic states in nonlinear dynamics
• Ultrafast dynamics of photocurrents in surface states of 3D topological insulators
• Ultrafast electron dynamics in a topological surface state observed in two-dimensional momentum space
• A versatile setup for symmetry-resolved ultrafast dynamics of quantum materials
• Probing and controlling terahertz-driven structural dynamics with surface sensitivity