Ultrafast Dynamics in Topological Insulators

Abstract

Ultrafast dynamics of carriers and phonons in topological insulator Bi 2 Se 3, Cu x Bi 2 Se 3 (x = 0, 0.1, 0.125) single crystals were studied by time-resolved pump-probe spectroscopy. The coherent optical phonon (A 1g 1) is found via the damped oscillation in the transient reflectivity changes (∆R/R) for Cu x Bi 2 Se 3. The observed red shift of A 1g 1 phonon frequency suggests the intercalation of Cu atoms between a pair of the quintuple layers of Bi 2 Se 3 crystals. Moreover, the relaxation processes of Dirac fermion near the Dirac point of Bi 2 Se 3 are studied by optical pump and mid-infrared probe spectroscopy through analyzing the negative peak of the ∆R/R. The Dirac fermion-phonon coupling strength was found in the range of 0.08-0.19 and the strength is reduced as it gets closer to the Dirac point. The ultrafast dynamics and fundamental parameters revealed by time-resolved pump-probe spectroscopy are important for designing the optoelectronics in the mid-IR and THz ranges.

Effects of Stoichiometry on Structural, Morphological and Nanomechanical Properties of Bi2Se3 Thin Films Deposited on InP(111) Substrates by Pulsed Laser Deposition

“…Bismuth selenide (Bi 2 Se 3 ) is of great interest owing to its intriguing physical properties as a three-dimensional topological insulator [1][2][3][4][5], and potential applications in spintronics [6], optoelectronics [7] and quantum computation [8]. In addition, Bi 2 Se 3 possesses excellent thermoelectric properties at room-temperature [9,10] and low temperature regimes [11].…”