Temperature-dependent carrier–phonon coupling in topological insulator Bi2Se3

Abstract

Temperature-dependent (11.0 KÀ294.5 K) carrier-phonon coupling in Bi 2 Se 3 is investigated by ultrafast pumpÀprobe spectroscopy. The rise time of the differential reflectivity is interpreted by a combined effect of electron temperature relaxation and hot-phonon lifetime. The electronÀphonon coupling constant of the bulk state (k ¼ 0:6360:05) is deduced from theoretical fitting. Increasing hot-phonon lifetime with decreasing temperature is attributed to a decreasing phononÀphonon collision rate. A complete analysis of the thermalization process is presented. Understanding carrier and phonon dynamics is essential for future optoelectronic and spintronic applications of topological insulators. V

Effect of Mn doping on ultrafast carrier dynamics in thin films of the topological insulator Bi2Se3

“…Figure 2 shows the longer delay-time TR traces that are negative in accordance with their absorption bleaching nature and are characterized by a rise and multiple decay behavior [4,[12][13][14][15][16]. The corresponding rise-time (τ R ) and decay-time (τ Di ) constants were estimated using a multiexponential fitting function [27],…”

“…In the latter case, the ultrafast low-energy dynamics of free carriers residing in Dirac SS are found to take a few tens of ps, thus being much longer than the characteristic decaytime in graphene (1-2 ps) [18,19]. Alternatively, the ultrafast carrier relaxation dynamics probed at photon energy ~1.5 eV includes fast electron-electron thermalization (~0.3-0.5 ps) and longitudinal-optical(LO)-phonon relaxation in the bulk (~1.5-3.5 ps) that leads to a metastable population of the conduction band edge [4,[12][13][14][15][16], which continuously feeds a non-equilibrium population of Dirac SS (~5-220 ps) [4,6,15] being likely mediated by the coherent acoustic phonon dynamics [20]. Afterwards the quasi-equilibrium carrier population in Dirac SS is reached within extremely long times of ⩾10 ns [4,8,15,20,21].…”

“…Ultrafast carrier dynamics in TIs have been studied using time-and angle-resolved photoemission spectroscopy (TrARPES) [6][7][8][9][10][11], transient reflectivity (TR) at photon energy ~1.5 eV [4,[12][13][14][15][16], and ultrafast optical-pump terahertz-probe spectroscopy (probe photon energy ~1.0 meV) [17]. In the latter case, the ultrafast low-energy dynamics of free carriers residing in Dirac SS are found to take a few tens of ps, thus being much longer than the characteristic decaytime in graphene (1-2 ps) [18,19].…”

Influence of coherent optical phonon on ultrafast energy relaxation

“…The rise and fall of the transient reflectance are usually complicated, and there is still a lack of consistency in the interpretations. [2][3][4][5][6] The photo-excited carriers also change the equilibrium position of the atoms instantaneously. 7 If the pulse duration is shorter than the periods of atomic vibrations, atoms can oscillate around their new equilibrium position collectively, which is referred to as coherent OP.…”

Enhancement of a photovoltaic cell performance by a coupled cooled nanocomposite thermoelectric hybrid system, using extended thermodynamics

“…The phonon velocity is 2900 m/s [44]. For the phonon specific heat, we have obtained the value from [45,46] being 0.255 MJ/m 3 K. We can deduce via (24) that the phonon mean free path is 2.7 nm. The total heat capacity being 1.33 MJ/m 3 K [3], we can calculate the electron heat capacity to be 1.08 MJ/m 3 K. The Seebeck coefficient is -50 µV/K [3].…”