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

Abstract

Transient reflectivity (TR) measured at laser photon energy 1.51 eV from the indirectly intersurface coupled topological insulator Bi 2-x Mn x Se 3 films (12 nm thick) revealed a strong dependence of the rise-time and initial decay-time constants on photoexcited carrier density and Mn content. In undoped samples (x = 0), these time constants are exclusively governed by electron-electron and electron-phonon scattering, respectively, whereas in films with x = 0.013 -0.27 ultrafast carrier dynamics are completely controlled by photoexcited electron trapping by ionized Mn 2+ acceptors and their dimers. The shortest decay-time (~0.75 ps) measured for the film with x = 0.27 suggests a great potential of Mn-doped Bi 2 Se 3 films for applications in high-speed optoelectronic devices. Using Raman spectroscopy exploiting similar laser photon energy (1.58 eV), we demonstrate that due to indirect intersurface coupling in the films, the photoexcited electron trapping in the bulk enhances the electron-phonon interaction strength in Dirac surface states.

Nonlinear optical observation of coherent acoustic Dirac plasmons in thin-film topological insulators

“…The TR-peak, TR-BG, TR-UBG, TSHG-peak, TSHG-BG and TSHG-UBG intensities all increase with increasing probe beam power, but at different rates in accordance with their linear (for TR processes) and quadratic (for TSHG processes) power dependences 53 62 . The TR traces are similar to those reported previously 48 55 62 63 , while the TSHG traces show an oscillatory behaviour that is not present in the TR traces.…”

“…Figure 3c shows the normalized TR and TSHG traces for the 10 nm thick film. As we discussed above, the TR signal increases with due to the electron-electron thermalization and subsequently decreases with due to the electron-LO-phonon scattering 48 55 62 63 . In contrast, the TSHG signal increases more slowly with and decays faster with .…”

“…However, by choosing the appropriate light polarization geometry, the in-plane and out-of-plane tensor components contributing to the TSHG response can be separately monitored. In contrast, an isotropic TR response is negative due to an absorption bleaching process associated with Pauli blocking, thus exposing exclusively the carrier population dynamics mainly through the out-of-plane refractive index modulation as a consequence of a normal incidence pumping geometry applied and the same spot size of the focused pump and probe beams (see the methods section) 48 55 62 63 .…”

Synthesis of WS1.76Te0.24 alloy through chemical vapor transport and its high-performance saturable absorption

“…Notably, the decay time was 3.8 ps fitted by a single exponential function. The decay time of WS 1.76 Te 0.24 was significantly shorter than 13 ps of WS 2 29 and 5 ps of WTe 2 6 , as a result of higher density of trapping states induced by Te doping in the nanoflake 30 .…”

Linear-optical access to topological insulator surface states

“…Moreover, the investigation of the ultrafast spin dynamics is virtually impossible by electrical transport techniques. All-optical access, [9][10][11][12] on the other hand, provides a very powerful method for noninvasive investigation of ultrafast processes in TIs, [13][14][15][16] while separating the surface response from that of the bulk is still extremely challenging. Recently, a nonlinear-optical approach was employed to study the TI surface.…”