Snapshots of Dirac Fermions near the Dirac Point in Topological Insulators

Abstract

The recent focus on topological insulators is due to the scientific interest in the new state of quantum matter as well as the technology potential for a new generation of THz optoelectronics, spintronics and quantum computations. It is important to elucidate the dynamics of the Dirac fermions in the topologically protected surface state. Hence we utilized a novel ultrafast optical pump mid-infrared probe to explore the dynamics of Dirac fermions near the Dirac point. The femtosecond snapshots of the relaxation process were revealed by the ultrafast optics. Specifically, the Dirac fermion-phonon coupling strength in the Dirac cone was found to increase from 0.08 to 0.19 while Dirac fermions were away from the Dirac point into higher energy states. Further, the energy-resolved transient reflectivity spectra disclosed the energy loss rate of Dirac fermions at room temperature was about 1 meV/ps. These results are crucial to the design of Dirac fermion devices.

Unveiling the hidden nematicity and spin subsystem in FeSe

“…The abrupt decrease in τ 1,0 at 90 K, i.e., the relaxation of QPs becoming efficient, probably indicates that an increased density of states is involved in the relaxation processes along k x . 43,44 In this scenario, the results of Fig. 3a, c also imply that the reconstruction of FS at the M point occurs mainly near 90 K, with no significant fluctuation of electronic nematicity at the M point above 100 K. As ultrafast spectroscopy is a bulk probe, the present results provide bulk evidence to support the electronic structure according to the surface-sensitive ARPES.…”

Tunable Fano quantum-interference dynamics using a topological phase transition in(Bi1−xInx)Sim1, Koirala2, Brahlek3 et al. 2015Phys. Rev. B423270View full textAdd to dashboardCite

“…Numerous prior investigations have indeed shown that the electron density in the TSS rises via transition from the bulk to the TSS [16,21,[29][30][31][32][33][34]. In our case, the time scale of this transition is about 1 ps (see again the upper and middle panels of Fig.…”

Subpicosecond spin dynamics of excited states in the topological insulator Bi2Te3

“…In parallel with material efforts to obtain more bulkinsulating samples so that the bulk contribution to the conductivity can be completely suppressed [13][14][15], recent time-resolved (tr) experiments without spin resolution so far revealed the critical role of bulk-mediated electron-phonon scattering in the decay process of hot electrons across the linear energy-momentum dispersion of TSSs [16][17][18][19][20][21][22][23][24]. These findings indicate promising routes to overcome the problem of the bulk conductivity on ultrafast time scales, for example by generating low-energy excitations using fs-laser pulses, so that only electrons transiently occupying the TSS are excited within the bulk band gap [25].…”