Ionic and electronic properties of the topological insulator Bi2Te2Se investigated via β -detected nuclear magnetic relaxation and resonance of

Abstract

We report measurements on the high temperature ionic and low temperature electronic properties of the 3D topological insulator Bi 2 Te 2 Se using ion-implanted 8 Li β-detected nuclear magnetic relaxation and resonance. With implantation energies in the range 5-28 keV, the probes penetrate beyond the expected range of the topological surface state, but are still within 250 nm of the surface. At temperatures above ∼150 K, spin-lattice relaxation measurements reveal isolated 8 Li + diffusion with an activation energy E A = 0.185(8) eV and attempt frequency τ −1 0 = 8(3) × 10 11 s −1 for atomic site-to-site hopping. At lower temperature, we find a linear Korringa-like relaxation mechanism with a field dependent slope and intercept, which is accompanied by an anomalous field dependence to the resonance shift. We suggest that these may be related to a strong contribution from orbital currents or the magnetic freezeout of charge carriers in this heavily compensated semiconductor, but that conventional theories are unable to account for the extent of the field dependence. Conventional NMR of the stable host nuclei may help elucidate their origin. arXiv:1810.07879v3 [cond-mat.mtrl-sci]

Ultrathin 2D ternary Bi2Te2Se flakes for fast-response photodetectors with gate-tunable responsivity

“…Ternary BTS has a layered rhombohedral structure, in ARTICLES SCIENCE CHINA Materials which units of quintuple layers (QL) stack continuously through weak van der Waals interactions [24,25]. And the stacking sequence of each QL is Te-Bi-Se-Bi-Te with strong covalent bonding, as shown in Fig.…”

“…The ordered stacking sequence of Te-Bi-Se-Bi-Te has the following three features [20][21][22]: (i) the Se atomic layer is sandwiched in the middle of the stacking, rather than exposing to the outermost, which could avoid the Se vacancy defects caused by evaporation; (ii) the Bi atoms prefer to bond with the Se atoms due to the stronger chemical interaction, which could suppress the anti-site defects coming from the Bi-Te bonding; (iii) the determined stoichiometric ratio and atomic occupancy minimize the other disorder defects resulting from Te/Se randomness. Hence, BTS is expected to have much fewer defects, in a sharp contrast to Bi 2 Se 3 , Bi 2 Te 3 , and Bi 2 Te 3−x Se (0 < x < 3, x ≠ 1), resulting in a larger resistivity [23,24]. What is more, 2D BTS was theoretically predicted to have promising potentials for optoelectronic applications due to the good thermal and dynamical stability, suitable band gap, broad spectral absorption and high electron mobility [25][26][27][28].…”

Investigation of ionic and anomalous magnetic behavior in CrSe2 using 8Li β-NMR

“…In the slow fluctuation limit, where the ionic hop rate is much less than the NMR frequency, one expects a stronger field dependence to A than observed [36], but exceptions to this are not unprecendented [38]. Fitting to this simple model provides the curves in Figure 4a and a shared E a = 0.12(1) eV, in the range expected from other vdW materials [31].…”

“…For example, there is also no resolved quadrupolar splitting in another TMD, 2H -NbSe 2 , where the 8 Li line is much narrower [30]. This is not universal, though, since in some vdW crystals, there is a small splitting, but such splittings are less than the linewidth in CrSe 2 [31]. Similarly, conventional 7 Li NMR in closely related LiCrS 2 found no quadrupole splitting, despite comparable quadrupole moments of 7 Li and 8 Li [32].…”

“…When ν hop matches the NMR frequency, 1/T 1 is maximized at a Bloembergen-Purcell-Pound (BPP) peak [36]. From this, one can determine the coupling constant and measure ν hop as well as the associated activation energy barrier, E a , unambiguously [12,31]. However, absence of a clear 1/T 1 maximum at high temperatures prevents extracting quantitative information from this BPP model.…”