Weak antilocalization beyond the fully diffusive regime in Pb1−xSnxSe topological quantum wells

Abstract

We report the measurements and analysis of weak antilocalization (WAL) in Pb1-xSnxSe topological quantum wells in a new regime where the elastic scattering length is larger than the magnetic length. We achieve this regime through the development of high-quality epitaxy and doping of topological crystalline insulator (TCI) quantum wells. We obtain elastic scattering lengths that exceeds 100nm and become comparable to the magnetic length. In this transport regime, the Hikami-Larkin-Nagaoka model is no longer valid. We employ the model of Wittmann and Schmid to extract the coherence time from the magnetoresistance. We find that despite our improved transport characteristics, the coherence time may be limited by scattering channels that are not strongly carrier dependent, such as electron-phonon or defect scattering.

Signatures of dephasing by mirror-symmetry breaking in weak-antilocalization magnetoresistance across the topological transition in Pb1−xSnxSe

“…Nevertheless, but in agreement with our theoretical expectations, we observe for any x robust WAL MR, well described by the HLN formula in the limit of strong spin-orbit scattering and with the prefactor α = −1/2 [5]. This insight elucidates why robust WAL MR has previously been observed not only for topological SnTe epilayers [31][32][33][34] or Pb 0.7 Sn 0.3 Se quantum wells [35], but also for nontopological PbTe/(Pb,Eu)Te quantum wells [36]. Importantly, our data reveal striking differences between WAL MR in uncapped films compared to samples in which the amorphous Se surface layer intentionally breaks the mirror symmetry.…”

“…A fascinating question then arises to what extent surprising saturations of τ φ (T ) at low temperature observed since decades in many systems [38], and most recently in Dirac materials [35,[39][40][41][42], have been caused by the hidden spatial symmetry breaking, the mechanisms brought into light by our work.…”

“…Our results, together with those for graphene [14,15], lead to a rather striking conclusion that specific space symmetries can account for an apparent low-temperature saturation of τ φ (T ) determined from WAL MR studies. This finding suggests that hidden spatial-symmetry properties, together with decoherence specific to amorphous solids [37], might have often been responsible for a hitherto mysterious low-temperature saturation of τ φ (T ) observed in many systems [38], including recently studied Dirac materials [35,[39][40][41][42].…”

Observation of Coexisting Weak Localization and Superconducting Fluctuations in Strained Sn1–xInxTe Thin Films

“…However, the absolute value of the negative magnetoconductance cusp is high and can reach 10 e 2 / h , as shown in Figure c. There is a 20-fold enhancement of its magnitude for x > 0.18 which cannot be simply attributed to the WAL effect that typically yields corrections on the order of 1 e 2 / h . ,− This is especially the case at low temperature below 6 K ( T / T c < 2) as seen for x = 0.18 in Figure d. Therefore, superconducting fluctuations must be contributing to the conductance above T c .…”

“…The MT term differs from the HLN model only by a prefactor (Supporting Information S3). ,,,− Our fitting formula is obtained by combining all possible contributions from fluctuations with WL − …”