Signatures of long-range-correlated disorder in the magnetotransport of ultrathin topological insulators

Abstract

In an ultrathin topological insulator (TI) film, a hybridization gap opens in the TI surface states, and the system is expected to become either a trivial insulator or a quantum spin Hall insulator when the chemical potential is within the hybridization gap. Here we show, however, that these insulating states are destroyed by the presence of a large and long-range-correlated disorder potential, which converts the expected insulator into a metal. We perform transport measurements in ultrathin, dual-gated topological insulator films as a function of temperature, gate voltage, and magnetic field, and we observe a metallic-like, non-quantized conductivity, which exhibits a weak antilocalizationlike cusp at low magnetic field and gives way to a nonsaturating linear magnetoresistance at large field. We explain these results by considering the disordered network of electron-and hole-type puddles induced by charged impurities. We argue theoretically that such disorder can produce an insulator-to-metal transition as a function of increasing disorder strength, and we derive a condition on the band gap and the impurity concentration necessary to observe the insulating state. We also explain the linear magnetoresistance in terms of strong spatial fluctuations of the local conductivity, using both numerical simulations and a theoretical scaling argument.

Ferromagnetic phase transition in topological crystalline insulator thin films: Interplay of anomalous Hall angle and magnetic anisotropy

“…with ∆ the energy gap at the Dirac cone and E F the Fermi level. Since the TSS residing at the (111) surface of the SnTe are gapless, then A b = π [46,76,77] and the accumulation of a π Berry phase leads to the observed WAL. However, by applying an external field µ 0 H, the destructive interference of the two time reversed paths brings about a negative ∆σ, as evidenced in Fig.…”

Current-induced breakdown of the quantum anomalous Hall effect

“…In addition, the large dielectric constant of TI films slows down the decay of the Coulomb potential in space and greatly enhances the puddle formation [33]. Indeed, signatures of puddle formation have been observed in the resistivity of ultrathin films of (Bi x Sb 1−x ) 2 Te 3 [35].…”

“…It is prudent to mention that runaway electron heating [11,37] and Zenner tunneling [33,35] could provide alternative breakdown mechanisms for the QAHE. However, the heating effect in our QAHI films should be small due 4.…”

Absence of strong localization at low conductivity in the topological surface state of low-disorder Sb2Te3

“…Disorder decidedly affects the electrical conduction of TSS: the mobilities of typical thin film V-VI topological materials reach only of order 100 cm 2 /Vs. Furthermore, while electrostatic gating can tune the Fermi level to the charge neutrality point (CNP), charged impurities obscure low density transport physics in favor of transport through charge puddles [12][13][14]. Consequently, insulating (σ xx < e 2 /h) time-reversal symmetryprotected 3D TI systems have only been seen in the thinnest films, where the clean-limit hybridization gap far exceeds room temperature [15][16][17].…”