Spatially varying electronic dephasing in three-dimensional topological insulators

Abstract

Information processing devices operating in the quantum mechanical regime strongly rely on the quantum coherence of charge carriers. Studies of electronic dephasing in conventional metallic and semiconductor systems have not only paved the way towards high coherence quantum electronics, but also led to fundamental new insights in condensed matter physics. In this work, we perform a spatially resolved study of electronic dephasing in three dimensional topological insulators by exploiting an edge versus surface contacted measurement scheme. Unlike conventional two dimensional systems that are characterized by a single dephasing mechanism, we find that dephasing in our samples evolves from a variable-range-hopping type mechanism on the sample surface to a Nyquist type electron-electron interaction mechanism in the sub-surface layers. This is confirmed independently by the temperature and chemical potential dependence of the dephasing length, and gate dependent suppression/enhancement of the weak anti-localization effect. Our devices are fabricated using bulk insulating topological insulator BiSbTe 1.25 Se 1.75 capped with hexagonal-Boron Nitride in an inert environment, ruling out any extrinsic effects and confirming the topological surface state origin of our results. Our work introduces the idea of spatially resolved electronic dephasing and reveals a new regime of coherent transport in perhaps the most important topological insulator discovered so far. Our edge-vs-surface scheme may be applied to dephasing studies in a wide class of 2D materials.

Crossover from gapped-to-gapless Dirac surface states in magnetic topological insulator MnBi2Te4

“…This gapped surface state feature has been reported earlier in Mn-doped Bi 2 Se 3 thin films [46]. High-temperature magneto-transport measurements show the recovery of topological properties as the emergence of the WAL effect [33][34][35][36][37][38][39]. Multi-channel Hikami-Larkin-Nagaoka (HLN) analysis indicates the presence of gapless TSS for both devices [47].…”

“…In a TI, the WAL effect emerges as a sharp decrease in low-field magnetoconductivity. In the quantum diffusive regime, the surface carriers (Dirac fermions) while traversing time-reversal symmetric self-intersecting loops, interfere destructively due to the π-phase difference [33][34][35][36][37][38][39]. This results in a quantum correction (enhancement) to the zero-field longitudinal conductivity, known as WAL.…”

Topological Insulator Metamaterials

“…In addition, easier means to grow or procure large area films with controlled thicknesses can significantly help in expanding the gamut of metamaterial designs being employed. Another point of concern is the sensitivity of the topological properties to exposure to ambient conditions or other chemicals during nanofabrication/processing steps; suitable methodologies need to be employed to mitigate this issue, for example, using appropriate protective layers (practical demonstrations include a thin layer of Se 19 deposited in situ following TI film growth or a flake of h-BN placed on top of the exfoliated TI flake 213 ), and recovering surface states through thermal annealing. Another way to circumvent these issues is to avoid direct patterning of the topological material and instead placing it in close proximity to another nanostructured medium to alter light−matter interactions.…”

“…In addition, easier means to grow or procure large area films with controlled thicknesses can significantly help in expanding the gamut of metamaterial designs being employed. Another point of concern is the sensitivity of the topological properties to exposure to ambient conditions or other chemicals during nanofabrication/processing steps; suitable methodologies need to be employed to mitigate this issue, for example, using appropriate protective layers (practical demonstrations include a thin layer of Se deposited in situ following TI film growth or a flake of h-BN placed on top of the exfoliated TI flake), and recovering surface states through thermal annealing. Another way to circumvent these issues is to avoid direct patterning of the topological material and instead placing it in close proximity to another nanostructured medium to alter light–matter interactions. ,, Placing a Dirac material such as graphene or topological insulator in the proximity of a metamaterial has been shown to induce effects such as enhanced third harmonic generation in a system of metallic metamaterial and topological insulator film (Bi 2 Se 3 /Bi 2 Te 3 ), ultraconfined plasmonic modes in a graphene-insulator–metal-grating heterostructure, and strong, broadband THz modulation in a metallic wire grating loaded with graphene .…”

Electrical Transport Properties Driven by Unique Bonding Configuration in γ-GeSe

“…Figure 5d shows the temperature-dependent behavior of the fitting constants l φ and α. α is estimated to be slightly larger than 0.5 and is nearly constant below 20 K. The temperature dependence of the extracted l φ exhibits T −0.67 behavior, which shows a faster decay than that of Nyquist electron−electron scattering. 48 This deviation of the fitting parameters from 2D transport can be attributed to bulk-type conduction in γ-GeSe owing to the thickness of the measurement samples (∼80 nm). 49 A similar WAL was also reported for GeTe, 36 which is another similarity between γ-GeSe and GeTe.…”