Observation of surface dominated topological transport in strained semimetallic ErPdBi thin films

Abstract

In this Letter, we present experimental observation of surface-dominated transport properties in [110]-oriented strained (∼1.6%) ErPdBi thin films. The resistivity data show typical semi-metallic behavior in the temperature range of 3 K ≤ T ≤ 350 K with a transition from semiconductor- to metal-like behavior below 3 K. The metallic behavior at low temperature disappears entirely in the presence of an external magnetic field >1 T. The weak-antilocalization (WAL) effect is observed in magneto-conductance data in the low magnetic field region and follows the Hikami–Larkin–Nagaoka (HLN) model. HLN fitting estimated single coherent channel, i.e., α ∼ −0.51 at 1.9 K, and the phase coherence length (Lϕ) shows the Lϕ ∼ T−0.52 power law dependence on temperature in the range of 1.9 K–10 K, indicating the observation of 2D WAL. Shubnikov–de Haas (SdH) oscillations are observed in magneto-resistance data below 10 K and are fitted to standard Lifhsitz Kosevich theory. Fitting reveals the effective mass of charge carriers ∼0.15 me and a finite Berry phase of 0.86π ± 0.16. The sheet carrier concentration and mobility of carriers estimated using SdH data are ns ∼ 1.35 × 1012 cm−2 and μs = 1210 cm2 V−1 s−1, respectively, and match well with the data measured using the Hall measurement at 1.9 K to be n ∼ 1.22 × 1012 cm−2, μ = 1035 cm2 V−1 s−1. These findings indicate the non-trivial nature and surface-dominated transport properties of strained (110) ErPdBi thin films at low temperatures.

Strain driven emergence of topological non-triviality in YPdBi thin films

“…Figure 4 d shows the Dingle plots at 1.9 K, 3 K and 4 K, the slope of linear fitting to the data points gives Dingle temperature ~ 5 K. The transport lifetime ( ) and mean free path ( ) of carriers are estimated using the relations, and as ~ 2.43 × 10 –13 s and 78 nm, respectively. The carrier mobility ( ) ~ 3694 is estimated for strained YPdBi thin films, which is quite high among other non-trivial half Heusler alloys like LuPdBi (2100 ) 34 , ErPdBi (1035 ) 14 , DyPdBi (1780 ) 17 and YPtBi(1486 ) 18 . All the parameters extracted from the different fits are listed in the Table 1 .…”

“…Even more interestingly, a recent theoretical studies have indicated the possibility to engineer non-trivial topological states in an otherwise trivial half-Heusler system by strain engineering. While these non-trivial surface states can be detected in ultra-pure samples by angle resolved photoemission spectroscopy and other surface sensitive techniques 10 – 13 , whereas transport measurements provide a relatively easy way to detect the surface states 6 , 14 – 18 . This is possible since the surface states are topologically protected and conserve time reversal symmetry which can be broken by an applied external magnetic field providing a pathway to detect them using transport measurements 3 , 6 , 16 , 19 .…”

Structural and transport properties of Y1-x(Dy)xPdBi (0 ≤ x ≤ 1) topological semi-metallic thin films

“…Various band structure parameters are extracted from analysis of SdH oscillations, see Table S2. From these values listed in the ±for samples D0, D2, D5 and DPB respectively using the well-known method of Landau level fan diagram 9,24,36,44 , see Fig. S5.…”

“…Using DFT, Chadov et al predicted that band structure of YPdBi can be tuned between topologically trivial and non-trivial state by varying the lattice constant and/or spin orbit coupling strength of the material system 6 . Although the lattice could be strained by applying uniaxial pressure, an easier way is to grow epitaxial oriented thin films on carefully selected substrates to induce a lattice strain 9,[24][25][26] . We have shown in an earlier work using experimental and band structure computations that ~3.12% strained YPdBi (~30nm) thin films are topologically non-trivial 9 .…”

“…The thin film growth rate is optimized using XRR measurements. The electrical and magneto-transport measurements were performed on rectangular samples with dimensions 3mm 10mm with Ohmic contacts made by using silver paste cured at roomtemperature 9,24,26 . The temperature dependent longitudinal resistivity ( xx ) curves show a typical semi-metallic behavior for all samples in temperature range 1.9 K T 300 K and a sharp drop in resistivity is observed at low temperatures for samples D0 9 , D2 and D5.…”