Weak Anti-Localization and Quantum Oscillations in Topological Crystalline Insulator PbTe

Ke-Jie Wang, Wei Wang, Min-Hao Zhang, Xiao-Qian Zhang, Pei Yang, Bo Liu, Ming Gao, Da-Wei Huang, Jun-Ran Zhang, Yu-Jie Liu, Xue-Feng Wang, Feng-Qiu Wang (+3 others)
2017 Chinese Physics Letters  
Topological crystalline insulators (TCIs) have attracted worldwide interest since their theoretical predication and have created exciting opportunities for studying topological quantum physics and for exploring spintronic applications. In this work, we successfully synthesize PbTe nanowires via the chemical vapor deposition method and demonstrate the existence of topological surface states by their 2D weak anti-localization effect and Shubnikov-de Haas oscillations. More importantly, the
more » ... state contributes ∼61% of the total conduction, suggesting dominant surface transport in PbTe nanowires at low temperatures. Our work provides an experimental groundwork for researching TCIs and is a step forward for the applications of PbTe nanowires in spintronic devices. Topological crystalline insulators (TCIs) are a recently discovered topological phase with robust surface states residing on high-symmetry crystal surfaces. Different from conventional topological insulators (TIs), protection of the surface states comes from point-group symmetry instead of timereversal symmetry in TIs. [1−3] The distinct properties of TCIs make them promising candidates for spintronics, quantum computation, tunable pressure sensors, mid-infrared detectors and thermoelectric conversion. [4−7] The exciting discovery and novel properties of TCIs motivate scientists to search the quantum transport phenomenon from the surface states. Theoretical calculations predict that SnTe, PbTe and their related alloy Pb 1− Sn Te (Se), possessing highsymmetry rock-salt structure ( Fig. 1(a) ) with ordered or partially disordered atomic stacking, are stable TCIs. SnTe's surface states with linear Dirac dispersion on mirror-symmetry surfaces have been experimentally detected by angle-resolved photoemission spectroscopy (ARPES), [8, 9] and also confirmed through transport measurements. [10−12] In contrast, PbTe's surface states have rarely been observed, mostly due to the shadowing effect from the bulk carrier overwhelming the surface. [13] Thus we have fabricated PbTe nanowires, which possess much higher surfaceto-bulk ratio, to probe the topological surface states by transport measurements. In this work, we report the weak anti-localization (WAL) effect and Shubnikov-de Haas (SdH) oscillations originated from the surface states of PbTe nanowires. We have found that the WAL effect can be well described by the Hikami-Larkin-Nagaoka (HLN) model where the temperature-dependent phase coherent length exhibits a power-law behavior of Φ ∼ −0.47 . [14] Also, the SdH oscillations reveal a defined 2D surface state in the PbTe nanowire. More importantly, the surface contribution to the total conduction has been estimated as ∼61% at low temperatures, which suggests dominant surface transport in PbTe nanowires. Following the procedure reported by Tanaka et al., [15] crystal boules of PbTe were produced using a modified Bridgman method. High purity Pb (99.999%) and Te (99.999%) were mixed with an atomic ratio of 1 and were sealed in an evacuated quartz tube. The quartz tube was placed horizontally into a box furnace and heated to 950 ∘ C for two days. After that, the tube was slowly cooled to 770 ∘ C at a rate of 2 ∘ C/h and then rapidly cooled down to room temperature. The as-grown PbTe bulk crystal is shown in Fig. 1(b) . To check the phase purity, powder x-ray diffraction patterns were obtained, as shown in Fig. 1(c) , demonstrating the standard PbTe Bragg peaks. The PbTe nanowires then were synthesized by means of PbTe powder deposited on Si substrates via the chemical vapor deposition (CVD) method with gold catalysts by the vapor-liquid-solid (VLS) mechanism in quartz tube furnace. [16] PbTe powder was loaded in the center of the quartz tube and Au-coated Si substrates were placed at 10-15 cm downstream away from PbTe. The quartz tube was sealed and evacuated. Then high-purity Ar gas was used to flush the quartz tube three times to provide an oxygen-free en-*
doi:10.1088/0256-307x/34/2/026201 fatcat:6keq2vvwhfgcrn5nthw3pgnzzq