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

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 appli- cations. 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 surface state contributes ~61% of the total conduction, suggesting dom- inant 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.

Intrinsic V vacancy and large magnetoresistance in V_(1-δ)Sb_(2)single crystal

The binary pnictide semimetals have attracted considerable attention due to their fantastic physical properties that include topological effects, negative magnetoresistance, Weyl fermions, and large non-saturation magnetoresistance. In this paper, we have successfully grown the high-quality V_(1-δ)Sb_(2) single crystals by Sb flux method and investigated their electronic transport properties. A large positive magnetoresistance that reaches 477% under a magnetic field of 12 T at T = 1.8 K was observed. Notably, the magnetoresistance showed a cusp-like feature at the low magnetic fields and such feature weakened gradually as the temperature increased, which indicated the presence of a weak antilocalization effect(WAL). In addition, based upon the experimental and theoretical band structure calculations, V_(1-δ)Sb_(2) is a research candidate for a flat band.

Electrical transport properties of cerium doped Bi_(2)Te_(3)thin films grown by molecular beam epitaxy

Introducing magnetism into topological insulators(TIs)can tune the topological surface states and produce exotic physical effects.Rare earth elements are considered as important dopant candidates,due to their large magnetic moments from heavily shielded 4f electrons.As the first element with just one 4f electron,cerium(Ce)offers an ideal platform for exploring the doping effect of f-electron in TIs.Here in this work,we have grown cerium-doped topological insulator Bi_(2)Te_(3)thin films on an Al_(2)O_(3)(0001)substrate by molecular beam epitaxy(MBE).Electronic transport measurements revealed the Kondo effect,weak anti-localization(WAL)effect and suppression of surface conducting channels by Ce doping.Our research shows the funda-mental doping effects of Ce in Bi_(2)Te_(3)thin films,and demonstrates that such a system could be a good platform for further re-search.

Quantum transport in topological semimetals under magnetic fields

Topological semimetals are three-dimensional topological states of matter, in which the conduction and valence bands touch at a finite number of points, i.e., the Weyl nodes. Topological semimetals host paired monopoles and antimonopoles of Berry curvature at the Weyl nodes and topologically protected Fermi arcs at certain surfaces. We review our recent works on quantum transport in topo- logical semimetals, according to the strength of the magnetic field. At weak magnetic fields, there are competitions between the positive magnetoresistivity induced by the weak anti-localization effect and negative magnetoresistivity related to the nontrivial Berry curvature. We propose a fitting formula for the magnetoconductivity of the weak anti-localization. We expect that the weak localization may be induced by inter-valley effects and interaction effect, and occur in double-Weyl semimetals. For the negative magnetoresistance induced by the nontrivial Berry curvature in topological semimetals, we show the dependence of the negative magnetoresistance on the carrier density. At strong magnetic fields, specifically, in the quantum limit, the magnetoconductivity depends on the type and range of the scattering potential of disorder. The high-field positive magnetoconductivity nmy not be a com- pelling signature of the chiral anomaly. For long-range Gaussian scattering potential and half filling, the magnetoconductivity can be linear in the quantum limit. A minimal conductivity is found at the Weyl nodes although the density of states vanishes there.

Enhanced linear magneto-resistance near the Dirac point in topological insulator Bi2(Te1−xSex)3 nanowires

We report the composition and back-gate voltage tuned transport properties of ternary compound Bi2(Te1−xSex)3 nanowires synthesized by chemical vapor deposition(CVD).It is found that the population of bulk carriers can be suppressed effectively with increasing the Se concentration x.In Bi2(Te1−xSex)3 nanowires with x=25%±5%,the ambipolar surface conduction associated with tuning the Fermi energy across the Dirac point of topological surface states is induced by applying a back-gate voltage.Importantly,we find that while the magnetoresistance(MR)follows the weak antilocalization(WAL)behavior when the Fermi level is tuned away from the Dirac point,MR is enhanced in magnitude and turns more linear in the whole magnetic field range(between±9 T)near the Dirac point.The observation of the enhanced linear magneto-resistance(LMR)and crossover from WAL to LMR,near the Dirac point provides a deeper insight into understanding the nature of topological insulator’s surface transport and the relation between these two widely observed magneto-transport phenomena.