We have studied the carrier transport in two topological insulator (TI) Bi2Te3 microflakes between 0.3 and 10 K and under applied backgate voltages (VBG). Logarithmic temperature dependent resistance corrections due to the two-dimensional electron-electron interaction effect in the presence of weak disorder were observed. The extracted Coulomb screening parameter is negative, which is in accord with the situation of strong spin-orbit scattering as is inherited in the TI materials. In particular, positive magnetoresistances (MRs) in the two-dimensional weak-antilocalization (WAL) effect were measured in low magnetic fields, which can be satisfactorily described by a multichannelconduction model. Both at low temperatures of T < 1 K and under high positive VBG, signatures of the presence of two coherent conduction channels were observed, as indicated by an increase by a factor of ≈ 2 in the prefactor which characterizes the WAL MR magnitude. Our results are discussed in terms of the (likely) existence of the Dirac fermion surface states, in addition to the bulk states, in the three-dimensional TI Bi2Te3 material.

Single-crystalline zinc oxide (ZnO) nanowires (NWs) with diameters of 90-200 nm were synthesized by the thermal evaporation method. Four-probe Ti/Au electrodes were made by the standard electron-beam lithography technique, and the intrinsic resistivities, rho(T), of individual NWs were measured over a wide range of temperature from 300 down to 0.25 K. The temperature behavior of rho(T) between 300 and 5 K reveals that the intrinsic electrical-transport mechanisms through individual ZnO NWs are due to a combination of the thermal activation conduction and the nearest-neighbor hopping conduction processes. Three distinct activation and hopping contributions with discrete characteristic activation energies are observed. Above about 100 K, the charge transport mechanism is dominated by the thermal activation of electrons from the Fermi level, mu, to the conduction band. Between approximately 20 and 100 K, the charge transport mechanism is due to the activation of electrons from mu to the upper impurity (D-) band. Between approximately 5 and 20 K, the charge transport mechanism arises from the nearest-neighbor hopping conduction within the lower impurity (D) band. Such unique electrical conduction behaviors can be explained in terms of the intricate material properties (in particular, the presence of moderately high concentrations of n-type defects accompanied with a slight self-compensation) in natively doped ZnO NWs. In one heavily doped NW, a surface-related conduction process manifesting the two-dimensional attributes of quantum-interference transport phenomena is observed. The carrier concentrations in our NWs have been estimated, and they were found to lie close to the critical concentration for the Mott metal-insulator transition.

We have fabricated oxygen deficient polycrystalline ZnO films by the rf sputtering deposition method. To systematically investigate the charge transport mechanisms in these samples, the electrical resistivities have been measured over a wide range of temperature from 300 K down to liquid-helium temperatures. We found that below about 100 K, the variable-range-hopping (VRH) conduction processes govern the charge transport properties.In particular, the Mott VRH conduction process dominates at higher temperatures, while crossing over to the Efros-Shklovskii (ES) VRH conduction process at lower temperatures.The crossover occurred at temperatures as high as a few tens degrees Kelvin. Moreover, the temperature behavior of resistivity over the entire VRH conduction regime from the Mott-type to the ES-type process can be well described by a universal scaling law.

The temperature behavior of how electrons propagate through an insulating electronic contact formed at the interface between a submicron Cr/Au electrode and a metallic RuO(2) nanowire (NW) has been studied between 300 and 1 K. The NWs are typically of ∼70 nm in diameter and a few microns long. The submicron electrodes were fabricated by the standard electron-beam lithography technique. By employing the two-probe method, the electronic contact resistances, R(c)(T), have been determined. We found that, in general, R(c) increases rapidly with decreasing temperature but eventually saturates at liquid-helium temperatures. Such a temperature behavior can be well described by a thermal fluctuation-induced tunneling (FIT) conduction process which considers the crossover feature from thermal activation conduction at high temperatures to simple elastic tunneling conduction at low temperatures. The wide applicability of this FIT model has further been established by employing metallic IrO(2) and Sn-doped In(2)O(3-x) NWs. This work demonstrates that the underlying physics for the charge transport properties of an insulating electronic contact can be well understood.

Single-crystalline indium tin oxide (ITO) nanowires (NWs) were grown by the standard thermal evaporation method. The as-grown NWs were typically 100-300 nm in diameter and a few microm long. Four-probe submicron Ti/Au electrodes on individual NWs were fabricated by the electron-beam lithography technique. The resistivities of several single NWs have been measured from 300 down to 1.5 K. The results indicate that the as-grown ITO NWs are metallic, but disordered. The overall temperature behavior of resistivity can be described by the Bloch-Grüneisen law plus a low-temperature correction due to the scattering of electrons off dynamic point defects. This observation suggests the existence of numerous dynamic point defects in as-grown ITO NWs.