We study coherent electronic transport in charge-density-tunable microdevices patterned from thin films of the topological insulator (TI) Bi${}_{2}$Se${}_{3}$. The devices exhibit pronounced electric field effect, including ambipolar modulation of the resistance with an on-and-off ratio of 500%. We show that the weak antilocalization correction to conductance is sensitive to the number of coherently coupled channels, which in a TI includes the top and bottom surfaces and the bulk carriers. These are separated into coherently independent channels by the application of gate voltage and at elevated temperatures. Our results are consistent with a model where channel separation is determined by a competition between the phase coherence time and the surface-to-bulk scattering time.

Electrically tunable surface-to-bulk coherent coupling in topological insulator thin films

Recent advances in successful operation of silicon-based devices where transport is dependent on electron magnetic moment, or “spin”, could provide a path to a future alternative for logic processing. The basics of this spin-based electronics technology are discussed and the specific methods necessary for application to silicon are described. Mirroring the Haynes-Shockley experiment, which was used sixty years ago to measure minority-carrier transport parameters in semiconductors, here we have used a four-terminal device to make fundamental measurements of spin transport parameters.

http://ieeexplore.ieee.org/iel5/4832838/4897524/04897526.pdf

Silicon spintronics

We study interaction-induced quantum correction to the conductivity tensor of electrons in two dimensions for arbitrary T tau, where T is the temperature and tau the transport mean free time. A general formula is derived, expressing the correction in terms of classical propagators ("ballistic diffusons"). The formalism is used to calculate the interaction contribution to the magnetoresistance in a classically strong transverse field and smooth disorder in the whole range of temperatures from the diffusive (T tau 1) regime.

Interaction-induced magnetoresistance: From diffusive to ballistic regime

Chiral anomaly induced negative magnetoresistance (NMR) has been widely used as a critical transport evidence on the existence of Weyl fermions in topological semimetals. In this mini review, we discuss the general observation of the NMR phenomena in non-centrosymmetric NbP and NbAs. We show that NMR can be contributed by intrinsic chiral anomaly of Weyl fermions and/or extrinsic effects, such as superimposition of Hall signals, field-dependent inhomogeneous current flow in the bulk, i.e. current jetting, and weak localization (WL) of coexistent trivial carriers. Such WL controlled NMR is heavily dependent on sample quality, and is characterized by pronounced crossover from positive to negative MR growth at elevated temperatures, as a result of the competition between the phase coherence time and the spin-orbital scattering constant of the bulk trivial pockets. Thus, the correlation of NMR and chiral anomaly needs to be scrutinized, without the support of other complimentary techniques. Due to the lifting of spin degeneracy, the spin orientations of Weyl fermions are either parallel or antiparallel to the momentum, a unique physical property known as helicity. The conservation of helicity provides strong protection for the transport of Weyl fermions, which can only be effectively scattered by magnetic impurities. Chemical doping of magnetic and non-magnetic impurities are thus more convincing in probing the existence of Weyl fermions than the NMR method.

Negative Magnetoresistance in Weyl semimetals NbAs and NbP: Intrinsic Chiral Anomaly and Extrinsic Effects

Strain-induced effects in p-type Si whiskers at low temperatures

Strain effect on magnetoresistance of SiGe solid solution whiskers at low temperatures

The low temperature studies of SOI-structures have been carried out in a temperature range of 4.2÷300K at magnetic fields up to 14T. The samples with initial boron concentration of about 2.41018сm-3 have been investigated. The results of the studies of SOI-structure conductance at low temperatures in the range of hopping conductance and a possibility to use this material in sensors are analyzed.

Properties of Low-Dimentional Polysilicon in SOI Structures for Low Temperature Sensors

Magnetic susceptibility and magnetoresistance of neutron-irradiated doped SI whiskers

Negative magnetoresistance of InSb whiskers with different impurity concentrations 4.4 × 1016–7.16 × 1017 cm−3 was studied in longitudinal magnetic field 0–14 T in the temperature range 4.2–77 K. The negative magnetoresistance reaches about 50% for InSb whiskers with impurity concentration in the vicinity to the metal–insulator transition. The negative magnetoresistance decreases to 35 and 25% for crystals with Sn concentration from the metal and dielectric side of the transition. The longitudinal magnetoresistance twice crosses the axis of the magnetic field induction for the lightly doped crystals. The behavior of the negative magnetoresistance could be explained by the existence of classical size effect, in particular boundary scattering in the subsurface whisker layer.

/pdf/negative-magnetoresistance-in-indium-antimonide-whiskers-1j95bv0dr9.pdf

Yu. Khoverko

Papers

Strain-induced effects in p-type Si whiskers at low temperatures

Strain effect on magnetoresistance of SiGe solid solution whiskers at low temperatures

Properties of Low-Dimentional Polysilicon in SOI Structures for Low Temperature Sensors

Magnetic susceptibility and magnetoresistance of neutron-irradiated doped SI whiskers

Negative magnetoresistance in indium antimonide whiskers doped with tin