Quantum simulation of ZnO nanowire piezotronics

We address the problem of quantum transport in a nanometre sized two-terminal ZnO device subject to an external strain. The two junctions formed between the electrodes and the ZnO are generally taken as Ohmic and Schottky type, respectively. Unlike the conventional treatment to the piezopotential, we treat it as a potential barrier which is only induced at the interfaces. By calculating the transmission coefficient of a Fermi-energized electron that flows from one end to the other, it is found that the piezopotential has the effect of modulating the voltage threshold of the current flowing. The calculations are based on the quantum scattering theory. The work is believed to pave the way for investigating the quantum piezotronics

Cyclotron resonance in a two-dimensional electron gas with long-range randomness

We show that the the cyclotron resonance in a two-dimensional electron gas has non-trivial properties if the correlation length of the disorder is larger than the de Broglie wavelength: (a) the lineshape assumes three different forms in strong, intermediate, and weak magnetic fields (b) at the transition from the intermediate to the weak fields the linewidth suddenly collapses due to an explosive growth in the fraction of electrons with a diffusive-type dynamics.Comment: A few typos correcte

Novel anisotropy in the superconducting gap structure of Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} probed by quasiparticle heat transport

Since the nature of pairing interactions is manifested in the superconducting gap symmetry, the exact gap structure, particularly any deviation from the simple d_{x^2-y^2} symmetry, would help elucidating the pairing mechanism in high-T_c cuprates. Anisotropic heat transport measurement in Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} (Bi-2212) reveals that the quasiparticle populations are different for the two nodal directions and thus the gap structure must be uniquely anisotropic, suggesting that pairing is governed by interactions with a rather complicated anisotropy. Intriguingly, it is found that the "plateau" in the magnetic-field dependence of the thermal conductivity is observed only in the b-axis transport.Comment: 4 pages, 5 figures, accepted for publication in Phys. Rev. Let

Two-dimensional electron liquid with disorder in a weak magnetic field

We present the effective theory for low energy dynamics of a two-dimensional interacting electrons in the presence of a weak short-range disorder and a weak perpendicular magnetic field, the filling factor $\nu \gg 1$. We investigate the exchange enhancement of the $g$-factor, the effective mass and the decay rate of the simplest spin wave excitations at $\nu = 2 N + 1$. We obtain the enhancement of the field-induced gap in the tunneling density of states and dependence of the tunneling conductivity on the applied bias.Comment: 17 pages, no figure

Electron transport properties in magnetic tunnel junctions with epitaxial NiFe (111) ferromagnetic bottom electrodes

科研費報告書収録論文(課題番号:13305001・基盤研究(A)(2) ・H13～H15/研究代表者:宮崎, 照宣/高品位微小トンネル接合へのスピン注入

Spin-charge gauge symmetry: A way to tackle HTS cuprates?

We propose an explanation of several experimental features of transport phenomena in the normal state of high Tc cuprates in terms of a spin-charge gauge theory of the 2D t-J model. The calculated doping-temperature dependence for a number of physical quantities is found in qualitative agreement with data. In particular, we recover: in the ``pseudogap phase'' the metal-insulator crossover of the in-plane resistivity and of the NMR ``relaxation time'' and the insulating behavior of the out-of-plane resistivity; in the ``strange metal phase'' (at higher temperature or doping) the linear in T behavior of the above quantities; the appearance of maxima in the in-plane far-infrared conductivity in strongly underdoped and overdoped samples.Comment: 8 pages, 14 figures; to appear without figures in Journal of Physics and Chemistry of Solid

Direct measurements of the spin and the cyclotron gaps in a 2D electron system in silicon

Using magnetocapacitance data in tilted magnetic fields, we directly determine the chemical potential jump in a strongly correlated two-dimensional electron system in silicon when the filling factor traverses the spin and the cyclotron gaps. The data yield an effective g-factor that is close to its value in bulk silicon and does not depend on filling factor. The cyclotron splitting corresponds to the effective mass that is strongly enhanced at low electron densities

Spin gap in the 2D electron system of GaAs/AlGaAs single heterojunctions in weak magnetic fields

We study the interaction-enhanced spin gaps in the two-dimensional electron gas confined in GaAs/AlGaAs single heterojunctions subjected to weak magnetic fields. The values are obtained from the chemical potential jumps measured by magnetocapacitance. The gap increase with parallel magnetic field indicates that the lowest-lying charged excitations are accompanied with a single spin flip at the odd-integer filling factor nu=1 and nu=3, in disagreement with the concept of skyrmions.Comment: as publishe