Amplitude Of Universal Conductance Fluctuations Research Articles

Phase-coherent transport in trigonal gallium nitride nanowires

Gallium nitride nanowires (GaN NWs) with triangular cross-section exhibit universal conductance fluctuations (UCF) originating from the quantum interference of electron wave functions in the NWs. The amplitude of UCF is inversely proportional to the applied bias current. The bias dependence of UCF, combined with temperature dependence of the resistance suggests that phase coherent transport dominates over normal transport in GaN NWs. A unique temperature dependence of phase-coherent length and fluctuation amplitude is associated with inelastic electron–electron scattering in NWs. The phase-coherence length extracted from the UCF is as large as 400 nm at 1.8 K, and gradually decreases as temperature increases up to 60 K.

Universal conductance fluctuations in Dirac semimetalCd3As2nanowires

Three-dimensional Dirac semimetals host bulk Dirac fermions characterized by a linear dispersion relation in momentum space along all three dimensions. It has been theoretically predicted that the breaking of ${C}_{4}$ rotational crystalline symmetry in the Dirac semimetal $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$ may give rise to the massive Dirac fermions. Here we report the phase-coherent transport in $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$ nanowires studied by measuring the universal conductance fluctuations (UCFs). It is found that the UCF amplitude is largely suppressed at the Dirac point by sweeping the magnetic field at different gate voltages, which is ascribed to the breaking of the ${C}_{4}$ rotational symmetry-induced band-gap opening. The temperature dependence of resistance demonstrates a magnetic-field-induced metal-insulator transition, consisting of the band-gap opening. Moreover, the UCF amplitude is reduced by a factor of $\ensuremath{\sim}2\sqrt{2}$ in the presence of a magnetic field, suggesting the phase transition from a Dirac-to-Weyl semimetal by breaking time-reversal symmetry.

Phase-coherent transport and spin relaxation in InAs nanowires grown by molecule beam epitaxy

We report low-temperature magnetotransport studies of individual InAs nanowires grown by molecule beam epitaxy. At low magnetic fields, the magnetoconductance characteristics exhibit a crossover between weak antilocalization and weak localization by changing either the gate voltage or the temperature. The observed crossover behavior can be well described in terms of relative scales of the transport characteristic lengths extracted based on the quasi-one-dimensional theory of weak localization in the presence of spin-orbit interaction. The spin relaxation length extracted from the magnetoconductance data is found to be in the range of 80–100 nm, indicating the presence of strong spin-orbit coupling in the InAs nanowires. Moreover, the amplitude of universal conductance fluctuations in the nanowires is found to be suppressed at low temperatures due to the presence of strong spin-orbit scattering.

Negative and positive magnetoresistance in bilayer graphene: Effects of weak localization and charge inhomogeneity

We report measurements of magnetoresistance in bilayer graphene as a function of gate voltage (carrier density) and temperature. We examine multiple contributions to the magnetoresistance, including those of weak localization (WL), universal conductance fluctuations (UCF), and inhomogeneous charge transport. A clear WL signal is evident at all measured gate voltages (in the hole doped regime) and temperature ranges (from 0.25 to 4.3 K), and the phase coherence length extracted from the WL data does not saturate at low temperatures. The WL data is fit to demonstrate that the electron–electron Nyquist scattering is the major source of phase decoherence. A decrease in UCF amplitude with increase in gate voltage and temperature is shown to be consistent with a corresponding decrease in the phase coherence length. In addition, a weak positive magnetoresistance at higher magnetic fields is observed, and attributed to inhomogeneous charge transport.

Long dephasing time and high temperature ballistic transport in an InGaAs open quantum dot

We report on measurements of the magnetoconductance of an open circular InGaAs quantum dot between 1.3 and 204 K . We observe two types of magnetoconductance fluctuations: universal conductance fluctuations (UCFs), and “focusing” fluctuations related to ballistic trajectories between openings. The electron phase coherence time extracted from UCFs amplitude is larger than in GaAs/AlGaAs quantum dots and follows a similar temperature dependence (between T −1 and T −2). Below 150 K , the characteristic length associated with “focusing” fluctuations shows a slightly different temperature dependence from that of the conductivity.

Sidewall damage in n+-GaAs quantum wires from reactive ion etching

Electron cyclotron resonance and radio frequency reactive ion etching have been used to fabricate narrow n+-GaAs wires employing CCl2F2/He as the etch gas. A comparison of the induced sidewall damage is made using room-temperature conductivity measurements of the etched structures and the effect of overetching is investigated. In addition, preliminary analysis of low-temperature transport reveals that the amplitude of universal conductance fluctuations is extremely sensitive to sidewall damage.