arXiv subjects

Diu Nghiem

Publications and source records attributed to Diu Nghiem.

3 recordsLinked to original sources

arXiv2008

Alkanethiol-Based Single-Molecule Transistors

The transport properties of unsubstituted and amino-substituted butanethiol molecules sandwiched between Au electrodes are investigated by using first-principles approaches. New states are observed around the Fermi levels when -NH2 is substituted for -H in the bridging butanethiol. The amino-substituted states lead to a sharp increase of the current which is credited to the resonant tunneling in the junction. We observe a novel conductance peak at VSD = 0.1 V and negative differential resistance (NDR) in a certain range of source-drain bias. In addition to the I-VSD characteristics, we also investigate the current as a function of gate voltage (I-VG) and find that, for a fixed source-drain bias (VSD = 0.01 V), the gate voltage can modulate the conductance by up to 30 times in the amino-substituted butanethiol junction. These I-VG characteristics suggest that the amino-substituted butanethiol molecular junction may be a promising candidate for field-effect transistors.

cond-mat.mes-hall↗

arXiv2007

Energy Level Statistics of Quantum Dots

We investigate the charging energy level statistics of disordered interacting electrons in quantum dots by numerical calculations using the Hartree approximation. The aim is to obtain a global picture of the statistics as a function of disorder and interaction strengths. We find Poisson statistics at very strong disorder, Wigner- Dyson statistics for weak disorder and interactions, and a Gaussian intermediate regime. These regimes are as expected from previous studies and fundamental considerations, but we also find interesting and rather broad crossover regimes. In particular, intermediate between the Gaussian and Poisson regimes we find a two-sided exponential distribution for the energy level spacings. In comparing with experiment, we find that this distribution may be realized in some quantum dots.

cond-mat.dis-nn↗

arXiv2007

Exact solution of qubit decoherence models by a transfer matrix method

We present a new method for the solution of the behavior of an ensemble of qubits in a random time-dependent external field. The forward evolution in time is governed by a transfer matrix. The elements of this matrix determine the various decoherence times. The method provides an exact solution in cases where the noise is piecewise constant in time. We show that it applies, for example, to a realistic model of decoherence of electron spins in semiconductors. Results are obtained for the non-perturbative regimes of the models, and we see a transition from weak relaxation to overdamped behavior as a function of noise anisotropy.

quant-ph↗