DNA double helices for single molecule electronics

The combination of self-assembly and electronic properties as well as its true nanoscale dimensions make DNA a promising candidate for a building block of single molecule electronics. We argue that the intrinsic double helix conformation of the DNA strands provides a possibility to drive the electric current through the DNA by the perpendicular electric (gating) field. The transistor effect in the poly(G)-poly(C) synthetic DNA is demonstrated within a simple model approach. We put forward experimental setups to observe the predicted effect and discuss possible device applications of DNA. In particular, we propose a design of the single molecule analog of the Esaki diode.Comment: 4 pages, 4 figur

Spin-dependent pump current and noise in an adiabatic quantum pump based on domain walls in a magnetic nanowire

We study the pump current and noise properties in an adiabatically modulated magnetic nanowire with double domain walls (DW). The modulation is brought about by applying a slowly oscillating magnetic and electric fields with a controllable phase difference. The pumping mechanism resembles the case of the quantum dot pump with two-oscillating gates. The pump current, shot noise, and heat flow show peaks when the Fermi energy matches with the spin-split resonant levels localized between the DWs. The peak height of the pump current is an indicator for the lifetime of the spin-split quasistationary states between the DWs. For sharp DWs, the energy absorption from the oscillating fields results in side-band formations observable in the pump current. The pump noise carries information on the correlation properties between the nonequilibrium electrons and the quasi-holes created by the oscillating scatterer. The ratio between the pump shot noise and the heat flow serves as an indicator for quasi-particle correlation.Comment: 18 pages, 5 figure

On a Method of Treating Polar-Optical Phonons in Real Space

Polar-optical phonon interactions with carriers in semiconductors are long range interactions due to their Coulombic nature. Generally, if one wants to treat these with non-equilibrium Green's functions, this long-range interaction requires two- and three-particle Green's functions to be evaluated by e.g. the Bethe-Salpeter equation. On the other hand, optical phonon scattering is thought to be phase-breaking, which, if true, would eliminate this concern over long-range interactions. In seeking to determine just to what extent phase breaking is important, one could treat the polar modes as a real space potential, as is done for impurities, and examine the occurrence of any such correlations. This latter approach suffers from the condition that it is not really known how to handle the polar modes in real space -- no one seems to have done it. Here, such an approach is described as one possible method.Comment: 7 pages, 2 figur

Using Ensemble Monte Carlo Methods to Evaluate Non-Equilibrium Green's Functions, II. Polar-Optical Phonons

In semi-classical transport, it has become common practice over the past few decades to use ensemble Monte Carlo (EMC) methods for the simulation of transport in semiconductor devices. This method utilizes particles while still addressing the full physics within the device, leaving the computational difficulties to the computer. More recently, the study of quantum mechanical effects within the devices, have become important, and have been addressed in semiconductor devices using non-equilibrium Green's functions (NEGF). In using NEGF, one faces considerable computational difficulties. Recently, a particle approach to NEGF has been proposed [ 1], and preliminary results presented for non-polar optical phonons, which are very localized scattering centers. Here, the problems with long-range polar-optical phonons are discussed and results of the particle-based simulation presented.Comment: 9 pages, 9 figure

Using Ensemble Monte Carlo Methods to Evaluate Non-Equilibrium Green's Functions

The use of ensemble Monte Carlo (EMC) methods for the simulation of transport in semiconductor devices has become extensive over the past few decades. This method allows for simulation utilizing particles while addressing the full physics within the device, leaving the computational difficulties to the computer. More recently, the study of quantum mechanical effects within the devices, effects which also strongly affect the carrier transport itself, have become important. While particles have continued to be useful in quantum simulations using Wigner functions, interest in analytical solutions based upon the non-equilibrium Green's functions (NEGF) have become of greater interest in device simulation. While NEGF has been adopted by many commercial semiconductor, there remains considerable computational difficulty in this approach. Here, a particle approach to NEGF is discussed, and preliminary results presented illustrating the computational efficiency that remains with the use of particles. This approach adopts the natural basis functions for use in a high electric field and the preliminary results are obtained for quantum transport in Si at 300 K. This approach appears to offer significant advantages for the use of NEGF.Comment: 12 pages, 8 figure

Improvement of current-control induced by oxide crenel in very short field-effect-transistor

A 2D quantum ballistic transport model based on the non-equilibrium Green's function formalism has been used to theoretically investigate the effects induced by an oxide crenel in a very short (7 nm) thin-film metal-oxide-semiconductor-field-effect-transistor. Our investigation shows that a well adjusted crenel permits an improvement of on-off current ratio Ion/Ioff of about 244% with no detrimental change in the drive current Ion. This remarkable result is explained by a nontrivial influence of crenel on conduction band-structure in thin-film. Therefore a well optimized crenel seems to be a good solution to have a much better control of short channel effects in transistor where the transport has a strong quantum behavior

Magnetoconductance of the quantum spin Hall state

We study numerically the edge magnetoconductance of a quantum spin Hall insulator in the presence of quenched nonmagnetic disorder. For a finite magnetic field B and disorder strength W on the order of the bulk gap E_g, the conductance deviates from its quantized value in a manner which appears to be linear in |B| at small B. The observed behavior is in qualitative agreement with the cusp-like features observed in recent magnetotransport measurements on HgTe quantum wells. We propose a dimensional crossover scenario as a function of W, in which for weak disorder W < E_g the edge liquid is analogous to a disordered spinless 1D quantum wire, while for strong disorder W > E_g, the disorder causes frequent virtual transitions to the 2D bulk, where the originally 1D edge electrons can undergo 2D diffusive motion and 2D antilocalization.Comment: 5 pages, 3 figure