arXiv subjects

R. I. Shekhter

Publications and source records attributed to R. I. Shekhter.

97 records · Page 6Linked to original sources

arXiv1994

Noise in a Quantum Point Contact due to a Fluctuating Impurity Configuration

We propose a theoretical model for the low-frequency noise observed in a quantum point contact (QPC) electrostatically defined in the 2D electron gas at a GaAs-AlGaAs interface. In such contacts electron scattering by soft impurity- or boundary potentials coherently splits an incoming wave function between different transverse modes. Interference between these modes have been suggested to explain observed non-linearities in the QPC-conductance. In this study we invoke the same mechanism and the time-dependent current due to soft dynamical impurity scattering in order to analyze the low-frequency (telegraph-like) noise which has been observed along with a nonlinear conductance. For the simplified case of a channel with two extended (current carrying) modes, a simple analytical formula for the noise intensity is derived. Generally we have found qualitative similarities between the noise and the square of the transconductance. Nevertheless, incidentally there may be situations when noise is suppressed but transconductance enhanced.

cond-mat↗

arXiv1994

Influence of Long-Range Coulomb Forces and Dissipation on the Persistent Current of a Wigner Crystal-Ring

The influence of long-range Coulomb forces on the persistent current of a pinned Wigner crystal-ring is considered. A simple method is proposed for how to take into account Coulomb effects for the macroscopic quantum tunneling of the Wigner crystal. It is shown that unscreened Coulomb interactions increase the stiffness of the Wigner lattice. This leads to additional suppression of the amplitude of Aharonov-Bohm oscillations, but makes the predicted anomalous temperature dependence of the persistent current more pronounced. The impact of dissipation on the persistent current of a Wigner crystal-ring is also studied.

cond-mat↗

arXiv1994

Influence of Long-Range Coulomb Interactions on the Metal-Insulator Transition in One-Dimensional Strongly Correlated Electron Systems

The influence of long-range Coulomb interactions on the properties of one-dimensional (1D) strongly correlated electron systems in vicinity of the metal-insulator phase transition is considered. It is shown that unscreened repulsive Coulomb forces lead to the formation of a 1D Wigner crystal in the metallic phase and to the transformation of the square-root singularity of the compressibility (characterizing the commensurate-incommensurate transition) to a logarithmic singularity. The properties of the insulating (Mott) phase depend on the character of the short-wavelength screening of the Coulomb forces. For a sufficiently short screening length the characteristics of the charge excitations in the insulating phase are totally determined by the Coulomb interaction and these quasipartic les can be described as quasiclassical Coulomb solitons.

cond-mat↗

arXiv1994

Non-Equilibrium Magnetization in a Ballistic Quantum Dot

We show that Aharonov-Bohm (AB) oscillations in the magnetic moment of an integrable ballistic quantum dot can be destroyed by a time dependent magnetic flux. The effect is due to a nonequilibrium population of perfectly coherent electronic states. For real ballistic systems the equilibrization process, which involves a special type of inelastic electron backscattering, can be so ineffective, that AB oscillations are suppressed when the flux varies with frequency $ω\sim$ 10$^7$-10$^8$ s$^{-1}$. The effect can be used to measure relaxation times for inelastic backscattering.

cond-mat↗

arXiv1994

Soft Disorder Effects in the Conductance Quantization in Quantum Point Contacts: Indirect Backscattering Statistics

The breakdown of conductance quantization in a quantum point contact in the presence of random long-range impurity potential is discussed. It is shown that in the linear response regime a decisive role is played by the indirect backscattering mechanism via quasilocalized states at the Fermi level; this can provide much higher backscattering rate than any direct backscattering process. For the realistic contact lengths ($\leq 2000$nm) the scattering processes prove to be independent, in spite of coherence of the electron wave. The distribution function of conductance fluctuations is obtained by direct numerical calculations as well as estimated within an analytical model for the first time. It is shown to be a generalized Poisson distribution. Estimates are made for quantum point contact performance at different choice of parameters. In particular, it is the better the larger the intermode distance is compared to the amplitude of the random impurity potential.

cond-mat↗

arXiv1994

Persistent Current of a One-Dimensional Wigner Crystal-Ring

We calculate the magnetic moment (`persistent current') in a strongly correlated electron system --- a Wigner crystal --- in a one-dimensional ballistic ring. The flux- and temperature dependence of the persistent current is shown to be essentially the same as for a system of non-interacting electrons. In contrast, by incorporating into the ring geometry a tunnel barrier, that pins the Wigner crystal, the current is suppressed and its temperature dependence is drastically changed. The competition between two temperature effects --- a reduced barrier height for macroscopic tunneling and a loss of quantum coherence --- results in a sharp peak in the temperature dependence, which for a rigid Wigner crystal appears at $T\sim 0.5\ \hbar s/L$, ($s$ is the sound velocity of the Wigner crystal, $L$ is the length of the ring).

cond-mat↗

arXiv1994

Nonlinear Transport in a Quantum Point Contact due to Soft Disorder Induced Coherent Mode Mixing

We show that the coherent mixing of different transverse modes, due to forward scattering of carriers by soft impurity- or boundary potentials leads to a nonlinear, asymmetric current response of quantum point contacts (QPC). The oscillating contribution to the current is sensitive both to driving voltage and to gate voltage in direct analogy to the electrostatic Aharonov-Bohm effect. Our calculations are in a good agreement with recent experimental data showing small-scale conductivity nonlinearities and asymmetry in QPC.

cond-mat↗