Biomedical subjects
Publications and source records attributed to Yu V Nazarov.
We study electronic transport through a ferromagnet normal-metal ferromagnet system and we investigate the effect of hyperfine interaction between electrons and nuclei in the normal-metal part. A switching of the magnetization directions of the ferromagnets causes nuclear spins to precess. We show that the effect of this precession on the current through the system is large enough to be observed in experiment.
We analyze the operation of a quantum tunneling detector coupled to a coherent conductor. We demonstrate that, in a certain energy range, the output of the detector is determined by two-photon processes, two-interacting-electron processes, and the interference of the two. We show how the individual contributions of these processes can be resolved in experiments.
We evaluate the full statistics of the current via a Coulomb island that is strongly coupled to the leads. This strong coupling weakens Coulomb interaction. We show that in this case the effects of the interaction can be incorporated into the renormalization of transmission eigenvalues of the scatterers that connect the island and the leads. We evaluate the Coulomb blockade gap in the current-voltage characteristics, the value of the gap being exponentially suppressed as compared to the classical charging energy of the island.
A harmonic nanomechanical oscillator with a high quality factor weakly coupled to a single-electron tunneling device can provide a strong feedback for electron transport. Strong feedback occurs in a narrow voltage range just above the Coulomb blockade threshold. In this regime, current is strongly modified and current noise is drastically enhanced compared to the Schottky value.
We discuss how threshold detectors can be used for a direct measurement of the full distribution of current fluctuations and how to exploit Josephson junctions in this respect. We propose a scheme to characterize the full counting statistics from the current dependence of the escape rate measured. We illustrate the scheme with explicit results for tunnel, diffusive, and quasiballistic mesoscopic conductors.
The energy-dependent Andreev reflection eigenvalues determine the transport properties of normal-superconducting systems. We evaluate the eigenvalue density to get insight into the formation of resonant electron-hole transport channels. The circuit-theory-like method developed can be applied to any generic mesoscopic conductor or combinations thereof. We present the results for experimentally relevant cases of a diffusive wire and a double tunnel junction.
We investigate the effect of weak interactions on the full counting statistics of charge transfer through an arbitrary mesoscopic conductor. We show that the main effect can be incorporated into an energy dependence of the transmission eigenvalues and study this dependence in a nonperturbative approach. An unexpected result is that all mesoscopic conductors behave at low energies such as either a single or a double tunnel junction, which divides them into two broad classes.
We consider the conductance of a one-dimensional wire interrupted by a double-barrier structure allowing for a resonant level. Using the electron-electron interaction strength as a small parameter, we are able to build a nonperturbative analytical theory of the conductance valid in a broad region of temperatures and for a variety of the barrier parameters. We find that the conductance may have a nonmonotonic crossover dependence on temperature, specific for a resonant tunneling in an interacting electron system.
We calculate the fluctuating voltage V(t) over a conductor driven out of equilibrium by a current source. This is the dual of the shot noise problem of current fluctuations I(t) in a voltage-biased circuit. In the single-channel case the distribution of the accumulated phase Phi=(e/ variant Planck's over 2pi ) integral Vdt is the Pascal (or binomial waiting-time) distribution-distinct from the binomial distribution of transferred charge Q= integral Idt. The weak-coupling limit of a Poissonian P(Phi) is reached in the limit of a ballistic conductor, while in the tunneling limit P(Phi) has the chi-square form.
We investigate the feasibility of manipulating individual spin in a superconducting junction where Bogoliubov quasiparticles can be trapped in discrete Andreev levels. We call this system an Andreev quantum dot (AQD) to be contrasted with a common semiconductor quantum dot. We show that the AQD can be brought into a spin-1/2 state. The coupling between the spin and superconducting current facilitates manipulation and measurement of this state. We demonstrate that one can operate two inductively coupled AQDs as a XOR gate; this enables quantum computing applications.
Poisson statistics predicts that the shot noise in a tunnel junction has a temperature independent third cumulant e(2)I, determined solely by the mean current I. Experimental data, however, show a puzzling temperature dependence. We demonstrate theoretically that the third cumulant becomes strongly temperature dependent and may even change sign as a result of feedback from the electromagnetic environment. In the limit of a noninvasive (zero-impedance) measurement circuit in thermal equilibrium with the junction, we find that the third cumulant crosses over from e(2)I at low temperatures to -e(2)I at high temperatures.
We extend the circuit theory of superconductivity to cover transport and proximity effect in mesoscopic systems that contain unconventional superconductor junctions. The approach fully accounts for zero-energy Andreev bound states forming at the surface of unconventional superconductors. As a simple application, we investigate the transport properties of a diffusive normal metal in series with a d-wave superconductor junction. We reveal the competition between the formation of Andreev bound states and proximity effect that depends on the crystal orientation of the junction interface.
We investigate nonequilibrium noise in a diffusive Andreev interferometer, in which currents emerging from two normal metal/superconductor (N-S) interfaces can interfere. We observe a modulation of the shot noise when the phase difference between the two N-S interfaces is varied by a magnetic flux. This is the signature of phase-sensitive fluctuations in the normal metal. The effective charge inferred from the shot noise measurement is close to q(eff) = 2e but shows phase-dependent deviations from 2e at finite energy, which we interpret as being due to pair correlations. Experimental data are in good agreement with predictions based on an extended Keldysh Green's function approach.
We propose a theory that treats the current, noise, and, generally, the full current statistics of electron transfer in a mesoscopic system in a unified, simple, and efficient way. The theory appears to be a circuit theory of 2 x 2 matrices associated with Keldysh Green functions. We illustrate the theory by considering the big fluctuations of currents in various three-terminal circuits.
Highly degenerate incoherent radiation has a Gaussian density matrix and a large occupation number of modes f. If it is passed through a weakly transmitting barrier, its counting statistics is close to Poissonian. We show that a second identical barrier, in series with the first, drastically modifies the statistics. The variance of the photocount is increased above the mean by a factor f times a numerical coefficient. The photocount distribution reaches a limiting form with a Gaussian body and highly asymmetric tails. These are general consequences of the combination of weak transmission and multiple scattering.
We investigate spin-dependent transport in hybrid superconductor-normal-metal-ferromagnet structures under conditions of the proximity effect. We demonstrate the feasibility of the absolute spin-valve effect for a certain interval of voltages in a system consisting of two coupled trilayer structures. Our results are also valid for noncollinear magnetic configurations of the ferromagnets.