Dmitri S. Golubev

Nonequilibrium theory of a hot-electron bolometer with normal metal-insulator-superconductor tunnel junction

The operation of the hot-electron bolometer with normal metal-insulator-superconductor (NIS) tunnel junction as a temperature sensor is analyzed theoretically. The responsivity and the noise equivalent power (NEP) of the bolometer are obtained numerically for typical experimental parameters. Relatively simple approximate analytical expressions for these values are derived. The time constant of the device is also found. We demonstrate that the effect of the electron cooling by the NIS junction, which serves as a thermometer, can improve the sensitivity. This effect is also useful in the presence of the finite background power load. We discuss the effect of the correlation of the shot noise and the heat flow noise in the NIS junction.

Thermally activated phase slips in superconducting nanowires

We re-analyze the problem of thermally activated phase slips (TAPS) which can dominate the behavior of sufficiently thin superconducting wires at temperatures close to TC . With the aid of an effective action approach we evaluate the TAPS rate which turns out to exceed the rate found by D.E. McCumber and B.I. Halperin, Phys. Rev. B 1, 1054 (1970) within the TDGL analysis by the factor ∼ (1 − T/TC) −1 ≫ 1. Additional differences in the results of these two approaches arise at bias currents close to the Ginzburg-Landau critical current where the TAPS rate becomes bigger. We also derive a simple formula for the voltage noise across the superconducting wire in terms of the TAPS rate. Our results can be verified in modern experiments with superconducting nanowires.

Spin torque switching of an in-plane magnetized system in a thermally activated region

The current dependence of the exponent of the spin torque switching rate of an in-plane magnetized system was investigated by solving the Fokker-Planck equation with low temperature and small damping and current approximations. We derived the analytical expressions of the critical currents, I_{c} and I_{c}^{*}. At I_{c}, the initial state parallel to the easy axis becomes unstable, while at I_{c}^{*} (\simeq 1.27 I_{c}) the switching occurs without the thermal fluctuation. The current dependence of the exponent of the switching rate is well described by (1-I/I_{c}^{*})^{b}, where the value of the exponent b is approximately unity for I < I_{c}, while b rapidly increases up to 2.2 with increasing current for I_{c} < I < I_{c}^{*}. The linear dependence for I < I_{c} agrees with the other works, while the nonlinear dependence for I_{c} < I < I_{c}^{*} was newly found by the present work. The nonlinear dependence is important for analysis of the experimental results, because most experiments are performed in the current region of I_{c} < I < I_{c}^{*}.

Non-local Andreev reflection in superconducting quantum dots

With the aid of the Keldysh technique, we develop a microscopic theory of non-local electron transport in three-terminal normal metal\char21{}superconductor\char21{}normal metal (NSN) structures consisting of a chaotic superconducting quantum dot attached to one superconducting and two normal electrodes. Our theory fully accounts for nonequilibrium effects and disorder in a superconducting terminal. We go beyond the perturbation theory in tunneling and derive a general expression for the system conductance matrix, which remains valid in both weak and strong tunneling limits. We demonstrate that the proximity effect yields a decrease of the crossed Andreev reflection (CAR). Beyond the weak tunneling limit, the contribution of CAR to the non-local conductance does not cancel that of the direct electron transfer between two normal terminals. We argue that the temperature dependence of the non-local resistance of NSN devices is determined by the two competing processes\char22{}Andreev reflection and charge imbalance\char22{}and it has a pronounced peak occurring at the crossover between these two processes. This behavior is in a good agreement with recent experimental observations.

Electron transport and current fluctuations in short coherent conductors

Employing a real-time effective action formalism we analyze electron transport and current fluctuations in comparatively short coherent conductors in the presence of electron-electron interactions. We demonstrate that, while Coulomb interaction tends to suppress electron transport, it may strongly enhance shot noise in scatterers with highly transparent conducting channels. This effect of excess noise is governed by the Coulomb gap observed in the current-voltage characteristics of such scatterers. We also analyze the frequency dispersion of higher current cumulants. Our results illustrate a direct relation between electron-electron interaction effects and current fluctuations in disordered mesoscopic conductors.

Interaction-induced quantum dephasing in mesoscopic rings

Combining nonperturbative techniques with Monte Carlo simulations, we demonstrate that quantum coherence effects for a particle on a ring are suppressed beyond a finite length L even at zero temperature if the particle is coupled to a diffusive electron gas by means of long-range Coulomb interaction. This length is consistent with L derived from a weak-localization–type analysis.

Statistics of current fluctuations in mesoscopic coherent conductors at nonzero frequencies

We formulate a general approach which describes statistics of current fluctuations in mesoscopic coherent conductors at arbitrary frequencies and in the presence of interactions. Applying this approach to the non-interacting case, we analyze frequency dispersion of the third cumulant of the current operator

Full Counting Statistics for a Single-Electron Transistor: Nonequilibrium Effects at Intermediate Conductance

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Crossed Andreev reflection and charge imbalance in diffusive normal-superconducting-normal structures.

at frequencies well below both the inverse charge relaxation time and the inverse electron dwell time. This dispersion turns out to be important in the frequency range comparable to applied voltages. For comparatively transparent conductors it may lead to the sign change of

Electron transport through interacting quantum dots in the metallic regime

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