Andrei D. Zaikin

Quantum coherent effects, phase transitions, and the dissipative dynamics of ultra small tunnel junctions

Abstract The quantum dynamics of tunnel junctions with very small capacitance, such that kBT

Quasiclassical Green’s function approach to mesoscopic superconductivity

Recent experiments on mesoscopic normal metal/superconductor heterostructures resolve properties on length scales and at low temperatures such that the temperature is below the Thouless energy k(B)T less than or equal to E-Th. We describe the properties of these systems within the framework of quasiclassical many-body techniques. Diffusive and ballistic systems are covered, both in equilibrium and nonequilibrium situations. Thereby we demonstrate the common physical basis of various subtopics.

Quantum Phase Slips and Transport in Ultrathin Superconducting Wires

We present a microscopic study of the quantum fluctuations of the superconducting order parameter in thin homogeneous superconducting wires at all temperatures below T{sub c}. The rate of quantum phase-slip processes determines the resistance R(T) of the wire, which is observable in very thin wires, even at low temperatures. Furthermore, we predict a new low-temperature metallic phase below a critical wire thickness in the 10-nm range, in which quantum phase slips proliferate. {copyright} {ital 1997} {ital The American Physical Society}

Josephson critical current in a long mesoscopic S-N-S junction

We carry out an extensive experimental and theoretical study of the Josephson effect in S-N-S junctions made of a diffusive normal metal ~N! embedded between two superconducting electrodes ~S!. Our experiments are performed on Nb-Cu-Nb junctions with highly transparent interfaces. We give the predictions of the quasiclassical theory in various regimes on a precise and quantitative level. We describe the crossover between the short- and the long-junction regimes and provide the temperature dependence of the critical current using dimensionless units eRNI c /e c and k BT/e c , where e c is the Thouless energy. Experimental and theoretical results are in excellent quantitative agreement.

Quantum Tunneling of the Order Parameter in Superconducting Nanowires

Quantum tunneling of the superconducting order parameter gives rise to the phase slippage process which controls the resistance of ultrathin superconducting wires at sufficiently low temperatures. If the quantum phase slip rate is high, superconductivity is completely destroyed by quantum fluctuations and the wire resistance never decreases below its normal state value. We present a detailed microscopic theory of quantum phase slips in homogeneous superconducting nanowires. Focusing our attention on relatively short wires we evaluate the quantum tunneling rate for phase slips, both the quasiclassical exponent and the pre-exponential factor. In very thin and dirty metallic wires the effect is shown to be clearly observable even at

Parity-Affected Superconductivity in Ultrasmall Metallic Grains

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Quantum Decoherence in Disordered Mesoscopic Systems

Our results are fully consistent with recent experimental findings [A. Bezryadin, C.N. Lau, and M. Tinkham, Nature (London) 404, 971 (2000)] which provide direct evidence for the effect of quantum phase slips.

Coulomb Interaction and Quantum Transport through a Coherent Scatterer

We investigate the breakdown of BCS superconductivity in {ital ultrasmall} metallic grains as a function of particle size (characterized by the mean spacing {ital d} between discrete electronic eigenstates), and the parity ({ital P}=even/odd) of the number of electrons on the island. Assuming equally spaced levels, we solve the parity-dependent BCS gap equation for the pairing parameter {Delta}{sub {ital P}}({ital d},{ital T}). The {ital T}=0 critical level spacing {ital d}{sub {ital c},{ital P}}, the critical temperature {ital T}{sub {ital c},{ital P}}({ital d}) (at which {Delta}{sub {ital P}}=0), and the condensation energy {ital E}{sub {ital P}} are parity dependent, and all are so much smaller in the odd than the even case that this should manifest itself in current experiments. {copyright} {ital 1996 The American Physical Society.}

Parity Effects on Electron Tunnelling Through Small Superconducting Islands

We point out that the low temperature saturation of the electron phase decoherence time in a disordered conductor can be explained within the existing theory of weak localization provided the effect of quantum (high frequency) fluctuations is taken into account. Making use of the fluctuation-dissipation theorem we evaluate the quantum decoherence time, the crossover temperature below which thermal effects become unimportant, and the weak localization correction

Quantum Fluctuations and Quantum Dynamics of Small Josephson Junctions

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