A. van Otterlo

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}

TUNNEL JUNCTIONS OF UNCONVENTIONAL SUPERCONDUCTORS

The phenomenology of Josephson tunnel junctions between unconventional superconductors is developed further. In contrast to s-wave superconductors, for d-wave superconductors the direction dependence of the tunnel matrix elements that describe the barrier is relevant. We find the full I-V characteristics and comment on the thermodynamical properties of these junctions. They depend sensitively on the relative orientation of the superconductors. The I-V characteristics differ from the normal s-wave RSJ-like behavior.

Electrostatics of Vortices in Type-II Superconductors.

In a type-II superconductor the gap variation in the core of a vortex line induces a local charge modulation. Accounting for metallic screening, we determine the line charge of individual vortices and calculate the electric field distribution in the half space above a field penetrated superconductor. The resulting field is that of an atomic size dipole

New Universality Class at the Superconductor-Insulator Transition

\mathbf{d}\ensuremath{\sim}{\mathrm{ea}}_{B}\stackrel{^}{z}

SUPERCONDUCTOR-INSULATOR TRANSITION IN A TUNABLE DISSIPATIVE ENVIRONMENT

,

Quantum Vortex Dynamics in Josephson Junction Arrays. Ballistic Motion, Dissipation, and Tunnelling

{a}_{B}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}{\ensuremath{\Elzxh}}^{2}/{\mathrm{me}}^{2}

Quantum vortex dynamics in Josephson junction arrays

is the Bohr radius, acting on a force microscope in the pico- to femto-Newton range.

On the phase transition of superconducting cuprates in zero and non-zero magnetic fields

We study transport properties of thin films near the superconductor-insulator transition. Formulated in a phase representation, the key new feature of our model is the assumption of a {bold {ital local}} Ohmic dissipative mechanism. Coarse graining leads to a Ginzburg-Landau description, with non-Ohmic dynamics for the order parameter. For strong enough damping a new universality class is found. It is characterized by a {bold {ital nonuniversal}} dc conductivity, and a damping-dependent dynamical critical exponent. The formulation also provides a description of the magnetic-field-tuned transition. Several microscopic mechanisms are proposed as the origin of the dissipation. {copyright} {ital 1997} {ital The American Physical Society}

Vortices in d-wave superconductors

We study the influence of a tunable dissipative environment on the dynamics of Josephson junction arrays near the superconductor-insulator transition. The experimental realization of the environment is a two dimensional electron gas coupled capacitively to the array. This setup allows for the well controlled tuning of the dissipation by changing the resistance of the two dimensional electron gas. The capacitive coupling cuts off the dissipation at low frequencies. We determine the phase diagram and calculate the temperature and dissipation dependence of the array conductivity. We find good agreement with recent experimental results. {copyright} {ital 1997} {ital The American Physical Society}

Vortex charge in type II superconductors

Vortices in arrays of low-capacitance Josephson junctions behave as quantum particles showing tunnelling and interference effects. Classical arguments predict a vortex mass, but simultaneously a strong damping due to the excitation of spin waves. We show that the discrete nature of the charges on the islands leads to qualitatively new results. the spin wave spectrum becomes stiffer, which substantially reduces the dissipation. Ballistic motion of vortices becomes possible in a wide range of velocities, consistent with recent experiments. The vortex properties change further near the superconductor-insulator transition found in these arrays.