Juhani Kurkijärvi

Noise in the superconducting quantum flux detector

An expression is derived for noise in the tank circuit of a superconducting quantum flux detector run at a radiofrequency. This noise is limited by the sensing element of the device, the superconducting ring with a weak link, and is therefore intimately related to the thermal fluctuations in the ring. Not considering external noise, the superconducting ring and the tank circuit together with the preamplifier should exhaust the important sources of noise in the flux detector.

Microscopic mechanics of fiber networks

We report simulations of two‐dimensional fiber networks of random geometry. The stress distribution along a fiber agrees with the mean‐field Cox prediction, but the stress transfer factor is determined by the properties of the whole fiber and not by just the local segment stiffness as suggested by micromechanical models. This leads to a linear density dependence of the Young’s modulus of a network. The initial loss of stiffness at small strain can be explained with an exponential frequency distribution of microscopic stresses, and the asymptotic stiffness at large external strain agrees with mean‐field predictions. The simulated behavior is independent of the microscopic fracture mechanism in both regions.

Low-temperature magnetic penetration depth in d-wave superconductors: Zero-energy bound state and impurity effects

We report a theoretical study on the deviations of the Meissner penetration depth

Quasiclassical theory of vortices in3He-B

\lambda(T)

Diffusely scattering surface in superfluid 3He

from its London value in d-wave superconductors at low temperatures. The difference arises from low-energy surface Andreev bound states. The temperature dependent penetration depth is shown to go through a minimum at the temperature

Pinhole junctions in d-wave superconductors

T_{m0}\sim \sqrt{\xi_0/\lambda_0}T_c

Binary tree approach to scaling in unimodal maps

if the broadening of the bound states is small. The minimum will straighten out when the broadening reaches

Fracture modes in fiber networks

T_{m0}

Andreev Scattering at a Rough Surface of ^3He-B : I. QUANTUM LIQUIDS AND SOLIDS : Superfluid ^3He

. The impurity scattering sets up the low-temperature anomalies of the penetration depth and destroys them when the mean free path is not sufficiently large. A phase transition to a state with spontaneous surface supercurrent is investigated and its critical temperature determined in the absence of a subdominant channel activated at low temperatures near the surface. Nonlinear corrections from Andreev low-energy bound states to the penetration length are obtained and shown, on account of their broadening, to be small in the Meissner state of strong type II superconductors.

Quantum Monte Carlo simulation method for spin systems

We report weak-coupling numerical calculations of the order parameter and the free energy of isolated vortices in superfluid3He in the framework of the quasiclassical theory of superfluid Fermi-liquids. Unlike earlier work with the Ginzburg-Landau theory, our results are not restricted to the vicinity ofTc. We show that Fermi-liquid effects play an important role at lower temperatures. It appears there is a transition from the double core vortex to an A-phase-core vortex at the vapor pressure just above 0.5Tc.