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M. V. Simkin

Publications and source records attributed to M. V. Simkin.

44 records · Page 3Linked to original sources
arXiv1997

Edge effects in a frustrated Josephson junction array with modulated couplings

A square array of Josephson junctions with modulated strength in a magnetic field with half a flux quantum per plaquette is studied by analytic arguments and dynamical simulations. The modulation is such that alternate columns of junctions are of different strength to the rest. Previous work has shown that this system undergoes an XY followed by an Ising-like vortex lattice disordering transition at a lower temperature. We argue that resistance measurements are a possible probe of the vortex lattice disordering transition as the linear resistance $R_{L}(T)\sim A(T)/L$ with $ A(T) \propto (T-T_{cI})$ at intermediate temperatures $T_{cXY}>T>T_{cI}$ due to dissipation at the array edges for a particular geometry and vanishes for other geometries. Extensive dynamical simulations are performed which support the qualitative physical arguments.

cond-mat.supr-con↗
arXiv1997

Numerical Study of a Superconducting Glass Model

An XY model with random phase shifts as a model for a superconducting glass is studied in two and three dimensions by a zero temperature domain wall renormalization group which allows one to follow the flows of both the coupling constant and the disorder strength with increasing length scale. Weak disorder is found to be marginal in two and probably irrelevant in three dimensions. For strong disorder the flow is towards a non-superconducting gauge glass fixed point in 2d and a superconducting glass in 3d. Our results are in agreement with recent analytic theory and are inconsistent with earlier predictions of a re-entrant transition to a disordered phase at very low temperature and with the loss of superconductivity for any finite amount of disorder.

cond-mat.supr-con↗
arXiv1997

Finite Size and Current Effects on IV Characteristics of Josephson Junction Arrays

The effects of finite size and of finite current on the current-voltage characteristics of Josephson junction arrays is studied both theoretically and by numerical simulations. The cross-over from non-linear to linear behavior at low temperature is shown to be a finite size effect and the non-linear behavior at higher temperature, $T>T_{KT}$, is shown to be a finite current effect. These are argued to result from competition between the three length scales characterizing the system. The importance of boundary effects is discussed and it is shown that these may dominate the behavior in small arrays.

cond-mat.supr-con↗
arXiv1997

Numerical Study of Competing Spin-Glass and Ferromagnetic Order

Two and three dimensional random Ising models with a Gaussian distribution of couplings with variance $J$ and non-vanishing mean value $J_0$ are studied using the zero-temperature domain-wall renormalization group (DWRG). The DWRG trajectories in the ($J_0,J$) plane after rescaling can be collapsed on two curves: one for $J_0/J > r_c$ and other for $J_0/J < r_c$. In the first case the DWRG flows are toward the ferromagnetic fixed point both in two and three dimensions while in the second case flows are towards a paramagnetic fixed point and spin-glass fixed point in two and three dimensions respectively. No evidence for an extra phase is found.

cond-mat↗
arXiv1996

On Mean-Field Theory of Quantum Phase Transition in Granular Superconductors

In previous work on quantum phase transition in granular superconductors, where mean-field theory was used, an assumption was made that the order parameter as a function of the mean field is a convex up function. Though this is not always the case in phase transitions, this assumption must be verified, what is done in this article.

supr-con↗
arXiv1996

Current-Induced Chiral Phase Transition in a Josephson-Junction Array

It is predicted that the fully frustrated Josephson-junction array on a square lattice with alternating columns of junctions having a reduced critical current $I_{weak}=μI_{0}$(with $μ<1$ and $I_{0}$ the critical current of all other junctions) in certain range of $μ$ will under increasing of the external current first change from the state with zero chirality to the state with nonzero one at the lower critical current $I_{c1}$ before entering nonsuperconducting state at the upper critical current $I_{c2}$.

cond-mat↗
arXiv1996

Comment on "Voltage-Current Characteristics of the Two-Dimensional Gauge Glass Model"

Li (Phys. Rev. Lett. {\bf 69},1819 (1992)) has computed the current-voltage characteristics (CVC) of a disordered two-dimensional (2D) Josephson-junction array and claimed that his data(nonlinear CVC for small temperatures), gives evidence for a finite-temperature phase transition in the 2D gauge-glass model in contradiction to the result of equilibrium simulations. In this Comment I show that the nonlinear CVC, found by Li, is merely a single-junction effect.

cond-mat↗