Fluctuation-induced pseudogap in high-temperature superconductors

We study the effect of fluctuations on the ac conductivity of a layered superconductor for c-axis electromagnetic wave polarization. The fluctuation contributions of different physical nature and sign (paraconductivity, Maki-Thompson anomalous contribution, one-electron density-of-states renormalization) are found to be suppressed by the external field at different characteristic frequencies (ω _AL∼T-T _c , ω _MT∼max{T-T _c ,τ _ϕ ⁻¹ }, ω _DOS∼min{T, τ ⁻¹}). As a result, the appearance of a nonmonotonic frequency dependence (pseudogap) in the infrared optical conductivity of high-temperature superconductor is predicted. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 6, 397–401 (25 September 1996) Department of Theoretical Physics Moscow Institute of Steel and Alloys. Published in English in the original Russian journal. Edited by Steve Torstveit.     

Fluctuation-induced forces in and out of equilibrium

In a fluctuating medium of quantum, thermal, or non-thermal origin, an interaction is induced between external objects that modify the fluctuations. These interactions can appear in a vast variety of systems, leading to a plethora of interesting phenomena. Notable examples of these include: (1) like-charge attraction in the presence of multivalent counterions, (2) Ludwig-Soret effect in charged colloids, (3) mass renormalization of moving defects in a phononic background and moving metallic objects in EM quantum vacuum, and (4) dissipation due to motion-induced radiation. The fluctuationinduced forces are statistical in nature, and this could make their measurement very difficult, because the actual value of the force might deviate most of the time from the predicted average value.     

Observation of structures of chain vortices inside anisotropic high- Tc superconductors

In order to elucidate the formation mechanism of unconventional arrangements of vortices in high- Tc superconducting thin films at an inclined magnetic field to the layer plane, we investigated the structures of vortex lines inside the films by Lorentz microscopy using our 1-MV field-emission electron microscope. Our observation results concluded that vortex lines are tilted to form linear chains in YBaCu3O(7,8). Vortex lines in the chain-lattice state in Bi2Sr2CaCu2O(8+delta), on the other hand, are all perpendicular to the layer plane, and therefore only vortices lined up along Josephson vortices form chains.     

Fluctuation-induced magnetotransport of superconductors in the quasiballistic regime

We study the fluctuation-induced magnetotransport of a two-dimensional superconductor in the quasiballistic regime, where ξ _GL(T) ≪ ℓ (ℓ is the electron mean free path and ξ _GL(T) is the Ginzburg-Landau coherence length). The magnetoconductivity is evaluated in the nonlocal fluctuation regime thereby extending the existing theory valid in the local limit. We show that the Maki-Thompson (MT) and density-of-states (DOS) contributions strongly compensate each other and their sum is negligible in comparison with the Aslamazov-Larkin (AL) term. The hierarchy of the fluctuation contributions to the magnetoconductivity in the high-field limit is also qualitatively discussed. Received 10 July 2002 / Received in final form 21 November 2002 Published online 7 May 2003     

On n-quantum vortices in superconductors

Taking into account terms of a higher order than those usually included in the expansion of free energy close to $\kappa = 1/\sqrt 2$ in the Ginzburg-Landau theory can lead either to the transition from the mixed to the intermediate state, as is commonly supposed, or to a chain of sequential transitions from one-to n-quantum vortices (n=2, 3, ...).     

Fluctuation-induced escape from the basin of attraction of a quasiattractor

Noise-induced escape from the basin of attraction of a strange attractor (SA) in a periodically excited nonlinear oscillator is investigated. It is shown by numerical simulation methods that escape occurs in two steps: transfer of the system from the SA to a close-lying saddle cycle along several optimal trajectories, and a subsequent fluctuation-induced transfer from the basin of attraction of the SA along a single optimal trajectory. The possibility of using the results of this work to solve problems of the optimal control of switchings from an attractor and for constructing theoretical estimates of the escape probability is discussed. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 11, 782–787 (10 June 1999)     

Effects of short-range attraction on Jamming transition

Enormous progresses to understand the jamming transition have been driven via simulating purely repulsive particles which were somehow idealized in the past two decades. While the attractive systems are both theoretical and practical compared with repulsive systems. By studying the statistics of rigid clusters, we find that the critical packing fraction φ_c varies linearly with attraction μ for different system sizes when the range of attraction is short. While for systems with long-range attractions, however, the slope of φ_c appears significantly different, which means that there are two distinct jamming scenarios. In this paper, we focus our main attention on short-range attractions scenario and define a new quantity named "short-range attraction susceptibility" χ_p, which describes the degree of response of the probability of finding jammed states pjto short-range attraction strength μ. Our central results are that χ_p diverges in the thermodynamic limit as χ_p ∝|φ-φ_c~∞|~(-γ_p), where φ_c~∞ is the packing fraction at the jamming transition for the infinite system in the absence of attraction. χ_p obeys scaling collapse with a scaling function in both two and three dimensions, illuminating that the jamming transition can be considered as a phase transition as proposed in previous work.     

Dynamics of quantum vortices in two-dimensional superconductors

The dynamics of rigid vortex translations in two-dimensional arrays of Josephson junctions is shown to be equivalent to the motion of a mass, proportional to the junction capacitance, in a periodic pinning potential. The quantum tunneling of the vortex through the potential barriers is predicted of importance in the existing Nb-arrays at very low temperatures. Above the vortex unbinding temperature there is a plasma resonance of the free vortices leading to an anomaly in the vortex frequency dependent dielectric constant, which could be observed via a radio frequency impedance measurement.     

Field-induced vortices in weakly anisotropic ferroelectrics

In microscale and nanoscale ferroelectric samples, the formation and growth of domains are the usual stages of the polarization switching mechanism. By assuming weak polarization anisotropy and by solving the Ginzburg–Landau–Khalatnikov equation we have explored an alternative mechanism which consists in ferroelectric switching induced by vortex formation. We have studied the polarization dynamics inside a ferroelectric circular capacitor where switching leads to the formation of a metastable vortex state with a rotational motion of the polarization. Our results are consistent with recent first-principle simulations [I.I. Naumov, H.X. Fu, Phys. Rev. Lett. 98, 077603 (2007)] and with experiments on PbZr_0.2Ti_0.8O₃ [A. Gruverman, D. Wu, H.J. Fan, I. Vrejoiu, M. Alexe, R.J. Harrison, J.F. Scott, J. Phys. Condens. Matter 20 342201(2008)] and demonstrate that vortex-induced polarization switching can be an effective mechanism for circular nanocapacitors.     

Stimulation effect in anisotropic superconductors

The stimulation of superconductivity in anisotropic superconductors by electromagnetic and acoustic pumping as well as by the injection of a tunnel current at temperatures close to the superconducting transition temperature is studied. The features distinguishing the stimulation effect from the isotropic case are indicated. Zh. éksp. Teor. Fiz. 111, 2134–2146 (June 1997)