Browsing by Author "Rosenstein, B"

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90 degrees reorientation in the vortex lattice of borocarbide superconductors
(2000-12-01)
Knigavko, A
;
Rosenstein, B
;
交大名義發表
;
電子物理學系
;
National Chiao Tung University
We explain 90 degrees reorientation in the vortex lattice of borocarbide superconductors on the basis of a phenomenological extension of the nonlocal London model that takes full account of the symmetry of the system. Microscopic mechanisms that could generate the correction terms are analyzed. We show that for any dispersion relation and longitudinal phonon-electron pairing mechanism the relevant quantity is strongly suppressed. Possible phenomenological interaction terms providing the effect are studied.
Alternating para/diamagnetic domains in a p-wave superconductor
(2003-11-01)
Bel, G
;
Rosenstein, B
;
Shapiro, BY
;
Shapiro, I
;
電子物理學系
The mesoscopic one-dimensional magnetic texture caused by small Zeeman coupling in a p-wave superconductor in the magnetic field is found. The field orientation is opposite on the two sides of the texture and the magnitude can be even smaller than H-c1. The texture is not built from various singular topological defects, like vortices, as previously found in the simplest three-component Ginzburg-Landau model of superconductors.
Anisotropic peak effect due to structural phase transition in the vortex lattice
(2000-05-01)
Rosenstein, B
;
Knigavko, A
;
電子物理學系
;
Department of Electrophysics
The recently observed new peak effect in YBCO is explained by softening of the vortex lattice (VL) due to a structural phase transition in the VL. At this transition, square lattice transforms into a distorted hexagonal one. While conventional peak effect is associated with softening of shear modes at melting, in this case the relevant mode is the point. The squash mode is highly anisotropic and we point out some peculiar effects associated with this feature. (C) 2000 Published by Elsevier Science B.V. All rights reserved.
Anisotropic peak effect due to structural phase transition in the vortex lattice
(1999-07-26)
Rosenstein, B
;
Knigavko, A
;
電子物理學系
;
Department of Electrophysics
It is shown that the recently observed new peak effect in YBCO could be explained by the softening of the vortex lattice due to a structural phase transition in the vortex lattice. At this transition square lattice transforms into a distorted hexagonal one. While conventional peak effect is associated with the softening of shear modes (elastic modulus c(66) vanishes) at melting, in this case the relevant mode is "squash" mode(c(11) + c(22) - 2c(12) vanishes).
Density of states of the interacting two-dimensional electron gas
(2005-06-01)
Kogan, E
;
Rosenstein, B
;
電子物理學系
;
Department of Electrophysics
We study the influence of electron-electron interactions on the density of states (DOS) of clean 2D electron gas. We confirm the linear cusp in the DOS around the Fermi level, which was obtained previously. The cusp crosses over to a pure logarithmic dependence further away from the Fermi surface.
Density of states of the interacting two-dimensional electron gas
(2004-03-01)
Kogan, E
;
Rosenstein, B
;
交大名義發表
;
電子物理學系
;
National Chiao Tung University
We study the influence of electron-electron interactions on the density of states (DOS) of a clean two-dimensional electron gas. We find that the linear cusp in the DOS around the Fermi level, which was obtained previously, has an additional logarithmic factor. The cusp crosses over to a pure logarithmic dependence further away from the Fermi surface.
Deviations from quantized Hall conductivity and current density distribution in finite 2DEG samples
(1997-09-10)
Bartos, I
;
Rosenstein, B
;
電子物理學系
;
Department of Electrophysics
Simple expressions for local and total Hall conductivities in finite two dimensional electron systems under magnetic field are obtained from the Kubo formula. The deviations of the Hall conductivity from integer values are always negative and their magnitude is inversely proportional to the effective width of the sample and proportional to the slope of the Landau branch dispersion relation at the Fermi level, Eq. (22). We also calculate the local conductivity in finite samples. The conductivity density is constant in the bulk and sums up to an integer value. Its spatial distribution is terminated in the bulk in a universal manner. Illustrations for simple models of the confinement barrier, as well as relation to recent experimental data for quantum wires are given.
Deviations from quantized Hall conductivity and current density distribution in finite 2DEG samples
(1997-09-10)
Bartos, I
;
Rosenstein, B
;
電子物理學系
;
Department of Electrophysics
Simple expressions for local and total Hall conductivities in finite two dimensional electron systems under magnetic field are obtained from the Kubo formula. The deviations of the Hall conductivity from integer values are always negative and their magnitude is inversely proportional to the effective width of the sample and proportional to the slope of the Landau branch dispersion relation at the Fermi level, Eq. (22). We also calculate the local conductivity in finite samples. The conductivity density is constant in the bulk and sums up to an integer value. Its spatial distribution is terminated in the bulk in a universal manner. Illustrations for simple models of the confinement barrier, as well as relation to recent experimental data for quantum wires are given.
Dynamical analysis of survival of Kosterlitz-Thouless pairs due to pinning
(1997-01-01)
Chang, D
;
Rosenstein, B
;
Wu, CL
;
電子物理學系
;
Department of Electrophysics
We investigate the process of annihilation between vortices of opposite flux in superconducting thin films in the presence of randomly distributed pinning centers. The number and distribution of pairs of vortex-antivortex that avoid annihilation due to pinning on two pinning centers is estimated analytically and compared with numerical simulations. The situation can be realized, for example, when the system is quenched from high temperature (above or below the Kosterlitz-Thouless temperature) or when the current is reduced abruptly. Qualitatively two different cases can be distinguished. The simpler one is when the pairs are well separated. In this case, the problem under mild assumptions can be solved analytically. When the vortex pairs are not very rare, the situation is much more complicated because a great variety of processes become significant. We isolate the important ones and construct an iterative (real-space renormalization-group) scheme to describe the behavior of the interacting multivortex system. Some dynamical aspects of pinning and vortex motion are discussed.
Dynamical analysis of survival of Kosterlitz-Thouless pairs due to pinning
(1997-01-01)
Chang, D
;
Rosenstein, B
;
Wu, CL
;
電子物理學系
;
Department of Electrophysics
We investigate the process of annihilation between vortices of opposite flux in superconducting thin films in the presence of randomly distributed pinning centers. The number and distribution of pairs of vortex-antivortex that avoid annihilation due to pinning on two pinning centers is estimated analytically and compared with numerical simulations. The situation can be realized, for example, when the system is quenched from high temperature (above or below the Kosterlitz-Thouless temperature) or when the current is reduced abruptly. Qualitatively two different cases can be distinguished. The simpler one is when the pairs are well separated. In this case, the problem under mild assumptions can be solved analytically. When the vortex pairs are not very rare, the situation is much more complicated because a great variety of processes become significant. We isolate the important ones and construct an iterative (real-space renormalization-group) scheme to describe the behavior of the interacting multivortex system. Some dynamical aspects of pinning and vortex motion are discussed.
Dynamics and thermal instability of magnetic flux in type-II superconductors
(2005-05-01)
Shapiro, BY
;
Shapiro, I
;
Rosenstein, B
;
Bass, F
;
電子物理學系
In recent experiments, trapped magnetic flux is initially generated by abrupt laser heating of a strip of a type-II superconducting film subjected to a weak magnetic field. We study herein the nonequilibrium penetration of the flux into the Meissner state area. Effects of the heal dissipation and transport on the motion and stability of the interface between the magnetic flux and flux-free domains are considered. It is shown that the magnetic induction and the temperature have the form of a shock wave moving with constant velocity as large as that corresponding to the depairing current. In the vicinity of the front, superconductivity is suppressed by strong screening currents. The front velocity is determined by the Joule heat caused by the electric current in the normal domain at the flux front. The stability of the shock wave solution is investigated both analytically and numerically. For sufficiently small heat diffusion constant a finger shaped thermal instability is found.
Emergence of quasimetallic state in a disordered two-dimensional electron gas due to strong interactions
(2003-12-01)
Rosenstein, B
;
Minh-Tien, T
;
交大名義發表
;
電子物理學系
;
National Chiao Tung University
The interrelation between disorder and interactions in two-dimensional electron liquid is studied beyond weak-coupling perturbation theory. Strong repulsion significantly reduces the electronic density of states on the Fermi level. This makes the electron liquid more rigid and strongly suppresses elastic scattering off impurities. As a result the weak localization, although ultimately present at zero temperature and infinite sample size, is unobservable at experimentally accessible temperature at high enough densities. Therefore practically there exists a well-defined metallic state. We study diffusion of electrons in this state and find that the diffusion pole is significantly modified due to "mixture" with static photons similar to the Anderson-Higgs mechanism in superconductivity. As a result several effects stemming from the long-range nature of diffusion such as the Aronov-Altshuler logarithmic corrections to conductivity are less pronounced.
Equilibrium first-order melting and second-order glass transitions of the vortex matter in Bi2Sr2CaCu2O8
(2005-12-16)
Beidenkopf, H
;
Avraham, N
;
Myasoedov, Y
;
Shtrikman, H
;
Zeldov, E
The thermodynamic H-T phase diagram of Bi2Sr2CaCu2O8 was mapped by measuring local equilibrium magnetization M(H,T) in the presence of vortex shaking. Two equally sharp first-order magnetization steps are revealed in a single temperature sweep, manifesting a liquid-solid-liquid sequence. In addition, a second-order glass transition line is revealed by a sharp break in the equilibrium M(T) slope. The first- and second-order lines intersect at intermediate temperatures, suggesting the existence of four phases: Bragg glass and vortex crystal at low fields, glass and liquid at higher fields.
Excitation of ''rotation'' collective modes in vortex lattice of clean type II superconductors
(2000-05-01)
Kasatkin, A
;
Rosenstein, B
;
電子物理學系
;
Department of Electrophysics
In superclean limit, the Magnus force on Abrikosov vortices is stronger than friction. Due to this nondissipative force, vortex segments rotate around pinning centers. Waves of such rotations under certain conditions are only weakly damped (not overdamped as is usually the case) and lead to resonances in ac response. Excitation of such waves by applied ac field near the surface is considered. Surface impedance, ac resistivity and magnetic permeability are calculated using elasticity theory of the vortex lattice. (C) 2000 Published by Elsevier Science B.V. All rights reserved.
Excitation of rotation collective modes in a vortex lattice of clean type-II superconductors
(1999-12-01)
Kasatkin, A
;
Rosenstein, B
;
電子物理學系
;
Department of Electrophysics
In a superclean limit the Magnus force on Abrikosov vortices is stronger than friction. Due to this, nondissipative force vortex segments rotate around pinning centers. Waves of such rotations under certain conditions are only weakly damped (not overdamped as is usually the case) and lead to resonances in the ac response. (The excitation of such waves by applied ac field near the-surface is considered. Surface impedance, ac resistivity, and magnetic permeability are calculated using elasticity theory of the vortex lattice. [S0163-1829(99)00442-7].
Explicit four-fold symmetry breaking effect on the vortex lattice in D-wave superconductors
(1998-04-01)
Chang, D
;
Mou, CY
;
Rosenstein, B
;
Wu, CL
;
電子物理學系
We use a recently developed effective Ginzberg-Landau equation to study the vortex lattice structure in d-wave superconductors. By introducing explicit four-fold symmetry breaking terms we are able to reproduce the small angle neutron scattering data on YBCO by Keimer et al. [9]. A phase diagram is also constructed and shows quite rich structures.
Ferromagnetic behavior of a triplet superconductor
(1999-04-15)
Knigavko, A
;
Rosenstein, B
;
Chen, YF
;
Huang, HL
;
Lin, MT
Properties of a type II triplet superconductor with equal spin pairing are investigated using the phenomenological Ginzburg-Landau approach. It is shown that there exist two kinds of fluxons: vortices and magnetic skyrmions. Vector nature of the order parameter allows a direct coupling of the effective spin of the condensate to a magnetic field. This coupling, which is reminiscent to Zeeman interaction in the form, significantly modifies the structure of an isolated vortex, as compared to the usual Abrikosov vortex, and changes the energetics of a vortex lattice. If the coupling is sufficiently strong, then magnetization of the triplet superconductor becomes positive at high magnetic fields. Formation of spontaneous vortex state is also possible. (C) 1999 American Institute of Physics. [S0021-8979(99)55408-X].
First-principles theory of fluctuations in vortex liquids and solids
(1999-08-01)
Rosenstein, B
;
電子物理學系
;
Department of Electrophysics
Consistent perturbation theory for thermodynamical quantities in type-II superconductors in magnetic field at low temperatures is developed. It is complementary to the existing expansion valid at high temperatures. Magnetization and specific heat are calculated to two-loop order and compare well to existing Monte Carlo simulations and experiments. [S0163-1829(99)01829-9].
Fluctuations in single-crystal YBa2Cu3O6.5: Evidence for crossover from two-dimensional to three-dimensional behavior
(2001-04-01)
Rosenstein, B
;
Shapiro, BY
;
Prozorov, R
;
Shaulov, A
;
Yeshurun, Y
Magnetization measurements as a function of temperature are reported for YBa2Cu3O6.5 crystal (T-c = 45.2 K) for fields between 0.2 and 3.5 T. All isochamps for H > 1 T intersect at T-2D(star) similar or equal to 42.8 K, implying a fluctuation contribution to the magnetization. These curves collapse into a single curve when magnetization and temperature are scaled according to the predicted "two-dimensional (20) scaling" in the fluctuation regime. Surprisingly, the low-field curves also intersect, at T-3D(star) similar or equal to 43.4 K, and they obey a 3D scaling. We provide a theoretical picture of the magnetization in the fluctuation regime based on the Lawrence-Doniach model. Within this model we calculate the field and temperature dependence of the magnetization. The two intersection points and the 2D --> 3D crossover are consistent with the experimental observation.
Hot spot in type-II superconductors: dynamics and instabilities
(2004-05-01)
Shapiro, B
;
Bel, G
;
Rosenstein, B
;
Shapiro, I
;
電子物理學系
The relaxation dynamics of a quenched normal spot in type-II superconductor is considered analytically and numerically. Various instabilities accompanying recovery of superconductivity are considered. Relaxation of the normal spot starts with appearance of a microscopic instability triggering the creation of the vortex clusters. (C) 2004 Elsevier B.V. All rights reserved.