Searcharxiv⌕ Search

arXiv subjects

B. Rosenstein

Publications and source records attributed to B. Rosenstein.

At least 37 records · Page 2Linked to original sources
arXiv2005

Equilibrium First-Order Melting and Second-Order Glass Transitions of the Vortex Matter in Bi$_2$Sr$_2$CaCu$_2$O$_8$

The thermodynamic $H-T$ phase diagram of Bi$_2$Sr$_2$CaCu$_2$O$_8$ was mapped by measuring local \emph{equilibrium} magnetization $M(H,T)$ in 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.

cond-mat.supr-con↗
arXiv2005

Density of states of the interacting two-dimensional electron gas

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.

cond-mat.str-el↗
arXiv2003

Emergence of quasi-metallic state in disordered 2D electron gas due to strong interactions

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 like the Aronov - Altshuler logarithmic corrections to conductivity are less pronounced.

cond-mat.dis-nn↗
arXiv2000

Fluctuations in $YBa_{2}Cu_{3}O_{6.5}$ single crystal: an evidence for 2D->3D crossover

Magnetization measurements as a function of temperature are reported for $YBa_{2}Cu_{3}O_{6.5}$ crystal (T_{c}=45.2 K) for fields between 0.2 to $3.5\ Tesla$. All isochamps for H>1 Tesla intersect at $T_{2D}^{\star}\simeq 42.8\ K$, implying fluctuations contribution to the magnetization. These curves collapse into a single curve when magnetization and temperature are scaled according to the predicted ''2D scaling'' in the fluctuation regime. Surprisingly, the low field curves also intersect, at $T_{3D}^{\star}\simeq 43.4 K$, 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 $2D\to 3D$ crossover are consistent with the experimental observation.

cond-mat.supr-con↗
arXiv2000

Nature of 45 degree vortex lattice reorientation in tetragonal superconductors

The transformation of the vortex lattice in a tetragonal superconductor which consists of its 45 degree reorientation relative to the crystal axes is studied using the nonlocal London model. It is shown that the reorientation occurs as two successive second order (continuous) phase transitions. The transition magnetic fields are calculated for a range of parameters relevant for borocarbide superconductors in which the reorientation has been observed.

cond-mat.supr-con↗
arXiv1999

Systematic low temperature expansion in Ginzburg - Landau model

Consistent perturbation theory for thermodynamical quantities in strongly 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 with existing Monte Carlo simulations, other theories and experiments.

cond-mat↗
arXiv1999

Magnetic skyrmions and their lattices in triplet superconductors

Complete topological classification of solutions in SO(3) symmetric Ginzburg-Landau free energy has been performed and a new class of solutions in weak external magnetic field carrying two units of magnetic flux has been identified. These solutions, magnetic skyrmions, do not have singular core like Abrikosov vortices and at low magnetic field become lighter for strongly type II superconductors. As a consequence, the lower critical magnetic field Hc1 is reduced by a factor of log(kappa). Magnetic skyrmions repel each other as 1/r at distances much larger then magnetic penetration depth forming relatively robust triangular lattice. Magnetic induction near Hc1 increases gradually as (H-Hc1)^2. This agrees very well with experiments on heavy fermion superconductor UPt3. Newly discovered Ru based compounds Sr2RuO4 and Sr2YRu(1-x)Cu(x)O6 are other possible candidates to possess skyrmion lattices. Deviations from exact SO(3) symmetry are also studied.

cond-mat.supr-con↗
arXiv1999

Magnetic skyrmion lattices in heavy fermion superconductor UPt3

Topological analysis of nearly SO(3)_{spin} symmetric Ginzburg--Landau theory, proposed for UPt$_{3}$ by Machida et al, shows that there exists a new class of solutions carrying two units of magnetic flux: the magnetic skyrmion. These solutions do not have singular core like Abrikosov vortices and at low magnetic fields they become lighter for strongly type II superconductors. Magnetic skyrmions repel each other as $1/r$ at distances much larger then the magnetic penetration depth $λ$, forming a relatively robust triangular lattice. The magnetic induction near $H_{c1}$ is found to increase as $(H-H_{c1})^{2}$. This behavior agrees well with experiments.

cond-mat.supr-con↗
arXiv1997

An Interpretation of the Neutron Scattering Data on Flux Lattices of Superconductors

Small angle neutron diffraction experiments are analyzed using recently developed and properly generalized one-field effective free energy method. In the case of experiment of Keimer et al on YBCO, we show that the fourfold symmetry of the underlying crystal is explicitly broken, but the reflection with respect to the [110] and [1\={1}0] axes remains a symmetry. The vortex lattice also becomes generally oblique instead of rectangular body centered. Unexpectedly rich phase diagram is described.

cond-mat.supr-con↗
arXiv1997

Static and Dynamical Anisotropy Effects in Mixed State of D - Wave Superconductors

We describe effects of anisotropy caused by the crystal lattice in d-wave superconductors with s-wave mixing using the effective free energy approach. Only the d-wave order parameter field $d$ is introduced, while the effect of the s wave mixing as well as other effects breaking the rotational symmetry down to the fourfold symmetry of the crystal are represented by a single four (covariant) derivative term: $ηd^{*}(Π_{y}^{2}-Π_{x}^{2})^{2}d $. The single vortex solution in a phenomenologically interesting range of parameters is almost identical to the two order parameters approach. We analytically consider the most general oblique lattice and orientation, but find that only rectangular body centered lattices are realized. A critical value $η_{c} $ at which a phase transition from the rectangular lattice to the square lattice takes place. The influence on the phase transition line is discussed. The formalism is extended to the time dependent anisotropic Ginzburg-Landau equations in order to calculate the effect of the anisotropy on the flux flow. The moving vortex structure is established and the magnetization as function of the current is calculated. Although the linear conductivity tensor is rotationally invariant due to the fourfold symmetry, the nonlinear one shows anisotropy. We calculate dependence of both direct and Hall I-V curves on the angle between the current and the crystal lattice orientation.

cond-mat.supr-con↗
arXiv1997

The Effect of Anisotropy on Vortex Lattice Structure and Flux Flow in d-Wave Superconductors

We describe effects of anisotropy caused by the crystal lattice in d-wave superconductors using effective free energy approach in which only one order parameter, the d-wave order parameter field, is used. All the effects of rotational symmetry breaking, including that of the s-wave mixing, can be parametrized by a single four derivative term. We find solutions for single vortex and the vortex lattice. Extending the formalism to include the time dependence, effects of anisotropy on moving vortex structure are calculated. Both direct and Hall I-V curves as functions of the angle between the current and the crystal lattice orientation are obtained.

cond-mat.supr-con↗
arXiv1995

Electron Structure Near Abrupt Edges in 2DEG under Strong Magnetic Field

Energies and wave functions of edge states in twodimensional electron gas are evaluated for a finite step potential barrier model. The spectrum, instead of smooth bending of Landau branches in the vicinity of the barrier acquires a steplike form; unexpected edge plateaus and significant energy gap reduction take place between the neighbouring Landau branches above the barrier tops. The origin of these phenomena is traced. Stability with respect to modifications is established. Manifestation of the qualitatively new features of electron densities of states in abrupt confinements through magnetooptical and nuclear magnetic spin relaxation effects is proposed.

cond-mat↗
arXiv1995

Strong Coupling Hadron Masses in $1/d$ Expansion for Wilson fermions

Motivated by the weak-strong coupling expansion \cite{Rosenstein}, we calculate the spectrum of hadrons using a systematic $1/d$ ($d$ - dimensionality of spacetime) in addition to a strong coupling expansion in $β$. The $1/d$ expansion is pushed to the next to leading order in ($1/d$) for mesons and next to next to leading order for baryons. We do the calculation using Wilson fermions with arbitrary $r$ and show that doublers decouple from the spectrum only when $r$ is close to the Wilson's value $r=1$. For these $r$ the spectrum is much closer to the lattice results and the phenomenological values than those obtained by using either the (nonsystematic) "randomwalk" approximation or the hopping parameter expansion. In particular, the value of the nucleon to $ρ$ - meson mass ratio is lowered to $\frac {3 \log d -1/4}{2 {\rm arccosh} 2}+O(1/d)\approx 1.48$. The result holds even for $β$ as large as 5, where the weak-strong coupling expansion is applicable and therefore these results are expected to be reasonable.

hep-th↗
arXiv1995

Renormalization Group transformations of the decimation type in more than one dimension

We develop a formalism for performing real space renormalization group transformations of the "decimation type" using low temperature perturbation theory. This type of transformations beyond $d=1$ is highly nontrivial even for free theories. We construct such a solution in arbitrary dimensions and develop a weak coupling perturbation theory for it. The method utilizes Schur formula to convert summation over decorated lattice into summation over either original lattice or sublattice. We check the formalism on solvable case of $O(N)$ symmetric Heisenberg chain. The transformation is particularly useful to study models undergoing phase transition at zero temperature (various $d=1$ and $d=2$ spin models, $d=2$ fermionic models, $d=3,4$ nonabelian gauge models...) for which the weak coupling perturbation theory is a good approximation for sufficiently small lattice spacing. Results for one class of such spin systems, the d=2 O(N) symmetric spin models ($N\ge 3$) for decimation with scale factor $η=2$ (when quarter of the points is left) are given as an example

cond-mat↗
arXiv1995

Decimation in more then one dimension

We develop a formalism for performing real space renormalization group transformations of the "decimation type" using perturbation theory. The type of transformations beyond $d=1$ is nontrivial even for free theories. We check the formalism on solvable case of $O(N)$ symmetric Heisenberg chain. The transformation is particularly useful to study asymptotically free theories. Results for one class of such models, the d=2 O(N) symmetric $σ$ models ($N\ge 3$) for decimation with scale factor $η=2$ (when quarter of the points is left) are given as an example.

cond-mat↗
arXiv1995

Double expansion in asymptotically free theories

I propose an approximation scheme for asymptotically free field theories combining both weak coupling and strong coupling series. The weak coupling expansion is used to integrate the high frequency modes and the resulting low energy effective theory is solved using the strong coupling expansion. In some models there exists an intermediate scale at which both expansions make sense. The method is tested on few low dimensional models for which an exact solution is known.

hep-th↗
arXiv1994

Landau Level Gap Reduction at Abrupt Edges

For an electron localized near a finite rectangular step potential under strong magnetic field we found a profound local reduction of the gap between neighbouring Landau levels. We investigate under what conditions the effect persists when the barrier gets smoother. The conclusion is that to get a substantial gap reduction the barrier gradient has to be larger than $\hbarω_c/a_L$ ($a_L$ is the magnetic length). The sensitivity of the gap reduction is illustrated using tilted and multiple step barriers and finite stripe configurations.

cond-mat↗