arXiv subjects

L. Fruchter

Publications and source records attributed to L. Fruchter.

28 records · Page 2Linked to original sources

arXiv2006

Upper critical field from normal state fluctuations in Bi$_2$Sr$_2$CuO$_{6+δ}$

The in-plane magnetoresistance of an epitaxial Bi$_2$Sr$_2$CuO$_{6+δ}$ thin film was systematically investigated as a function of doping, above $T_c$. The orbital magnetoconductance is used to extract the crossover field line $H_{c2}^*(T)$ in the fluctuation regime. This field is found in good agreement with the upper critical field obtained from resistivity data below $T_c$, and exhibits a similar upward curvature, thus pointing toward the existence of a critical correlation length. The consequences regarding the nature of the resistive transition are discussed.

cond-mat.supr-con↗

arXiv2005

Current dependent fluctuations in a Bi$_2$Sr$_2$CuO$_{6+δ}$ thin film

The current dependence of the excess conductivity is measured up to $\simeq 3 T_c$ for a Bi$_2$Sr$_2$CuO$_{6+δ}$ thin film, as a function of doping. It is found to be anomalously sensitive to the transport current and to behave as a universal function of $T/T_c$ in the whole doping range. We discuss these results in the perspective of a granular superconductor with a gapless-like behavior.

cond-mat.supr-con↗

arXiv2004

Non linear excess conductivity of Bi$_2$Sr$_2$Ca$_{n-1}$Cu$_n$O$_{2n+4+x}$ (n = 1,2), thin films

The suppression of excess conductivity with electric field is studied for Bi$_2$Sr$_2$Ca$_{n-1}$Cu$_n$O$_{2n+4+x}$ ($n$ = 1, 2) thin films. A pulse-probe technique is used, which allows for an estimate of the sample temperature. The characteristic electric field for fluctuations suppression is found well below the expected value for all samples. For the $n=1$ material, a scaling of the excess conductivity with electric field and temperature is obtained, similar to the scaling under strong magnetic field.

cond-mat.supr-con↗

arXiv2003

Continuous melting of a driven two-dimensional flux lattice with strong pins

The phase diagram of a driven two-dimensional vortex lattice in the presence of dense quasi-point pins is investigated. The transition from the crystal to the liquid is found continuous at intermediate inductions. The correlations in the pseudo random force that allow for an uncomplete unbinding of the dislocations is proposed as a key mechanism to account for the continuous transition.

cond-mat.supr-con↗

arXiv2002

Ordering in Heisenberg Spin Glasses

For five different Heisenberg spin glass systems, torque experiments were performed in applied magnetic fields up to $4 T$. The Dzyaloshinski-Moriya random anisotropy strengths, the in-field torque onset temperatures, and the torque relaxation were measured. Critical exponents were estimated independently using a standard protocol. The data are strong evidence for a true spin glass ordered state which survives under high applied magnetic fields; they can be interpreted consistently in terms of a chiral ordering model with replica symmetry breaking as proposed by Kawamura and coworkers.

cond-mat.dis-nn↗

arXiv2001

Transition to plastic motion as a critical phenomenon and anomalous interface layer of a 2D driven vortex lattice

The dynamic transition between the ordered flow and the plastic flow is studied for a two-dimensional driven vortex lattice, in the presence of sharp and dense pinning centers, from numerical simulations. For this system, which does not show smectic ordering, the lattice exhibits a first order transition from a crystal to a liquid, shortly followed by the dynamical transition to the plastic flow. The resistivity provides a critical order parameter for the latter, and critical exponents are determined in analogy with a percolation transition. At the boundary between a pinned region and an unpinned one, an anomalous layer is observed, where the vortices are more strongly pinned than in the bulk.

cond-mat.supr-con↗

arXiv2001

Metastable states of a driven flux lattice in a superconductor with strong pins

The flux lattice driven by a uniform driving force in a superconductor with hot, strong, sharp and randomly distributed pinning centers, with applied magnetic field half the matching field is simulated. At low temperature both a non activated regime, where flux motion occurs within a robust percolative flux flow channel, and an activated regime are obtained depending on the sample preparation. These two regimes exhibit distinct resistivity and magnetic induction. In the non activated regime, a clear fingerprint is observed in the autocorrelation function of the longitudinal resitivity, which oscillates at a frequency close to the inverse lattice diffusion time.

cond-mat.supr-con↗

arXiv2000

Fluid and plastic flow dynamics of the critical state for a strongly pinned 2D superconductor

We present simulations of the dynamic critical state for a 2D superconductor with strong pinning centers, corresponding to a matching field twice the applied magnetic field. The sharp crossover between the plastic regime, at low current density and temperature, and the fluid flow regime for flux motion is characterized by the activation energy for flux motion and the transverse diffusion of the vortices trajectory.

cond-mat.supr-con↗

arXiv1999

Ordering in a spin glass under applied magnetic field

Torque, torque relaxation, and magnetization measurements on a AuFe spin glass sample are reported. The experiments carried out up to 7 T show a transverse irreversibility line in the (H,T) plane up to high applied fields, and a distinct strong longitudinal irreversibility line at lower fields. The data demonstrate for that this type of sample, a Heisenberg spin glass with moderately strong anisotropy, the spin glass ordered state survives under high applied fields in contrast to predictions of certain "droplet" type scaling models. The overall phase diagram closely ressembles those of mean field or chiral models, which both have replica symmetry breaking transitions.

cond-mat.dis-nn↗

arXiv1999

Evidence for an angular dependent contribution from columnar defects to the equilibrium magnetization of YBa_2Cu_3O_{7-d}

We have measured an angle-dependent contribution to the equilibrium magnetization of a YBa_2Cu_3O_{7-d} single crystal with columnar defects created by 5.8GeV Pb ions. This contribution manifests itself as a jump in the equilibrium torque signal, when the magnetic field crosses that of the defects. The magnitude of the signal, which is observed in a narrow temperature interval less than 2K and for fields up to about twice the irradiation field, is used to estimate the the energy gained by vortex pinning on the defects. The vanishing of the effective pinning energy at a temperature below Tc is attributed to its renormalization by thermal fluctuations.

cond-mat.supr-con↗