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Search Results: 1 - 10 of 50529 matches for " Y. Yeshurun "
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Unified order-disorder vortex phase transition in high-Tc superconductors
Y. Radzyner,A. Shaulov,Y. Yeshurun
Physics , 2002, DOI: 10.1103/PhysRevB.65.100513
Abstract: The diversity of vortex melting and solid-solid transition lines measured in different high-T$_{c}$ superconductors is explained, postulating a unified order-disorder phase transition driven by both thermally- and disorder-induced fluctuations. The temperature dependence of the transition line and the nature of the disordered phase (solid, liquid, or pinned liquid) are determined by the relative contributions of these fluctuations and by the pinning mechanism. By varying the pinning mechanism and the pinning strength one obtains a spectrum of monotonic and non-monotonic transition lines similar to those measured in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$%_{8}$, YBa$_{2}$Cu$_{3}$O$_{7-\delta}$, Nd$_{1.85}$Ce$_{0.15}$CuO$%_{4-\delta}$, Bi$_{1.6}$Pb$_{0.4}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ and (La$% _{0.937}$Sr$_{0.063}$)$_{2}$CuO$_{4}$
Dynamics of transient disordered vortex states in BSCCO
B. Kalisky,Y. Bruckental,A. Shaulov,Y. Yeshurun
Physics , 2003, DOI: 10.1103/PhysRevB.68.224515
Abstract: The dynamics of transient disordered vortex states in BSCCO was magneto-optically traced in three experiments: (i) during continuous injection of transient vortex states while ramping up the external magnetic field, (ii) during annealing of injected transient states while keeping the external field constant, and (iii) during annealing of transient 'supercooled' disordered states while ramping down the external field. The results reveal front-like propagation (experiment i) or retreat (experiments ii and iii) of the transient vortex states, at a rate governed by the rate of change of the external field, the annealing time tau of the transient states and the creep rate. The experimental results are theoretically analyzed in terms of competition between generation and annealing of transient disordered vortex states. Extraction of the annealing time tau from the above three experiments, yields the same results for tau as a function of the induction, B, and temperature T. Knowledge of tau(B,T) allows for correct determination of the thermodynamic order-disorder vortex phase transition line.
Irreversible magnetization in thin YBCO films rotated in external magnetic field
R. Prozorov,A. Poddar,E. Sheriff,A. Shaulov,Y. Yeshurun
Physics , 1996, DOI: 10.1016/0921-4534(96)00266-3
Abstract: The magnetization M of a thin YBaCuO film is measured as a function of the angle $\theta $ between the applied field H and the c-axis. For fields above the first critical field, but below the Bean's field for first penetration H*, M is symmetric with respect to $\theta =\pi $ and the magnetization curves for forward and backward rotation coincide. For H>H* the curves are asymmetric and they do not coincide. These phenomena have a simple explanation in the framework of the Bean critical state model.
Magnetic irreversibility and relaxation in assembly of ferromagnetic nanoparticles
R. Prozorov,Y. Yeshurun,T. Prozorov,A. Gedanken
Physics , 1998, DOI: 10.1103/PhysRevB.59.6956
Abstract: Measurements of the magnetic irreversibility line and time-logarithmic decay of the magnetization are described for three $Fe_{2}O_{3}$ samples composed of regular amorphous, acicular amorphous and crystalline nanoparticles. The relaxation rate is the largest and the irreversibility temperature is the lowest for the regular amorphous nanoparticles. The crystalline material exhibits the lowest relaxation rate and the largest irreversibility temperature. We develop a phenomenological model to explain the details of the experimental results. The main new aspect of the model is the dependence of the barrier for magnetic relaxation on the instantaneous magnetization and therefore on time. The time dependent barrier yields a natural explanation to the time-logarithmic decay of the magnetization. Interactions between particles as well as shape and crystalline magnetic anisotropies define a new energy scale that controls the magnetic irreversibility. Introducing this energy scale yields a self-consistent explanation of the experimental data.
Possibility of Kauzmann points in the vortex matter phase diagram of single crystal YBa$_2$Cu$_3$O$_{7-δ}$
S. B. Roy,Y. Radzyner,D. Giller,Y. Wolfus,A. Shaulov,P. Chaddah,Y. Yeshurun
Physics , 2001,
Abstract: We highlight interesting thermomagnetic history effects across the transition line between the (quasi) ordered and disordered vortex states in single crystal YBa$_2$Cu$_3$O$_{7-\delta}$, and argue that these features are indicative of the first order nature of the transition line. We suggest that the destruction of the ordered vortex state in YBa$_2$Cu$_3$O$_{7-\delta}$ leading to vortex liquid (at high temperatures and low fields) and amorphous vortex solid (at low temperatures and high fields), takes place along a unified first-order transition line. The nonmonotonic behavior of this first order transition line gives rise to the possibility of more than one Kauzmann point where the entropies of the ordered and disordered vortex states are equal. In the high temperature region, one may order the vortex lattice by warming it, giving rise to an inverse melting effect.
Disorder and thermally driven vortex-lattice melting in La{2-x}Sr{x}CuO{4} crystals
Y. Radzyner,A. Shaulov,Y. Yeshurun,I. Felner,K. Kishio,J. Shimoyama
Physics , 2001, DOI: 10.1103/PhysRevB.65.100503
Abstract: Magnetization measurements in La{2-x}Sr{x}CuO{4} crystals indicate vortex order-disorder transition manifested by a sharp kink in the second magnetization peak. The transition field exhibits unique temperature dependence, namely a strong decrease with temperature in the entire measured range. This behavior rules out the conventional interpretation of a disorder-driven transition into an entangled vortex solid phase. It is shown that the transition in La{2-x}Sr{x}CuO{4} is driven by both thermally- and disorder-induced fluctuations, resulting in a pinned liquid state. We conclude that vortex solid-liquid, solid-solid and solid to pinned-liquid transitions are different manifestations of the same thermodynamic order-disorder transition, distinguished by the relative contributions of thermal and disorder-induced fluctuations.
Pure and Random-Field Quantum Criticality in the Dipolar Ising Model: Theory of $Mn_{12}$ acetates
A. J. Millis,A. D. Kent,M. P. Sarachik,Y. Yeshurun
Physics , 2009, DOI: 10.1103/PhysRevB.81.024423
Abstract: A theoretical model for the $Mn_{12}$ acetates is derived including a 'random field' effect arising from isomer effects in some families of host acetate materials. Estimates for the important energy scales are given. Phase boundaries are determined using a mean field approximation. Predictions for experiment are presented
On the origin of the irreversibility line in thin YBaCuO7 films with and without columnar defects
R. Prozorov,M. Konczykowski,B. Schmidt,Y. Yeshurun,A. Shaulov,C. Villard,G. Koren
Physics , 1996, DOI: 10.1103/PhysRevB.54.15530
Abstract: We report on measurements of the angular dependence of the irreversibility temperature $T_{irr}(\theta) $ in $YBa_2Cu_3O_{7-\delta }$ thin films, defined by the onset of a third harmonic signal and measured by a miniature Hall probe. From the functional form of $T_{irr}(\theta)$ we conclude that the origin of the irreversibility line in unirradiated films is a dynamic crossover from an unpinned to a pinned vortex liquid. In irradiated films the irreversibility temperature is determined by the trapping angle.
Flux-flow resistivity anisotropy in the instability regime in the a-b plane of epitaxial YBCO thin films
B. Kalisky,P. Aronov,G. Koren,A. Shaulov,Y. Yeshurun,R. P. Huebener
Physics , 2006, DOI: 10.1103/PhysRevLett.97.067003
Abstract: Measurements of the nonlinear flux-flow resistivity $\rho$ and the critical vortex velocity $\rm v^*_\phi$ at high voltage bias close to the instability regime predicted by Larkin and Ovchinnikov \cite{LO} are reported along the node and antinode directions of the d-wave order parameter in the \textit{a-b} plane of epitaxial $YBa_2Cu_3O_{7-\delta}$ films. In this pinning-free regime, $\rho$ and $\rm v^*_\phi$ are found to be anisotropic with values in the node direction larger on average by 10% than in the antinode direction. The anisotropy of $\rho$ is almost independent of temperature and field. We attribute the observed results to the anisotropic quasiparticle distribution on the Fermi surface of $YBa_2Cu_3O_{7-\delta}$.
Quantum Fluctuations and Long-Range Order in Molecular Magnets
P. Subedi,Bo Wen,Y. Yeshurun,M. P. Sarachik,A. J. Millis,A. D. Kent
Physics , 2013, DOI: 10.1016/j.poly.2013.05.009
Abstract: We review our studies of the effect of transverse fields on the susceptibility and magnetization of single crystals of the prototype single molecule magnet (SMM), Mn$_{12}$-acetate, and of a new high-symmetry variant, Mn$_{12}$-acetate-MeOH. SMM single crystals can exhibit long range ferromagnetic order associated with intermolecular dipole interactions. Transverse fields increase quantum spin fluctuation and quantum tunneling of the magnetization suppressing long range order. However, we have found that suppression of the Curie temperature by a transverse field in Mn$_{12}$-acetate is far more rapid than predicted by the Transverse-Field Ising Ferromagnetic Model (TFIFM). It appears that solvent disorder in Mn$_{12}$-acetate that results in an intrinsic distribution of small discrete tilts of the molecular magnetic easy axis from the global easy axis of the crystal ($\approx \pm 1^\circ$) gives rise to a distribution of random-fields that further suppresses long-range order. Semiquantitative agreement with the predictions of a Random-Field Ising Ferromagnet Model is found. Subsequent susceptibility studies we have conducted of the high symmetry Mn$_{12}$ variant, Mn$_{12}$-acetate-MeOH, with the same spin structure and similar lattice constants but without the same solvent disorder as Mn$_{12}$-acetate, agrees with the TFIFM. An important implication of our studies is that long-range order in these two chemically very similar SMMs are described by distinct physical models.
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