arXiv subjects

E. Polturak

Publications and source records attributed to E. Polturak.

21 records · Page 2Linked to original sources

arXiv2000

Appearance of spontaneous macroscopic magnetization at the superconducting transition of YBCO

We report the observation of a weak spontaneous magnetic field appearing at the transition temperature of $\rm YBa_2Cu_3O_{7-δ}$ into the superconducting state. The effect is observed in 14 out of 15 epitaxial films grown on different substrates and by two distinct techniques. The average magnetic field sensed by the SQUID magnetometer is of the order of 10$^{-5}$ G. The effect indicates a breaking of both parity and time reversal symmetries in the superconductor. We consider two different interpretations: (i) The condensate carries an intrinsic magnetic moment. At T=0, this moment is between $\rm 10^{-2} μ_B$ and $\rm 10^{-4} μ_B$ per plaquette, depending whether the width of the unscreened region near the edge of the film is the coherence length or the penetration length. (ii) $π$ junctions which may exist near the edges produce circulating supercurrents and magnetic flux. Constraints imposed on these scenarios by temperature and geometry dependence of the data are discussed.

cond-mat.supr-con↗

arXiv1999

Correlated atomic motion, phonons and spin-ordering in bcc $^{3}$He

We propose a new way to treat nuclear magnetism of solid $^{3}$He. We argue that the magnetic interaction arises indirectly as a consequence of correlated zero-point motion of the ions. This motion lowers the energy of the ground state, and results in a coherent state of oscillating electric dipoles. Distortion of the electronic wavefunctions leads to hyperfine magnetic interactions with the nuclear spin. Our model describes both the phonon spectra and the nuclear magnetic ordering of bcc $^{3}$He using a single parameter, the dipolar interaction energy $E_{0}$. The model yields correctly both the u2d2 symmetry of the ordered phase and the volume dependence of the magnetic interaction.

cond-mat↗

arXiv1999

Local modes, phonons, and mass transport in solid $^4$He

We propose a model to treat the local motion of atoms in solid $^{4}$He as a local mode. In this model, the solid is assumed to be described by the Self Consistent Harmonic approximation, combined with an array of local modes. We show that in the bcc phase the atomic local motion is highly directional and correlated, while in the hcp phase there is no such correlation. The correlated motion in the bcc phase leads to a strong hybridization of the local modes with the T$_{1}(110)$ phonon branch, which becomes much softer than that obtained through a Self Consistent Harmonic calculation, in agreement with experiment. In addition we predict a high energy excitation branch which is important for self-diffusion. Both the hybridization and the presence of a high energy branch are a consequence of the correlation, and appear only in the bcc phase. We suggest that the local modes can play the role in mass transport usually attributed to point defects (vacancies). Our approach offers a more overall consistent picture than obtained using vacancies as the predominant point defect. In particular, we show that our approach resolves the long standing controversy regarding the contribution of point defects to the specific heat of solid $^{4}$He.

cond-mat↗