Moshe Schechter

Magnetization of small lead particles.

The magnetization of an ensemble of isolated lead grains of sizes ranging from 4 to 1000 nm is measured. A sharp disappearance of the Meissner effect with a lowering of the grain size is observed for the smaller grains. This is a direct observation by magnetization measurement of the occurrence of a critical particle size for superconductivity, which is consistent with Andersons criterion.

Thermodynamic properties of a small superconducting grain

The reduced BCS Hamiltonian for a metallic grain with a finite number of electrons is considered. The crossover between the ultrasmall regime, in which the level spacing d is larger than the bulk superconducting gap D and the small regime, where D*d, is investigated analytically and numerically. The condensation energy, spin magnetization, and tunneling peak spectrum are calculated analytically in the ultrasmall regime, using an approximation controlled by 1/ln N as a small parameter, where N is the number of interacting electron pairs. The condensation energy in this regime is perturbative in the coupling constant l and is proportional to dNl 2 5l 2 v D . We find that also in a large regime withD.d, in which pairing correlations are already rather well developed, the perturbative part of the condensation energy is larger than the singular, BCS part. The condition for the condensation energy to be well approximated by the BCS result is found to be roughly D.Adv D. We show how the condensation energy can, in principle, be extracted from a measurement of the spin magnetization curve and find a reentrant susceptibility at zero temperature as a function of magnetic field, which can serve as a sensitive probe for the existence of superconducting correlations in ultrasmall grains. Numerical results are presented, which suggest that in the large N limit the 1/N correction to the BCS result for the condensation energy is larger than D.

LiHo x Y 1 − x F 4 as a random-field Ising ferromagnet

As a result of the interplay between the intrinsic off-diagonal terms of the dipolar interaction and an applied transverse field

Magnetic response of disordered metallic rings: large contribution of far levels.

{H}_{t}

Two pairing parameters in superconducting grains

, the diluted

Reflectionless tunneling in ballistic normal-metal–superconductor junctions

{\mathrm{LiHo}}_{x}{\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{F}}_{4}

Significance of the hyperfine interactions in the phase diagram of LiHoxY1-xF4.

system at

Spectrum and thermodynamic currents in one-dimensional Josephson elements

xg0.5

Low-temperature1/fnoise in microwave dielectric constant of amorphous dielectrics in Josephson qubits

is equivalent to a ferromagnet in a longitudinal random field (RF). At low

Derivation of the low- T phase diagram of LiHo x Y 1 − x F 4 : A dipolar quantum Ising magnet

{H}_{t}