Specific heat of single crystal MgB2: a two-band superconductor with two different anisotropies

Heat-capacity measurements of a 39 microg MgB2 single crystal in fields up to 14 T and below 3 K allow the determination of the low-temperature linear term of the specific heat, its field dependence, and its anisotropy. Our results are compatible with two-band superconductivity, the band carrying the smaller gap being isotropic, that carrying the larger gap having an anisotropy of approximately 5. Three different upper critical fields are thus needed to describe the superconducting state of MgB2.     

Revue des propriétés magnétiques et électroniques des composés des terres rares avec les anions du 5ième groupe du système périodique

This report reviews the most important publications, as well as many unpublished measurements by the authors. The influence of the cubic crystal field on the magnetic properties of binary compounds containing the trivalent Ions Pr³⁺, Sm³⁺, Tm³⁺ and Yb³⁺ is studied. Crystalfield- and exchange parameters (molecularfield approximation) were determined for the ferromagnetic nitrides GdN, TbN, DyN, HoN and ErN. The mechanism of the electrical conductivity is still unknown.     

A “Generalized Trace Formula” for Bell numbers

The nth Bell number B_n is the number of ways to partition a set of n elements into nonempty subsets. We generalize the “trace formula” of Barsky and Benzaghou [1], which asserts that for an odd prime p and an appropriate constant τ_p, the relation B_n=-Tr(^n-1-τ_p)B_τp holds in , where is a root of and is the trace form. We deduce some new interesting congruences for the Bell numbers, generalizing miscellaneous well-known results including those of Radoux [4].     

Thermal expansion and specific heat of intermediate valent YbCuAl

The specific heat, thermal expansion and resistivity was measured for the intermediate valence compound YbCuAl and its reference compound LuCuAl between 1.5 and 400 K. All quantities show strong anomalies. The entropy of the specific heat anomaly is found to be nearR·ln9, the value expected for the entropy of a high temperature mixture of Yb-ions in the ratio dictated by the degeneracies of the Hund's rule groundstates of 4f ¹⁴ and 4f ¹³. TheT ³ coefficient of the low temperature specific heat of YbCuAl contains a large electronic contribution. The integrated thermal expansion anomaly indicates a shift of the valence by at least 3.5% towards 3⁺ between 1.5 and 310 K.     

Corrections of counting losses in gamma-spectrometry of short-lived radionuclides

A short-lived radionuclide is characterized essentially by the decrease of its activity even while it is counted. The relations used between the number of counts recorded in a given time and the half-life in order to obtain the true counting rate are reviewed. Moreover, in gamma-spectrometry with multichannel analysers having variable dead-time, counting losses are observed. Exact corrections are calculated for pure short-lived radionuclides and for mixtures of one short-lived and one or more long-lived radionuclides. Based on these calculations, the approximations given by the built-in “live-timer” device of the analysers and by a new “actual-time” concept (with external live-time measurement) are evaluated. Curves are drawn as functions of the ratio counting time vs. half-life, to ensure minimal errors of less then 1%.     

Correlation between the “fishtail” effect in the magnetization and the Schottky contribution in the specific heat of high purity YBA2Cu3O7−δ crystals

The irreversibility of the magnetization and the low temperature specific heat of high purity YBa₂Cu₃O_7– crystals are investigated. We find that the heat treatment that suppresses the magnetic fishtail effect also suppresses the Schottky component of the heat capacity. Both effects originate from the distribution of oxygen states.     

D-wave specific heat in Y-123 and Bi-2212 single crystals: new data,alternative explanation

The low temperature specific heat of Bi-2212 and Y-123 is measured for 1.2≤T≤7K and 0≤B≤14 T. We find that the field-induced “linear” term λ^*(B)?λ^*(0) near 1–3K saturates for B≥8 T, decreases as a function of temeprature, and has nearly the same amplitude for both compounds. This is not easily reconciled with the predicted d-wave contribution C∝γT(B/B_c2)^1/2. Oscillations of 2D vortices offer an alternative explanation.     

Effet d’ordre dans le supraconducteur V3Au: Effet électronique ou phononique?

Specific heat measurements from1 to 40 K give some insight into the phonon spectrum of the alloy V₃Au. The minute differences between the as-cast and annealed states indicate that the drastic change of the superconducting transition temperature upon ordering is not likely to be of phononic origin. Alternatively, this behaviour can be understood as a consequence of an electronic density-of-states change in the presence of a large Coulomb pseudopotential term. This assumption is supported by susceptibility measurements.