No abstract

No abstract

No abstract

We investigate the thermal-driven charge density wave (CDW) transition of two cubic superconducting intermetallic systems Lu(Pt 1−x Pd x) 2 In and (Sr 1−x Ca x) 3 Ir 4 Sn 13 by means of x-ray diffraction technique. A detailed analysis of the CDW modulation superlattice peaks as function of temperature is performed for both systems as the CDW transition temperature T CDW is suppressed to zero by an nonthermal control parameter. Our results indicate an interesting crossover of the classical thermal-driven CDW order parameter critical exponent from a three-dimensional universality class to a mean-field tendency, as T CDW vanishes. Such behavior might be associated with the presence of quantum fluctuations which influences the classical second-order phase transition, strongly suggesting the presence of a quantum critical point (QCP) at T CDW = 0. This also provides experimental evidence that the effective dimensionality exceeds its upper critical dimension due to a quantum phase transition.

Mö ssbauer spectroscopy measurements at room temperature (RT) and at liquid helium temperature (4.2 K) were carried out on bulk and glass samples from the D'Orbigny (angrite) and Cachari (eucrite) meteorites. The RT Mö ssbauer spectrum of the bulk sample of D'Orbigny shows the presence of Fe 2+ in olivine and pyroxene and that of bulk Cachari contains only pyroxene. Very small amounts of Fe 3+ are also present in the bulk samples, but are attributed to surface contamination. The RT spectra of the D'Orbigny and Cachari glasses are fitted with three doublets, which are assigned to Fe 2+ at three different octahedral positions. No Fe 3+ was detected in the glass samples. The spectra of the glasses measured at 4.2 K show the presence of relaxation effects. The results suggest a certain degree of structural ordering in these glasses.

No abstract

The 119 Sn Mössbauer spectra for the (Ru 1Ϫx Sn x )Sr 2 GdCu 2 O 8 system, with nominal compositions xϭ0.05-0.30, were measured from room temperature down to 4.2 K in samples exhibiting magnetic order followed by a resistive superconducting transition on cooling. Two contributions to the spectra are observed in the samples at room temperature: a doublet, dominating at low x, and a singlet, probably coming from the impurity phase SrSnO 3 . A part of the doublet evolves into a magnetic structure at low temperatures and is identified to sense the matrix properties. The isomer shift indicates that Sn enters into the RuO 2 layers as Sn 4ϩ . The appearance of a magnetic phase, in the spectra, matches with the onset of the Ru-sublattice long-range order, as detected by susceptibility measurements. The area of this component exhibits a smooth decrease with the increase in the Sn content, which is well described by a random distribution in the (Ru, Sn)O 2 layers. An average in-plane transferred hyperfine field of 4.29 T was sensed at 4.2 K for the sample with xϭ0.05, gradually decreasing with an increase in x. This high value may be indicative of the emergence of a -phase state for the superconducting order parameter across the magnetically ordered planes, with low pair-breaking effects.

Measurements of thermoelectric power and electrical resistivity of granular BiPb Sr C a Cu 0 are reported. Rounding of thermoelectric power near anh'8bov~'?hezcrihca? yemperature is analysed in terms of thermodynamic fluctuations of the superconducting order parameter.