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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.

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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.