arXiv subjects

C. M. Chaves

Publications and source records attributed to C. M. Chaves.

21 records · Page 2Linked to original sources

arXiv2003

Magnon Specific Heat of Single Crystal Borocarbides RNi2B2C (R=Tm, Er, Ho, Dy, Tb, Gd)

Zero-field specific heat of the single crystals RNi2B2C (R= Er, Ho, Dy, Tb, Gd) was measured within the temperature range 0.1 K<T<25 K. Linearized spin wave analysis was successfully applied to account for and to rationalize the thermal evolution of the low--temperature magnetic specific heats of all the studied compounds (as well as the one reported for TmNi2B2C) in terms of only two parameters, namely an energy gap, delta, and a characteristic temperature, theta. The evolution of the gap and theta across the studied compounds correlates very well with the known magnetic properties. Theta, as a measure of the effective RKKY exchange couplings, scales reasonably well with the de Gennes factor. The gap, on the other hand, reflects predominately the anisotropic properties: ~2 K for GdNi2B2C, ~6 K for ErNi2B2C, ~7 K for TbNi2B2C, and ~8 K for each of HoNi2B2C and DyNi2B2C. The equality in the gap of HoNi2B2C and DyNi2B2C, coupled with the similarity in their magnetic configurations, indicates that a variation of x in the solid solution HoxDy1-xNi2B2C (x<0.8 and Tc<Tn) would not lead to any softening of the gap. This supports the hypothesis of Cho et al (PRL 77,163(1996)) concerning the influence of the collective magnetic excitations on the superconducting state. This work underlines the importance of spin-wave excitations for a valid description of low-temperature thermodynamics of borocarbides.

cond-mat.mtrl-sci↗

arXiv1998

Magneto-Roton Modes of the Ultra Quantum Crystal: Numerical Study

The Field Induced Spin Density Wave phases observed in quasi-one-dimensional conductors of the Bechgaard salts family under magnetic field exhibit both Spin Density Wave order and a Quantized Hall Effect, which may exhibit sign reversals. The original nature of the condensed phases is evidenced by the collective mode spectrum. Besides the Goldstone modes, a quasi periodic structure of Magneto-Roton modes, predicted to exist for a monotonic sequence of Hall Quantum numbers, is confirmed, and a second mode is shown to exist within the single particle gap. We present numerical estimates of the Magneto-Roton mode energies in a generic case of the monotonic sequence. The mass anisotropy of the collective mode is calculated. We show how differently the MR spectrum evolves with magnetic field at low and high fields. The collective mode spectrum should have specific features, in the sign reversed "Ribault Phase", as compared to modes of the majority sign phases. We investigate numerically the collective mode in the Ribault Phase.

cond-mat.mes-hall↗

arXiv1997

Magneto-Roton Modes in the Ultra Quantum Crystal: Life and Death at Large Magnetic Field

The Ultra Quantum Crystal (UQC) phases observed in quasi-one-dimensional conductors of the Bechgaard salts family under magnetic field exhibit both Spin Density Wave order and a Quantized Hall Effect, which may exhibit sign reversals. We examine the case with no sign reversals. Collective modes in the UQC have been shown to have a rich spectrum, with local Magneto-Roton like minima. As the field increases, Magneto-Roton modes, which have minima at quantized wave vectors, merge, or not, in the single particle excitation continuum. In the high field phase, the Hall conductivity at zero temperature is zero; at the transition from the N=1 phase, it has two Magneto-Roton modes, the energies of which increase rapidly with magnetic field. The modes survive until a critical field above which the high field phase looks more like a perfect nesting insulating Spin Density Wave.

cond-mat↗