On the destruction of the hidden order in URu2_2Si2_2 by a strong magnetic field

We present a study of transport properties of the heavy fermion URu$_2$Si$_2$ in pulsed magnetic field. The large Nernst response of the hidden order state is found to be suppressed when the magnetic field exceeds 35 T. The combination of resistivity, Hall and Nernst data outlines the reconstruction of the Fermi surface in the temperature-field phase diagram. The zero-field ground state is a compensated heavy-electron semi-metal, which is destroyed by magnetic field through a cascade of field-induced transitions. Above 40 T, URu$_2$Si$_2$ appears to be a polarized heavy fermions metal with a large density of carriers whose effective mass rapidly decreases with increasing magnetic polarization.Comment: published versio

Toward equilibrium ground state of charge density waves in rare-earth tritellurides

We show that the charge density wave (CDW) ground state below the Peierls transition temperature, $T_{CDW}$, of rare-earth tritellurides is not at its equilibrium value, but depends on the time where the system was kept at a fixed temperature below $T_{CDW}$. This ergodicity breaking is revealed by the increase of the threshold electric field for CDW sliding which depends exponentially on time. We tentatively explain this behavior by the reorganization of the oligomeric (Te$_x$)$^{2-}$ sequence forming the CDW modulation.Comment: 10 pages, 5 figures, accepted in PR

Total suppression of superconductivity by high magnetic fields in YBa2 Cu3O6.6

We have studied in fields up to 60T the variation of the transverse magnetoresistance (MR) of underdoped YBCO6.6 crystals either pure or with Tc reduced down to 3.5K by electron irradiation. We evidence that the normal state MR is restored above a threshold field H'c(T), which is found to vanish at T'c>>Tc. In the pure YBCO6.6 sample a 50 Tesla field is already required to completely suppress the superconducting fluctuations at Tc. While disorder does not depress the pseudogap temperature, it reduces drastically the phase coherence established at Tc and weakly H'c(0), T'c and the onset Tnu of the Nernst signal which are more characteristic of the 2D local pairing.Comment: 4 pages, 4 figure

Low energy magnetic excitation spectrum of the unconventional ferromagnet CeRh3_{3}B2_{2}

The magnetic excitation spectrum of the unconventional ferromagnet CeRh$_{3}$B$_{2}$ was measured by inelastic neutron scattering on single crystal sample in the magnetically ordered and paramagnetic phases. The spin-wave excitation spectrum evidences high exchange interaction along the c-axis about two orders of magnitude higher than the ones in the basal plane of the hexagonal structure. Both strong out of plane and small in plane anisotropies are found. This latter point confirms that considering the $J$=5/2 multiplet alone is not adequate for describing the ground state of CeRh$_{3}$B$_{2}$. Quasielastic scattering measured above $T_{Curie}$ is also strongly anisotropic between the basal plane and the c-axis and suggests localized magnetism.Comment: 8 Figure

Field-induced magnetic behavior in quasi-one-dimensional Ising-like antiferromagnet BaCo2V2O8: A single-crystal neutron diffraction study

BaCo2V2O8 is a nice example of a quasi-one-dimensional quantum spin system that can be described in terms of Tomonaga-Luttinger liquid physics. This is explored in the present study where the magnetic field-temperature phase diagram is thoroughly established up to 12 T using single-crystal neutron diffraction. The transition from the N\'eel phase to the incommensurate longitudinal spin density wave (LSDW) phase through a first-order transition, as well as the critical exponents associated with the paramagnetic to ordered phase transitions, and the magnetic order both in the N\'eel and in the LSDW phase are determined, thus providing a stringent test for the theory.Comment: 17 pages with 15 figure