RESUMEN
Strong evidence for charge-density correlation in the underdoped phase of the cuprate YBa2Cu3O y was obtained by NMR and resonant X-ray scattering. The fluctuations were found to be enhanced in strong magnetic fields. Recently, 3D charge-density-wave (CDW) formation with long-range order (LRO) was observed by X-ray diffraction in [Formula: see text] 15 T. To elucidate how the CDW transition impacts the pair condensate, we have used torque magnetization to 45 T and thermal conductivity [Formula: see text] to construct the magnetic phase diagram in untwinned crystals with hole density p = 0.11. We show that the 3D CDW transitions appear as sharp features in the susceptibility and [Formula: see text] at the fields [Formula: see text] and [Formula: see text], which define phase boundaries in agreement with spectroscopic techniques. From measurements of the melting field [Formula: see text] of the vortex solid, we obtain evidence for two vortex solid states below 8 K. At 0.5 K, the pair condensate appears to adjust to the 3D CDW by a sharp transition at 24 T between two vortex solids with very different shear moduli. At even higher H (41 T), the second vortex solid melts to a vortex liquid which survives to fields well above 41 T. de Haas-van Alphen oscillations appear at fields 24-28 T, below the lower bound for the upper critical field [Formula: see text].
RESUMEN
We report the Hall resistivity, ρ(xy), of polycrystalline SmFeAsO(1-x)F(x) for four different fluorine concentrations from the onset of superconductivity through the collapse of the structural phase transition. For the two more highly doped samples, ρ(xy) is linear in magnetic field up to 50 T with only weak temperature dependence, reminiscent of a simple Fermi liquid. For the lightly doped samples with x<0.15, we find a low temperature regime characterized as ρ(xy)(H) being both nonlinear in magnetic field and strongly temperature-dependent even though the Hall angle is small. The onset temperature for this nonlinear regime is in the vicinity of the structural phase (SPT)/magnetic ordering (MO) transitions. The temperature dependence of the Hall resistivity is consistent with a thermal activation of carriers across an energy gap. The evolution of the energy gap with doping is reported.
