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Berisso, M. G., O. Trovarelli, P. Pedrazzini, G. Zwicknagl, C. Geibel, F. Steglich, and J. G. Sereni. "Nonmonotonous evolution of the Kondo temperature in the phase diagram of Ce(Pd1-xCux)(2)Si-2." Physical Review B – Condensed Matter and Materials Physics 58, no. 1 (1998): 314–321.
Abstract: The evolution of the behavior of the Ce 4f electron with the Cu content in the alloy Ce(Pd1-xCux)(2)Si-2 was investigated by determining its structural, magnetic, transport, and thermal properties. Results obtained on 15 samples with compositions distributed along the whole concentration range allow us to draw a magnetic phase diagram showing three distinct regions. The first region at low Cu concentrations corresponds to the antiferromagnetic-ordered regime. The fast suppression of this magnetic order between x = 0.2 and x = 0.25 suggests the presence of a critical point which separates this region from the second one at larger.x values where no magnetic order is observed. The main characteristic of this second region, which extends up to x = 0.7, is a pronounced increase of the Kondo temperature T-K, from T-K approximate to 15 K at x = 0.25 to T-K approximate to 50 K at x = 0.7. This is in contrast with the fast decrease of T-K in the region with x > 0.7. In this region a small anomaly with a ferromagnetic character is observed in the specific hear arround 4 K. The change in the evolution of T-K with x coincides with a change in the composition dependence of the c lattice parameter of the tetragonal structure, pointing to a structure-related origin of this unusual T-K(x) behavior. This nonmonotonous T-K(x) dependence is reproduced using local-density-approximation band-structure calculations, which show a maximum of the hybridization strength between conduction electrons and Ce 4f stares for intermediate Cu concentrations. Such a T-K(x) dependence which contradicts the monotonous dependence observed in all other Ce-based alloy systems is the hallmark of the Ce(Pd1-xCux)(2)Si-2 alloy, which cannot be described as a Fermi-Liquid system in the nonmagnetic region. [S0163-1829(98)02118-3].
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Fainstein, A., B. Maiorov, J. Guimpel, G. Nieva, and E. Osquiguil. "Annealing disorder and photoinduced order of oxygen chains in detwinned YBa2Cu3O6.65 single crystals probed by Raman scattering." Physical Review B – Condensed Matter and Materials Physics 61, no. 6 (2000): 4298–4304.
Abstract: Raman scattering in detwinned YBa2Cu3O6.65 single crystals is studied as a function of photoexcitation and annealing. Copper-oxygen chain-related forbidden Raman bands that are known to strongly bleach with illumination at low temperatures, increase their intensity with chain fragmentation induced by annealing at high temperature. This contrasting behavior proves the conjunction of short Cu-O fragments into longer chains on photoexcitation. We interpret the Raman modes as due to vibrations at the end of CuO chain fragments and Cu-O-Cu monomers, and use their evolution with illumination and annealing as anisotropic sensitive markers of oxygen reordering processes. The identification of the “forbidden” Raman bands is discussed in the context of our results and recent literature in the subject. We also present absorption measurements performed on GdBa2Cu3Ox thin films with varying oxygen content. These experiments show that the 2.2-eV absorption and the chain-related Raman peaks have different dependencies with oxygen content and illumination, ruling out an explanation that suggests that the Raman intensity reduction of these modes is due to a photobleaching of intermediate defect states. These results highlight the potentialities of Raman scattering for oxygen dynamics studies and demonstrate the presence of photoinduced oxygen ordering in these high-Tc superconductor compounds.
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Grigera, S. A., and Morr. "Two-step liquid-solid vortex transition with the field along the ab planes in YBa2Cu3O7-? crystals." Physical Review B – Condensed Matter and Materials Physics 59, no. 17 (1999): 11201–11204.
Abstract: Resistivity measurements for different Lorentz force configurations and the detection of the longitudinal vortex velocity correlation length, with the magnetic field applied parallel to the ab planes, in the mixed state of clean and twinned YBa2Cu3O7-? single crystals, support the existence of a vortex-smectic phase when the vortices interact with an attractive periodic potential. The transition from the vortex-liquid to the vortex-solid state is shown to be achieved in two steps, a continuous transition from a liquid to a possible smectic phase and another continuous one from the smectic phase to a solid.
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Guimpel, J., B. Maiorov, E. Osquiguil, G. Nieva, and F. Pardo. "Interrelation between persistent photoconductivity and oxygen order in GdBa2Cu3Ox thin films." Physical Review B – Condensed Matter and Materials Physics 56, no. 7 (1997): 3552–3555.
Abstract: We study the metastable states induced by photoexcitation, oxygen disorder, and both effects combined in superconducting GdBa2Cu3Ox thin films. The states are identified by the temperature dependence of the resistivity. The relaxation dynamics is characterized through the time evolution of the conductivity. The results show that photoexcitation and oxygen disorder behave as noninteracting and do not cancel each other out. However, in both cases the relaxation dynamics is related to oxygen movement .
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Lee, S. - C., M. Sullivan, G. R. Ruchti, S. M. Anlage, B. S. Palmer, B. Maiorov, and E. Osquiguil. "Doping-dependent nonlinear Meissner effect and spontaneous currents in high-Tc superconductors." Physical Review B – Condensed Matter and Materials Physics 71, no. 1 (2005).
Abstract: We measure the local harmonic generation from superconducting thin films at microwave frequencies to investigate the intrinsic nonlinear Meissner effect near Tc in the zero magnetic field. Both second and third harmonic generation are measured to identify time-reversal symmetry breaking (TRSB) and time-reversal symmetric (TRS) nonlinearities. We perform a systematic doping-dependent study of the nonlinear response and find that the TRS characteristic nonlinearity current density scale follows the doping dependence of the depairing critical current density. We also extract a spontaneous TRSB characteristic current density scale that onsets at Tc, grows with decreasing temperature, and systematically decreases in magnitude (at fixed T/TC) with underdoping. The origin of this current scale could be Josephson circulating currents or the spontaneous magnetization associated with a TRSB order parameter.
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Maiorov, B., G. Nieva, and E. Osquiguil. "First-order phase transition of the vortex lattice in twinned YBa2Cu3O7 single crystals in tilted magnetic fields." Physical Review B – Condensed Matter and Materials Physics 61, no. 18 (2000): 12427–12432.
Abstract: We present an exhaustive analysis of transport measurements performed in twinned YBa2Cu3O7 single crystals which establishes that the vortex solid-liquid transition is first order when the magnetic field H is applied at an angle ? away from the direction of the twin planes. We show that the resistive transitions are hysteretic and the V-I curves are nonlinear, displaying a characteristic S shape at the melting line Hm(T), which scales as ?(?)Hm(T,?), where ?(?) is the anisotropy factor. These features are gradually lost when the critical point H*(?) is approached. Above H*(?) the V-I characteristics show a linear response in the experimentally accessible V-I window, and the transition becomes reversible. Finally we show that the first-order phase transition takes place between a highly correlated vortex liquid in the field direction and a solid state of unknown symmetry. As a consequence, our data support the scenario for a vortex-line melting in twinned YBa2Cu3O7 crystals in contrast to a vortex sublimation as recently suggested for untwinned La2-xSrxCuO4, YBa2Cu3O7 and Bi2Sr2CaCu2O8 [T. Sasagawa et al., Phys. Rev. Lett. 80, 4297 (1998)].
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Maiorov, B., and E. Osquiguil. "Vortex solid state in YBa2Cu3O7-? twinned crystals." Physical Review B – Condensed Matter and Materials Physics 64, no. 5 (2001): 0525111–0525114.
Abstract: We report on the scaling of transport properties around the vortex melting in YBa2Cu3O7-? oriented-twin single crystals in applied magnetic fields between 1 T and 18 T. We find that for the whole measured field range the linear resistivity scales as ?(t,?)?tsyF
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R. Nath, A. A. Tsirlin, E. E. Kaul, M. Baentiz, N. Buettgen, H. Rosner y C. Geibel. "Strong frustration due to competing ferro- and antiferromagnetic interactions: magnetic properties of M(VO)2(PO4)2 (M = Ca and Sr)." Physical Review B – Condensed Matter and Materials Physics 78 (2008): 024418.
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R. Nath, Y. Furukawa, F. Borsa, E. E. Kaul, M. Baenitz, C. Geibel y D. C. Johnston. "Single crystal 31P NMR studies of the frustrated square lattice compound Pb2VO(PO4)2." Physical Review B – Condensed Matter and Materials Physics 80 (2009): 214430.
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Sereni, J. G., M. Gomez Berisso, A. Braghta, G. Schmerber, and J. P. Kappler. "Unstable Shastry-Sutherland phase in Ce2Pd2Sn." Physical Review B – Condensed Matter and Materials Physics 80, no. 2 (2008): 022428.
Abstract: Thermal (CP) , magnetic ( M and χac ), and transport (Ï) measurements on Ce2Pd2Sn are reported. High-temperature properties are well described by the presence of two excited crystal-field levels at (65±5)K and (230±20)K , with negligible hybridization (Kondo) effects. According to literature, two transitions were observed at TM=4.8K and TC=2.1K , respectively. The upper transition cannot be considered as a standard antiferromagnetic because of frustration effects in a triangular network of Ce atoms and the positive sign of the paramagnetic temperature θPLT=4.4K . The nature of the intermediated phase is described accounting for the formation of ferromagnetic (F) Ce dimers disposed in a quasi-two-dimensional square lattice, resembling a Shastry-Sutherland pattern. According to hysteretic features in Ï(T) and χac(T) , the lower F transition is of first order, with CP(T<TC) revealing a gap of anisotropy Eg≈7K .
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