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Blanco, M. C., D. G. Franco, Y. Jalit, E. V. Pannunzio Miner, G. Berndt, A. Paesano Jr., G. Nieva, and R. E. Carbonio. "Synthesis, magnetic properties and Mössbauer spectroscopy for the pyrochlore family Bi2BB′O7 with B=Cr and Fe and B′=Nb, Ta and Sb." Physica B: Condensed Matter 407, no. 16 (2012): 3078–3080.
Abstract: The samples Bi2BB′O7, with B=Cr and Fe and B′=Nb, Ta and Sb were prepared by solid state method. The crystallographic structure was investigated on the basis of X-ray powder diffraction data. Rietveld refinements show that the crystal structure is cubic, space group Fd-3m. The Bi3+ cation on the eight-coordinate pyrochlore A-site shows displacive disorder, as a consequence of its lone pair electron conï¬guration. There is also a considerable A-site disorder shown by Rietveld Analysis and confirmed in the case of the iron containing samples with Mössbauer spectroscopy. The magnetic measurements show paramagnetic behavior at all temperatures for the Cr oxides. The Fe pyrochlores show antiferromagnetic order around 10 K.
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Encina, S., P. Pedrazzini, J. G. Sereni, and C. Geibel. "Low temperature thermopower and magnetoresistance of Sc-rich CeSc1-xTixGe." Physica B: Condensed Matter 536 (2018): 133–136.
Abstract: In CeSc1-xTixGe, Ti-alloying reduces the record-high antiferromagnetic (AFM) ordering temperature found in CeScGe at TN=46K and induces ferromagnetism for x≥0.5. In this work we focus on the AFM side, i.e. Sc-rich samples, and study their thermopower S(T) and magnetoresistance Ï(H,T). The measured S(T) is small in comparison with the thermopower of other Ce-systems and shows some features that are compatible with a weak hybridization between the 4f and band states. This is a further hint pointing to the local character of magnetism in this alloy. Magnetic fields up to 16T have a minor effect on the electrical resistivity of stoichiometric CeScGe. On the other hand, for x=0.65, we find that fields above 4T suppress the hump in Ï(T). Furthermore, the 4.2K magnetoresistance displays a strong decrease in the same field range, also in coincidence with magnetization results from the literature. Our results indicate that Ï(T,H) is a proper tool to assess the H−T phase diagram of this system.
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Fasano, Y., P. Szabó, J. KaÄmarÄík, Z. Pribulová, P. Pedrazzini, P. Samuely, and V. F. Correa. "Unconventional superconductivity in the strong-coupling limit for the heavy fermion system CeCoIn5." Physica B: Condensed Matter 536 (2018): 798–802.
Abstract: We present scanning tunneling spectroscopy measurements of the local quasiparticles' excitation spectra of the heavy fermion CeCoIn5 between 440mK and 3K in samples with a bulk Tc=2.25K. The spectral shape of our low-temperature tunneling data, quite textbook nodal-Δ conductance, allow us to confidently fit the spectra with a d-wave density of states considering also a shortening of quasiparticles' lifetime term Γ. The Δ(0) value obtained from the fits yields a BCS ratio 2Δ/kTc=7.73 suggesting that CeCoIn5 is an unconventional superconductor in the strong coupling limit. The fits also reveal that the height of coherence peaks in CeCoIn5 is reduced with respect to a pure BCS spectra and therefore the coupling of quasiparticles with spin excitations should play a relevant role. The tunneling conductance shows a depletion at energies smaller than Δ for temperatures larger than the bulk Tc, giving further support to the existence of a pseudogap phase that in our samples span up to T*∼1.2Tc. The phenomenological scaling of the pseudogap temperature observed in various families of cuprates, 2Δ/kT*∼4.3, is not fulfilled in our measurements. This suggests that in CeCoIn5 the strong magnetic fluctuations might conspire to close the local superconducting gap at a smaller pesudogap temperature-scale than in cuprates.
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Kappler, J. P., M. J. Besnus, P. Haen, and J. G. Sereni. "Ce ground state in CePd1-xNix." Physica B: Condensed Matter 230-232 (1997): 162–164.
Abstract: Alloying ferromagnetic CePd (Tc = 6.5 K) with the intermediate valence compound CeNi compresses the lattice, though the ferromagnetic order is present up to x = 0.94 in CePd1−xNix. We report here the competition of magnetic order and Kondo effect, through specific heat, magnetization and resistivity measurements. Detailed results gathered on the x = 0.95 sample show several features suggesting a non-Fermi liquid behaviour which may be due to the proximity to magnetic order: ϱ = ϱ0 + AT1.1 (3 < T ⩽ 30 K) and C/T ∠− ln T(T ⩾ 0.9 K). At lower temperatures C/T tends to saturate at a value of 0.225 J/K2 mol, about three times the value observed for CeNi.
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Kappler, J. P., M. J. Besnus, A. Herr, A. Meyer, and J. G. Sereni. "Crossover between intermediate valence and magnetic order in CeRh1-xPdx." Physica B: Condensed Matter 171, no. 1-4 (1991): 346–349.
Abstract: Magnetic, resistivity and specific-heat measurements on the system CeRh1-xPd(x) are presented. The results indicate a continuous decrease of the hybridization when substituting Pd for Rh in the intermediate-valence compound CeRh. The transition to a magnetically ordered state occurs near x = 0.4. The experimental data suggest the coexistence of Kondo effect and magnetic order for Pd contents around 40-50 at.%. The present results show evidence for a crossover from an IV state with full degeneracy through Kondo-lattice behaviour to a local-moment magnetic state.
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López, D., E. Rodríguez, G. Nieva, F. de la Cruz, and S. W. Cheong. "Three-dimensional vortex flux flow in LSCO and YBCO through pseudo dc flux transformer measurements." Physica B: Condensed Matter 194-196, no. 2 (1994): 1977–1978.
Abstract: A pseudo dc flux transformer configuration shows that the flux flow in La2−xSrxCuO4 (x=0.075) and YBa2Cu3O7 single crystals is due to the movement of 3-D vortices across the sample. We show that the loss of c-axis long range vortex correlation is achieved either by thermal fluctuations or by an inhomogeneus Lorentz force acting on the vortices.
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Núñez Regueiro, M., D. Castello, and M. Jaime. "Thermal conductivity of high temperature superconductors." Physica B: Condensed Matter 169, no. 1-4 (1991): 631–632.
Abstract: We have measured the thermal conductivity of Tl1Ba2Cu3O9 and of the related compounds CuO and La2CuO4. For the superconducting sample we observe the characteristic T2 behaviour at low temperatures, that does not appear in the non-superconducting samples. The superconducting transition and the antiferromagnetic ordering are detected by our measurements.
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Pedrazzini, P., and D. Jaccard. "The critical pressure of chromium." Physica B: Condensed Matter 403, no. 5-9 (2008): 1222–1224.
Abstract: We present first results of high-pressure resistivity measurements on pure chromium. Two pieces of evidence show that spin density wave magnetism is suppressed at a critical pressure pc?10GPa, namely, the evolution of the ordering temperature TN(p) and the rapid decrease of the residual resistivity close to pc. Our discussion profits from the comparison between pressurized-Cr and the Cr1-xVx alloy, for which a large amount of information on its electronic properties is available.
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Pedrazzini, P., D. Jaccard, M. Deppe, C. Geibel, and J. G. Sereni. "Multiprobe high-pressure experiments in CePd0.6Rh0.4 and CePd3." Physica B: Condensed Matter 404, no. 19 (2009): 2898–2903.
Abstract: Results of recent multiprobe high-pressure experiments on ferromagnetic CePd0.6Rh0.4 and intermediate-valent CePd3 are presented. Simultaneous resistivity (ρ), thermopower (S), and ac heat capacity measurements show that the long-range ferromagnetic state of CePd0.6Rh0.4 vanishes in the proximity of a sharp valence-crossover pressure , i.e. before reaching a quantum critical point. However, a magnetic signal that is progressively suppressed is still detected at higher pressures. For CePd3, the results of simultaneous ρ(T,p) and S(T,p) measurements up to and down to the mK temperature range show a surprisingly weak pressure dependence.
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Sereni, J. G. "Role of entropy in the ground state formation of frustrated systems." Physica B: Condensed Matter 536 (2018): 397–400.
Abstract: The absence of magnetic order in Rare Earth-based frustrated compounds allows to recognize the action of the third law of thermodynamics in the low temperature behavior of those systems. One of the most relevant findings is the appearance of a coincident specific heat Cm/T|T→0≈7J/molK2 ‘plateau’ in six Yb systems. This characteristic feature occurs after a systematic modification of the thermal trajectory of their entropies Sm(T) in the range of a few hundred milikelvin degrees. Such behavior is explained by the formation of an entropy-bottleneck imposed by the third law constraint (Sm|T→0≥0), that drives the system into alternative ground states. Based in these finding, three possible approaches to the Sm|T→0 limit observed in real systems are analyzed in terms of the ∂2Sm/∂T2 dependencies.
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