BAJAS TEMPERATURAS
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Examinando BAJAS TEMPERATURAS por Autor "Amigó, M.L."
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Ítem Acceso Abierto A quantitative experiment on the fountain effect in superfluid helium(IOP Publishing, 2017-08-17) Amigó, M.L.; Herrera, T.; Neñer, L.; Peralta Gavensky, L.; Turco, F.; Luzuriaga, J.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasSuperfluid helium, a state of matter existing at low temperatures, shows many remarkable properties. One example is the so called fountain effect, where a heater can produce a jet of helium. This converts heat into mechanical motion; a machine with no moving parts, but working only below 2 K. Allen and Jones first demonstrated the effect in 1938, but their work was basically qualitative. We now present data of a quantitative version of the experiment. We have measured the heat supplied, the temperature and the height of the jet produced. We also develop equations, based on the two-fluid model of superfluid helium, that give a satisfactory fit to the data. The experiment has been performed by advanced undergraduate students in our home institution, and illustrates in a vivid way some of the striking properties of the superfluid state.Ítem Acceso Abierto Influence of the Fe Concentration on the Superconducting Properties of Fe1-ySe(Springer, 2015-00-00) Amigó, M.L.; Ale Crivillero, M.V.; Franco, D.G.; Guimpel, J.; Nieva, G.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasWe present a comparative study of electrical transport properties in the normal state and in the dissipative superconducting state between pure β-FeSe phase and Fe deficient Fe1−y Se crystals. We discuss the influence of the intergrowth of the magnetic hexagonal phase (Fe7 Se8 ) in Fe deficient samples when compared to pure β-FeSe samples. In the superconducting state, we measured the ab-plane electrical resistivity with magnetic field up to 16 T and the electrical resistivity as a function of the angle between the c axis and the applied field. The angular dependence at fixed temperature below the superconducting critical temperature, Tc(H = 0), is very different for both sets of crystals. The Fe deficient samples display a vortex pinning-related feature at ∼57◦ off the plane while the pure β-FeSe phase samples show the persistence of a strong angular-dependent magnetoresistance characteristic of the normal state electronic structure.Ítem Acceso Abierto Intrinsic pinning by naturally occurring correlated defects in FeSe1-xTex superconductors(IOP Publishing, 2017-07-12) Amigó, M.L.; Ale Crivillero, M.V.; Franco, D.G.; Badía-Majós, A.; Guimpel, J.; Campo, J.; Damay, F.; Porcher, F.; Condó, A.M.; Nieva, G.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasWe study the angular dependence of dissipation in the superconducting state of FeSe and Fe(Se1−xTex) through electrical transport measurements, using crystalline intergrown materials. We reveal the key role of the inclusions of the non superconducting magnetic phase Fe1−y(Se1−xTex), growing into the Fe(Se1−xTex) pure β-phase, in the development of a correlated defect structure. The matching of both atomic structures defines the growth habit of the crystalline material as well as the correlated planar defects orientation.Ítem Acceso Abierto Vortex dynamics in β-FeSe single crystals: effects of proton irradiation and small inhomogeneous stress(IOP Publishing, 2017-11-17) Amigó, M.L.; Haberkorn, N.; Pérez, P.; Suárez, S.; Nieva, G.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasWe report on the critical current density Jc and the vortex dynamics of pristine and 3 MeV proton irradiated (cumulative dose equal to cm−2) β-FeSe single crystals. We also analyze a remarkable dependence of the superconducting critical temperature Tc, Jc and the flux creep rate S on the sample mounting method. Free-standing crystals present Tc = 8.4(1) K, which increases to 10.5(1) K when they are fixed to the sample holder by embedding them with GE-7031 varnish. On the other hand, the irradiation has a marginal effect on Tc. The pinning scenario can be ascribed to twin boundaries and random point defects. We find that the main effect of irradiation is to increase the density of random point defects, while the embedding mainly reduces the density of twin boundaries. Pristine and irradiated crystals present two outstanding features in the temperature dependence of the flux creep rate: presents large values at low temperatures, which can be attributed to small pinning energies, and a plateau at intermediate temperatures, which can be associated with glassy relaxation. From Maley analysis, we observe that the characteristic glassy exponent μ changes from ∼1.7 to 1.35–1.4 after proton irradiation.Ítem Acceso Abierto Vortex pinning by intrinsic correlated defects in Fe1-ySe(IOP Publishing, 2014-00-00) Amigó, M.L.; Crivillero, V.A.; Franco, D.G.; Badía-Majós, A.; Guimpel, J.; Nieva, G.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasWe present a study on the transport and magnetic properties of superconducting Fe1−ySe single crystals. In the superconducting state, the in-plane electrical resistivity of the crystal is measured for fields up to 16 T and as a function of field direction, in order to understand how the vortex dynamics is affected by the presence of defects. A strong deviation from the slightly anisotropic crystal (electronic anisotropy constant 7 ∼ 1.08) is observed as a steep angular dependence, which is interpreted as a signature of the presence of correlated defects. The influence of the correlated defects on the critical current is studied through the angular dependence of the magnetization, and compared to numerical simulations.