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Register a new userField-induced confinement in (TMTSF)2ClO4 under accurately aligned magnetic fields
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Authors
Nada Joo
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We present transport measurements along the least conducting c direction of the organic superconductor (TMTSF)2ClO4, performed under an accurately aligned magnetic field in the low temperature regime. The experimental results reveal a two-dimensional confinement of the carriers in the (a,b) planes which is governed by the magnetic field component along the b direction. This 2-D confinement is accompanied by a metal-insulator transition for the c axis resistivity. These data are supported by a quantum mechanical calculation of the transverse transport taking into account in self consistent treatment the effect of the field on the interplane Green function and on the intraplane scattering time.
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Using a proper cooling procedure, a controllable amount of non-magnetic structural disorder can be introduced at low temperature in (TMTSF)2ClO4. Here we performed simultaneous measurements of transport and magnetic properties of (TMTSF)2ClO4 in its normal and superconducting states, while finely covering three orders of magnitude of the cooling rate around the anion ordering temperature. Our result reveals, with increasing density of disorder, the existence of a crossover between homogeneous defect-controlled d-wave superconductivity and granular superconductivity. At slow cooling rates, with small amount of disorder, the evolution of superconducting properties is well described with the Abrikosov-Gorkov theory, providing further confirmation of non-s-wave pairing in this compound. In contrast, at fast cooling rates, zero resistance and diamagnetic shielding are achieved through a randomly distributed network of superconducting puddles embedded in an normal conducting background and interconnected by proximity effect coupling. The temperature dependence of the AC complex susceptibility reveals features typical for a network of granular superconductors. This makes (TMTSF)2ClO4 a model system for granular superconductivity where the grain size and their concentration are tunable within the same sample.
We report the magnetic field-amplitude and field-angle dependence of the superconducting onset temperature Tc_onset of the organic superconductor (TMTSF)2ClO4 in magnetic fields H accurately aligned to the conductive ab plane. We revealed that the rapid increase of the onset fields at low temperatures occurs both for H // b and H // a, irrespective of the carrier confinement. Moreover, in the vicinity of the Pauli limiting field, we report a shift of a principal axis of the in-plane field-angle dependence of Tc_onset away from the b axis. This feature may be related to an occurrence of Fulde-Ferrell-Larkin-Ovchinnikov phases.
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We predict that superconductivity in thin films can be stabilized in high magnetic fields if the superconductor is driven out of equilibrium by a DC voltage bias. For realistic material parameters and temperatures, we show that superconductivity is restored in fields many times larger than the Chandrasekhar-Clogston limit. After motivating the effect analytically, we perform rigorous numerical calculations to corroborate the findings, and present concrete experimental signatures. On the technical side, we also introduce a new form for the nonequilibrium kinetic equations, which generalizes and simplifies previous formulations of the problem.
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