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V. Zhuravlev and T. Maniv
The unusual superconducting (SC) phase transitions occurring under competing orbital and spin pair breaking, which characterize some clean heavy fermion superconductors at low temperatures and high magnetic fields, are investigated within a non-perturbative approach, which avoids the difficulties encountered in various perturbative methods and enables comparison with recent experimental data. It is shown that in quasi 2D systems, such as the heavy fermion superconductor CeCoIn5, where the orbital pair breaking (in the plane perpendicular to the magnetic field) is relatively strong, the type of the normal-to-SC phase transition changes from second to first order at a sufficiently low temperature. In a 3D system, where the orbital pair breaking is partly suppressed by the electronic motion along the field direction, a spatial (FFLO) modulation of the order parameter along this direction restores the continuous nature of the SC transition. However, at a magnetic field slightly below Hc2 the FFLO state becomes unstable, transforming discontinuously into a uniform SC state via a first-order phase transition. This narrow double-stage transition picture is shown to account for recent experimental results of de-Haas van-Alphen oscillations and thermal conductivity measurements carried out on the 3D heavy fermion superconductor URu2Si2. |
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