Reentrant superconductivity in URhGe

Abstract

There is presented a phenomenological description of phase diagram of ferromagnet superconductor URhGe. In frame of the Landau phenomenological theory it was found that phase transition between anisotropic ferromagnetic and paramagnetic states under strong enough magnetic field perpendicular to direction of easy magnetization changes from the second to the first order type. It is shown that magnetic susceptibility corresponding to longitudinal magnetic fluctuations strongly increases in vicinity of the first order transition stimulating reentrance of superconducting state. The reentrant superconductivity observed near the first order transition line at temperatures about twice lower than the tricritical point temperature exists both in ferromagnet and paramagnet state. The critical temperature of transition to superconducting state falls down at intersection with line of ferromagnet-paramagnet phase transition.

Reentrant Superconductivity Driven by Quantum Tricritical Fluctuations in URhGe: Evidence fromCo59NMR inURh0.

“…Obviously, the RSC occurs in almost the same region as that where we have observed the critical enhancement of fluctuations. This close interplay between the RSC and the fluctuations provides strong evidence that the RSC is actually induced by these critical fluctuations around H R , most probably by reinforcing the pairing interactions [12,13]. The RSC has been known to be extremely sensitive to the field alignment; only about θ ¼ 7°misorientation suppresses the RSC [10,32], and our results (Fig.…”

“…Our results, however, reveal that the situation is more complex, at least in URhGe, and cannot be interpreted with a single type of excitations, in particular, near the TCP where the RSC emerges. This calls for an extension of the theory by involving fluctuations perpendicular to the Ising axis, and, indeed, a very recent study in the frame of Landau phenomenological theory shows that the strong enhance in magnetic susceptibility corresponding to the longitudinal fluctuation stimulates reentrance of the superconductivity near the first-order transition line [12].…”

“…This quantum phase transition is strongly reminiscent of the textbook example of an Ising chain in a transverse field [5,6] and is considered to be responsible for the emergence of RSC [4,[7][8][9][10][11], a trend that is by now well established in condensed matter physics. On theoretical grounds, it has been argued that ferromagnetic fluctuations provide the pairing glue in this new type of superconducting state [12,13], but microscopic experimental evidence is still lacking. Moreover, since the critical point at H R is not an ordinary quantum critical point (QCP) but suggested to be a tricritical point (TCP) [4,8] followed by a phase bifurcation towards quantum critical end points (QCEPs), the nature of the spin fluctuations is thus expected to be different and more complex.…”

Wing structure in the phase diagram of the Ising ferromagnet URhGe close to its tricritical point investigated by angle-resolved magnetization measurements

“…with A being a constant [38]. Even though M c shows an infinite change of slope at T C (H b ), dM b /dH b does not exhibit a strong singularity; from Eqs.…”

“…Up to now, no established microscopic theory is at hand for the field-induced phase transition in URhGe. We thus rely on the phenomenological model [38] that treats the phase transition of an Ising ferromagnet in a magnetic field perpendicular to the spontaneous magnetization. According to the theory, M b can be expressed in terms of M c as…”