Describing Sr2RuO4 superconductivity in a generalized Ginzburg–Landau theory

Abstract

We propose a simple explanation of unconventional thermodynamical and magnetic properties observed for Sr2RuO4. Actually, our two-phase model of superconductivity, based on a straight generalization of the Ginzburg-Landau theory, does predict two jumps in the heat capacity as well as a double curve for the dependence of the critical temperature on an external magnetic field. Such theoretical previsions well agree with the currently available experimental data for Sr2RuO4. 74.20.De; 74.70.Pq; In a recent series of papers [1,2,3,4] we have succeeded in obtaining a straightforward generalizations of the original Ginzburg-Landau (GL) theory [5] in order to describe s-wave superconductors endowed with two critical temperatures, or even spin-triplet one-phase superconductors. The basic idea has been to introduce two different order parameters represented by two charged scalar fields (really only one mean field with two distinct gauge representations, see below) describing Cooper pairs with electrons bound by a weaker or stronger attractive force, respectively. The resulting theoretical model is therefore able to describe superconductors with two distinct superconducting phases, since the two order parameters condensate, in general, at different critical temperatures. Peculiar thermal and magnetic properties of these kinds of superconductors have been discussed in [2,3]. Here we only mention that an additional discontinuity in the specific heat is predicted, with respect to the conventional case, when passing from a superconducting phase to the other one. Moreover, at low temperature the London penetration length for the superconductors considered is strongly reduced, and the Ginzburg-Landau parameter κ becomes a function of temperature. Instead, in temperature region between the two phase transition, κ is constant and the system behaves as a type I or a type II superconductors depending on the ratio between the two critical temperatures. Such a ratio may be as large as 4/3 [2, 3] (that is, a maximum difference of ∼ 15% between the two critical temperatures) for very large selfinteraction of the Cooper pairs with respect to the electromagnetic coupling. By allowing a suitable non-linear interaction among the two scalar fields, the same theoretical model may as well account for rotational degrees of freedom in superconductivity, that is spin-triplet superconductors with a single phase (the two mutually interacting order parameters condensate simultaneously at a same temperature). In the corresponding model, the main thermodynamical and magnetic properties of these p-wave superconductors turn out to be essentially the same as for the conventional s-wave superconductors.All the above-seen properties have prompted us to explore the possibility to use the proposed model in order to understand the intriguing properties exhibited by Sr 2 RuO 4 superconductors, which still wait for a comprehensive and solid explanation (see, for example, the review in [6]). The layered Sr 2 RuO 4 is a superconductor with a very low critical te...

Searching for an equation: Dirac, Majorana and the others

“…Moreover, several other investigations suggest that exotic quasiparticle excitations in a variety of interesting condensed matter systems follow, instead, the Majorana equation (25), that is they are fermionic excitations that are their own antiparticles (Majorana fermions) [72]. Other exotic phenomena (such as, for example, that considered in [73]) exist that, in principle, could be described by other equations (such as, for example, the Kemmer equation ( 28) for describing electrons in these exotic materials grouped in s-wave or p-wave pairs).…”

Tunable superconducting effective gap in graphene-TMDC heterostructures

“…The unconventional triplet superconductivity induction to the 2D structures, like graphene or ML-MDS, can be possible by using Sr 2 RuO 4 material [38]. The effect of p-wave paring symmetry on the superconducting excitation has been theoretically investigated in graphene and M oS 2 Ref.…”

Dependence of the critical temperature on the Higgs field parametrization

“…( 3), affect the expression of the critical temperature of the system or, through the free energy (35), all the thermodynamical quantities of the standard GL models (applied, e.g., to superconductors and superfluids). This study is relevant only for physical systems that exhibit more than one critical temperatures, as the case, for example, of the superconductivity of strontium ruthenate [11]. Changing the possible representation of the scalar fields φ results (with some interesting exceptions, discussed above in detail) in different values for the Higgs mass and, through this parameter, in different critical temperatures.…”

“…In this case, the difference between the critical temperatures leads to distinct superconductive phases, entailing two discontinuities in the specific heat and unusual magnetic properties. In a recent series of our papers [10][11][12] we have, indeed, studied in detail this possibility, and it is very remarkable that the two different representations mentioned above (real and imaginary parts versus modulus and phase) account, in a very simple manner, for the apparently exotic properties observed in the superconductivity of strontium ruthenate [12][13][14]. These observations evidently urge to consider accurately the problem of the field reparametrization in the Higgs mechanism; actually, in the present paper we shall expound a sufficiently general and comprehensive analysis of the physical implications of the field representation gauge.…”