LAYERED SUPERCONDUCTOR IN a MAGNETIC FIELD: BREAKDOWN OF THE EffECTIVE MASSES MODEL

Abstract

We theoretically study the upper critical magnetic fields at zero temperature in a quasi-twodimensional (Q2D) superconductor in the parallel and perpendicular fields, H c2 (0) and H ⊥ c2 (0), respectively. We find that H c2 (0) ≈ 0.75 |dH c2 /dT |T c Tc and that H ⊥ c2 (0) ≈ 0.59 |dH ⊥ c2 /dT |T c Tc, where |dH c2 /dT |T c and |dH ⊥ c2 /dT |T c are the corresponding Ginzburg-Landau slopes of the upper critical magnetic fields. Our results demonstrate the breakdown of the so-called effective mass model in Q2D case and may be partially responsible for the experimentally observed deviations from the effective mass model in a number of layered superconductors, including M gB2.

A Chiral Triplet Quasi-Two-Dimensional Superconductor in a Parallel Magnetic Field

“…[9] (see also recent Ref. [16]) we calculated the ratio H (0)/(|dH GL /dT | T =Tc T c ) = 0.75, where |dH GL /dT | T =Tc is the so-called Ginzburg-Landau (GL) slope, for s-wave Q2D superconductivity and compared it with the experimental one, 0.45-0.5 [17][18][19]. To make our argument against the chiral triplet scenario to be firm, below we calculate the above mentioned ratio exactly for the in-plane isotropic chiral triplet superconductor with d vector order parameter [4,20],…”

“…[23][24][25][26][27][28], it has also to restore superconductivity in very high magnetic fields due to quantum effects of the Bragg reflections from boundaries of the Brillouin zone. In this Letter, we consider the so-called quasi-classical parallel orbital upper critical magnetic field [29,16,30], H (0), which destroys superconductivity in Q2D superconductors at low temperatures in an intermediate region of the fields.…”

“…[23][24][25][26][27][28]). As we already mentioned, below we calculate the so-called quasiclassical upper critical magnetic field [29,16,30] and, thus, do not take into account possible stabilization of superconductors in very high magnetic fields [23][24][25][26][27][28], which is possibly observed in the Q2D superconductor UTe 2 .…”

“…As mentioned before, below, we study the quasi-classical case, where, as shown in Refs. [16] and [30], it is possible to take into account only linear term with respect to magnetic field. As a result, we obtain:…”

FOUR-FOLD ANISOTROPY OF THE PARALLEL UPPER CRITICAL MAGNETIC FIELD IN a PURE LAYERED D-Wave SUPERCONDUCTOR AT T = 0

“…To summarize, for the first time, we have suggested an adequate mathematical apparatus to calculate the fourfold anisotropy of the parallel upper critical magnetic field in Q2D d-wave superconductors at any temperatures and numerically have calculated its maximum value at T = 0 in the absence of the paramagnetic effects. We stress that our theory has been elaborated for such Q2D superconductors [20], where ξ ⊥ ≥ c * , with ξ ⊥ being perpendicular to the conducting layers coherent length and c * being the inter-layer distance. This is in contrast to the so-called Lawrence-Doniach model (see, for example, Refs.…”