I present a Ginzburg-Landau theory for hexagonal oscillations of the upper critical field of (Formula presented) near (Formula presented). The model is based on a two-dimensional representation for the superconducting order parameter, η→=((Formula presented),(Formula presented)), coupled to an in-plane antiferromagnetic (AFM) order parameter, m(Formula presented). Hexagonal anisotropy of (Formula presented) arises from the weak in-plane anisotropy energy of the AFM state and the coupling of the superconducting order parameter to the staggered field. The model explains the important features of the observed hexagonal anisotropy [N. Keller et al., Phys. Rev. Lett. 73, 2364 (1994)] including (i) the small magnitude, (ii) persistence of the oscillations for T→(Formula presented), and (iii) the change in sign of the oscillations for T≳(Formula presented) and T<(Formula presented) (the temperature at the tetracritical point). I also show that there is a low-field crossover (observable only very near (Formula presented)) below which the oscillations should vanish.
|Original language||English (US)|
|Number of pages||6|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - 1996|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics