30 research outputs found
Non-linear spin wave theory results for the frustrated S = 1/2 Heisenberg antiferromagnet on a body-centered cubic lattice
At zero temperature the sublattice magnetization of the quantum spin-1/2
Heisenberg antiferromagnet on a body-centered cubic lattice with competing
first and second neighbor exchange (J1 and J2) is investigated using the
non-linear spin wave theory. The zero temperature phases of the model consist
of a two sublattice N\'{e}el phase for small J_2 (AF_1) and a collinear phase
at large J_2 (AF_2). We show that quartic corrections due to spin-wave
interactions enhance the sublattice magnetization in both the AF_1 and the AF_2
phase. The magnetization corrections are prominent near the classical
transition point of the model and in the J_2> J_1 regime. The ground state
energy with quartic interactions is also calculated. It is found that up to
quartic corrections the first order phase transition (previously observed in
this model) between the AF_1 and the AF_2 phase survives.Comment: 6 pages, 3 figure
Ginzburg-Landau theory of vortices in a multi-gap superconductor
The Ginzburg-Landau functional for a two-gap superconductor is derived within
the weak-coupling BCS model. The two-gap Ginzburg-Landau theory is, then,
applied to investigate various magnetic properties of MgB2 including an upturn
temperature dependence of the transverse upper critical field and a core
structure of an isolated vortex. Orientation of vortex lattice relative to
crystallographic axes is studied for magnetic fields parallel to the c-axis. A
peculiar 30-degree rotation of the vortex lattice with increasing strength of
an applied field observed by neutron scattering is attributed to the multi-gap
nature of superconductivity in MgB2.Comment: 11 page
Evaluation of Spin-Triplet Superconductivity in Sr2RuO4
This review presents a summary and evaluations of the superconducting
properties of the layered ruthenate Sr2RuO4 as they are known in the autumn of
2011. This paper appends the main progress that has been made since the
preceding review by Mackenzie and Maeno was published in 2003. Here, special
focus is placed on the critical evaluation of the spin-triplet, odd-parity
pairing scenario applied to Sr2RuO4. After an introduction to superconductors
with possible odd-parity pairing, accumulated evidence for the pairing symmetry
of Sr2RuO4 is examined. Then, significant recent progress on the theoretical
approaches to the superconducting pairing by Coulomb repulsion is reviewed. A
section is devoted to some experimental properties of Sr2RuO4 that seem to defy
simple explanations in terms of currently available spin-triplet scenario. The
next section deals with some new developments using eutectic boundaries and
micro-crystals, which reveals novel superconducting phenomena related to chiral
edge states, odd-frequency pairing states, and half-fluxoid states. Some of
these properties are intimately connected with the properties as a topological
superconductor. The article concludes with a summary of knowledge emerged from
the study of Sr2RuO4 that are now more widely applied to understand the physics
of other unconventional superconductors, as well as with a brief discussion of
relatively unexplored but promising areas of ongoing and future studies of
Sr2RuO4.Comment: 31 pages, 35 figures, published in J. Phys. Soc. Jpn. as a review
article of Special Topic