The ground state of chargeless fermions with finite magnetic moment

We consider the ground state of a system of chargeless fermions, such as neutrinos, of mass m and magnetic moment p interacting through long-range magnetic dipole interaction, within the framework of a Hartree-Fock variational approach. At high densities the uniform paramagnetic state becomes unstable towards a ferromagnetic state with quadrupolar deformation of the Fermi surface. The exchange energy which is attractive dominates the repulsive kinetic energy. If we let the density be a variable, then above a certain density the system will collapse to an infinite density state unless another short-range interaction stops the collapse. In the case of large deformations, the possibility of a purely dipolar deformation exists

Ground state of interacting quantum magnetic dipoles: Transition from a ferromagnetic Fermi liquid to an antiferromagnetic solid

We show that the ground state of a system of magnetic dipoles, with no electric charge, is a ferromagnetic quantum Fermi liquid at high densities, driven by the dipolar exchange energy. As in the system of classical point dipoles, the direct dipole energy is zero in this case. With decreasing density, there is a transition to an antiferromagnetic lattice state. An addition of short range hard core repulsive potential will arrest the infinite density collapse of the ferromagnetic state, and possible melting of the low density antiferromagnetic lattice state

Stability of the high-density ferromagnetic ground state of a chargeless, magnetic-dipolar, quantum Fermi liquid

We obtain the best upper bound for the ground-state energy of a system of chargeless fermions of mass m, spin s=1/2, and magnetic moment mu(s) over right arrow as a function of its density in the fully spin-polarized Hartree-Fock determinantal state, specified by a prolate spheroidal plane-wave single-particle occupation function n(up arrow)((k) over right arrow), by minimizing the total energy E at each density with respect to the variational spheroidal deformation parameter beta(2),0 <=beta(2)<= 1. We find that at high densities, this spheroidal ferromagnetic state is the most likely ground state of the system, but it is still unstable towards the infinite-density collapse. This optimized ferromagnetic state is shown to be a stable ground state of the dipolar system at high densities, if one has an additional repulsive short-range hardcore interaction of sufficient strength and nonvanishing range

A theory of the upper critical field in antiferromagnetic superconductors

A generalized Ginzburg-Landau approach is used to study the nonmonotonic temperature dependence of the upper critical field H c 2(T) in antiferromagnetic superconductors RE(Mo)6S8; RE = Dy, Tb, Gd. It is found that electrodynamic effects incorporated through screening and indirect coupling between the staggered magnetization M Q (T) and superconducting order parameter psgr cannot explain the observed nonmonotonicity. This suggests that the direct coupling between the two order parameters should be considered to understand the experimental results, a finding which is consistent with recent microscopic calculations

Structural aspects of changes induced in PbTe by doping with Mn, In and Ga

The paper presents the extended results of structural investigations of Pb0.9Mn0.1Te, and Pb0.9Mn0.1Te systems doped with In (2 at.%) and Ga (4 at.%) by means of EXAFS (extended X-ray absorption fine structure) technique. EXAFS measurements performed at Te-, Mn-, In- and Ga-K absorption edges at different temperatures are complemented with X-ray diffraction, flame absorption and X-ray fluorescence analysis. That way the complete information about elemental concentration; crystal structure; local environment around constitutive and impurity atoms (including their displacements from the regular lattice positions); local and long-range ordering; and the overall influence of doping on the host crystal structure is derived. The obtained results represent an important step towards understanding the structural aspects of doping of lead telluride-based semiconductors with Mn and group III elements and their connection to electronic and optical phenomena important for their applications