Magnetic field effects in a correlated electron system with spin-state degree of freedom - Implication of an excitonic insulator -

Magnetic field (H) effects on a correlated electron system with the spin-state degree of freedom are examined. The effective Hamiltonian derived from the two-orbital Hubbard model is analyzed by the mean-field approximation. Applying H to the low-spin (LS) phase induces the excitonic insulating phase, as well as the spin-state ordered phase where the LS and high-spin (HS) states are ordered alternately. In the case where H is applied to the HS phase, a reentrant transition for the HS phase appears. A rich variety of the phase diagrams are attributed to the spin-state degree of freedom and their combinations in the wave function as well as in the real-space configuration

The universe out of a monopole in the laboratory?

To explore the possibility that an inflationary universe can be created out of a stable particle in the laboratory, we consider the classical and quantum dynamics of a magnetic monopole in the thin-shell approximation. Classically there are three types of solutions: stable, collapsing and inflating monopoles. We argue that the transition from a stable monopole to an inflating one could occur either by collision with a domain wall or by quantum tunneling.Comment: to appear in Phys. Rev. D with changing title into "Is it possible to create a universe out of a monopole in the laboratory?", text and figures revised, 21 pages, 6 figure