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Large moments in external fields of cubic group symmetry  [PDF]
V. A. Kalatsky,V. L. Pokrovsky
Physics , 1998, DOI: 10.1209/epl/i1998-00507-2
Abstract: We predict that large moments $J$, placed into a crystal field with the cubic point symmetry group, differ by their spectrum and magnetic properties. E. g., properties of the odd-integer moments are different from those of the even-integer. The effect is due to Berry's phases gained by the moment, when it tunnels between minima of the external field. Two cases of the group $O$ are classified, namely, 6- and 8-fold coordinations. The spectrum and degeneration of energy levels depend on a remainder $\{J/n\}$, where the divisor $n=4$ and 3 for 6-fold and 8-fold coordination respectively. %High symmetry results in a finite magnetic moment for half-integer %and some integer moments, for example odd $J$ at 6-fold coordination. Large moments in the cubic environment can be realized by diluted alloys ${R}_{1-x}{R}_{x}'$Sb, where R=Lu, La, and R$'$=Tb, Dy, Ho, Er.
Dynamical symmetry breaking in the external gravitational and constant magnetic fields  [PDF]
T. Inagaki,S. D. Odintsov,Yu. I. Shil'nov
Physics , 1997, DOI: 10.1142/S0217751X99000245
Abstract: We investigate the effects of the external gravitational and constant magnetic fields to the dynamical symmetrybreaking. As simple models of the dynamical symmetry breaking we consider the Nambu-Jona-Lasinio (NJL) model and the supersymmetric Nambu-Jona-Lasinio (SUSY NJL) model non-minimally interacting with the external gravitational field and minimally interacting with constant magnetic field. The explicit expressions for the scalar and spinor Green functions are found up to the linear terms on the spacetime curvature and exactly for a constant magnetic field. We obtain the effective potential of the above models from the Green functions in the magnetic field in curved spacetime. Calculating the effective potential numerically with the varying curvature and/or magnetic fields we show the effects of the external gravitational and magnetic fields to the phase structure of the theories. In particular, increase of the curvature in the spontaneously broken chiral symmetry phase due to the fixed magnetic field makes this phase to be less broken. On the same time strong magnetic field quickly induces chiral symmetry breaking even at the presence of fixed gravitational field within nonbroken phase.
On chiral symmetry breaking by external magnetic fields in QED$_3$  [PDF]
Rajesh R. Parwani
Physics , 1995, DOI: 10.1016/0370-2693(95)00964-M
Abstract: A recent result of Gusynin, Miransky and Shovkovy concerning chiral symmetry breaking by a constant external magnetic field in parity-invariant three-dimensional QED is generalised to the case of inhomogeneous fields by relating the phenomenon to the zero modes of the Dirac equation. Virtual photon radiative corrections and four-dimensional QED are briefly discussed.
Cold polar molecules in 2D traps: Tailoring interactions with external fields for novel quantum phases  [PDF]
A. Micheli,G. Pupillo,H. P. Büchler,P. Zoller
Physics , 2007, DOI: 10.1103/PhysRevA.76.043604
Abstract: We discuss techniques to engineer effective long-range interactions between polar molecules using external static electric and microwave fields. We consider a setup where molecules are trapped in a two-dimensional pancake geometry by a far-off-resonance optical trap, which ensures the stability of the dipolar collisions. We detail how to modify the shape and the strength of the long-range part of interaction potentials, which can be utilized to realize interesting quantum phases in the context of cold molecular gases.
Statistics of non-affine defect precursors: tailoring defect densities in colloidal crystals using external fields  [PDF]
Saswati Ganguly,Surajit Sengupta,Peter Sollich
Physics , 2015,
Abstract: Coarse-graining atomic displacements in a solid produces both local affine strains and "non-affine" fluctuations. Here we study the equilibrium dynamics of these coarse grained quantities to obtain space-time dependent correlation functions. We show how a subset of these thermally excited, non-affine fluctuations act as precursors for the nucleation of lattice defects and suggest how defect probabilities may be altered by an {\it experimentally realisable} "external" field conjugate to the global non-affinity parameter. Our results are amenable to verification in experiments on colloidal crystals using commonly available holographic laser tweezer and video microscopy techniques, and may lead to simple ways of controlling the defect density of a colloidal solid.
Chiral Symmetry Breaking in Planar QED in External Magnetic Fields  [PDF]
Paolo Cea,Leonardo Cosmai,Pietro Giudice,Alessandro Papa
Physics , 2012, DOI: 10.1103/PhysRevD.85.094505
Abstract: We investigate planar quantum electrodynamics (QED) with two degenerate staggered fermions in an external magnetic field on the lattice. We argue that in external magnetic fields there is dynamical generation of mass for two-dimensional massless Dirac fermions in the weak-coupling region. We extrapolate our lattice results to the quantum Hall effect in graphene.
Chiral symmetry breaking in d=3 NJL model in external gravitational and magnetic fields  [PDF]
D. M. Gitman,S. D. Odintsov,Yu. I. Shil'nov
Physics , 1996, DOI: 10.1103/PhysRevD.54.2968
Abstract: The phase structure of $d=3$ Nambu-Jona-Lasinio model in curved spacetime with magnetic field is investigated in the leading order of the $1/N$-expansion and in linear curvature approximation (an external magnetic field is treated exactly). The possibility of the chiral symmetry breaking under the combined action of the external gravitational and magnetic fields is shown explicitly. At some circumstances the chiral symmetry may be restored due to the compensation of the magnetic field by the gravitational field.
Dynamical symmetry breaking in the Nambu-Jona-Lasino model with external gravitational and constant electric fields  [PDF]
E. Elizalde,Yu. I. Shil'nov,V. V. Chitov
Physics , 1997, DOI: 10.1088/0264-9381/15/4/003
Abstract: An investigation of the Nambu-Jona-Lasino model with external constant electric and weak gravitational fields is carried out in three- and four- dimensional spacetimes. The effective potential of the composite bifermionic fields is calculated keeping terms linear in the curvature, while the electric field effect is treated exactly by means of the proper- time formalism. A rich dynamical symmetry breaking pattern, accompanied by phase transitions which are ruled, independently, by both the curvature and the electric field strength is found. Numerical simulations of the transitions are presented.
Dynamical symmetry breaking in Nambu-Jona-Lasinio model under the influence of external electromagnetic and gravitational fields  [PDF]
E. Elizalde,Yu. I. Shil'nov
Physics , 1998, DOI: 10.1063/1.57134
Abstract: Dynamical symmetry breaking is investigated for a four-fermion Nambu-Jona-Lasinio model in external electromagnetic and gravitational fields. An effective potential is calculated in the leading order of the large-N expansion using the proper-time Schwinger formalism. Phase transitions accompanying a chiral symmetry breaking in the Nambu-Jona-Lasinio model are studied in detail. A magnetic calalysis phenomenon is shown to exist in curved spacetime but it turns out to lose its universal character because the chiral symmetry is restored above some critical positive value of the spacetime curvature.
Symmetry operators and separation of variables for Dirac's equation on two-dimensional spin manifolds with external fields  [PDF]
Lorenzo Fatibene,Raymond G. McLenaghan,Giovanni Rastelli
Physics , 2014, DOI: 10.1142/S0219887815500127
Abstract: The second order symmetry operators that commute with the Dirac operator with external vector, scalar and pseudo-scalar potentials are computed on a general two-dimensional spin-manifold. It is shown that the operator is defined in terms of Killing vectors, valence two Killing tensors and scalar fields defined on the background manifold. The commuting operator that arises from a non-trivial Killing tensor is determined with respect to the associated system of Liouville coordinates and compared to the the second order operator that arises from that obtained from the unique separation scheme associated with such operators. It shown by the study of several examples that the operators arising from these two approaches coincide.
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