Spin dynamics from majorana fermions

Using the Majorana fermion representation of spin-1/2 local moments, we show how the dynamic spin correlation and susceptibility are obtained directly from the one-particle Majorana propagator. We illustrate our method by applying it to the spin dynamics of a nonequilibrium quantum dot, computing the voltage-dependent spin relaxation rate and showing that, at weak coupling, the fluctuation-dissipation relation for the spin of a quantum dot is voltage dependent. We confirm the voltage-dependent Curie susceptibility recently found by Parcollet and Hooley [Phys. Rev. B 66, 085315 (2002)]].     

Spin fluctuations and superconductivity in heavy fermions

We study within a scaling theory, recently proposed to describe the coherence transition in heavy fermions, the importance of spin fluctuations for the superconductivity of these systems.     

Spin waves propagation in Fibonacci quasiperiodic metamagnet superlattices

In this work we present a fractal analysis of the spin wave modes propagating in a Fibonacci quasiperiodic metamagnetic superlattices consisting of a ferromagnetic material (layer A being Fe) and a metamagnetic material (layer B being FeBr₂). The spin wave modes are obtained in the exchange regime, using the transfer matrix technique. Our numerical results show that the power law for this system is independent of the dimensionless in-plane wavevector kxa$k_{x}a$, and that the spectrum present a multifractal characteristic, exhibiting several scale invariant windows for a fixed value of the in-plane wavevector. The results reported here can be experimentally observed by light scattering techniques.     

Spin dynamics in trans-polyacetylene

Detailed spin-echo and cw EPR measurements on trans-(CD)_x and trans-(CH)_x are reported. The magnitude of the on-chain diffusion rate, and its temperature dependence are evaluated. The results do not agree with predictions of the soliton model nor with results evaluated from recent NMR measurements.     

Nonlinear dynamics of fermions during preheating

We study the role of dynamical fermions during preheating after inflation. We compute the nonequilibrium dynamics of Dirac fermions coupled to a scalar (inflaton) field at next-to-next-to-leading order in a coupling expansion of the 2PI effective action. Besides the well-known parametric production of bosons and fermions and their back-reaction on the background inflaton field, this includes direct interactions between produced particles, which have been neglected in previous studies. We present preliminary numerical results in 3+1 dimensions which indicates that, for intermediate Yukawa couplings, the latter can dramatically affect the usual picture of preheating.     

Self-trapping of bosons and fermions in optical lattices

We theoretically investigate the enhanced localization of bosonic atoms by fermionic atoms in three-dimensional optical lattices and find a self-trapping of the bosons for attractive boson-fermion interaction. Because of this mutual interaction, the fermion orbitals are substantially squeezed, which results in a strong deformation of the effective potential for bosons. This effect is enhanced by an increasing bosonic filling factor leading to a large shift of the transition between the superfluid and the Mott-insulator phase. We find a nonlinear dependency of the critical potential depth on the boson-fermion interaction strength. The results, in general, demonstrate the important role of higher Bloch bands for the physics of attractively interacting quantum gas mixtures in optical lattices and are of direct relevance to recent experiments with 87Rb-40K mixtures, where a large shift of the critical point has been found.     

Wilson fermions and axion electrodynamics in optical lattices

We show that ultracold Fermi gases in optical superlattices can be used as quantum simulators of relativistic lattice fermions in 3+1 dimensions. By exploiting laser-assisted tunneling, we find an analogue of the so-called naive Dirac fermions, and thus provide a realization of the fermion doubling problem. Moreover, we show how to implement Wilson fermions, and discuss how their mass can be inverted by tuning the laser intensities. In this regime, our atomic gas corresponds to a phase of matter where Maxwell electrodynamics is replaced by axion electrodynamics: a 3D topological insulator.     

Non-abelian gauge dynamics of slowly moving fermions

We study the dynamics generated by local gauge invariance under a non-abelianSU(N) group for two nonrelativistic particles interacting through the effect of the group charges. We describe the local gauge invariant potential which contains the exchange of infinitely many gluons. We discuss the possible implications of our result.     

Spin dynamics in general relativity

The energy-momentum tensor of a fluid composed of spinning particles is presented in a form that is structurally similar to that of a fluid with the energy flux q^a with respect to the fluid velocity u^a, isotropic pressure p and the trace-free anisotropic pressure π^ab. The effect of spin in the evolution of a shear free cosmological model with irrotational geodesic flow is considered.     

Spin dynamics in orthogonal fields

The technique of Lorentz transformations is used to obtain exact solutions of the classical vector and tensor equations of motion of a spin in constant homogeneous and orthogonal fields (E < H). It is shown that the vector and tensor variants of the solutions go over into one another uniquely. The invariants of the motion are written down explicitly. The results of the paper agree with the quantum theory of the motion of a spin.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 44–48, January, 1981.     

Spin fluctuation contribution to the specific heat of strongly correlated fermions

We calculate the free energy of a system of fermions at low temperatures within the Hubbard model using a slave boson representation, which generalizes the approach of Kotliar and Ruckenstein. The mean field approximation is identical to Gutzwiller's solution. The one-loop corrections provide aT ³ lnT spin fluctuation contribution to the specific heat, which reduces for weak coupling to the result of paramagnon theory first derived by Brenig et al.Dedicated to Professor W. Brenig on the occasion of his 60th birthday     

Spin fluctuation rates from Mössbauer spectra of high-spin ferrous rubredoxin

Spin fluctuation rates deduced from ⁵⁷Fe Mössbauer spectra of the iron protein rubredoxin in applied fields between 10 K and 150 K are reproduced by a one-parameter model based on the direct process using Blume's stochastic theory of line shape.     

Stability of superflow for ultracold fermions in optical lattices

We investigate the stability of superflow of paired fermions in an optical lattice. We show that there are two distinct dynamical instabilities which limit the superflow in this system. One dynamical instability occurs when the superfluid stiffness becomes negative; this evolves, with increasing pairing interaction, from the fermion pair breaking instability to the well-known dynamical instability of lattice bosons. The second, more interesting, dynamical instability is marked by the emergence of a transient atom density wave. Both dynamical instabilities can be experimentally accessed by tuning the pairing interaction and the fermion density.