Paramagnon-induced dispersion anomalies in the cuprates

We report the self-energy associated with RPA magnetic susceptibility in the hole-doped Bi_2Sr_2CuO_6 (Bi2201) and the electron-doped Nd_{2-x}Ce_xCuO_4 (NCCO) in the overdoped regime within the framework of a one-band Hubbard model. Strong weight is found in the magnetic spectrum around (pi, 0) at about 360 meV in Bi2201 and 640 meV in NCCO, which yields dispersion anomalies in accord with the recently observed `waterfall' effects in the cuprates.Comment: Submitted to PRL, Dec. 21, 2006; 4 eps figures, revte

Itinerant ferromagnetism in a two-dimensional atomic gas

Motivated by the first experimental evidence of ferromagnetic behavior in a three-dimensional ultracold atomic gas, we explore the possibility of itinerant ferromagnetism in a trapped two-dimensional atomic gas. Firstly, we develop a formalism that demonstrates how quantum fluctuations drive the ferromagnetic reconstruction first order, and consider the consequences of an imposed population imbalance. Secondly, we adapt this formalism to elucidate the key experimental signatures of ferromagnetism in a realistic trapped geometry.Comment: Accepted for publication in Phys. Rev.

Thomas-Ehrman shifts in nuclei around ^{16}O and role of residual nuclear interaction

The asymmetry in the energy spectra between mirror nuclei (the Thomas-Ehrman shifts) around $^{16}$O is investigated from a phenomenological viewpoint. The recent data on proton-rich nuclei indicates that the residual nuclear interaction is reduced for the loosely bound s-orbit by as much as 30%, which originates in the broad radial distribution of the proton single-particle wave function.Comment: to appear in Phys. Lett. B, with 3 eps figure

SU(N) Coherent States and Irreducible Schwinger Bosons

We exploit the SU(N) irreducible Schwinger boson to construct SU(N) coherent states. This construction of SU(N) coherent state is analogous to the construction of the simplest Heisenberg-Weyl coherent states. The coherent states belonging to irreducible representations of SU(N) are labeled by the eigenvalues of the $(N-1)$ SU(N) Casimir operators and are characterized by $(N-1)$ complex orthonormal vectors describing the SU(N) group manifold.Comment: 12 pages, 3 figure

Spin 3/2 dimer model

We present a parent Hamiltonian for weakly dimerized valence bond solid states for arbitrary half-integral S. While the model reduces for S=1/2 to the Majumdar-Ghosh Hamiltonian we discuss this model and its properties for S=3/2. Its degenerate ground state is the most popular toy model state for discussing dimerization in spin 3/2 chains. In particular, it describes the impurity induced dimer phase in Cr8Ni as proposed recently. We point out that the explicit construction of the Hamiltonian and its main features apply to arbitrary half-integral spin S.Comment: 5+ pages, 6 figures; to appear in Europhysics Letter

Addendum to: Capillary floating and the billiard ball problem

We compare the results of our earlier paper on the floating in neutral equilibrium at arbitrary orientation in the sense of Finn-Young with the literature on its counterpart in the sense of Archimedes. We add a few remarks of personal and social-historical character.Comment: This is an addendum to my article Capillary floating and the billiard ball problem, Journal of Mathematical Fluid Mechanics 14 (2012), 363 -- 38

Phase-space characterization of complexity in quantum many-body dynamics

We propose a phase-space Wigner harmonics entropy measure for many-body quantum dynamical complexity. This measure, which reduces to the well known measure of complexity in classical systems and which is valid for both pure and mixed states in single-particle and many-body systems, takes into account the combined role of chaos and entanglement in the realm of quantum mechanics. The effectiveness of the measure is illustrated in the example of the Ising chain in a homogeneous tilted magnetic field. We provide numerical evidence that the multipartite entanglement generation leads to a linear increase of entropy until saturation in both integrable and chaotic regimes, so that in both cases the number of harmonics of the Wigner function grows exponentially with time. The entropy growth rate can be used to detect quantum phase transitions. The proposed entropy measure can also distinguish between integrable and chaotic many-body dynamics by means of the size of long term fluctuations which become smaller when quantum chaos sets in.Comment: 10 pages, 9 figure

Critical properties and Bose Einstein Condensation in dimer spin systems

We analyze the spin relaxation time $1/T_1$ for a system made of weakly coupled one dimensional ladders.This system allows to probe the dimensional crossover between a Luttinger liquid and a Bose-Einstein condensateof magnons. We obtain the temperature dependence of $1/T_1$ in the various dimensional regimes, and discuss the experimental consequences.Comment: 4 pages, RevTeX 4, 3 EPS figure

Routes towards Anderson-Like localization of Bose-Einstein condensates in disordered optical lattices

We investigate, both experimentally and theoretically, possible routes towards Anderson-like localization of Bose-Einstein condensates in disordered potentials. The dependence of this quantum interference effect on the nonlinear interactions and the shape of the disorder potential is investigated. Experiments with an optical lattice and a superimposed disordered potential reveal the lack of Anderson localization. A theoretical analysis shows that this absence is due to the large length scale of the disorder potential as well as its screening by the nonlinear interactions. Further analysis shows that incommensurable superlattices should allow for the observation of the cross-over from the nonlinear screening regime to the Anderson localized case within realistic experimental parameters.Comment: 4 pages to appear in Phys. Rev. Let

Intra-Landau level Cyclotron Resonance in Bilayer Graphene

Interaction driven integer quantum Hall effects are anticipated in graphene bilayers because of the near-degeneracy of the eight Landau levels which appear near the neutral system Fermi level. We predict that an intra-Landau-level cyclotron resonance signal will appear at some odd-integer filling factors, accompanied by collective modes which are nearly gapless and have approximate $k^{3/2}$ dispersion. We speculate on the possibility of unususal localization physics associated with these modes.Comment: 5 pages, 2 figure