Quantum critical 5f-electrons avoid singularities in U(Ru,Rh)2Si2

We present specific heat measurements of 4% Rh-doped U(Ru,Rh)2Si2 at magnetic fields above the proposed metamagnetic transition field Hm~34 T, revealing striking similarities to the isotructural Ce analog CeRu2Si2, suggesting that strongly renormalized hybridized band models apply equally well to both systems. The vanishing bandwidths as H --> Hm are consistent with a putative quantum critical point close to Hm. The existence of a phase transition into an ordered phase in the vicinity of Hm for 4% Rh-doped U(Ru,Rh)2Si2, but not for CeRu2Si2, is consistent with a stronger super-exchange in the case of the U 5-f system, with irreversible processes at the transition revealing a strong coupling of the 5f orbitals to the lattice, most suggestive of orbital or electric quadrupolar order.Comment: 4 pages, 4 figure

Diffusion behavior of water confined in deformed carbon nanotubes

We use molecular dynamics simulations to study the diffusion of water inside deformed carbon nanotubes, with different degrees of eccentricity at 300K. We found a water structural transition between tubular-like to single-file for the (7,7) nanotubes associated with a change from a high to low mobility regimes. The water which in the undeformed (9,9) nanotubes is frozen, becomes liquid for the distortion above a certain threshold. These water diffusion enhancement (suppresion) is related to a reduction (increase) in the number of hydrogen bonds. This suggests that the shape of the nanotube is a particularly important ingredient when considering the dynamical and structural properties of confined water.Comment: 16 pages, 9 figure

Infestação natural de piolhos em búfalos.

bitstream/item/33512/1/CPATU-CirTec1.pd

Exact Bond Ordered Ground State for the Transition Between the Band and the Mott Insulator

We derive an effective Hamiltonian $H_{eff}$ for an ionic Hubbard chain, valid for $t\ll U,\Delta$, where $t$ is the hopping, $U$ the Coulomb repulsion, and $\Delta$ the charge transfer energy. $H_{eff}$ is the minimal model for describing the transition from the band insulator (BI) ($\Delta -U\gg t$) and the Mott insulator (MI) ($U-\Delta \gg t$). Using spin-particle transformations (Phys. Rev. Lett. \textbf{86}, 1082 (2001)), we map $H_{eff}(U=\Delta)$ into an SU(3) antiferromagnetic Heisenberg model whose exact ground state is known. In this way, we show rigorously that a spontaneously dimerized insulating ferroelectric phase appears in the transition region between the BI and MI

Geometric Frustration and Dimensional Reduction at a Quantum Critical Point

We show that the spatial dimensionality of the quantum critical point associated with Bose--Einstein condensation at T=0 is reduced when the underlying lattice comprises a set of layers coupled by a frustrating interaction. Our theoretical predictions for the critical temperature as a function of the chemical potential correspond very well with recent measurements in BaCuSi$_{2}$O$_{6}$ [S. E. Sebastian \textit{et al}, Nature \textbf{411}, 617 (2006)].Comment: 5 pages, 2 figure

Phonon Thermal Transport of URu2Si2: Broken Translational Symmetry and Strong-Coupling of the Hidden Order to the Lattice

A dramatic increase in the total thermal conductivity (k) is observed in the Hidden Order (HO) state of single crystal URu2Si2. Through measurements of the thermal Hall conductivity, we explicitly show that the electronic contribution to k is extremely small, so that this large increase in k is dominated by phonon conduction. An itinerant BCS/mean-field model describes this behavior well: the increase in kappa is associated with the opening of a large energy gap at the Fermi Surface, thereby decreasing electron-phonon scattering. Our analysis implies that the Hidden Order parameter is strongly coupled to the lattice, suggestive of a broken symmetry involving charge degrees of freedom.Comment: 17 pages including figures, updated author institutions and acknowledgement

Extending automatic transcripts in a unified data representation towards a prosodic-based metadata annotation and evaluation

This paper describes a framework that extends automatic speech transcripts in order to accommodate relevant information coming from manual transcripts, the speech signal itself, and other resources, like lexica. The proposed framework automatically collects, relates, computes, and stores all relevant information together in a self-contained data source, making it possible to easily provide a wide range of interconnected information suitable for speech analysis, training, and evaluating a number of automatic speech processing tasks. The main goal of this framework is to integrate different linguistic and paralinguistic layers of knowledge for a more complete view of their representation and interactions in several domains and languages. The processing chain is composed of two main stages, where the first consists of integrating the relevant manual annotations in the speech recognition data, and the second consists of further enriching the previous output in order to accommodate prosodic information. The described framework has been used for the identification and analysis of structural metadata in automatic speech transcripts. Initially put to use for automatic detection of punctuation marks and for capitalization recovery from speech data, it has also been recently used for studying the characterization of disfluencies in speech. It was already applied to several domains of Portuguese corpora, and also to English and Spanish Broadcast News corpora

Superconductivity from correlated hopping

We consider a chain described by a next-nearest-neighbor hopping combined with a nearest-neighbor spin flip. In two dimensions this three-body term arises from a mapping of the three-band Hubbard model for CuO$_2$ planes to a generalized $t-J$ model and for large O-O hopping favors resonance-valence-bond superconductivity of predominantly $d$-wave symmetry. Solving the ground state and low-energy excitations by analytical and numerical methods we find that the chain is a Luther-Emery liquid with correlation exponent $K_{\rho} = (2-n)^2/2$, where $n$ is the particle density.Comment: 10 pages, RevTeX 3.0 + 2 PostScript figs. Accepted for publication in Phys.Rev.

Irreversible dynamics of the phase boundary in U(Ru0.9)Rh0.04)2Si2 and implications for ordering

We report measurements and analysis of the specific heat and magnetocaloric effect at the phase boundary into the single magnetic field-induced phase (phase II) of U(Ru{0.96}Rh{0.04})2Si2, which yield striking similarities to the valence transition of Yb{1-x}YxInCu4. To explain these similarities, we propose a bootstrap mechanism by which a structural distortion causes an electric quadrupolar order parameter within phase II to become coupled to the 5f-electron hybridization, giving rise to a valence change at the transition.Comment: 4 pages including 4 figure