Signature of the Ground-State Topology in the Low-Temperature Dynamics of Spin Glasses

We numerically address the issue of how the ground state topology is reflected in the finite temperature dynamics of the $\pm J$ Edwards-Anderson spin glass model. In this system a careful study of the ground state configurations allows to classify spins into two sets: solidary and non-solidary spins. We show that these sets quantitatively account for the dynamical heterogeneities found in the mean flipping time distribution at finite low temperatures. The results highlight the relevance of taking into account the ground state topology in the analysis of the finite temperature dynamics of spin glasses.Comment: 4 pages, 4 figures, content change

Low-energy properties of two-dimensional quantum triangular antiferromagnets: Non-perturbative renormalization group approach

We explore low temperature properties of quantum triangular Heisenberg antiferromagnets in two dimension in the vicinity of the quantum phase transition at zero temperature. Using the effective field theory described by the $SO(3)\times SO(2)/SO(2)$ matrix Ginzburg-Landau-Wilson model and the non-perturbative renormalization group method, we clarify how quantum and thermal fluctuations affect long-wavelength behaviors in the parameter region where the systems exhibit a fluctuation-driven first order transition to a long-range ordered state. We show that at finite temperatures the crossover from a quantum $\phi^6$ theory to a renormalized two-dimensional classical nonlinear sigma model region appears, and in this crossover region, massless fluctuation modes with linear dispersion a la spin waves govern low-energy physics. Our results are in good agreement with the recent experimental observations for the two-dimensional triangular Heisenberg spin system, NiGa$_2$S$_4$.Comment: 14 pages,7 figures, version accepted for publication in Physical Review

Comparison of Portable Metabolic Devices during Walking, Jogging, and Running

Oxygen uptake measurements enable performance professionals, clinicians, and scientists to quantify energy expenditure and aerobic work capacity for various purposes. Devices that accurately detect the composition of expired gases and changes in oxygen uptake, open new possibilities in research methodology and accessibility. PURPOSE: The purpose of this study was to compare the O2 uptake measurements of the VO2 Master Pro (VM) to the Cosmed K5 (K5) during walking, jogging, and running in field and lab conditions. METHODS: Twelve proficient runners, with a current 10k pace \u3c 5:19 min/km, performed 3 matched intervals at 3 different speeds (4.82, 8.05, 11.27 kph) on a treadmill and on an outdoor track while expired gasses were measured. Each interval was 10 minutes and data from minutes 6-9 were averaged for comparisons. An airflow test was performed on both devices by forcing air through the devices using a 3 L syringe timed to a metronome at 15, 25, and 35 strokes/min. RESULTS: During walking intervals, the VM did not report data for the majority of participants, and therefore were excluded from analysis. Jogging and running measurements were analyzed using a repeated measures ANOVA and Tukey multiple comparison test to analyze pairwise comparisons. The indoor running analysis revealed significant differences in VO2 (3017 vs. 1880 ml/min), VE (71 vs 57 ml/min), and TV (1.89 vs 1.56 L) between the K5 and VM respectively (p \u3c .023). Outdoor analysis revealed a significant difference between devices in VO2, VE­, and TV (p \u3c .035). The airflow test also demonstrated significant differences between the devices in VE and TV (p \u3c .001). Neither the jogging nor running analysis showed a significant difference in FeO2 or HR (p \u3e .16). CONCLUSION: We concluded that there were significant discrepancies between the K5 and the VM due to differences in TV measurement

Phonons in the multiferroic langasite Ba_3\_3NbFe_3\_3Si_2\_2O_14\_{14} : evidences for symmetry breaking

The chiral langasite Ba$\_3$NbFe$\_3$Si$\_2$O$\_{14}$ is a multiferroic compound. While its magnetic order below T$\_N$=27 K is now well characterised, its polar order is still controversial. We thus looked at the phonon spectrum and its temperature dependence to unravel possible crystal symmetry breaking. We combined optical measurements (both infrared and Raman spectroscopy) with ab initio calculations and show that signatures of a polar state are clearly present in the phonon spectrum even at room temperature. An additional symmetry lowering occurs below 120~K as seen from emergence of softer phonon modes in the THz range. These results confirm the multiferroic nature of this langasite and open new routes to understand the origin of the polar state

Deep Spin-Glass Hysteresis Area Collapse and Scaling in the d=3d=3 ±J\pm J Ising Model

We investigate the dissipative loss in the $\pm J$ Ising spin glass in three dimensions through the scaling of the hysteresis area, for a maximum magnetic field that is equal to the saturation field. We perform a systematic analysis for the whole range of the bond randomness as a function of the sweep rate, by means of frustration-preserving hard-spin mean field theory. Data collapse within the entirety of the spin-glass phase driven adiabatically (i.e., infinitely-slow field variation) is found, revealing a power-law scaling of the hysteresis area as a function of the antiferromagnetic bond fraction and the temperature. Two dynamic regimes separated by a threshold frequency $\omega_c$ characterize the dependence on the sweep rate of the oscillating field. For $\omega < \omega_c$, the hysteresis area is equal to its value in the adiabatic limit $\omega = 0$, while for $\omega > \omega_c$ it increases with the frequency through another randomness-dependent power law.Comment: 6 pages, 6 figure

Full optimization of Jastrow-Slater wave functions with application to the first-row atoms and homonuclear diatomic molecules

We pursue the development and application of the recently-introduced linear optimization method for determining the optimal linear and nonlinear parameters of Jastrow-Slater wave functions in a variational Monte Carlo framework. In this approach, the optimal parameters are found iteratively by diagonalizing the Hamiltonian matrix in the space spanned by the wave function and its first-order derivatives, making use of a strong zero-variance principle. We extend the method to optimize the exponents of the basis functions, simultaneously with all the other parameters, namely the Jastrow, configuration state function and orbital parameters. We show that the linear optimization method can be thought of as a so-called augmented Hessian approach, which helps explain the robustness of the method and permits us to extend it to minimize a linear combination of the energy and the energy variance. We apply the linear optimization method to obtain the complete ground-state potential energy curve of the C_2 molecule up to the dissociation limit, and discuss size consistency and broken spin-symmetry issues in quantum Monte Carlo calculations. We perform calculations of the first-row atoms and homonuclear diatomic molecules with fully optimized Jastrow-Slater wave functions, and we demonstrate that molecular well depths can be obtained with near chemical accuracy quite systematically at the diffusion Monte Carlo level for these systems.Comment: 15 pages, 3 figures, to appear in Journal of Chemical Physic

Quantum Spin Nematic States in Bose-Einstein Condensates

We review some recent results on discrete symmetries and topological order in spinor Bose-Einstein condensates (BECs) of $^{23}Na$. For spin one bosons with two-body scatterings dominated by a total spin equal to two channel, the BECs are in quantum spin nematic states at a low density limit. We study spin correlations in condensates at different limits and analyze hidde$symmetries using a non-perturbative approach developed recently. We further more investigate the influence of hidden$Z_2$ symmetries and U(1) quantum orders in symmetry partially retored states, particularly the effects on topological excitations.Comment: 30 pages, 13 figs included. to appear in Int. Jour. Mod. Phys.

A renormalization-group analysis of the interacting resonant level model at finite bias: Generic analytic study of static properties and quench dynamics

Using a real-time renormalization group method we study the minimal model of a quantum dot dominated by charge fluctuations, the two-lead interacting resonant level model, at finite bias voltage. We develop a set of RG equations to treat the case of weak and strong charge fluctuations, together with the determination of power-law exponents up to second order in the Coulomb interaction. We derive analytic expressions for the charge susceptibility, the steady-state current and the conductance in the situation of arbitrary system parameters, in particular away from the particle-hole symmetric point and for asymmetric Coulomb interactions. In the generic asymmetric situation we find that power laws can be observed for the current only as function of the level position (gate voltage) but not as function of the voltage. Furthermore, we study the quench dynamics after a sudden switch-on of the level-lead couplings. The time evolution of the dot occupation and current is governed by exponential relaxation accompanied by voltage-dependent oscillations and characteristic algebraic decay.Comment: 24 pages, 13 figures; revised versio