Absence of a true long-range orbital order in a two-leg Kondo ladder

We investigate, through the density-matrix renormalization group and the Lanczos technique, the possibility of a two-leg Kondo ladder present an incommensurate orbital order. Our results indicate a staggered short-range orbital order at half-filling. Away from half-filling our data are consistent with an incommensurate quasi-long-range orbital order. We also observed that an interaction between the localized spins enhances the rung-rung current correlations.Comment: 7 pages, 6 figures, changed the introduction and added some discussion

Coexistence of Pairing Tendencies and Ferromagnetism in a Doped Two-Orbital Hubbard Model on Two-Leg Ladders

Using the Density Matrix Renormalization Group and two-leg ladders, we investigate an electronic two-orbital Hubbard model including plaquette diagonal hopping amplitudes. Our goal is to search for regimes where charges added to the undoped state form pairs, presumably a precursor of a superconducting state.For the electronic density $\rho=2$, i.e. the undoped limit, our investigations show a robust $(\pi,0)$ antiferromagnetic ground state, as in previous investigations. Doping away from $\rho=2$ and for large values of the Hund coupling $J$, a ferromagnetic region is found to be stable. Moreover, when the interorbital on-site Hubbard repulsion is smaller than the Hund coupling, i.e. for $U'<J$ in the standard notation of multiorbital Hubbard models, our results indicate the coexistence of pairing tendencies and ferromagnetism close to $\rho=2$. These results are compatible with previous investigations using one dimensional systems. Although further research is needed to clarify if the range of couplings used here is of relevance for real materials, such as superconducting heavy fermions or pnictides, our theoretical results address a possible mechanism for pairing that may be active in the presence of short-range ferromagnetic fluctuations.Comment: 8 pages, 4 Fig

Defect-dependent colossal negative thermal expansion in UiO-66(Hf) metal-organic framework

Thermally-densified hafnium terephthalate UiO-66(Hf) is shown to exhibit the strongest isotropic negative thermal expansion (NTE) effect yet reported for a metal-organic framework (MOF). Incorporation of correlated vacancy defects within the framework affects both the extent of thermal densification and the magnitude of NTE observed in the densified product. We thus demonstrate that defect inclusion can be used to tune systematically the physical behaviour of a MOF.Comment: 8 pages, 4 figures, revise

Current noise through a Kondo quantum dot in a SU(N) Fermi liquid state

The current noise through a mesoscopic quantum dot is calculated and analyzed in the Fermi liquid regime of the SU(N) Kondo model. Results connect the Johnson-Nyquist noise to the shot noise for an arbitrary ratio of voltage and temperature, and show that temperature corrections are sizeable in usual experiments. For the experimentally relevant SU(4) case, quasiparticle interactions are shown to increase the shot noise.Comment: 4 pages, 2 figures, to be published in Phys. Rev. Lett. (revised version

New method for obtaining complex roots in the semiclassical coherent-state propagator formula

A semiclassical formula for the coherent-state propagator requires the determination of specific classical paths inhabiting a complex phase-space through a Hamiltonian flux. Such trajectories are constrained to special boundary conditions which render their determination difficult by common methods. In this paper we present a new method based on Runge-Kutta integrator for a quick, easy and accurate determination of these trajectories. Using nonlinear one dimensional systems we show that the semiclassical formula is highly accurate as compared to its exact counterpart . Further we clarify how the phase of the semiclassical approximation is correctly retrieved under time evolution.Comment: 8 pages, 4 figures. Submitted to Brazilian Journal of Physic