Generation of chiral solitons in antiferromagnetic chains by a quantum quench

We analyze the time evolution of a magnetic excitation in a spin-1/2 antiferromagnetic Heisenberg chain after a quantum quench. By a proper modulation of the magnetic exchange coupling, we prepare a static soliton of total spin 1/2 as an initial spin state. Using bosonization and a numerical time dependent density matrix renormalization group algorithm, we show that the initial excitation evolves to a state composed of two counter-propagating chiral states, which interfere to yield = 1/4 for each mode. We find that these dynamically generated states remain considerably stable as time evolution is carried out. We propose spin-Peierls materials and ultracold-atom systems as suitable experimental scenarios in which to conduct and observe this mechanism.Comment: Published version. Title changed due to reinterpretation of results. 5 pages, 4 figure

Haldane phase in one-dimensional topological Kondo insulators

We investigate the groundstate properties of a recently proposed model for a topological Kondo insulator in one dimension (i.e., the $p$-wave Kondo-Heisenberg lattice model) by means of the Density Matrix Renormalization Group method. The non-standard Kondo interaction in this model is different from the usual (i.e., local) Kondo interaction in that the localized spins couple to the "$p$-wave" spin density of conduction electrons, inducing a topologically non-trivial insulating groundstate. Based on the analysis of the charge- and spin-excitation gaps, the string order parameter, and the spin profile in the groundstate, we show that, at half-filling and low energies, the system is in the Haldane phase and hosts topologically protected spin-1/2 end-states. Beyond its intrinsic interest as a useful "toy-model" to understand the effects of strong correlations on topological insulators, we show that the $p$-wave Kondo-Heisenberg model can be implemented in $p-$band optical lattices loaded with ultra-cold Fermi gases.Comment: 8 pages, 4 figures, 1 appendi

Width of the charge-transfer peak in the SU(N) impurity Anderson model and its relevance to nonequilibrium transport

We calculate the width 2ΔCT and intensity of the charge-transfer peak (the one lying at the on-site energy Ed) in the impurity spectral density of states as a function of Ed in the SU(N) impurity Anderson model (IAM). We use the dynamical density-matrix renormalization group (DDMRG) and the noncrossing approximation (NCA) for N=4 and a 1/N variational approximation in the general case. In particular, while for Ed Δ, where Δ is the resonant level half-width, ΔCT=Δ as expected in the noninteracting case, for Ed NΔ one has ΔCT=NΔ. In the N=2 case, some effects of the variation of ΔCT with Ed were observed in the conductance through a quantum dot connected asymmetrically to conducting leads at finite bias [J. Könemann, Phys. Rev. B 73, 033313 (2006)PRBMDO1098-012110.1103/PhysRevB.73.033313]. More dramatic effects are expected in similar experiments that can be carried out in systems of two quantum dots, carbon nanotubes or other, realizing the SU(4) IAM.Fil: Fernández, Joaquín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Lisandrini, Franco Thomas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Roura Bas, Pablo Gines. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gazza, Claudio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Aligia, Armando Ángel. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin

Microscopic model for magnetoelectric coupling through lattice distortions

We propose a microscopic magnetoelectric model in which the coupling between spins and electric dipoles is mediated by lattice distortions. The magnetic sector is described by a spin S=1/2 Heisenberg model coupled directly to the lattice via a standard spin-Peierls term and indirectly to the electric dipole variables via the distortion of the surrounding electronic clouds. Electric dipoles are described by Ising variables for simplicity. We show that the effective magnetoelectric coupling which arises due to the interconnecting lattice deformations is quite efficient in one-dimensional arrays. More precisely, we show using bosonization and extensive density matrix renormalization group numerical simulations that increasing the magnetic field above the spin-Peierls gap, a massive polarization switch-off occurs due to the proliferation of soliton pairs. We also analyze the effect of an external electric field when the magnetic system is in a gapped (plateau) phase and show that the magnetization can be electrically switched between clearly distinct values. More general quasi-one-dimensional models and two-dimensional systems are also discussed.Fil: Cabra, Daniel Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física de Líquidos y Sistemas Biológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física de Líquidos y Sistemas Biológicos; ArgentinaFil: Dobry, Ariel Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; ArgentinaFil: Gazza, Claudio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; ArgentinaFil: Rossini, Gerardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin

Evolution of Nagaoka phase with kinetic energy frustrating hopping

We investigate, using the density-matrix renormalization group, the evolution of the Nagaoka state with t′ hopping that frustrates the hole kinetic energy in the U=∞ Hubbard model on the square and anisotropic triangular lattices. We find that the Nagaoka ferromagnet survives up to a rather small t'c/t∼0.2. At this critical value, there is a transition to an antiferromagnetic phase that depends on the lattice: a Q=(Q,0) spiral order, which continuously evolves with t′, for the triangular lattice and the usual Q=(π,π) Néel order for the square lattice. Remarkably, the local magnetization takes its classical value for all considered t′ (t′/t≤1). Our results show that the recently found classical kinetic antiferromagnetism, a perfect counterpart of Nagaoka ferromagnetism, is a generic phenomenon in these kinetically frustrated electronic systems.Instituto de Física La Plat

Scaling of conductance through quantum dots with magnetic field

Using different techniques, and Fermi-liquid relationships, we calculate the variation with the applied magnetic field (up to second order) of the zero-temperature equilibrium conductance through a quantum dot described by the impurity Anderson model. We focus on the strong-coupling limit U, where U is the Coulomb repulsion and is half the resonant-level width, and consider several values of the dot level energy E d , ranging from the Kondo regime to the intermediate-valence regime F − E d ∼ , where F is the Fermi energy. We have mainly used the density-matrix renormalization group (DMRG) and the numerical renormalization group (NRG) combined with renormalized perturbation theory (RPT). Results for the dot occupancy and magnetic susceptibility from the DMRG and NRG + RPT are compared with the corresponding Bethe ansatz results for U → ∞, showing an excellent agreement once E d is renormalized by a constant Haldane shift. For U low-energy peak in the spectral density of the dot.Fil: Hamad, Ignacio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Gazza, Claudio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Andrade Hoyos, Jhon Alejandro. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Aligia, Armando Ángel. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Cornaglia de la Cruz, Pablo Sebastian. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Roura Bas, Pablo Gines. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Quasiparticle excitations in frustrated antiferromagnets

We have computed the quasiparticle wave function corresponding to a hole injected in a triangular antiferromagnet. We have taken into account multi-magnon contributions within the self consistent Born approximation. We have found qualitative differences, under sign reversal of the integral transfer t, regarding the multi-magnon components and the own existence of the quasiparticle excitations. Such differences are due to the subtle interplay between magnon-assisted and free hopping mechanisms. We conclude that the conventional quasiparticle picture can be broken by geometrical frustration without invoking spin liquid phases.Comment: 5 pages, 4 figures, presented at " At the Frontiers of the condensed Matter II, Buenos Aires. June, 2004 ". To be published in Physica

Excitations with fractional spin less than 1/2 in frustrated magnetoelastic chains

We study the magnetic excitations on top of the plateaux states recently discovered in spin-Peierls systems in a magnetic field. We show by means of extensive density matrix renormalization group (DMRG) computations and an analytic approach that one single spin-flip on top of M = 1-2/N (N=3,4,…) plateau decays into N elementary excitations each carrying a fraction 1/N of the spin. This fractionalization goes beyond the well-known decay of one magnon into two spinons taking place on top of the M=0 plateau. Concentrating on the 1/3 plateau (N=3) we unravel the microscopic structure of the domain walls which carry fractional spin-1/3, both from theory and numerics. These excitations are shown to be noninteracting and should be observable in x-ray and nuclear magnetic resonance experiments.Departamento de Físic

Anharmonic effects in magnetoelastic chains

We describe a new mechanism leading to the formation of rational magnetization plateau phases, which is mainly due to the anharmonic spin-phonon coupling. This anharmonicity produces plateaux in the magnetization curve at unexpected values of the magnetization without explicit magnetic frustration in the Hamiltonian and without an explicit breaking of the translational symmetry. These plateau phases are accompanied by magneto-elastic deformations, which are not present in the harmonic case.Facultad de Ciencias Exacta