arXiv subjects

D. Augier

Publications and source records attributed to D. Augier.

9 recordsLinked to original sources

arXiv2000

Low-energy excitations of spin-Peierls chains with modified bond-impurities

The introduction of modified bond-defects in spin-Peierls systems is investigated in a model of antiferromagnetic Heisenberg spin chains coupled to adiabatic phonons. Generically, new low-energy magnetic or non-magnetic excitations appear below the bulk spin gap energy. When two adjacent bonds are modified, these excitations can be interpreted in terms of boundstates of a soliton with the localized spin-1/2 located on the impurity site. It is shown that the confining potential occurs even in the case of {\it isolated} chains.

cond-mat.stat-mech↗

arXiv1999

Study of impurities in spin-Peierls systems including lattice relaxation

The effects of magnetic and non-magnetic impurities in spin-Peierls systems are investigated allowing for lattice relaxation and quantum fluctuations. We show that, in isolated chains, strong bonds form next to impurities, leading to the appearance of magneto-elastic solitons. Generically, these solitonic excitations do not bind to impurities. However, interchain elastic coupling produces an attractive potential at the impurity site which can lead to the formation of bound states. In addition, we predict that small enough chain segments do not carry magnetic moments at the ends.

cond-mat.str-el↗

arXiv1999

Investigation of soliton bound states in the Raman spectrum of pure and doped spin-Peierls chains

We investigate the occurrence of singlet bound states in the Raman spectrum of dimerized spin 1/2 chains by Exact Diagonalization and Density Matrix Renormalization Group techniques. We predict that several bulk $δ$-peaks could be observed in pure systems. Furthermore, we show that new low energy lines arise from non-magnetic impurity doping. These features are interpreted in terms of soliton-antisoliton and soliton-impurity bound states respectively. Energies and spectral weights associated with these bound states are sensitive to lattice relaxation effects. Our results are discussed in the context of the inorganic spin-Peierls compound CuGeO$_3$ and quantitatively compared to recent Raman experiments.

cond-mat.str-el↗

arXiv1999

Antiferromagnetism in doped anisotropic two-dimensional spin-Peierls systems

We study the formation of antiferromagnetic correlations induced by impurity doping in anisotropic two-dimensional spin-Peierls systems. Using a mean-field approximation to deal with the inter-chain magnetic coupling, the intra-chain correlations are treated exactly by numerical techniques. The magnetic coupling between impurities is computed for both adiabatic and dynamical lattices and is shown to have an alternating sign as a function of the impurity-impurity distance, hence suppressing magnetic frustration. An effective model based on our numerical results supports the coexistence of antiferromagnetism and dimerization in this system.

cond-mat.str-el↗

arXiv1998

Interaction between impurities and solitons in quasi one-dimensional spin-Peierls systems

The role of the spin-phonon coupling in spin-Peierls chains doped with spin-0 or spin-1 impurities is investigated by various numerical methods such as exact diagonalization, quantum Monte Carlo simulations and Density Matrix Renormalization Group. Various treatments of the lattice, in a fully quantum mechanical way, classically in the adiabatic approximation or using a fixed three-dimensional dimerization pattern are compared. For an isolated chain, strong bonds form between the two spin-1/2 sites next to the impurity site, leading to the appearance of magneto-elastic solitons. We also show that these excitations do not bind to spin-0 impurities but are weakly attracted by spin-1 impurities. However, the interchain elastic coupling generates an effective confining potential at the non-magnetic impurity site which can lead to the formation of soliton-impurity bound states. We also predict that a soliton and an antisoliton bound to two impurities on the same chain can annihilate each other when the separation between the impurities is smaller than a critical value depending on the interchain elastic constant.

cond-mat.str-el↗

arXiv1998

Soliton Approach to Spin-Peierls Antiferromagnets: Large-Scale Numerical Results

A simple intuitive picture of spin-Peierls antiferromagnets arises from regarding the elementary excitations as S=1/2 solitons. In a strictly one-dimensional system these excitations are assumed not to form bound-states and to be repelled by impurities. Couplings to the three-dimensional lattice are assumed to produce an effective confining potential which binds solitons to antisolitons and to impurities, with the number of bound-states increasing as the interchain coupling goes to 0. We investigate these various assumptions numerically in a phononless model where spontaneous dimerization arises from frustration and the interchain coupling is treated in mean field theory.

cond-mat.str-el↗

arXiv1998

Study of spin-Peierls transition in alpha'--NaV2O5 by infrared reflectivity

Polarized infrared reflectivity measurements have been performed on single crystals of the spin-Peierls compound alpha'-NaV2O5 in the temperature range 20-300 K. Pronounced spectral features associated with the formation of the dimerized phase were detected both in the a- and b-polarizations (perpendicular and parallel to the spin-1/2 chains, respectively). The temperature dependence of a salient spectral line at 718 cm^-1 sharply rising below the transition temperature T_SP obeys a (1-T/T_SP)^(2beta) law with T_SP \simeq 34.3$K and beta \simeq 0.25. In addition, a continuum signal is observed in the whole temperature range in the a-polarized optical conductivity spectra. In order to interpret these results, calculations of the static dimerization and of the optical conductivity based on a mean-field and a dynamical treatment of the lattice respectively are proposed.

cond-mat.str-el↗

arXiv1998

Dynamical effects of phonons on soliton binding in spin-Peierls systems

The role of dynamical magneto-elastic coupling in spin-Peierls chains is investigated by numerical and analytical techniques. We show that a Heisenberg spin chain coupled to dynamical optical phonons exhibits a transition towards a spontaneously dimerized state in a wide range of parameter space. The low energy excitations are characterized as solitons. No binding between solitons occurs in the isolated spin-phonon chain and the dynamical spin structure factor shows a broad magnon dispersion. However, elastic interchain coupling can lead to the formation of bound states.

cond-mat.str-el↗

arXiv1997

Dynamical properties of the spin-Peierls compound α'--NaV2O5

Dynamical properties of the novel inorganic spin-Peierls compound α'--NaV2O5 are investigated using a one-dimensional dimerized Heisenberg model. By exact diagonalizations of chains with up to 28 sites, supplemented by a finite-size scaling analysis, the dimerization parameter δis determined by requiring that the model reproduces the experimentally observed spin gap Δ. The dynamical and static spin structure factors are calculated. As for CuGeO3, the existence of a low energy magnon branch separated from the continuum is predicted. The present calculations also suggest that a large magnetic Raman scattering intensity should appear above an energy threshold of 1.9 Δ. The predicted photoemission spectrum is qualitatively similar to results for an undimerized chain due to the presence of sizable short-range antiferromagnetic correlations.

cond-mat.str-el↗