arXiv subjects

T. Ziman

Publications and source records attributed to T. Ziman.

25 records · Page 2Linked to original sources

arXiv2005

Exact soliton solution and inelastic two-soliton collision in spin chain driven by a time-dependent magnetic field

We investigate dynamics of exact N-soliton trains in spin chain driven by a time-dependent magnetic field by means of an inverse scattering transformation. The one-soliton solution indicates obviously the spin precession around the magnetic field and periodic shape-variation induced by the time varying field as well. In terms of the general soliton solutions N-soliton interaction and particularly various two-soliton collisions are analyzed. The inelastic collision by which we mean the soliton shape change before and after collision appears generally due to the time varying field. We, moreover, show that complete inelastic collisions can be achieved by adjusting spectrum and field parameters. This may lead a potential technique of shape control of soliton.

cond-mat.other↗

arXiv2004

Ordering and Excitations in the Field-Induced Magnetic Phase of Cs_3Cr_2Br_9

Field-induced magnetic order has been investigated in detail in the interacting spin 3/2 dimer system Cs_3Cr_2Br_9. Elastic and inelastic neutron scattering measurements were performed up to H = 6 T, well above the critical field H_c1 = 1.5 T. The ordering displays incommensurabilities and a large hysteresis before a commensurate structure is reached. This structure is fully determined. Surprisingly, the lowest excitation branch never closes. Above H_c1, the gap increases slowly with field. An analysis in terms of projected pseudo-spin is given.

cond-mat.str-el↗

arXiv2002

Static and Dynamical Dzyaloshinsky-Moriya interactions in gapped spin systems

Anisotropic spin-spin interactions of Dzyaloshinsky and Moriya symmetry are generally considered weak, as they depend on the spin-orbit couplings. In spin systems with gapped ground states they can, however, have rather strong effects. We will discuss recent results related to the results of neutron scattering and ESR for $\rm SrCu_2(BO_3)_2$. Inclusion of the Dzyaloshinsky-Moriya interactions can explain much of the dynamics of the systems discussed, in particular the splitting and dispersion of the triplet modes. Some effects remain to be explained, however. Symmetries of the crystal lead to the prediction of zero intensity for transitions, for example between the ground state and the triplets observed in ESR. We present recent calculations of the effects of anisotropic terms generated dynamically, ie linearly in the phonon coordinates. We discuss how this leads to a novel mechanism to explain the ESR intensities. For polarized neutron scattering experiments, we can calculate the mixing of nuclear and magnetic scattering amplitudes by such a term and how such mixing should be observed.

cond-mat.str-el↗

arXiv2002

Dynamics, Selection Rules and Dzyaloshinsky-Moriya interactions in Strongly Frustrated Magnets

Anisotropic spin-spin interactions of the symmetry described by Dzyaloshinsky and Moriya are generally considered weak, as they depend on the spin-orbit couplings. In frustrated spin systems with singlet ground states they can, however, have rather strong effects. We discuss recent results related to two gapped spin systems: $\rm CuGeO_3$ and $\rm SrCu_2(BO_3)_2$ in particular. In the first compound the Dzyaloshinsky-Moriya interactions effectively lower the symmetry of the magnetic unit cell and this leads to doubling of the low frequency mode. In the second case, the Dzyaloshinsky-Moriya interactions also split the lowest magnon mode linearly in the spin-orbit coupling. In addition, the relatively weak Dzyaloshinsky-Moriya interactions can dominate the dispersion. Consideration of the selection rules for optical transitions show that while the Dzyaloshinsky-Moriya interactions can explain much of the dynamics, they do not explain the observed transition amplitudes. This leads to a review of recent calculations of anisotropic spin-phonon couplings. We discuss how this leads to a novel mechanism to explain the ESR intensities in the spin gap systems discussed. Selection rules for this novel mechanism involving coupling to the electric field of the resonant probe are discussed and relation to polarised neutron experiments briefly mentioned.

cond-mat.str-el↗

arXiv2001

Dzyaloshinski-Moriya Interaction in the 2D Spin Gap System SrCu2(BO3)2

The Dzyaloshinski-Moriya interaction partially lifts the magnetic frustration of the spin-1/2 oxide SrCu2(BO3)2. It explains the fine structure of the excited triplet state and its unusual magnetic field dependence, as observed in previous ESR and new neutron inelastic scattering experiments. We claim that it is mainly responsible for the dispersion. We propose also a new mechanism for the observed ESR transitions forbidden by standard selection rules, that relies on an instantaneous Dzyaloshinski-Moriya interaction induced by spin-phonon couplings.

cond-mat.str-el↗

arXiv2001

Charge Ordering and Spin Dynamics in NaV2O5

We report high-resolution neutron inelastic scattering experiments on the spin excitations of NaV2O5. Below Tc, two branches associated with distinct energy gaps are identified. From the dispersion and intensity of the spin excitation modes, we deduce the precise zig-zag charge distribution on the ladder rungs and the corresponding charge order (about 0.6). We argue that the spin gaps observed in the low-T phase of this compound are primarily due to the charge transfer.

cond-mat.str-el↗

arXiv1999

Minimal model to describe the magnetism of $CuGeO_{3}$

We show that to describe properly the low energy excitations of $CuGeO_{3}$ one must include the effects of a transverse antiferromagnetic coupling, which is estimated to be $J_{\perp}=0.15 J$. Owing to this coupling the frustration in the chains is significantly lower than recent 1D estimates based on purely one-dimensional arguments, we find $J_{2}=0.2 J$. Furthermore we have found a strong modulation of the nearest neighbour coupling due to the static distortion $δ= 0.065$, which is 5 times higher than that previously deduced from a 1D chain approach. Our set of parameters gives, i) a value of the distorsion which agreeswell with some recent estimate for a lower bound, we are able to perfectly reproduce ii)the dispersions, iii) the experimental susceptibility at both high and low temperatures. By performing DMRG calculations for 2 coupled chains we have analysed the effect of the transverse coupling on the ratio of singlet to triplet gaps. The ratio is very sensitive to the parameters and the universality reported in the strict one dimensional case is lost. As an additional point, we provide a simple picture to explain the interesting new feature observed in recent inelastic neutron scattering experiments: the existence of a second branch of excitations.

cond-mat.str-el↗