Anomalous Larmour Frequency Dependence of Proton Spin-Lattice Relaxation Time (T1_1) in the Ferroelectric Glycine Phosphite

We report here the results of $^1$H NMR spin-lattice relaxation time (T$_1$) studies in Glycine phosphite which is a ferroelectric below 224 K. The experiments have been carried out in the temperature range from 200 K to 419 K and at two Larmour frequencies of 11.40MHz and 23.56 MHz. We have noticed a Larmour frequency dependence on the high temperature side of the T$_1$ minimum >. A model is proposed based on the BPP theory to explain the observation.Comment: 4 pages, 2 ps figs included, revtex forma

Generation of new classes of integrable quantum and statistical models

A scheme based on a unifying q-deformed algebra and associated with a generalized Lax operator is proposed for generating integrable quantum and statistical models. As important applications we derive known as well as novel quantum models and obtain new series of vertex models related to q-spin, q-boson and their hybrid combinations. Generic q, q roots of unity and q -> 1 yield different classes of integrable models. Exact solutions through algebraic Bethe ansatz is formulated for all models in a unified way.Comment: Latex, 9 pages + 1 figure (eps), Invited talk at Statphys-Kolkata I

Exact results on the Kondo-lattice magnetic polaron

In this work we revise the theory of one electron in a ferromagnetically saturated local moment system interacting via a Kondo-like exchange interaction. The complete eigenstates for the finite lattice are derived. It is then shown, that parts of these states lose their norm in the limit of an infinite lattice. The correct (scattering) eigenstates are calculated in this limit. The time-dependent Schr\"odinger equation is solved for arbitrary initial conditions and the connection to the down-electron Green's function and the scattering states is worked out. A detailed analysis of the down-electron decay dynamics is given.Comment: 13 pages, 9 figures, accepted for publication in PR

Quantum Phase Transition in Pr2CuO4 to Collinear Spin State in Inclined Magnetic Field: A Neutron Diffraction Observation

In the external field slightly inclined to the $x$- or y-axis of the frustrated tetragonal atiferromagnet Pr2CuO4, a transition is discovered from the phase with orthogonal antiferromagnetic spin subsystems along [1,0,0] and [0,1,0] to the phase with the collinear spins. This phase is shown to be due to the pseudodipolar interaction, and transforms into the spin-flop phase S perp H asymptotically at very high field. The discovered phase transition holds at T=0 and is a quantum one, with the transition field being the critical point and the angle between two subsystems being the order parameter

Electronic theory for itinerant in-plane magnetic fluctuations in Nax_xCoO2_2

Starting from {\it ab-initio} band structure for Na$_x$CoO$_2$, we derive the single-electron energies and the effective tight-binding description for the $t_{2g}$ bands using a projection procedure. We find that due to the presence of the next-nearest-neighbor hoppings a local minimum in the electronic dispersion close to the $\Gamma$ point of the first Brillouin zone forms. Therefore, in addition to a large Fermi surface an electron pocket close to the $\Gamma$ point emerges at high doping concentrations. The latter yields the new scattering channel resulting in a peak structure of the itinerant magnetic susceptibility at small momenta. This indicates itinerant in-plane ferromagnetic state above certain critical concentration $x_m$, in agreement with neutron scattering data. Below $x_m$ the magnetic susceptibility shows a tendency towards the antiferromagnetic fluctuations. We estimate the value of $0.58 < x_m < 0.7$ within the rigid band model and within the Hubbard model with infinite on-site Coulomb repulsion consistent with the experimental phase diagram.Comment: 4 pages, 4 figures; LDA calculations were done with Na in the symmetric 2d position contrary to the 6h position in a previous version of this pape

Doping-dependent evolution of low-energy excitations and quantum phase transitions within effective model for High-Tc copper oxides

In this paper a mean-field theory for the spin-liquid paramagnetic non-superconducting phase of the p- and n-type High-$T_c$ cuprates is developed. This theory applied to the effective $t-t'-t''-J^*$ model with the {\it ab initio} calculated parameters and with the three-site correlated hoppings. The static spin-spin and kinematic correlation functions beyond Hubbard-I approximation are calculated self-consistently. The evolution of the Fermi surface and band dispersion is obtained for the wide range of doping concentrations $x$. For p-type systems the three different types of behavior are found and the transitions between these types are accompanied by the changes in the Fermi surface topology. Thus a quantum phase transitions take place at $x=0.15$ and at $x=0.23$. Due to the different Fermi surface topology we found for n-type cuprates only one quantum critical concentration, $x=0.2$. The calculated doping dependence of the nodal Fermi velocity and the effective mass are in good agreement with the experimental data.Comment: 8 page

Enhancement of the Josephson current by magnetic field in superconducting tunnel structures with paramagnetic spacer

The dc Josephson critical current of a (S/M)IS tunnel structure in a parallel magnetic field has been investigated (here S is a superconductor, S/M is the proximity coupled S and paramagnet M bilayer and I is an insulating barrier). We consider the case when, due to the Hund's rule, in the M metal the effective molecular interaction aligns spins of the conducting electrons antiparallel to localized spins of magnetic ions. It is predicted that for tunnel structures under consideration there are the conditions when the destructive action of the internal and the applied magnetic fields on Cooper pairs is weakened and the increase of the applied magnetic field causes the field-induced enhancement of the tunnel critical current. The experimental realization of this interesting effect of the interplay between superconductivity and magnetism is also discussed.Comment: 5 pages 3 figure

Magnetic structure of an incommensurate phase of La-doped BiFe0.5Sc0.5O3: Role of antisymmetric exchange interactions

A 20% substitution of Bi with La in the perovskite Bi1-xLaxFe0.5Sc0.5O3 system obtained under high-pressure and high-temperature conditions has been found to induce an incommensurately modulated structural phase. The room-temperature x-ray and neutron powder diffraction patterns of this phase were successfully refined using the Imma(0,0,gamma)s00 superspace group (gamma = 0.534(3)) with the modulation applied to Bi/La and oxygen displacements. The modulated structure is closely related to the prototype antiferroelectric structure of PbZrO3 which can be considered as the lock-in variant of the latter with gamma = 0.5. Below T-N similar to 220 K, the neutron diffraction data provide evidence for a long-range G-type antiferromagnetic ordering commensurate with the average Imma structure. Based on a general symmetry consideration, we show that the direction of the spins is controlled by the antisymmetric exchange imposed by the two primary structural distortions, namely oxygen octahedral tilting and incommensurate atomic displacements. The tilting is responsible for the onset of a weak ferromagnetism, observed in magnetization measurements, whereas the incommensurate displacive mode is dictated by the symmetry to couple a spin-density wave. The obtained results demonstrate that antisymmetric exchange is the dominant anisotropic interaction in Fe3+-based distorted perovskites with a nearly quenched orbital degree of freedom

Local elongation of stretched filled rubber surface

Local elongation of the surface of a stretched rubber is estimated by comparing the stiffness of stretched filled (30 or 50 phr of silicica) styrene-butadiene vulcanizate and the results of finite element simulation of the indentation of the unfilled elastomer. The local strain exceeds the macroscopic value, yet the weakly loaded areas are also present. As the macroscopic elongation increases, the oriented polymer strands are formed, whose strain is particularly high. An increase in the filler content significantly increases the number and local elongation of strands. The highest tensile loads of the filled matrix occur in the gaps with the initial size of 100 nm. The limitations of the dynamic indentation of stretched elastomers are shown