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A. Zheludev

Publications and source records attributed to A. Zheludev.

At least 145 records · Page 8Linked to original sources
arXiv2003

Distribution of exchange energy in a bond-alternating S=1 quantum spin chain

The quasi-one-dimensional bond-alternating S=1 quantum antiferromagnet NTENP is studied by single crystal inelastic neutron scattering. Parameters of the measured dispersion relation for magnetic excitations are compared to existing numerical results and used to determine the magnitude of bond-strength alternation. The measured neutron scattering intensities are also analyzed using the 1st-moment sum rules for the magnetic dynamic structure factor, to directly determine the modulation of ground state exchange energies. These independently determined modulation parameters characterize the level of spin dimerization in NTENP. First-principle DMRG calculations are used to study the relation between these two quantities.

cond-mat.str-el↗
arXiv2003

Helimagnetism in a disordered and geometrically frustrated quantum spin chain

Neutron diffraction and bulk measurements are used to determine the nature of the low-temperature ordered state in LiCu$_2$O$_2$, a $S=1/2$ spin-chain compound with competing interactions. The magnetic structure is found to be helimagnetic, with a propagation vector $(0.5,ζ,0)$, $ζ=0.174$. The nearest-neighbor exchange constant and frustration ratio are estimated to be $J=5.8$ meV and $J_2/J_1=0.29$, respectively. For idealized spin chains these parameter values would signify a gapped spin-liquid ground state. Long-range ordering is attributed to intrinsic non-stoichiometry.

cond-mat.str-el↗
arXiv2003

Dynamics of an anisotropic Haldane antiferromagnet in strong magnetic field

We report the results of elastic and inelastic neutron scattering experiments on the Haldane gap quantum antiferromagnet Ni(C5D14N2)2N3(PF6) performed at mK temperatures in a wide range of magnetic field applied parallel to the S = 1 spin chains. Even though this geometry is closest to an ideal axially symmetric configuration, the Haldane gap closes at the critical field Hc~4T, but reopens again at higher fields. The field dependence of the two lowest magnon modes is experimentally studied and the results are compared with the predictions of several theoretical models. We conclude that of several existing theories, only the recently proposed model [Zheludev et al., cond-mat/0301424 ] is able to reproduce all the features observed experimentally for different field orientations.

cond-mat↗
arXiv2003

BiCu$_2$VO$_6$: a new narrow-band spin-gap material

A new spin-ladder family material BiCu$_2$VO$_6$ is studied by means of the magnetic susceptibility, heat capacity and neutron inelastic scattering measurements on powder sample. Singlet ground state and a finite spin gap are confirmed by thermal-activated type susceptibility and by distinct peak at 16 meV in spin excitation. Triple narrow band structure in spin excitation spectrum, probably due to complex crystal structure, is observed and the possibility of weakly-interacting spin-cluster system is discussed.

cond-mat.str-el↗
arXiv2003

Spin waves and the origin of commensurate magnetism in Ba2CoGe2O7

The square-lattice antiferromagnet Ba2CoGe2O7 is studied by means of neutron diffraction and inelastic scattering. This material is isostructural to the well-known Dzyaloshinskii-Moriya helimagnet Ba2CuGe2O7, but exhibits commensurate long-range Neel order at low temperatures. Measurements of the spin wave dispersion relation reveal strong in-plane anisotropy that is the likely reason for the suppression of helimagnetism.

cond-mat.str-el↗
arXiv2003

Massive triplet excitations in a magnetized anisotropic Haldane spin chain

Inelastic neutron scattering experiments on the Haldane-gap quantum antiferromagnet \nd are performed at mK temperatures in magnetic fields of almost twice the critical field $H_c$ applied perpendicular to the spin cahins. Above $H_c$ a re-opening of the spin gap is clearly observed. In the high-field Néel-ordered state the spectrum is dominated by three distinct long-lived excitation branches. Several field-theoretical models are tested in a quantitative comparison with the experimental data.

cond-mat.str-el↗
arXiv2002

Polarization dependence of spin excitations in BaCu2Si2O7

The polarization dependence of magnetic excitations in the quasi one-dimensional antiferromagnet BaCu2Si2O7 is studied as a function of momentum and energy transfer. The results of inelastic neutron scattering measurements are directly compared to semi-analytical calculations based on the chain-Mean Field and Random Phase approximations. A quantitative agreement between theoretically calculated and experimentally measured dynamic structure factors of transverse spin fluctuations is obtained. In contrast, substantial discrepancies are found for longitudinal polarization. This behavior is attributed to intrinsic limitations of the RPA that ignores correlation effects.

cond-mat.str-el↗
arXiv2002

Dominance of excitation continuum in the longitudinal spectrum of weakly coupled Heisenberg S=1/2 chains

A low-field spin flop transition in the quasi one-dimensional antiferromagnet \ba is exploited to study the polarization dependence of low-energy magnetic excitations. The measured longitudinal spectrum is best described as single broad continuum, with no sharp ``longitudinal mode'', in apparent contradiction with the commonly used chain-MF/RPA theories. The observed behavior is also quite different than that previously seen in the related \kcuf material, presumably due to a large difference in the relative strength of inter-chain interactions. The results highlight the limitations of the chain-MF/RPA approach.

cond-mat.str-el↗
arXiv2002

A microscopic model for a class of mixed-spin quantum antiferromagnets

We propose a microscopic model that describes the magnetic behavior of the mixed-spin quantum systems R$_2$BaNiO$_5$ (R= magnetic rare earth). An evaluation of the properties of this model by Quantum Monte Carlo simulations shows remarkable good agreement with the experimental data and provides new insight into the physics of mixed-spin quantum magnets.

cond-mat.str-el↗
arXiv2001

Structure of the exotic spin-flop states in BaCu2Si2O7

The unusual 2-stage spin flop transition in BaCu2Si2O7 is studied by single-crystal neutron diffraction. The magnetic structures of the various spin-flop phases are determined. The results appear to be inconsistent with the previously proposed theoretical explanation of the 2-stage transition.

cond-mat.str-el↗
arXiv2001

Spin dynamics in the $S=1/2$ weakly-coupled chains antiferromagnet BaCu$_2$Si$_2$O$_7$

Inelastic neutron scattering is used to identify single-particle and continuum spin excitations in the quasi-one-dimensional $S=1/2$ antiferromagnet \ba. In the data analysis, close attention is given to resolution effects. A gap in the continuum spectrum at $Δ_c=4.74.8$ meV is directly observed. The gap energy is in excellent agreement with existing theoretical predictions. Below the gap, the spectrum is dominated by sharp accoustic spin wave excitations.

cond-mat.str-el↗
arXiv2001

Field-induced commensurate long-range order in the Haldane-gap system NDMAZ

High-field neutron diffraction studies of the new quantum-disordered S=1 linear-chain antiferromagnet Ni(C$_5$H$_{14}$N$_2$)$_2$N$_3$(ClO$_4$) (NDMAZ) are reported. At T=70 mK, at a critical field $H_c=13.4$ T applied along the (013) direction, a phase transition to a commensurate Néel-like ordered state is observed. The results are discussed in the context of existing theories of quantum phase transitions in Haldane-gap antiferromagnets, and in comparions with previous studies of the related system Ni(C$_5$H$_{14}$N$_2$)$_2$N$_3$(PF$_6$).

cond-mat.str-el↗
arXiv2001

Zone-boundary excitations in coupled Haldane spin chain compounds PbNi2V2O8 and SrNi2V2O8

Magnetic excitations in the quasi-one-dimensional quantum antiferromagnets PbNi2V2O8 and SrNi2V2O8 are measured all the way up to the zone boundary energy using inelastic neutron scattering from powder samples. An estimate for next-nearest-neighbor in-chain interactions is obtained. The role played by these interactions in spin-vacancy induced magnetic ordering in PbNi2V2O8 is discussed.

cond-mat.str-el↗
arXiv2000

Magnetic order and spin-waves in the quasi-1D S=1/2 antiferromagnet ${\bf BaCu_{2}Si_{2}O_{7}}$

Elastic and inelastic neutron scattering were used to study the ordered phase of the quasi-one-dimensional spin-1/2 antiferromagnet ${\rm BaCu_{2}Si_{2}O_{7}}$. The previously proposed model for the low-temperature magnetic structure was confirmed. Spin wave dispersion along several reciprocal-space directions was measured and inter-chain, as well as in-chain exchange constants were determined. A small gap in the spin wave spectrum was observed and attributed to magnetic anisotropy effects. The results are discussed in comparison with existing theories for weakly-coupled quantum spin chain antiferromagnets.

cond-mat.str-el↗
arXiv2000

Field-induced 3- and 2-dimensional freezing in a quantum spin liquid

Field-induced commensurate transverse magnetic ordering is observed in the Haldane-gap compound \nd by means of neutron diffraction. Depending on the direction of applied field, the high-field phase is shown to be either a 3-dimensional ordered Néel state or a short-range ordered state with dominant 2-dimensional spin correlations. The structure of the high-field phase is determined, and properties of the observed quantum phase transition are discussed.

cond-mat.str-el↗
arXiv2000

Energy separation of single-particle and continuum states in a S=1/2 weakly-coupled chains antiferromagnet

Inelastic neutron scattering is used to study transverse-polarized magnetic excitations in the quasi-one-dimensional S=1/2 antiferromagnet BaCu_2Si_2O_7, where the saturation value for the Néel order parameter is $m_0=0.12 μ_{\rm B}$ per spin. At low energies the spectrum is totally dominated by resolution-limited spin wave-like excitations. An excitation continuum sets in above a well-defined threshold frequency. Experimental results are discussed in the context of current theories for weakly-interacting quantum half-integer spin chains.

cond-mat.str-el↗