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Search Results: 1 - 10 of 462059 matches for " A. Zheludev "
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Neutron Scattering Study of Quantum Phase Transitions in Integral Spin Chains
A. Zheludev
Physics , 2005, DOI: 10.1063/1.2355046
Abstract: Quite a few low-dimensional magnets are quantum-disordered ``spin liquids'' with a characteristic gap in the magnetic excitation spectrum. Among these are antiferromagnetic chains of integer quantum spins. Their generic feature are long-lived massive (gapped) excitations (magnons) that are subject to Zeeman splitting in external magnetic fields. The gap in one of the magnon branches decreases with field, driving a soft-mode quantum phase transition. The system then enters a qualitatively new high-field phase. The actual properties at high fields, particularly the spin dynamics, critically depend on the system under consideration. Recent neutron scattering studies of organometallic polymer crystals NDMAP (Haldane spin chains with anisotropy) and NTENP (dimerized S=1 chains) revealed rich and unique physics.
Coexistence of Haldane gap excitations and long-range order in R_2BaNiO_5 ($R$=rare earth)
A. Zheludev
Physics , 1997,
Abstract: $R_2BaNiO_5$ ($R=$ rare earth) quasi-1-D antiferromagnets are structurally equivalent to the well-studied 1-D S=1 Haldane-gap compound Y_2BaNiO_5. Unlike the Y-nickelate though, these materials undergo 3-D magnetic ordering at finite temperatures. Recent inelastic neutron scattering studies of Pr_2BaNiO_5 and (Nd_{x}Y_{1-x})_2BaNiO_5 revealed purely 1-dimensional gap excitations that propagate exclusively on the Ni-chains and are strikingly similar to Haldane gap modes in Y_2BaNiO_5. In the ordered phase these excitations survive and actually coexist with conventional spin waves. Below $T_{N}$ the gap energy increases and scales as the square of the ordered moment on the Ni sites. The results suggest that the Haldane singlet ground state of the Ni-chains is not fully destroyed by N\'{e}el ordering.
Interacting quantum spin chains. [Invited paper for the International Conference on Neutron Scattering ICNS-2001.]
A. Zheludev
Physics , 2001,
Abstract: A brief review of recent advances in neutron scattering studies of low-dimensional quantum magnets is followed by a particular example. The separation of single-particle and continuum states in the weakly-coupled $S=1/2$ chains system BaCu2Si2O7 is described in some detail.
Comment on "Field-driven phase transitions in a quasi-two-dimensional quantum antiferromagnet"
A. Zheludev,D. Huvonen
Physics , 2013,
Abstract: In a recent publication [M. B. Stone et al., New Journal of Physics 9, 31 (2007)] a "Renormalized Classical 2D" (RC) phase has been reported in a quasi-two-dimensional quantum antiferromagnet PHCC. Its key signature is a sharp cusp-like feature in the magnetic susceptibility which appears below the critical field of magnetic ordering indicated by specific heat anomaly and emergence of a Bragg peak. Here we present experimental data which shows that regardless of experimental geometry, the specific heat and susceptibility anomalies in PHCC both coincide with the onset of true long range order. This leaves no room for any additional intermediate "RC" phase.
Coexistence of Haldane gap excitations and long range antiferromagnetic order in mixed-spin nickelates R_2 Ba Ni O_5
S. Maslov,A. Zheludev
Physics , 1997, DOI: 10.1103/PhysRevB.57.68
Abstract: The spin dynamics of the S=1 Ni-chains in mixed-spin antiferromagnets Pr_2 Ba Ni O_5 and Nd_x Y_2-x Ba Ni O_5 is described in terms of a simple Ginzburg-Landau Lagrangian coupled to the sublattice of rare-earth ions. Within this framework we obtain a theoretical explanation for the experimentally observed coexistence of Haldane gap excitations and long-range magnetic order, as well as for the increase of the Haldane gap energy below the Neel point. We also predict that the degeneracy of the Haldane triplet is lifted in the magnetically ordered phase. The theoretical results are consistent with the available experimental data.
Comment on "Transition from Bose glass to a condensate of triplons in Tl$_{1-x}$K$_x$CuCl$_3$"
A. Zheludev,D. Hüvonen
Physics , 2011, DOI: 10.1103/PhysRevB.83.216401
Abstract: We argue that the interpretation of the calorimetric data for disordered quantum antiferromagnets Tl$_{1-x}$K$_x$CuCl$_3$ in terms of Bose Glass physics by F. Yamada {\it et al.} in [Phys. Rev. B {\bf 83}, 020409(R) (2011)] is not unambiguous. A consistent analysis shows no difference in the crossover critical index for the disorder-free TlCuCl$_3$ and its disordered derivatives. Furthermore, we question the very existence of a proper field-induced thermodynamic phase transition in Tl$_{1-x}$K$_x$CuCl$_3$.
Active Plasmonics: Controlling Signals in Au/Ga Waveguide using Nanoscale Structural Transformations
A. V. Krasavin,N. I. Zheludev
Physics , 2003, DOI: 10.1063/1.1650904
Abstract: We develop a new concept for active plasmonics exploiting nanoscale structural transformations which is supported by rigorous numerical analysis. We show that surface plasmon-polariton signals in a metal-on-dielectric waveguide containing a gallium section a few microns long can be effectively controlled by switching the structural phase of gallium. The switching may be achieved by either changing the waveguide temperature or by external optical excitation. The signal modulation depth could exceed 80 percent and switching times are expected to be in the picosecond-microsecond time scale.
Spin dimers under staggered and random field in Cu$_2$Fe$_2$Ge$_4$O$_{13}
T. Masuda,K. Kakurai,A. Zheludev
Physics , 2009,
Abstract: We study $S=1/2$ dimer excitation in a coupled chain and dimer compound Cu$_2$Fe$_2$Ge$_4$O$_{13} by inelastic neutron scattering technique. The Zeeman split of the dimer triplet by a staggered field is observed at low temperature. With the increase of temperature the effect of random field is detected by a drastic broadening of the triplet excitation. Basic dynamics of dimer in the staggered and random fields are experimentally identified in Cu$_2$Fe$_2$Ge$_4$O$_{13}.
Spin Structures of Spin-Orbit Coupled Square-Lattice Antiferromagnets
Jia-Wei Mei,A. Zheludev
Physics , 2012,
Abstract: We have realized that our results have a strong overlap with those previously published in J Chovan, N Papanicolaou, and S Komineas, Phys.Rev.B65,064433(2002).
A microscopic model for a class of mixed-spin quantum antiferromagnets
J. V. Alvarez,Roser Valenti,A. Zheludev
Physics , 2001, DOI: 10.1103/PhysRevB.65.184417
Abstract: 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.
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