Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session Q27: Focus Session: Onedimensional Spin Chains 
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Sponsoring Units: GMAG Chair: Christopher Landee, Clark University Room: Morial Convention Center 219 
Wednesday, March 12, 2008 11:15AM  11:27AM 
Q27.00001: From geometry and characteristic length scales to different relaxation regimes in SingleChain Magnets Alessandro Vindigni The recently discovered SingleChain Magnets can be considered a novel class of nanomagnets, representing the ultimate miniaturization limit of bistable magnetic nanowires. The name highlights the analogy with SingleMolecule Magnets: Both SMMs and SCMs show remanent magnetization in zero magnetic field due to slow dynamics, in spite of the reduced dimensionality (0D and 1D respectively) which forbids the occurrence of magnetic ordering. Beyond this common feature, the origin of slow dynamics is remarkably different. In particular, for a genuine 1D magnetic system slow dynamics at low temperature comes from the divergence of the relaxation time as the critical point, T=0, is approached. This scenario is actually encountered in SCMs at relatively high T in a regime where each spin chain behaves as if it were infinite. However, for a wide class of molecular chains (i) naturally occurring defects and (ii) noncollinearity between the singlespin anisotropy directions and the crystal axes break the sitebysite translational invariance along the chain. Both these phenomena affect slow relaxation. We will show how this fact can be accounted for through \textit{ad hoc} extensions of Glauber dynamics. Different relaxation regimes are observed depending on the relationship between the correlation length and the actual distance between two defects, the lattice spacing and the domainwall size. [Preview Abstract] 
Wednesday, March 12, 2008 11:27AM  11:39AM 
Q27.00002: Dynamical correlations of spin1/2 chains Rodrigo Pereira, Steven White, Ian Affleck We show that the longtime behavior of the selfcorrelation function $\langle0S_j^z(t)S_j^z(0)0\rangle$ of the S=1/2 XXZ model in the critical regime is dominated by highenergy excitations. We relate the exponents of the longtime decay to phase shifts which are known exactly from the Bethe ansatz. The same exponents are connected with the singularities of the dynamical structure factor $S^{zz}(q,\omega)$. By combining the analytical results with the timedependent density matrix renormalization group (tDMRG), we calculate $S^{zz}(q,\omega)$ to very high precision. [Preview Abstract] 
Wednesday, March 12, 2008 11:39AM  11:51AM 
Q27.00003: Finitetemperature lineshapes in gapped quantum spin chains Robert Konik, Fabian Essler We consider the finitetemperature dynamical structure factor (DSF) of gapped quantum spin chains such as the spin one Heisenberg model and the transverse field Ising model in the disordered phase. At zero temperature the DSF in these models is dominated by a deltafunction line arising from the coherent propagation of single particle modes. Using methods of integrable quantum field theory we determine the evolution of the lineshape at low temperatures. We show that the line shape is in general asymmetric in energy and becomes Lorentzian only at temperatures far below the gap. We discuss the relevance of our results for the analysis of inelastic neutron scattering experiments on gapped spin chain systems such as ${\rm CsNiCl_3}$ and ${\rm YBaNiO_5}$. [Preview Abstract] 
Wednesday, March 12, 2008 11:51AM  12:03PM 
Q27.00004: A topological classification of gapped spin chains by quantized Berry phases: VBS picture and the fractionalization Takaaki Hirano, Hosho Katsura, Yasuhiro Hatsugai We define a local order parameter of gapped integer spin chains by the Berry phase, where a local spin twist is used as a cyclic parameter to define the Berry connection of the ground state[1]. It is topologically stable against small perturbations unless the level crossing occurs since the Berry phase is quantized to 0 or $\pi$ if the system has the time reversal symmetry. We calculate this Berry phase for the S = 1, 2 dimerized Heisenberg model and the S = 2 Heisenberg model with Dterm. The Berry phases of the generalized valence bond solid states are also evaluated analytically. The results are consistently understood by the valence bond pictures. It implies fundamental objects of the gapped integer spin systems are of spin 1/2 (fractionalization)[2]. [1] Y. Hatsugai, J. Phys. Soc. Jpn. 75, 123601 (2006), arXiv:condmat/ 0603230. [2] T. Hirano, H. Katsura, and Y. Hatsugai, arXiv:0710.4198 (2007). [Preview Abstract] 
Wednesday, March 12, 2008 12:03PM  12:15PM 
Q27.00005: Correlation amplitude and entanglement entropy in random spin chains Jos\'e Hoyos, Andr\'e Vieira, Nicolas Laflorencie, Eduardo Miranda Using strongdisorder renormalization group, numerical exact diagonalization, and quantum Monte Carlo methods, we revisit the random antiferromagnetic XXZ spin1/2 chain focusing on the longlength and groundstate behavior of the average timeindependent spinspin correlation function $C(l)=\upsilon l^{\eta}$. In addition to the wellknown universal (disorderindependent) powerlaw exponent $\eta=2$, we find interesting universal features displayed by the prefactor $\upsilon=\upsilon_o/3$, if $l$ is odd, and $\upsilon=\upsilon_e/3$, otherwise. Although $\upsilon_o$ and $\upsilon_e$ are nonuniversal (disorder dependent) and distinct in magnitude, the combination $\upsilon_o + \upsilon_e = 1/4$ is universal if $C$ is computed along the symmetric (longitudinal) axis. The origin of the nonuniversalities of the prefactors is discussed in the renormalizationgroup framework where a solvable toy model is considered. Moreover, we relate the average correlation function with the average entanglement entropy, whose amplitude has been recently shown to be universal. The nonuniversalities of the prefactors are shown to contribute only to surface terms of the entropy. Finally, we discuss the experimental relevance of our results by computing the structure factor whose scaling properties, interestingly, depend on the correlation prefactors. [Preview Abstract] 
Wednesday, March 12, 2008 12:15PM  12:27PM 
Q27.00006: Electronic and magnetic properties of the chain compounds K$_3$T$_2$O$_4$ (T=Ni, Pd, Pt) Klaus Koepernik, Deepa Kasinathan, Walter Schnelle, Helge Rosner Recent susceptibility measurements on the chain compound K$_3$Pd$_2$O$_4$ were interpreted in terms of localized spin 1/2 Pd moments on one of the two crystallographically different Pd sites, only [{\it R.V. Panin et al., J. Solid St. Chem. {\bf 180}, 1566 (2007)}]. The main exchange interaction was reported to be antiferromagnetic from the negative CurieWeiss temperature $\Theta$=$$80K. Earlier measurements for the isostructural and isovalent Ni and Pt compounds suggest an antiferromagnetic coupling for T=Ni whereas it is ferromagnetic for T=Pt. [{\it H. Zentgraf et al., Z. Aanorg. allg. Chem., {\bf 462}, 92 (1980)}] Here, we report an electronic structure study focusing on the interplay of covalency, spinorbit coupling and correlation to describe the behavior of this compound family. The inclusion of strong Coulomb repulsion at the transitionmetal sites is necessary to obtain the correct insulating ground state observed in recent measurements for the Pd system. The origin of the different magnetic behavior will be discussed. [Preview Abstract] 

Q27.00007: ABSTRACT WITHDRAWN 
Wednesday, March 12, 2008 12:39PM  12:51PM 
Q27.00008: muSR study on quasionedimensional cobalt/rhodium oxides Peter Russo, Jun Sugiyama, H. Nozaki, Y. Ikedo, K. Mukai, T. Takami, H. Ikuta, Daniel Andreica, Alex Amato Thanks to the unique power of muonspin spectroscopy, we found that the quasionedimensional CoRh oxides $A_{n+2}$CoRh$_{n}$O$_{3n+3}$ ($A$ = Ca, Sr; $n$=1, 2, and 3) exhibit a twodimensional antiferromagnetic transition that ranges from $T_{\rm N}^{\rm on}$=185~K for $n$=1 to 125~K for $n$=3 with a transition width ($\Delta T$) of about 80~K. The variation of $T_{\rm N}^{\rm on}$ with $n$ is explained by the increase in the distance between the neighboring CoRh$_n$O$_{3n+3}$ chains. Static magnetic order is observed below the endpoint of $T_{\rm N}$ (=$T_{\rm N}^{\rm on}$$\Delta T$) for each of the three samples. The existence of the twofrequency components in the ZFspectrum indicates the appearance of ferrimagnetic order for Ca$_3$CoRhO$_6$ below 20~K. [Preview Abstract] 
Wednesday, March 12, 2008 12:51PM  1:03PM 
Q27.00009: Magnetic field versus temperature phase diagram of the spin1/2 bondalternatingchain antiferromagnet F$_{5}$PNN Yasuo Yoshida, Tatsuya Kawae, Bohdan Andraka, Yasumasa Takano, Yuko Hosokoshi, Katsuya Inoue, Nobuya Maeshima, Kouichi Okunishi, Kiyomi Okamoto, Toru Sakai The S = 1/2 Heisenberg bondalternatingchain antiferromagnet pentafluorophenyl nitronyl nitroxide (F$_{5}$PNN) exhibits TomonagaLuttingerliquid behavior in the temperature dependence of the specific heat above the fieldinduced magnetic ordering temperature [1]. We have determined the magnetic phase diagram of this compound from the specific heat. For a single crystal, the boundary of the ordered phase in the fieldvstemperature diagram is symmetric with respect to the central field of the gapless region H$_{c1} \quad \le $ H $\le $ H$_{c2}$, whereas a distorted phase boundary is observed for a powder sample, whose ordering temperature is reduced. Calculations based on the finitetemperature densitymatrix renormalization group suggest the possibility of a novel incommensurate phase due to frustration in the powder, in a narrow field range near the central field. [1]Y. Yoshida \textit{et al.,} Phys. Rev. Lett.\textbf{94}, 037203 (2005). [Preview Abstract] 
Wednesday, March 12, 2008 1:03PM  1:15PM 
Q27.00010: $^{51}$V NMR Study of a quasi1D XXZ spin chain system BaCo$_{2}$V$_{2}$O$_{8}$ K.Y. Choi We present $^{51}$V NMR measurements on the quasionedimensional $S$=1/2 XXZ antiferromagnet BaCo$_{2}$V$_{2}$O$_{8}$ along the chain. The $^{51}$V NMR spectrum shows that the quantum phase transition takes place from the N\'{e}el ordered phase to the incommensurately ordered phase around Tc$_{1}\approx $4 T. In addition, we studied a spinlattice relaxation rate, 1/T$_{1}$, as a function of temperature and field. Our results are compared to a theoretical prediction and are discussed in terms of a softening of spinons in an external field. [Preview Abstract] 
Wednesday, March 12, 2008 1:15PM  1:27PM 
Q27.00011: Spin Supersolid in Anisotropic SpinOne Heisenberg Chain Pinaki Sengupta, Cristian Batista We consider an $S=1$ Heisenberg chain with strong exchange ($\Delta=J_z/J_{\perp}$) and singleion uniaxial anisotropy ($D$) in a magnetic field ($B$) along the symmetry axis. The low energy spectrum is described by an effective $S=1/2$ XXZ model that acts on two different low energy sectors for a finite range of fields. The vacuum of each sector exhibits Isinglike antiferro magnetic ordering coexisting with the finite spin stiffness obtained from the exact solution of the XXZ model. In this way, we demonstrate the existence of a spin supersolid phase. We also compute the full $\DeltaB$ quantum phase d iagram using a quantum Monte Carlo (QMC) method. [Preview Abstract] 
Wednesday, March 12, 2008 1:27PM  1:39PM 
Q27.00012: Interacting vs. free quasiparticle description for the spin1/2 chain Sebastian Eggert, Michael Bortz, Michael Karbach, Imke Schneider We consider the individual excitations of the antiferromagnetic spin1/2 chain in the Luttinger Liquid formalism. The inclusion of Umklapp scattering and other irrelevant operators introduces an interaction between quasiparticles, which lifts the degeneracy in the linearized spectrum. So far this effect has been systematically understood only for the lowest excited state in each sector. We now show for a number of low lying excitations how rotations in the degenerate subspaces diagonalize the Umklapp term perturbatively. Our results are verified by taking advantage of the Bethe solution of the spin chain to perform an exact finite size scaling analysis for individual excited levels. From this we can identify the correspondence of quantum numbers between the bosonic and Bethe states. We also make contact to the well known quantum numbers at the noninteracting free fermion point. [Preview Abstract] 
Wednesday, March 12, 2008 1:39PM  1:51PM 
Q27.00013: Magnetic Susceptibilities of Finite Ising Chains in the Presence of Defect Sites Serguei Goupalov, Daniel Mattis Any antiferromagnet with zero net magnetic moment exhibits limited response to an external homogeneous magnetic field. This changes dramatically in the presence of defect sites, even those that carry no spin. We examine the excess susceptibilities, longitudinal and transverse, due to one or more defects at arbitrary separations in a finite Ising chain with nearestneighbor couplings. Adapting matrix methods to finite chains we derive exact formulas valid at all $T \ge 0$. [Preview Abstract] 
Wednesday, March 12, 2008 1:51PM  2:03PM 
Q27.00014: Excitation spectrum and magnetic properties of the new Haldanegap material NENB Sergei Zvyagin, E. \v{C}i\v{z}m\'{a}r, M. Ozerov, O. Ignatchik, T. Papageorgiou, J. Wosnitza, J. Krzystek, Z. Zhou, J.L. Wikaira, C.P. Landee, M.M. Thurnbull Results of highfield ESR and magnetization studies of the new spin1 Haldanechain material [Ni(C$_2$H$_8$N$_2$)$_2$NO$_2$](BF$_4$) (NENB) are reported. A definite signature of the Haldane state in NENB was obtained. From the analysis of the frequencyfield dependence of magnetic excitations in NENB, the spinHamiltonian parameters were calculated, yielding $\Delta/k_{B} = 17.4$~K, $g_{\parallel} =2.14$, $D/k_{B}=7.5$~K, and $E/k_{B}=0.7$~K for the Haldane gap, $g$ factor and the crystalfield anisotropy constants, respectively. The presence of fractional $S=1/2$ chainend states, revealed by ESR and magnetization measurements, is found to be responsible for spinglass freezing effects. In addition, extra states in the excitation spectrum of NENB have been observed in the vicinity of the Haldane gap, which origin is discussed. [Preview Abstract] 
Wednesday, March 12, 2008 2:03PM  2:15PM 
Q27.00015: Direct comparison of hole doping effects due to cation and to oxygen content on magnetic properties of the spinchain system Ca$_{2+x}$Y$_{2x}$Cu$_5$O$_{10\delta}$ Keeseong Park, Theodore Cackowski, John Markert A quasione dimensional system, Ca$_{2+x}$Y$_{2x}$Cu$_5$O$_{10\delta}$ (CaYCuO) is studied to compare the magnetic effects of cation doping with those of oxygen deficiency. Hole doping ($p$) due to cation concentration ($x$) and oxygen deficiency ($\delta$) in other copper oxides is often observed to obey $p = x  2 \delta$. CaYCuO has a simple edge shared CuO structure and is hole dopable up to a formal copper valence of 2.4. Various Ca doped CaYCuO specimens were fabricated in different oxygen environments, including high pressure oxygen up to 170 atm. Xray diffraction and iodometric titration were used to confirm phase and oxygen content. Samples are found to be more oxygen deficient with increasing cation doping. Magnetic moment and specific heat were measured. The antiferromagnetic phase was observed up to $x = 1.0$ doping for fully oxygenated specimens. N\'eel temperatures decreased with increasing cation doping and decreasing oxygen deficiency. The decrease in N\'eel temperature is found to be more than expected from hole doping $p = x  2 \delta$. A new quantity that describes all of the behavior of N\'eel temperature, $p' = x  (2/3) \delta$, is proposed. [Preview Abstract] 
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