Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session X18: Focus Session: Low D/Frustrated Magnetism - Spin Chains & Ladders |
Hide Abstracts |
Sponsoring Units: GMAG DMP Chair: Marcelo Jamie, Los Alamos National Laboratory Room: D172 |
Thursday, March 24, 2011 2:30PM - 3:06PM |
X18.00001: Quantum criticality, kink confinement, and emergent symmetries in coupled Ising chains and ladders Invited Speaker: In this talk I cover the physics in three of the central quantum phase transitions in 1D. First, the transverse Ising model which is realized in CoNb2O6. While this is perhaps the simplest textbook case of a quantum phase transition, a remarkable emergence of E8 symmetry arises close to the quantum critical point. This manifests itself in an octave of bound states. We observe these experimentally and in particular the interval of the first two resonances on this octave which are found to match the golden ratio 1.618{\ldots} - just as predicted for the emergence of this extraordinary symmetry. I then plan to show with the example of the Heisenberg chain how we can probe the quantum critical volume experimentally and show the characteristic scaling behaviour in space and time. The third example is of a spin ladder CaCu2O3 which is near the long sought after Wess-Zumino-Novikov-Witten quantum critical point. [Preview Abstract] |
Thursday, March 24, 2011 3:06PM - 3:18PM |
X18.00002: Evidence for strong orbital fluctuations below the Jahn-Teller transition in Sr$_{3}$Cr$_2$O$_8$ J. Deisenhofer, Zhe Wang, M. Schmidt, A. G\"{u}nther, S. Schaile, N. Pascher, F. Mayr, Y. Goncharov, H.-A. Krug von Nidda, A. Loidl, D.L. Quintero-Castro, A.T.M.N. Islam, B. Lake We report on the magnetic and phononic excitation spectrum of SrCrO~determined by THz and infrared (IR) spectroscopy, specific heat, and electron spin resonance measurements. We identify the singlet-triplet excitations in the dimerized ground state and observe an extended temperature range $T^{*}(=$ 125 K)$<$ $T<$ $T_{JT}(=$ 285 K$)$ below the Jahn-Teller transition, where the IR active phonons change only gradually with decreasing temperature. A clear anomaly in the specific heat marks the onset of orbital ordering at $T_{JT}$, but a detailed analysis of the orbital contribution to the specific heat shows the persistence of strong fluctuations down to $T^{*}$ in agreement with the IR data. Due to these fluctuations we can observe electron spin resonance absorptions only below $T^{*}$ with a linewidth \begin{math}\propto \exp{(-\Delta/k_BT)}\end{math} indicating an Orbach-type spin relaxation via the excited orbital state of the Cr $e$ doublet split by $\Delta/k_B$ = 388~K. [Preview Abstract] |
Thursday, March 24, 2011 3:18PM - 3:30PM |
X18.00003: NMR in the high-field magnetic phase of LiCuVO$_4$ Wolfgang Kraetschmer, Norbert Buettgen, Alois Loidl, Leonid E. Svistov, Lyudmila A. Prozorova, Andrey Prokofiev LiCuVO$_4$ is a quasi-one-dimensional antiferromagnetic spin-$1/2$ system with strong magnetic frustration due to competing interactions within the Cu spin chain. Consequently, a complex magnetic phase diagram with three critical magnetic field values evolves [arXiv:1005.5668]. Furthermore, spiral spin order below $T_{\mathrm{N}}$=2.7K induces ferroelectricity thus rendering LiCuVO$_4$ multiferroic. The ferroelectric polarization can be switched by reorienting the spin helix through application of external magnetic fields [PRB \textbf{77}, 144101 (2008)]. Above $H>H_{\mathrm{c}2}$ LiCuVO$_4$ becomes paraelectric and the magnetic order changes to a collinear spin-modulated phase. Employing Nuclear Magnetic Resonance we study the nature of this high-field phase by analysis of $^7$Li and $^{51}$V spectra recorded around $H>H_{\mathrm{c}2}$=7.5T. We find, together with simulations for different scenarios, that Cu-spins of neighboring planes along the c-axis have a random phase-relation thus implying a two-dimensional character of the spin order [PRB \textbf{77}, 144101 (2008)]. [Preview Abstract] |
Thursday, March 24, 2011 3:30PM - 3:42PM |
X18.00004: Density Functional Study of the magnetic structure on spin frustrated MnSb$_{2}$S$_{4 }$ and Sr$_{2}$MOsO$_{6}$ (M = Cu, Ni) Chuan Tian, Changhoon Lee, Erjun Kan, Fang Wu, Mike Whangbo We explored the electronic structures of two spin-frustrated magnetic systems monoclinic MnSb$_{2}$S$_{4}$ and Sr$_{2}$MOsO$_{6}$ (M = Cu, Ni) on the basis of first principles DFT calculations. The spin exchanges of MnSb$_{2}$S$_{4}$ are frustrated within each MnS$_{4}$ chain and between adjacent MnS$_{4}$ chains, which explains the observed helical spin order of MnSb$_{2}$S$_{4}$. We predict that MnSb$_{2}$S$_{4}$ is multiferroic with ferroelectric polarization of $\sim $14 $\mu $C/m$^{2}$ along the chain direction, and a field-induced reversal of the ferroelectric polarization occurs by reversing the direction of the helical spin rotation. The ordered double perovskites Sr$_{2}$MOsO$_{6}$ (M = Cu, Ni), reported to be half-metallic, are found to be magnetic insulators. The magnetic structures of Sr$_{2}$MOsO$_{6}$ were probed by evaluating their spin exchanges. [Preview Abstract] |
Thursday, March 24, 2011 3:42PM - 3:54PM |
X18.00005: Ultra-slow Magnetic Order-Order Transition in the Spin Chain Antiferromagnet Ca3Co2O6 O.A. Petrenko, S. Agrestini, C.L. Fleck, L.C. Chapon, C. Mazzoli, A. Bombardi, M.R. Lees We report the observation of a highly unusual time-dependent
magnetic phenomena in which a transition from one long-range
magnetically ordered state to another occurs over a timescale of
several hours.
We have used powder neutron diffraction to
investigate the magnetic structure of Ising spin chain compound
$\rm Ca_3Co_2O_6$.
Our investigation focuses on the low-temperature regime
($T<14$~K$< |
Thursday, March 24, 2011 3:54PM - 4:06PM |
X18.00006: Magnetic structure and superexchange pathways in CsV$_2$O$_5$ Andres Saul, Guillaume Radtke The study of low dimensional spin-1/2 quantum systems has been a very prolific field of condensed matter physics during the last decades. The family of vanadates, in particular, has provided a rich variety of compounds with different behaviours and topologies. Their magnetic structure and properties are primarily determined by the magnitude and the sign of the different exchange couplings arising between magnetic ions and therefore on the very details of their atomic and electronic structures. The sole consideration of the topology of a compound, based on idealized crystal structures, is often incomplete and even misleading. In this work, the magnetic properties of the layered compound CsV$_2$O$_5$ have been investigated using density-functional calculations. The results show that this compound is built from strongly dimerized alternating chains oriented along the ${\bf c}$ axis. Moreover, we demonstrate that the largest interaction along the chains direction arises \textit{between} the structural dimers, involving a superexchange pathway through the covalently bonded V$^{(5+)}$O$_4$ bridging groups. [Preview Abstract] |
Thursday, March 24, 2011 4:06PM - 4:18PM |
X18.00007: Thermal Conductivity due to Magnon Heat Transport in Ca$_{2+x}$Y$_{2-x}$Cu$_{5}$O$_{10}$ Raheem Bello, Isaac Manzanera Esteve, John Markert In the spin-chain structure Ca$_{2+x}$Y$_{2-x}$Cu$_{5}$O$_{10}$, the thermal conductivity in some samples is observed to exhibit two peaks attributed to the thermal transport contributions by phonons and magnons. We have built a thermal conductivity probe, with a 2D rotation stage, to study the magnon contribution to the thermal conductivity of ceramic samples over the range 4--300 K. We plan to measure changes in the magnon contribution by varying the orientation of the lattice with respect to the magnetic field. We have prepared a set of samples with small deviations in oxygen stoichiometry to examine the effects of the defects on magnon thermal transport. [Preview Abstract] |
Thursday, March 24, 2011 4:18PM - 4:30PM |
X18.00008: The origin of the incommesurate phase in the spin Peierls compound TiOCl Ariel Dobry, Diego Mastrogiuseppe, Claudio Gazza TiOX (X=Cl,Br) are recently characterized Spin-Peierls compounds. They are unusual due to the appearance of an intermediate incommensurate phase between the dimerized and the uniform ones. We show that the incommensurate phase is stabilized by a linear dependency of the phononic dispersion near the dimerized mode. A model based on antiferromagnetic chains with position dependent exchanges accounts for the evolution of the atomic coordinates with temperature within the incommensurate phase. The magnetic gap closes in the intermediate phase. Finally, we find that the magnetic static structure factor has incommensurate peaks situated at twice the wave vector of the structural ones. These peaks could be found in future elastic neutron scattering measurements. [Preview Abstract] |
Thursday, March 24, 2011 4:30PM - 4:42PM |
X18.00009: Singlet-Triplet Excitations in the Unconventional Spin-Peierls System TiOBr J.P. Clancy, B.D. Gaulin, C.P. Adams, G.E. Granroth, A.I. Kolesnikov, T.E. Sherline, F.C. Chou TiOBr belongs to a select group of quasi-one-dimensional materials which undergo a spin-Peierls (SP) phase transition and develop a dimerized singlet ground state at low temperatures. However, unlike conventional SP systems, TiOBr exhibits not one, but two successive phase transitions upon cooling: a continuous transition into an incommensurate SP state at T$_{C2}$ $\sim$ 48 K, followed by a discontinuous transition into a commensurate SP state at T$_{C1}$ $\sim$ 27 K. We have performed time-of-flight neutron scattering measurements on powder samples of TiOBr using the fine-resolution Fermi chopper spectrometer (SEQUOIA) at the Spallation Neutron Source. These measurements reveal two branches of magnetic excitations within the commensurate and incommensurate SP phases, which we associate with n = 1 and n = 2 triplet excitations out of the singlet ground state. This study represents the first direct measure of the singlet-triplet energy gap in TiOBr, which we have determined to be E$_{g}$ = 21.2 $\pm$ 1.0 meV. [Preview Abstract] |
Thursday, March 24, 2011 4:42PM - 4:54PM |
X18.00010: Field-Induced Gap in a Quantum Spin-1/2 Chain in a Strong Magnetic Field S. Zvyagin, M. Ozerov, J. Wosnitza, E. \v{C}i\v{z}m\'{a}r, R. Feyerherm, S.R. Manmana, F. Mila Magnetic excitations in copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating $g$-tensor and Dzyaloshinskii-Moriya interactions that exhibits a field-induced spin gap, are probed by means of pulsed-field electron spin resonance spectroscopy. In particular, we report on a minimum of the gap in the vicinity of the saturation field $H_{sat}=48.5$ T associated with a transition from the sine-Gordon region (with soliton-breather elementary excitations) to a spin-polarized state (with magnon excitations). This interpretation is fully confirmed by the quantitative agreement over the entire field range of the experimental data with the DMRG investigation of the spin-1/2 Heisenberg chain with a staggered transverse field. [Preview Abstract] |
Thursday, March 24, 2011 4:54PM - 5:06PM |
X18.00011: Non-equlibrium energy dynamics in spin chains and ladders Fabian Heidrich-Meisner, Stephan Langer, Markus Heyl, Ian McCulloch We investigate the real-time dynamics of the energy density in spin-1/2 chains and ladders, starting from initial states with an inhomogeneous profile of bond energies, extending our previous work on the dynamics of spin-density wave packets [1]. These simulations are carried out using the adaptive time-dependent density matrix renormalization group algorithm. We analyze the time-dependence of the spatial variance of the bond energies which yields necessary criteria for ballistic or diffusive energy dynamics. In the case of the XXZ chain, our results are consistent with ballistic behavior, both in the massless and the massive phase. For the massless regime, we compare our numerical results to predictions from bosonization for, e.g., the velocity that the initial perturbation spreads with. In the case of ladders, we find an involved dynamics whose qualitative interpretation is still under scrutiny. \\[4pt] [1] Langer et al. Phys. Rev. B 79, 214409 (2009) [Preview Abstract] |
Thursday, March 24, 2011 5:06PM - 5:18PM |
X18.00012: Nonmagnetic impurities in a frustrated spin ladder Erik Wulf, Sebastian M\"uhlbauer, Tatiana Yankova, Vasily Glazkov, Andrey Zheludev Sul-Cu$_2$Cl$_4$ is a representative of the spin S=1/2 4-leg ladders. Due to weak interladder interactions it shows almost perfect 1D character. The singlet ground state is separated from the excited triplet state by a gap of $\Delta$=0.52meV which can be closed by a critical field of H$_c$=3.7T. At H$_c$ the disordered spin liquid undergoes a phase transition to chiral helimagnetic order. By replacing nonmagnetic chlorine atoms by nonmagnetic bromine atoms random bond disorder is introduced in Sul-Cu$_2$(Cl$_{1-x}$Br$_x$)$_4$. Measurements of the magnetization and the specific heat show a drastically changed behavior in an applied field even at low bromine concentrations. At T$>$0 the material exhibits an intermediate phase between the spin liquid phase and the helimagnetic ordered phase for x=0.01, while the phase transition to the helimagnetic order is suppressed already for x=0.025. Nevertheless, the critical field H$_c$ to overcome the excitation gap is independent from the impurity concentration. [Preview Abstract] |
Thursday, March 24, 2011 5:18PM - 5:30PM |
X18.00013: Exotic gapless Bose metals and insulators on multi-leg ladders Ryan V. Mishmash, Matt S. Block, Ribhu K. Kaul, Donna N. Sheng, Olexei I. Motrunich, Matthew P.A. Fisher We present recent work establishing compelling evidence for the existence of quasi-1D descendants of the $d$-wave Bose liquid (DBL), a novel 2D quantum phase of itinerant bosons first discussed in [1]. In particular, we study a model of hard-core bosons moving on the $N$-leg ladder square lattice with frustrating four-site ring exchange. In this talk, we focus on two novel phases: an incompressible gapless Mott insulator on the 3-leg ladder and a compressible gapless Bose metal on the 4-leg ladder. The former is a fundamentally quasi-1D phase that is insulating along the ladder but has two 1D gapless modes and power law transverse density-density correlations at incommensurate wave vectors; extensions of this phase to full 2D will be discussed. The latter, on the other hand, is conducting along the ladder and has five 1D gapless modes, one more than the number of legs; this represents a significant step forward in establishing the existence of the DBL in two dimensions. In both cases, we can understand the nature of the phase using slave-particle-inspired variational wave functions consisting of a product of two distinct Slater determinants, the properties of which compare impressively well to a DMRG solution of the model Hamiltonian. [1] O. I. Motrunich and M. P. A. Fisher, PRB {\bf 75}, 235116 (2007). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700