Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Z4: Focus Session: Magnetization Plateaus and Quantum Phase Transitions |
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Sponsoring Units: GMAG Chair: Vivien Zapf, National High Magnetic Field Lab Room: 112/110 |
Friday, March 7, 2014 11:15AM - 11:51AM |
Z4.00001: Magnetic Texture {\&} Frustration in Quantum Magnets via Strain Measurements to 100 Tesla Invited Speaker: Marcelo Jaime Strong geometrical frustration in magnets leads to exotic states, such as spin liquids, spin supersolids, magnetic solitons, and complex magnetic textures. SrCu$_{2}$(BO$_{3})_{2}$, a spin-1/2 Heisenberg antiferromagnet in the archetypical Shastry-Sutherland lattice, exhibits a rich spectrum of magnetization plateaus and stripe-like magnetic textures in applied fields. We observed new magnetic textures via optical FBG magnetostriction and magnetocaloric measurements in fields up to 100.75 Tesla at 73.6 T and at 82 T [1] which we attribute, using a controlled density matrix renormalization group approach, to a 2/5 plateau and to the long-predicted 1/2-saturation plateau. The plateau predicted at 2/5 saturation is particularly interesting since strain appears to be the only experimental probe with enough sensitivity to reveal it as magnetization probes see a much more gradual change in the same field range [2,3]. BiCu$_{2}$PO$_{6}$ is a frustrated two-leg spin ladder compound with a spin gap that can be closed with a magnetic field of approximately 20T to induce a soliton lattice [4,5]. Time permitting, I will also discuss magnetization, magnetostriction and specific heat vs magnetic fields to 65 T used to obtain the anisotropic (H,T) phase diagram in BiCu$_{2}$PO$_{6}$ single crystal samples. Work at the NHMFL was supported by the National Science Foundation, the US Department of Energy Office of Basic Energy Science through the project ``Science at 100 Tesla,'' and the State of Florida.\\[4pt] [1] M. Jaime, et al. \textit{Proc. Natl. Acad. Sci.} \textbf{109}, 12407 (2012).\\[0pt] [2] S.E. Sebastian, et al., \textit{Proc. Natl. Acad.} Sci. \textbf{105}, 20157 (2009).\\[0pt] [3] Y.H. Matsuda, et al., \textit{Phys. Rev. Lett.} \textbf{111}, 137204 (2013).\\[0pt] [4] Y. Kohama, et al., Phys. Rev. Lett. \textbf{109}, 167204 (2012). \\[0pt] [5] F. Cassola, et al., Phys. Rev. Lett. \textbf{110}, 187201 (2013). [Preview Abstract] |
Friday, March 7, 2014 11:51AM - 12:03PM |
Z4.00002: Novel Spin Flop Transition of the S=1/2 Square-Kagome-Lattice Antiferromagnet Toru Sakai, Hiroki Nakano By means of the numerical diagonalization method, we study the S=1/2 Heisenberg antiferromagnet on the square-kagome lattice, similar to the kagome lattice. We examine the ground-state properties and the magnetization process of the model. It is found that a magnetization jump appears at the higher-field-side edge of the manetization plateau at the one-third height of the saturation. A spin-flop phenomenon is clearly observed at the jump even when the system is isotropic in the spin space. [Preview Abstract] |
Friday, March 7, 2014 12:03PM - 12:15PM |
Z4.00003: Magnetic Field Induced Quantum Phase Transition in Multiferroic Vanadium Spinels E.-D. Mun, G.-W. Chern, V. Pardo, F. Rivadulla, R. Sinclair, H.D. Zhou, V.S. Zapf, C.D. Batista Vanadium spinels with the formula AV2O4 (A $=$ Cd, Mg, Zn, etc) show strong magnetic frustration due to a structure of corner-sharing tetrahedra. A tetragonal structural distortion and an ``up up down down'' magnetic ordering along diagonal chains result at low temperatures, which breaks spatial-inversion symmetry. CdV2O4 is insulating enough that this magnetic order produces ferroelectricity. Here we present data on CdV2O4 and MgV2O4, showing a field-induced quantum phase transition near 40 Tesla, which is a very small energy scale compared to the dominant magnetic exchange interactions. This transition suppresses ferroelectricity and produces a magnetization jump. We show that this transition can be explained by a model that includes spin-orbit coupling effects, and also a trigonal structural distortion at zero and applied magnetic fields. [Preview Abstract] |
Friday, March 7, 2014 12:15PM - 12:27PM |
Z4.00004: Magnetization of rare earth kagome systems in pulsed fields Michael Hoch, Eun Mun, Neil Harrison, Haidong Zhou The rare earth kagome systems $R_{3}Ga_{5}SiO_{14}$ (R = Nd or Pr) exhibit cooperative paramagnetism at low temperatures. Evidence for correlated spin clusters in these weakly frustrated systems has previously been obtained in neutron scattering experiments. The present pulsed field (0 - 60 T) low temperature magnetization measurements on single crystals of $Nd_{3}Ga_{5}SiO_{14}$ (NGS) and $Pr_{3}Ga_{5}SiO_{14}$ (PGS) have revealed striking differences in the magnetic responses of these two materials. At 1.6 K NGS shows a low field plateau, saturation of the magnetization for $\mu_{0}H$ $>$ 10 T and significant hysteresis while the PGS magnetization does not saturate in fields up to 60 T and shows no hysteresis or plateaus. While $Nd^{3+}$ (J = 9/2) is a Kramers ion $Pr^{3+}$ (J = 4) is not. The exchange couplings J $\sim$ 1 K are similar for PGS and NGS but the crystal field splittings and anisotropies are quite different. The marked contrast in the behavior of the two kagome systems is attributed to differences in the spin cluster structures and dynamics. The pulsed field approach has great potential for investigating kagome cluster dynamics at low temperatures. [Preview Abstract] |
Friday, March 7, 2014 12:27PM - 12:39PM |
Z4.00005: Pressure-induced quantum phase transitions in a frustrated spin liquid Alexandra Mannig, Matthias Thede, Dan H\"{u}vonen, Martin M{\aa}nsson, Andrey Zheludev, Rustem Khasanov, Elvezio Morenzoni With the frustrated gapped spin-1/2 quantum antiferromagnet $\mathrm{(C_4H_{12}N_2)Cu_2Cl_6}$ piperazinium hexachlorodicuprate (PHCC) we present an example of a pressure-induced quantum phase transition from the quantum spin liquid state to a magnetically ordered phase [1]. PHCC was investigated at hydrostatic pressures of up to 23.6 kbar with $\mu$SR techniques. The evaluation of the obtained data provided local field dependencies on temperature as well as pressure and allowed the mapping of a detailed $P$-$T$ phase diagram of PHCC. Thus, the quantum critical point that separates the non-ordered phase and a magnetically ordered phase at low pressures was found to lie between 4.2 and 4.4 kbar, which disagrees with recent suggestions of inelastic neutron scattering studies. The oscillations of this magnetically ordered phase indicate an incommensurate structure. In addition, an unexpected second magnetically ordered phase that exhibits a different oscillation behavior and considerably higher saturation fields occured at around 14 kbar.\\[4pt] [1] arXiv:1310.7807 [Preview Abstract] |
Friday, March 7, 2014 12:39PM - 12:51PM |
Z4.00006: Low temperature specific heat of frustrated antiferromagnet HoInCu$_{4}$ Franziska Weickert, Veronika Fritsch, Ryan Bambaugh, John Sarrao, Joe D. Thompson, Roman Movshovich We present low temperature specific heat measurements of single crystal HoInCu$_{4}$, down to 35 mK and in magnetic field up to 12 Tesla. Ho atoms are arranged in an FCC lattice of the edge-sharing tetrahedra, and undergo an antiferromagnetic ordering at $T_{N}=$0.76 K, with the frustration parameter $f =-\Theta_{\mathrm{CW}}$/T$_{\mathrm{N}}$ of 14.3 [1]. Magnetic AF order is suppressed in field $H_{0} \approx $ 4 T. The low temperature Schottky anomaly due to Ho evolves smoothly as a function of field through $H_{0}$ and $T_{N}$. The peak value of the anomaly remains roughly constant from 0 T to 12 T. The temperature of the anomaly's peak remains constant at $T_{Sch} \approx $ 170 mK for \textit{H\textless H}$_{0}$, and gradually increases above $H_{0}$ up to 300 mK at 12 T. This indicates a complete ordering of Ho spins in zero field as well as an increasing moment on Ho once the AF order is suppressed. The measured entropy of HoInCu$_{\mathrm{4}}$ at 12 T and 2K is 17.32 J/mol-K $\approx $ Rln8 expected for an I$=$7/2 nuclear spin of Ho. \\[4pt] [1] V. Fritsch, J. D. Thompson, and J. L. Sarrao, ``Spin and orbital frustration in $R$InCu4 ($R=$Gd, Dy, Ho, and Er)'', PRB \textbf{71}, 132401 (2005). [Preview Abstract] |
Friday, March 7, 2014 12:51PM - 1:03PM |
Z4.00007: Critical properties of the phase transition between a Bose glass and a magnetic Bose-Einstein condensate in a spin-1 Heisenberg model Stephan Haas, Rong Yu, Tommaso Roscilde Motivated by recent experiments on the disordered quantum magnets Ni(Cl$^{\mathrm{1-x}}$Br$^{\mathrm{x}})^{\mathrm{2}}$4SC(NH$^{\mathrm{2}})^{\mathrm{2}}$ (Br-doped DTN), we study the critical properties of the magnetic field induced phase transition between a Bose glass and a magnetic Bose-Einstein condensate in a spin-1 Heisenberg model for this system. We determine the location of the critical field of the transition and the order parameter critical exponent via quantum scaling from quantum Monte Carlo simulations. We find that the extracted value of the order parameter critical exponent is sensitive to both the location of the critical field and the field regime of the scaling. We have also calculated the spin excitations across the transition for this system with a SU(3) slave-boson mean-field method, and discuss the connections of our results to the recent neutron measurements. [Preview Abstract] |
Friday, March 7, 2014 1:03PM - 1:15PM |
Z4.00008: Critical Exponents of the Superfluid-Bose Glass Transition in Three-Dimensions Zhiyuan Yao, Mikhail Kiselev, Karine da Costa, Nikolay Prokof'ev Disordered Bose-Hubbard model is key to understanding a number of strongly interacting systems from magnets and disordered superconductors to ultra-cold atoms in optical lattice. Although the emergence of the Bose glass phase is widely accepted, some basic features of the superfluid-to-Bose glass transition remain controversial. Specifically, recent experimental and numerical studies find that the values of the correlation length exponent $\nu \approx 0.7$ and the critical temperature exponent $\phi \approx 1.1$, are in strong violation of the key quantum critical relation $\phi=\nu z$ with $z=d=3$, where $z$ is the dynamic exponent. We present results of a Monte-Carlo (for the disordered Bose-Hubbard model and its classic J-current counterpart) that clearly demonstrate that previous investigations were done away from the quantum critical region and were severely influenced by strong density dependence on the chemical potential. When the quantum critical point is reached by increasing the disorder strength, the fluctuation region is broad and we find that $\phi \approx 3.0(3)$. [Preview Abstract] |
Friday, March 7, 2014 1:15PM - 1:27PM |
Z4.00009: Magnetic structure and excitations in modified pyrochlore fluoride CsCr$_{2}$F$_{6}$ Sachith Dissanayake, Y. Qiu, M. Matsuda, H. Ueda, A. Hoser, S.-H. Lee In the newly synthesized fluorides, RbCr$_{2}$F$_{6}$ and CsCr$_{2}$F$_{6}$, the magnetic Cr ions have mixed ionic value of 3$+$ (Cr1) and 2$+$ (Cr2), and the two Cr1 and two Cr2 ions form a network of corner sharing tetrahedra. CsCr$_{2}$F$_{6}$ is an antiferromagnet with T$_{\mathrm{cw}}=$-40 K which long range orders below 18 K and undergoes a field induced transition around 4 T. Using elastic and inelastic neutron scattering measurements with and without application of an external magnetic field H, we examined the magnetic structure and excitations of CsCr$_{2}$F$_{6}$. Our results show that Cr2 spins are antiparallel along the c-axis while Cr1 spins are also antiparallel almost along c-axis but canted towards a-axis by 20$^{\circ}$. Upon application of H field, around 4 T, Cr1 moments spin-flop and start canting which corresponds to the jump in magnetization data. Linear spinwave calculations were also performed to shed light in understanding an effective spin hamiltonian for this system that explains our inelastic neutron scattering data with prominent excitation modes centered at 2.2 meV, 3.1 meV and 4.2 meV. [Preview Abstract] |
Friday, March 7, 2014 1:27PM - 1:39PM |
Z4.00010: Quantum and Classical Criticality in a Dimerized Quantum Antiferromagnet Christian Rueegg, Philip Merchant, Desmond F. McMorrow, Karl. W. Kraemer, Martin Boehm, Bruce Normand We perform high-resolution neutron spectroscopy experiments to probe the spin excitations of the quantum antiferromagnet TlCuCl$_3$ throughout the phase diagram by controlling the pressure and temperature. Because this material has a pressure-induced quantum critical point (QCP) at $p_c = 1.07$ kb and a thermal ordering transition at $T_N(p)$ for $p > p_c$ [1], we demonstrate a number of remarkable properties arising at the interface between quantum and classical physics. Quantum and thermal fluctuations have very similar effects in melting the magnetically ordered phase and in opening excitation gaps, but they operate quite independently close to the QCP. In the QC regime there is robust $\omega/T$ scaling of the energies and $\Gamma/T$ scaling of the widths of the critically damped excitations. This scaling crosses over to a classical critical form in a narrow region around $T_N(p)$. The critically damped longitudinal, or Higgs, mode of the ordered phase [2] is exquisitely sensitive to thermal fluctuations and becomes overdamped in the classical regime. \\[4pt] [1] Ch. R\"uegg {\it et al.}, PRL {\bf 93}, 257201 (2004). \\[0pt] [2] Ch. R\"uegg {\it et al.}, PRL {\bf 100}, 205701 (2008). [Preview Abstract] |
Friday, March 7, 2014 1:39PM - 1:51PM |
Z4.00011: Constructing Two Distinct Spin Liquid States in a Layered Cubic Lattice Jin Xu, Kevin Beach We construct a family of short-range resonating-valence-bond wave functions on a layered cubic lattice, allowing for a tunable anisotropy in the amplitudes assigned to nearest-neighbour valence bonds along one axis. Monte Carlo simulations reveal that four phases are stabilized over the full range of the anisotropy parameter. They are separated from one another by a sequence of continuous quantum phase transitions. An antiferromagnetic phase, centered on the perfect isotropy point, intervenes between two {\it distinct} quantum spin liquid states. One of them is continuously deformable to the two-dimensional U(1) spin liquid, which is known to exhibit critical bond correlations. The other has both spin and bond correlations that decay exponentially. The existence of this second phase is proof that, contrary to expectations, neither a bipartite lattice structure nor a conventional Marshall sign rule is an impediment to realizing a fully gapped quantum spin liquid. [Preview Abstract] |
Friday, March 7, 2014 1:51PM - 2:03PM |
Z4.00012: $Z_2$ Spin Liquid and Valence Bond Solid Quantum Phase Transition Kevin Slagle, Cenke Xu We propose a theory to describe the quantum phase transition between a $Z_2$ spin liquid and a valence bond solid (VBS) on a triangular lattice. This phase transition can not be described using the standard Landau-Ginzburg-Wilson (LGW) theory of spontaneous symmetry breaking because a $Z_2$ spin liquid has topological order, which can't be described by an order parameter. We develop a duality formalism which treats the spin liquid's topological vison excitation as a local particle, whose condensation will drive the $Z_2$ topological order into a VBS state. We have considered both isotropic and anisotropic triangular lattices, and second order phase transitions are found in both cases. At these transitions, the VBS order parameters are expected to have an enormous anomalous dimension. [Preview Abstract] |
Friday, March 7, 2014 2:03PM - 2:15PM |
Z4.00013: Plasticity-Induced Magnetism in Frustrated Amorphous Solids George Hentschel, Itamar Procaccia, Bhaskar Sen Gupta Amorphous magnetic solids, like metallic glasses, with no macroscopic magnetic order due to random locally favoured orientations for individual spins exhibit a novel effect: the emergent growth of a macroscopic magnetic Order in the presence of an imposed mechanical strain in athermal conditions in the presence of a imposed magnetic field. The magnetic moment increases in steps whenever there is a plastic event. Thus plasticity induces the magnetic moment, acting as the effective noise driving the system towards equilibrium. We present results of atomistic simulations of this effect in a model of a magnetic amorphous solid subjected to pure shear and a magnetic field. While to elucidate the dependence on external strain and magnetic field we offer a mean-field theory that provides an adequate qualitative understanding of the observed phenomenon. [Preview Abstract] |
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