Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session J54: Mott Insulators and Fermi Fluids |
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Sponsoring Units: GMAG Chair: Clarina dela Cruz, Oak Ridge National Laboratory Room: Mile High Ballroom 1B |
Tuesday, March 4, 2014 2:30PM - 2:42PM |
J54.00001: Probing the World of Correlated electron systems: Materials Characterization and Neutron Scattering studies Clarina dela Cruz An important field of experimental Condensed Matter Physics focuses on studying correlated electron systems including unconventional superconductors, iron-based superconductors and multifunctional systems such as multiferroic compounds. The use of various bulk measurement techniques to characterize the physical properties in these systems is an essential first step in revealing the novel electronic and magnetic ground states. Further studies using powerful microscopic probes such as neutron scattering methods are crucial in advancing the central theme in understanding correlated electron systems, which is to make the correlation between structure, magnetism and physical properties. As is common across correlated electron systems, highly degenerate ground states abound which are readily disturbed by chemical dopants and perturbing fields such as an applied magnetic field or pressure. Thus, studying these systems, using neutron scattering techniques in particular, in various extreme conditions reveals new emergent ground states with tunable magnetic, electronic or ferroelectric order parameters. [Preview Abstract] |
Tuesday, March 4, 2014 2:42PM - 2:54PM |
J54.00002: Novel Itinerant Antiferromagnet With Nonmagnetic Constituents Eteri Svanidze, Jiakui Wang, Tiglet Besara, Monica Gamza, Theo Siegrist, Meigan Aronson, Andryi Nevidomskyy, Emilia Morosan While many systems exhibit both local and itinerant magnetism, only two are known to display magnetism while being composed of non-magnetic elements - Sc$_3$In and ZrZn$_2$. Drastic differences in dimensionality, critical scaling and susceptibility to perturbations suggest that more systems like this would be useful in identifying the origin of their magnetic properties. In this talk, the properties of a new itinerant antiferromagent with no magnetic constituents, are presented. Specific heat, resistivity and magnetization data indicate magnetic ordering below $T_N \approx$ 36 K. Above this temperature, the susceptibility displays Curie-Weiss-like behavior, with an unexpectedly large paramagnetic moment $\mu_{PM}\approx 0.8~\mu_B~F.U.^{-1}$. The magnetism is confirmed by band structure calculations, which suggest a spin-density wave ground state with a modulation wavevector $Q$ = $(0, 2\pi/3b, 0)$. [Preview Abstract] |
Tuesday, March 4, 2014 2:54PM - 3:06PM |
J54.00003: Phase interference and sub-femtosecond time dynamics of resonant inelastic X-ray scattering from Mott insulators L. Andrew Wray, Shih-Wen Huang, Yuqi Xia, M. Zahid Hasan, Charles Mathy, Hiroshi Eisaki, Zahid Hussain, Yi-De Chuang Resonant inelastic X-ray scattering (RIXS) is a powerful technique for observing the energy states of many-body quantum materials. The core hole resonance states that make RIXS possible are strongly correlated, and undergo complex time evolution that shapes scattering spectra. However, current inelastic scattering measurements cannot be converted to a time resolved picture, because techniques that determine relative phase information from elastic scattering have not been adapted to the greater complexity of inelastic spectra. We will show that inelastic scattering phases can be identified from quantum interference in sharply resolved (dE $<$ 35meV) M-edge RIXS spectra of Mott insulators (e.g. SrCuO$_2$ and NiO), and provide new information for identifying excitation symmetries and many-body time dynamics. [Preview Abstract] |
Tuesday, March 4, 2014 3:06PM - 3:18PM |
J54.00004: Novel magnetic state in $d^4$ Mott insulators Oinam Nganba Meetei, William Cole, Mohit Randeria, Nandini Trivedi We show that the interplay of strong Hubbard interaction $U$ and spin-orbit coupling $\lambda$ in systems with the $d^4$ electronic configuration leads to several unusual magnetic phases. While in the atomic limit the system is in a non-magnetic $J=0$ singlet state, we find that the competition between superexchange and atomic spin-orbit coupling dramatically changes the local moment, which challenges the conventional wisdom that local moments are well-defined in a Mott insulator. Most notably, we find that in the Mott limit at strong $U$ there is a phase transition from a non-magnetic insulator of uncoupled $J=0$ singlets to an orbitally entangled ferromagnetic insulator. We identify candidate materials and present predictions for Resonant X-ray Scattering (RXS) signatures for the unusual magnetism in $d^4$ Mott insulators and contrast them with the well-studied $d^5$ case. [Preview Abstract] |
Tuesday, March 4, 2014 3:18PM - 3:30PM |
J54.00005: Mott Glass Phase in the Disordered Quantum Spin Systems Dao-Xin Yao, Nvsen Ma, Anders Sandvik We use quantum Monte Carlo method to study the disordered $S=1/2$ quantum spins on the square lattice with three different nearest neighbor interactions $J_{1}$, $J_{2}$ and $J_{3}$. Here $J_{1}$ represents weak bonds, and $J_{2}$ and $J_{3}$ correspond to stronger bonds which are randomly distributed on columnar rungs forming coupled 2-leg ladders. By tuning the average value of $J_{2}$ and $J_{3}$, the system undergoes N$\acute{e}$el-glass-paramagnetic quantum phase transition. A wide range of Mott glass phase has been found. We notice that its uniform susceptibility in the glass phase follows $ \chi\sim\exp(-b/T^{\alpha})$, where $0.5<\alpha<1$. Furthermore, this dimerized disordered quantum spin system shows the violation of Harris criterion. [Preview Abstract] |
Tuesday, March 4, 2014 3:30PM - 3:42PM |
J54.00006: Fractionalized liquid states in doped Mott insulators Andrej Mesaros, Shenghan Jiang, Ying Ran We study Mott insulator phases at specifically chosen doping levels on several lattices. Using analytical and numerical techniques we identify interesting quantum liquid phases with fractionalized excitations. [Preview Abstract] |
Tuesday, March 4, 2014 3:42PM - 3:54PM |
J54.00007: Ultrafast dynamics of the nanoscale metal-insulator transition in VO$_2$ Joanna Atkin, Brian O'Callahan, Sven Doenges, Andrew Jones, Markus Raschke The metal-insulator transition (MIT) of vanadium dioxide (VO$_2$) exhibits a rich phase behavior involving two monoclinic (M1, M2), a triclinic, and a tetragonal phase that form a complex domain structure and lead to spatial inhomogeneities in the electronic transition. The interplay of these different phases with strain can affect the progress of both the thermal and photoinduced MIT. We report on nano-optical imaging of the MIT in individual microcrystals and thin films of VO$_2$, in order to probe the effects of substrate and crystallite strain, morphology, and orientation on the emergent metallic phase. We find a large variation in transition rates and dynamical behavior among single crystal microrods, indicating intrinsic inhomogeneities in the MIT. [Preview Abstract] |
Tuesday, March 4, 2014 3:54PM - 4:06PM |
J54.00008: Iridate spin models: magnetism, 3D spin liquids and an infinite-D entanglement approximation Itamar Kimchi, James Analytis, Ashvin Vishwanath We present three-dimensional threefold-coordinated structures for iridates which may generate Kitaev-type magnetic exchanges. The resulting solvable 3D quantum spin liquid exhibits the uniquely 3D property of stability to finite temperature ($T_c \sim J_k/100$). Adding Heisenberg couplings spoils exact solubility; however, the large loop length $\ell$ of the lattice suggests an approximation with large $\ell \rightarrow \infty$. The Kitaev-Heisenberg model can be solved on the resulting Bethe lattice using tensor product states; we present the phase diagrams, finding multiple magnetic order parameters and identifying gapped spin liquid phases by an entanglement fingerprint. [Preview Abstract] |
Tuesday, March 4, 2014 4:06PM - 4:18PM |
J54.00009: Ferromagnetism in flat bands and Pauli-correlated percolation Mykola Maksymenko, Andreas Honecker, Roderich Moessner, Johannes Richter, Oleg Derzhko, Kirill Shtengel Flat-band ferromagnetism is an exotic case of itinerant-electron magnetism in a wide class of geometrically frustrated lattices. We develop an exact mapping between the ground state of the many-body problem and a novel site-percolation problem. This allows us to study the ferromagnetic transition using tools from equilibrium statistical physics. In the case of Hubbard model on the Tasaki lattice, we provide a complete and exact solution in 1D and show that for D $>$ 1, the paramagnetic phase persist beyond the uncorrelated percolation point, with a transition in the form of a first-order jump to an unsaturated ferromagnetic phase. [Preview Abstract] |
Tuesday, March 4, 2014 4:18PM - 4:30PM |
J54.00010: Theory of spin density wave glasses David Mross, T. Senthil We study the effects of non-magnetic impurities on an easy-plane spin density wave at $\vec Q$ accompanied by a charge density wave at $2\vec Q$ in two and three dimensions. Even though any amount of disorder dramatically reduces both spin and charge correlations, spin nematic correlations remain essentially unaffected. This is due to the proliferation of only certain kinds of defects, leading to a uniaxial spin glass. The presence of a Goldstone mode distinguishes this phase from a conventional spin glass, and can serve as an experimental signature. Similarly, in superconductors with finite momentum pairing, a charge-4 condensate persists in the presence of weak disorder, while pair density wave order (the FFLO state) is lost due to impurities. [Preview Abstract] |
Tuesday, March 4, 2014 4:30PM - 4:42PM |
J54.00011: Excitations of a Fermi fluid with coupled magnetic and nematic order parameters Pengtao Shen, Khandker Quader We study possible stable phases of 2D and 3D Fermi fluids with coupled magnetic and nematic order parameters by considering appropriate Ginzburg-Landau free energies, and performing necessary minimizations. In Fermi liquid language, nematic order corresponds to L=2 distortions of the Fermi surface, so here we consider such distortions in a magnetically ordered Fermi fluid. We use Landau kinetic equation to study propagating collective modes and corresponding dispersions of the modes. [Preview Abstract] |
Tuesday, March 4, 2014 4:42PM - 4:54PM |
J54.00012: Low-temperature evolution of the spectral weight of a spin-up carrier moving in a ferromagnetic background Mirko Moeller, Mona Berciu The motion of a charged particle in a magnetically ordered background determines the electronic behavior of many weakly doped, magnetically ordered insulators and semiconductors. This problem can be solved exactly for a single charge carrier in a ferromagnetic background at T=0. There are two different cases to be considered (i) the carrier spin is oriented antiparallel with respect to the FM background and (ii) the carrier spin is aligned with the background. For the former case the solution is a spin-polaron, a dressed quasiparticle consisting of a charged particle and a bound magnon. For the latter case, on the other hand, the formation of a spin-polaron is impossible at T=0 due to the absence of spin-flip excitations. The T=0 spectrum of the spin-up carrier is therefore identical to that of a free carrier shifted by the $z$-part of the magnetic interaction. This changes at finite-T where thermal magnons are present in the system. To study this change, we derived the lowest-T correction to the self-energy of the spin-up carrier. This allows us to investigate how the T=0 quasiparticle peak broadens into a continuum at finite-T. Furthermore we find that spectral weight is shifted to energies outside of this continuum, which can be associated with the spin-polaron state. [Preview Abstract] |
Tuesday, March 4, 2014 4:54PM - 5:06PM |
J54.00013: Plaquette ordered phase and quantum spin liquid in the spin-1/2 J1-J2 square Heisenberg model Shoushu Gong, Wei Zhu, Olexei I. Motrunich, Matthew P.A. Fisher, DongNing Sheng We study the spin-1/2 Heisenberg model on the square lattice with first- and second-neighbor antiferromagnetic interactions $J_1$ and $J_2$. We use the density matrix renormalization group with implementing $SU(2)$ spin rotation symmetry and study the model accurately on open cylinders with different boundary conditions. With increasing $J_2$, we find a N\'{e}el phase, a plaquette valence-bond (PVB) phase with a finite spin gap, and a possible spin liquid in a small region of $J_2$ between these two phases. From the finite-size scaling of the magnetic order parameter, we estimate that the N\'{e}el order vanishes at $J_2/J_1\simeq 0.44$. For $0.5 < J_2/J_1 < 0.61$, we find dimer correlations and PVB textures whose decay length grows strongly with increasing system width, consistent with a long-range PVB order in the two-dimensional limit. The dimer-dimer correlation function reveals the s-wave character of the PVB order. For $0.44 < J_2/J_1 < 0.5$, both spin and dimer orders are weak on finite-size systems and appear to scale to zero with increasing system width, which is consistent with a possible SL or a near-critical behavior. We compare and contrast our results with earlier numerical studies. [Preview Abstract] |
Tuesday, March 4, 2014 5:06PM - 5:18PM |
J54.00014: ABSTRACT WITHDRAWN |
Tuesday, March 4, 2014 5:18PM - 5:30PM |
J54.00015: Fragile antiferromagnetic order in the heavy-fermion YbBiPt B.G. Ueland, A. Kreyssig, K. Proke\v{s}, J.W. Lynn, L.W. Harriger, D.K. Pratt, D.K. Singh, T.W. Heitmann, S. Sauerbrei, S.M. Saunders, E.D. Mun, S.L. Bud'ko, R.J. McQueeney, P.C. Canfield, A.I. Goldman YbBiPt is a heavy-fermion compound ($\gamma\approx$ 8 J/molK$^2$) possessing antiferromagnetic order below a N\'{e}el temperature of $T_{\rm{N}}$= 0.4 K, and a proposed quantum critical point at a magnetic field of $H_{\rm{c}}\approx$ 0.4 T. We report results from neutron scattering experiments on single crystals which characterize the antiferromagnetic order. The magnetic scattering is described in terms of two components: a narrow component that appears below $T_{\rm{N}}$ which corresponds to the onset of antiferromagnetic order observed in bulk thermodynamic and transport measurements, and a broad component corresponding to antiferromagnetic correlations extending over $\approx$ 20 $\rm{\AA}$ that persists up to $T^{\rm{*}}\approx$ 0.7 K. These results illustrate the unconventional nature of the magnetism in YbBiPt and may be a consequence of its competing low-energy magnetic interactions and proximity to a quantum critical point.\\ Work at the Ames Laboratory was supported by the Department of Energy, Basic Energy Sciences under Contract No. DE-AC02-07CH11358. [Preview Abstract] |
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