Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session R15: Focus Session: Spin/charge in Frustrated Lattices |
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Sponsoring Units: GMAG DMP Chair: Daniel Arovas, University of California at San Diego Room: 317 |
Wednesday, March 20, 2013 2:30PM - 3:06PM |
R15.00001: Spin-charge interplay on frustrated lattices Invited Speaker: Yukitoshi Motome Frustration has gained increasing interest in the study of itinerant electron systems. There, not only spin but also charge degree of freedom of electrons plays a crucial role in the structure of the energetically degenerate manifold, providing a new frontier of the frustration physics. A particular interest is in Kondo-type spin-charge coupled systems, in which itinerant electrons couple with localized moments on a frustrated lattice. In these systems, localized moments act as internal local magnetic fields for itinerant electrons, which significantly affect the electronic and transport properties. On the other hand, the kinetic motion of electrons induces effective magnetic interactions between localized moments, resulting in exotic magnetic correlations and orders. It is highly nontrivial what kind of electronic and magnetic state is realized as a consequence of the spin-charge interplay. In this contribution, we review our recent theoretical and numerical studies of the Kondo-type models on frustrated lattices. We have investigated several types of models, with Heisenberg and Ising spins for localized moments defined on 2D triangular and kagome lattices and 3D pyrochlore lattice. Complementary theoretical techniques have been adopted, such as perturbation, mean-field approximation, variational calculation, exact diagonalization, and Monte Carlo simulation. We found that these models exhibit emergent electronic and magnetic properties, such as a spontaneous spin scalar chiral order and topological Hall effect, non-Kondo resistivity upturn in spin-ice liquid, partial disorder accompanied by charge disproportionation, emergence of Dirac electrons under particular magnetic ordering, quantum anomalous Hall effect in spin scalar chiral liquid, and spin-Hall effect by spontaneous inversion symmetry breaking. These works have been done in collaboration with Y. Akagi, S. Hayami, H. Ishizuka, and M. Udagawa. For references, visit http://www.motome-lab.t.u-tokyo.ac.jp/index-e.html. [Preview Abstract] |
Wednesday, March 20, 2013 3:06PM - 3:18PM |
R15.00002: Mott Physics at Integer Filling Enforced by Crystalline Symmetries D.P. Arovas, S.A. Parameswaran, Ari M. Turner, Ashvin Vishwanath Insulating states of matter in a crystalline system can be either band insulators or Mott insulators. It is well known that band insulators appear only when the filling (the number of electrons per unit cell and spin projection) is an integer. An insulating phase at fractional filling is a Mott insulator, for which interactions are manifestly required. Here we pose and answer the converse question - at an integer filling is a band insulator always possible? Surprisingly, we find that crystalline symmetries may forbid a band insulator even at certain integer fillings. In these cases, the ground state is either conducting or is a Mott insulator, despite being at integer filling. The lattices on which this occurs have a simple property, they have non-symmorphic space groups. These include lattices with essential glide or screw symmetries, which comprise the majority of three dimensional crystal structures. This is shown to be a consequence of gauge invariance using a flux threading argument, which applies to free and interacting systems alike. For several non-symmorphic lattices we determine the minimum integer filling at which band insulators are possible. This result has several immediate implications for band structures as well as the phases of quantum magnets and bosonic insulat [Preview Abstract] |
Wednesday, March 20, 2013 3:18PM - 3:30PM |
R15.00003: Many-Variable Variational Monte Carlo Study of Triangular Hubbard Model Ryui Kaneko, Satoshi Morita, Masatoshi Imada Motivated by the previous numerical studies on the triangular Hubbard model, we study low-energy states of the model at half filling up to 144 sites by using the many-variable variational Monte Carlo method. We consider the variational wave functions with the fermionic singlet-pairing wave functions, with the Gutzwiller-Jastrow factor, and the quantum-number projection to the total spin singlet. We reproduce the metallic state for the small Coulomb interaction, and the antiferromagnetic insulating state with 120$^{\circ}$ spin structure for the large Coulomb interaction. We discuss the energetic and magnetic properties of the intermediate Coulomb interaction region. [Preview Abstract] |
Wednesday, March 20, 2013 3:30PM - 3:42PM |
R15.00004: Magnetic frustration in itinerant systems: the Kondo polaron problem Leonid Isaev, Cristian Batista, Ilya Vekhter We study the interplay between magnetic frustration and Kondo screening in Kondo lattices by analyzing the $J_1$-$J_2$ antiferromagnetic chain coupled to a conduction band. The system is tuned to the Majumdar-Ghosh point $J_2=J_1/2$ which stabilizes a dimer valence-bond solid at weak Kondo coupling $J_K$. We use an effective low-energy theory to demonstrate that sufficiently large $J_K$ results in a proliferation of ``Kondo polarons'', i.e. Kondo-screened domain-wall excitations of the dimer state, and collapse of the dimer order via a 2nd order quantum phase transition. At the quantum critical point, $J_K=J_K^c$, these polarons become gapless, and we argue that the transition itself belongs to a 2D Ising universality class. For $J_K>J_K^c$ increasing concentration of the polarons leads to a continuous growth of the electron Fermi momentum until all spins are absorbed by the Fermi sea. [Preview Abstract] |
Wednesday, March 20, 2013 3:42PM - 3:54PM |
R15.00005: Itinerant Kagome Ice: an Anomalous Quantum Hall Liquid Armin Rahmani, Gia-Wei Chern, Ivar Martin, Cristian Batista We show that all magnetic-charge-ordered kagome ice configurations, i.e., a highly disordered energetically stable manifold of Ising spins on the kagome lattice, support a quantized anomalous quantum Hall effect when coupled to itinerant electrons. Despite the strong disorder experienced by the electrons, the Hall effect is robust for almost all canting angles of the Ising spins. Due to the absence of magnetic long-range order, this phase of matter is characterized by the coexistence of a (classical) chiral spin liquid and an anomalous integer quantum Hall one. We further demonstrate that the magnetic monopole defects in this ice-like manifold bind a fluctuating electric dipole. [Preview Abstract] |
Wednesday, March 20, 2013 3:54PM - 4:06PM |
R15.00006: Exotic correlated electron phases in the Kagome Hubbard model Ronny Thomale We employ different renormalization group (RG) schemes to investigate the Kagome Hubbard model at low, intermediate, and strong coupling. At weak coupling where our RG calculation is asymptotically exact, we develop a new notion of sublattice interference mechanism to describe the Fermi surface instabilities at van Hove filling. For intermediate coupling, we observe an intricate interplay of the Fermi surface topology, sublattice interference, and range of interactions. In particular, we find a charge and spin bond order phase as well as a d+id Pomeranchuk instability. At strong coupling, we employ our recently developed slave particle RG schemes to investigate the J1-J2 Kagome Heisenberg model. We discuss its quantum phase diagram in the light of experiments and evidence from other approaches. [Preview Abstract] |
Wednesday, March 20, 2013 4:06PM - 4:18PM |
R15.00007: Quantum Fluctuation Effect on a Spin Scalar Chiral Ordering in Frustrated Kondo Lattice System Yutaka Akagi, Masafumi Udagawa, Yukitoshi Motome Recently, noncoplanar spin configurations with spin scalar chirality have drawn considerable attention as an origin of the anomalous Hall effect. As a typical example, a scalar chiral state with noncoplanar four-sublattice magnetic ordering was stabilized through the spin-charge coupling in a Kondo lattice model on a triangular lattice at 1/4 and 3/4 fillings [1,2]. In previous studies however, localized moments are approximated as classical spins. It is interesting to ask how quantum spin fluctuations affect the nontrivial chiral order and electronic state of the system. Here, we examine the effect of quantum fluctuations by the spin-wave approximation with introducing the Holstein-Primakoff transformation to the localized spins. As a result, we find that the four-sublattice order is fragile against quantum fluctuations at 3/4 filling, whereas it remains robust at 1/4 filling. We discuss the magnon excitations in the spin-charge coupled system in details. We also discuss the quantum correction on the thermal Hall effect. [1] Y. Akagi and Y. Motome, J. Phys. Soc. Jpn. {\bf 79}, 083711 (2010). [2] Y. Akagi, M. Udagawa, and Y. Motome, Phys. Rev. Lett. {\bf 108}, 096401 (2012). [Preview Abstract] |
Wednesday, March 20, 2013 4:18PM - 4:30PM |
R15.00008: Featureless and Non-Fractionalized Bose Insulator on the Honeycomb Lattice at 1/2 site-filling Itamar Kimchi, S. A. Parameswaran, Ari Turner, Fa Wang, Ashvin Vishwanath We consider bosons on the Honeycomb lattice at filling one half per site. It is known that free fermions at this filling of the tight binding model cannot form an insulating state while preserving all symmetries, even though there is an integer number of particles per unit cell. We argue, however, that interacting bosons can form an insulating state that preserves all symmetries. We propose a wave function for this state and by a mapping to a classical partition function we compute its properties and demonstrate that the state is insulating, fully symmetric and has no topological order. Our construction suggests that featureless insulators are generically allowed for at a filling of one boson per unit cell on any symmorphic lattice in any dimension. We also discuss related wavefunctions of hard core bosons that model spin 1/2 magnets on this lattice. [Preview Abstract] |
Wednesday, March 20, 2013 4:30PM - 4:42PM |
R15.00009: Demonstration of a D-metal from a chiral spin liquid Victor Chua, Gregory Fiete We report recent results on a study of a 2D disordered but exactly solvable gapless chiral spin-liquid ground state whose fractionalised quasiparticle excitations are Majorana fermions and are classified as being in the D-class of the Altland-Zirnbauer 10-fold classification scheme [Phys. Rev. B 55, 1142 (1997)]. Transport and quasiparticle localisation properties of this Majorana metal in nanowire configurations are studied and contrasted with the previously predicted D-metal phase of Senthil and Fisher [Phys. Rev. B 61, 9690 (2000)]. The role of Z2 vortices play towards transport properties are also discussed. [Preview Abstract] |
Wednesday, March 20, 2013 4:42PM - 4:54PM |
R15.00010: Fluctuation Driven Spirals Near Ferromagnetic Quantum Critical Points in Disordered Electron Systems Steven Thomson, Frank Kruger, Andrew G. Green The magnetic properties of itinerant electron systems represent an area of growing experimental and theoretical interest, particularly the peculiar ordered magnetic phases that can occur at low temperatures. It has previously been shown that the quantum order-by-disorder mechanism predicts a spiral magnetic phase in the vicinity of an itinerant ferromagnetic quantum critical point in three spatial dimensions. Here, we present an analytical model of how both charge and spin disorder affect the formation of this spiral magnetic phase at low temperatures, supplemented by numerical evaluation of the fluctuation corrections to the free energy. We show the effect of disorder on the position of the tricritical point and on the stability of the ordered phases. We further discuss the possibility of a helical spin-glass phase and discuss our findings in the context of recent experiments. [Preview Abstract] |
Wednesday, March 20, 2013 4:54PM - 5:06PM |
R15.00011: The effect of non-magnetic impurities on the motion of a hole in a 2D Ising antiferromagnet Hadi Ebrahimnejad, Mona Berciu A hole in a 2D Ising antiferromagnet was initially believed to be infinitely heavy due to the string of wrongly-oriented spins it creates as it propagates, which trap it near its original location. Trugman showed that, in fact, the hole acquires a finite effective mass due to contributions from so-called {\it Trugman loops} processes, where the hole goes one and a half times around a closed loop and removes the defects it created during the first round, but ends up at a different site. This results in an effective next-nearest-neighbour hoping of the hole which keeps it on the sublattice it was created on. Here we investigate the trapping of such a hole near a single non-magnetic impurity, using a variational calculation of the hole's real-space Green's function. We consider the two cases with the hole and impurity being on the same versus on different sublattices, and contrast the differences between them. [Preview Abstract] |
Wednesday, March 20, 2013 5:06PM - 5:18PM |
R15.00012: Magnetization and Hall effect measurements on the pyrochlore iridate Nd2Ir2O7 Steven Disseler, Sean Giblin, Chetan Dhital, Kevin Lukas, Stephen Wilson, Michael Graf We present magnetization and Hall effect measurements on the pyrochlore iridate Nd$_2$Ir$_2$O$_7$. Previous muon spin rotation measurements have shown that the system undergoes an unusual transition at T$_M$ $\sim$ 110 K into a magnetic phase lacking long-range order, followed by a transition at T$_{LRO}$ $\sim$ 6 K into a state with long-range magnetic order. We observe a small remnant magnetization when cycling through zero magnetic field at temperatures below T$_M$. Below T$_{LRO}$ an additional hysteresis effect appears at a higher field B$_c$ = 2.8 T, together with the appearance of non-monotonic and hysteretic Hall resistance with a maximum at B$_c$. The dependence on field sweep direction suggests a non-trivial transition in the magnetically ordered state similar to that of spin-ice systems. This work was supported in part by National Science Foundation Materials World Network grant DMR-0710525 and by NSF CAREER award DMR-1056625. [Preview Abstract] |
Wednesday, March 20, 2013 5:18PM - 5:30PM |
R15.00013: Non-Kramers spin liquids on the pyrochlore lattice Jeffrey G. Rau, Hae Young Kee At low temperatures the pyrochlore iridates Pr$_2$Ir$_2$O$_7$ shows the puzzling combination of an anomalous Hall effect in the absence of experimentally observed magnetic order. The breaking of time-reversal symmetry indicated by the anomalous Hall effect, but without the usual accompanying magnetic order, points to an exotic state, possibly a chiral spin liquid. Considering the most general symmetry allowed model for the Pr non-Kramers doublets, we use the slave-fermion approach to analyze possible spin liquids at the mean field level. A variety of spin liquids can be generated using the projective symmetry group, with novel properties due to the nature of the non-Kramers doublet states. Applications to Pr$_2$Ir$_2$O$_7$ will be discussed. [Preview Abstract] |
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