Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session F22: Strongly Correlated Electron Theory I |
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Sponsoring Units: DCMP Chair: Steve Hellberg, Naval Research Laboratory Room: 324 |
Tuesday, March 19, 2013 8:00AM - 8:12AM |
F22.00001: Spin flip in spin-orbit split quantum wires in magnetic field Oleg A. Tretiakov, K. S. Tikhonov, V. L. Pokrovsky We study spin-flip processes induced by ac electromagnetic field in quantum wires with strong spin-orbit coupling in the presence of an external magnetic field. The dc magnetic field is essential to enable the electric dipolar excitation of the spin-flip processes. We consider the electron spin-flip resonance in the framework of Luttinger liquid theory. The electron-electron interaction is strong in quantum wires and changes the shape of the spin-flip resonance curve at the spin wave frequency and produces an additional cusp at the frequency of collective charge excitation. We discuss how this spin flip is affected by the dissipation processes and the dispersion curvature. [Preview Abstract] |
Tuesday, March 19, 2013 8:12AM - 8:24AM |
F22.00002: Theoretical study of a one-dimensional chain of alternating spin-1 and electron sites with spin-mediated hopping Wing-Ho Ko, Hong-Chen Jiang, Jeffrey Rau, Leon Balents Motivated by the nickel valance controversy in the perovskite nickelate RNiO$_3$, we consider a one-dimensional chain consisting of alternating spin-1 (``nickel'') and electron (``oxygen'') sites, which in addition to the usual electron hopping and spin-spin interaction between the spin-1 and the electron also contains a spin-1 mediated electron hopping term. Using density-matrix renormalization group (DMRG), we obtain the phase diagram of such model, as well as various correlation functions in each phase. Importantly, for certain range of parameters the model exhibits a quasi-long-range spiral (QS) order. To understand the DMRG results, we construct a mean-field theory based on Schwinger fermion decomposition of the spin-1 spins, from which we argue that the QS phase corresponds to a phase in proximity to the spin Bose metal state proposed by Sheng, Motrunich, and Fisher [Phys. Rev. B, 79, 205112 (2009)]. [Preview Abstract] |
Tuesday, March 19, 2013 8:24AM - 8:36AM |
F22.00003: Magnetic Phase Transition Induced by the Hubbard and Spin-orbit Interactions in a Nanoribbon Geometry Hyeong Jun Lee, Moo Young Choi, Gun Sang Jeon The local repulsive Coulomb interaction between the electrons tends to cause a Mott transition into a magnetically ordered phase. In a honeycomb lattice, particularly, the magnetic order is known to emerge on the edges of graphene, which is attributed to the electron interactions. Meanwhile, the introduction of the spin-orbit interaction gives rise to metallic boundary states, which is a prominent characteristic of the topologically nontrivial materials. We study the effect of the spin-orbit interaction on the edge states as well as the bulk properties of the electron system on the honeycomb lattice. By employing a Hartree-Fock approximation, we compute the local magnetization in the half-filled nanoribbon system at zero temperature. We pay particular attention to the decaying behavior of the local magnetization from the edge toward the center. It is found that the characteristic length associated with the decay is divergent on the phase boundaries. Such slow decay is found to be algebraic in the thermodynamic limit. We discuss the relation between the bulk phase transitions and the decay of magnetization at the edges. [Preview Abstract] |
Tuesday, March 19, 2013 8:36AM - 8:48AM |
F22.00004: Nonequilibrium thermal transport and its relation to linear response Christoph Karrasch, Roni Ilan, Joel Moore We study the real-time dynamics of spin chains driven out of thermal equilibrium by an initial temperature gradient $T_L\neq T_R$. We demonstrate that the nonequilibrium energy current saturates fast to a finite value if the linear-response thermal conductivity is infinite, i.e. if the Drude weight $D$ is nonzero. Our data suggests that a nonintegrable dimerized chain might support such dissipationless transport ($D > 0$). We show that the steady-state value of the current for arbitrary $T_L \neq T_R$ is completely determined by the linear conductance. Inhomogeneous systems exhibiting different bulk parameters as well as Luttinger liquid boundary physics induced by single impurities are discussed shortly. [Preview Abstract] |
Tuesday, March 19, 2013 8:48AM - 9:00AM |
F22.00005: Quantum Monte-Carlo simulation of spin-one antiferromagnets with single-ion anisotropy Yasuyuki Kato, Keola Wierschem, Yusuke Nishida, Cristian Batista, Pinaki Sengupta We study a spin-one Heisenberg model with uniaxial single-ion anisotropy, $D$, and Zeeman coupling to a magnetic field, B, parallel to the symmetry axis. We compute the $(D/J, B/J)$ quantum phase diagram for square and simple cubic lattices by combining analytical and Quantum Monte Carlo approaches, and find a transition between XY-antiferromagnetic and ferronematic phases that spontaneously break the U(1) symmetry of the model. In the language of bosonic gases, this is a transition between a Bose-Einstein condensate (BEC) of single bosons and a BEC of pairs. For the efficient simulation of ferronematic phase, we developed and implemented a new multi-discontinuity algorithm based on the directed-loop algorithm. The ordinary quantum Monte-Carlo methods fall into freezing problems when we apply them to this system at large $D/J$ and finite $B/J\sim 1$. The new method does not suffer from the freezing problems. [Preview Abstract] |
Tuesday, March 19, 2013 9:00AM - 9:12AM |
F22.00006: Majorana dimerised order in magnetic systems Edmund Bennett We consider the analysis of quantum critical points (QCPs) using a Majorana fermion\footnote{W. Mao, P. Coleman, C. Hooley \& D. Langreth; PRL, 91, 20, p. 2072031-2072034; 2003} representation of spin. Majorana fermions are a useful spin representation as they obey Wick`s theorem and automatically provide the correct $S_{\rm tot.}^{2} = 3/4$ for stationary spin-$1/2$ lattice spins. We consider an Ising model in various dimensions in an applied transverse field, a model which exhibits a QCP and has an exact solution in 1D. In the Majorana fermion representation, the interaction vertex may be decoupled into either a ``Majorana dimerisation (MD)'' decoupling or an Ising magnetic decoupling. A mean-field analysis of the MD decoupling (which involves two Majorana fermions of the same flavour on adjacent lattice sites) suggests an ordered phase in the region above the QCP extant in the model, which extends through to high magnetic fields. Full RPA corrections to this mean-field theory are also presented, which give insight into the stability of this ordered phase to quantum perturbations. [Preview Abstract] |
Tuesday, March 19, 2013 9:12AM - 9:24AM |
F22.00007: Spin Orbit Magnetism and Unconventional Superconductivity Yi Zhang, Kevin Bedell We find an exotic spin excitation in a magnetically ordered system with spin orbit magnetism in 2D, where the order parameter has a net spin current and no net magnetization. Starting from a Fermi liquid theory, similar to that for a weak ferromagnet, we show that this excitation emerges from an exotic magnetic Fermi liquid (EMFL) state that is protected by a generalized Pomeranchuck condition. We derive the propagating mode using the Landau kinetic equation, and find that the dispersion of the mode has a q$^{\mathrm{1/2}}$ behavior in leading order in 2D. We find an instability toward superconductivity induced by this exotic mode, and a further analysis based on the forward scattering sum rule strongly suggests that this superconductivity has p-wave pairing symmetry. We perform similar studies in the 3D case, with a slightly different magnetic system and find that the mode leads to a Lifshitz-like instability most likely toward an inhomogeneous magnetic state in one of the phases. [Preview Abstract] |
Tuesday, March 19, 2013 9:24AM - 9:36AM |
F22.00008: Magnetic properties of $d-$atomic systems with unquenched orbital moments Victor Antonov, Liqin Ke, Anton Jesche, Vladimir Antropov Many systems of $d$-atoms with unquenched orbital moments demonstrate unusually large values of atomic magnetic moments, high magnetic anisotropy and small magnetic ordering temperatures. Using electronic structure analysis, we study a mechanism of the formation of strong on-site electronic correlations that lead to a strong orbital polarization, and in turn, generate a highly orbitally polarized hybridization with non-magnetic host atoms. In this case, even a small spin orbital coupling of $3d$-atoms can create a significant effect. We introduce a consistent model of the formation of large orbital moments and magnetic anisotropy both in the metallic and insulating cases, and apply it to several realistic systems. Detailed calculations of magnetic properties, including magneto-optical studies of the Kerr angle rotation, are performed for several nitrometalates of Mn, Fe and Co where a rather large (3-5 degrees) Kerr angle rotation is predicted for the first time. We further discuss the nature of critical temperature in magnetic phase transition in such systems and the opportunity to increase it. [Preview Abstract] |
Tuesday, March 19, 2013 9:36AM - 9:48AM |
F22.00009: ABSTRACT WITHDRAWN |
Tuesday, March 19, 2013 9:48AM - 10:00AM |
F22.00010: Fractional Chern insulator on the triangular lattice Stefanos Kourtis, J\"orn Venderbos, Jeroen van den Brink, Maria Daghofer The opportunity for the formation of fractional quantum-Hall (FQH) states in 3-orbital Hubbard and Kondo lattice models on the triangular lattice without an external magnetic field has been recently demonstrated [1,2]. With this as motivation, an effective interacting spinless-fermion model, which is designed to capture the essential relevant physics, has been extensively studied. Its numerically obtained ground states at several fillings exhibit features which suggest that the former are spontaneously occurring FQH states on a lattice, i.e. fractional Chern insulator (FCI) states. The most unequivocal feature of such states is arguably their fractionally quantized Hall conductivity. This effect, as seen in numerical calculations for finite clusters, will be presented and discussed. Having thus identified FCI states, further signatures of their nature are highlighted, e.g. fractional quasihole statistics. \\[4pt] [1] J.W.F. Venderbos, S. Kourtis, J. van den Brink, and M. Daghofer, Phys. Rev. Lett. 108, 126405.\\[0pt] [2] S. Kourtis, J.W.F. Venderbos, and M. Daghofer, arXiv:1208.3481. [Preview Abstract] |
Tuesday, March 19, 2013 10:00AM - 10:12AM |
F22.00011: ABSTRACT WITHDRAWN |
Tuesday, March 19, 2013 10:12AM - 10:24AM |
F22.00012: Magnetic phase transitions in the chiral helimagnet Cr$_{1/3}$NbS$_2$ Nirmal Ghimire, Michael McGuire, Brian Sales, Lisa Debeer-Schmitt, Huibo Cao, Bryan Chakoumakos, Adam Aczel, Balazs Sipos, Siwei Tang, Yuen Yiu, Jiaqiang Yan, Stephen Nagler, David Mandrus Cr$_{1/3}$NbS$_{2}$ is a long period chiral helimagnet crystallizing in the noncentrosymmetric, hexagonal~space group P6$_3$22. Helimagnetic ordering along the c-axis is attributed to the competition between the symmetric exchange interaction, favoring parallel moments, and the anti-symmetric Dzyaloshinsky-Moriya interaction, favoring perpendicular moments. Recently, the ground state helical ordering is found to be destabilized by a magnetic field applied perpendicular to c, forming a chiral soliton lattice phase, and, above a critical field, a commensurate ferromagnetic state. Thermal and transport properties also show interesting behaviors in the vicinity of the transition temperature. Here we present magnetic, thermal and transport properties of Cr$_{1/3}$NbS$_{2}$ measured on single crystals, along with recent results from neutron scattering experiments conducted on the four circle single crystal diffractometer and general purpose SANS at the High Flux Isotope Reactor, ORNL. [Preview Abstract] |
Tuesday, March 19, 2013 10:24AM - 10:36AM |
F22.00013: ABSTRACT WITHDRAWN |
Tuesday, March 19, 2013 10:36AM - 10:48AM |
F22.00014: Possible non-coplanar spin structure and large Hall effect in Na$_{x}$CoO$_{2}$ J.W. Kim, E.D. Mun, R.D. McDonald, V. Zapf, J.D. Thompson, L. Balicas, I. Marting, D. Argyriou We present magnetotransport studies of Na$_{x}$CoO$_{2}$ ($x=$0.46) and its relation to possible non-coplanar spin texture. This compound exhibits a unique insulating state below temperature ($T)$ of 53 K related to charge-order which is different from other composition with metallic behavior. It also has frustrated local spin texture owing to its hexagonal structure. Previous works report a very large Hall signal for composition $x=$0.5 (M. Foo \textit{et al.}, Phys. Rev. Lett. 92, 247001 (2004)) at low magnetic field ($B)$ and prior high-field studies (L. Balicas \textit{et al.}, Phys. Rev. Lett. 94, 236402 (2005)) have found the existence of a small Fermi surface in the system and a two-fold angular magnetoresistance. Using pulse and hybrid magnets at NHMFL, we mapped out a detailed $T$-$B$ phase diagram up to 65 T which is strong enough to suppress the charge-order. When $B$ is applied along the $c$-axis, the charge-ordered state is suppressed at $B$ $\sim$ 41 T with highly non-monotonic shape in $\rho_{xy}$. We found that this Hall signal reaches a maximum around $T \sim$ 30 K and $B \sim$ 27 T and on further cooling the absolute change of $\rho_{xy}$ decreases significantly. Interestingly, we found no significant changes in field-dependent magnetization which suggests that this behavior does not come from the ordinary anomalous Hall effect. We discuss the origin of this unique Hall signal by existence of a non-coplanar spin structure that may exist in this compound (I. Martin, C. D. Batista, Phys. Rev. Lett. 101, 156402 (2008)). [Preview Abstract] |
Tuesday, March 19, 2013 10:48AM - 11:00AM |
F22.00015: Combined Transport, Magnetization and Neutron Studies of Structural and Magnetic Behavior in Ca3Ir4Sn13 Zhensong Ren, Mani Pokharel, Tom Hogan, Athena Sefat, Clarina de la Cruz, Huibo Cao, Bo Li, Cyril Opeil, Stephen Wilson Ca3Ir4Sn13, synthesized by Espinosa and his coworkers almost 30 years ago, was recently suggested to possess an unconventional superconducting ground state in the presence of a background of strong spin fluctuations. This signature for this claim stemmed from charge transport and magnetization anomalies near 45K, yet, later a detailed single crystal XRD investigation revealed that the anomaly is produced by a second order superlattice transition and that this transition can be tuned to zero temperature---suggesting a structural quantum critical point. Here in an attempt to characterize this phase further, we present a picture of the evolution of the structural and magnetic behavior in Ca3Ir4(Sn1-xSbx)13 via a combined transport, magnetization and neutron scattering study. [Preview Abstract] |
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