Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Z32: Focus Session: Strongly Correlated Oxide Systems |
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Sponsoring Units: GMAG DMP Chair: Jian Liu, University of California, Berkeley Room: 207B |
Friday, March 6, 2015 11:15AM - 11:27AM |
Z32.00001: Turning a strongly correlated Mott insulator into a weakly correlated metal Y. F. Kung, E. A. Nowadnick, C. J. Jia, S. Johnston, B. Moritz, T. P. Devereaux As Mott insulators, such as cuprate superconductors, are doped with charge carriers, strong electron-electron interactions give rise to fascinating novel phenomena. Much of the interesting physics arises in the intermediate doping regime where the system displays metallic behavior strongly renormalized by correlations, in contrast with the naive expectation that the correlations would weaken rapidly away from half filling. To shed light on this issue, we examine the doping evolution of spin and charge excitations in the strongly correlated single-band Hubbard model using determinant quantum Monte Carlo (DQMC). Compared to the behavior predicted by the random phase approximation (RPA), the evolution of the excitations from DQMC shows that significant correlations remain up to relatively high doping levels ($40\%$ hole doping and $15\%$ electron doping), near the maximum of what can be achieved in cuprates. The comparison improves with additional doping (up to $75\%$ hole doping) as the system approaches a metallic state in which the spin and charge excitation spectra are essentially the same. [Preview Abstract] |
Friday, March 6, 2015 11:27AM - 11:39AM |
Z32.00002: The electromagnetic field induced excitation of magnons in spin-orbit coupled Mott insulators Rohit Hegde, Allan MacDonald The spin-only description of the Hubbard model's low-energy states belies an active charge degree of freedom that can in principle couple to external electromagnetic fields. The precise way in which the charge and current densities manifest in the spin sector is constrained when the electronic system possesses $SU(2)$ spin-rotational symmetry, thus limiting the response to electric and magnetic fields. This constraint lifts in the presence of spin-orbit coupling, leading to the emergence of novel responses like that of an electron's spin to an external magnetic field resulting from induced orbital currents in addition to the usual direct Zeeman coupling. Magnons mediate the linear response of electrons to time varying fields of low-frequency $(\hbar \omega \ll U)$. We study the electric and magnetic susceptibilities of single band Hubbard models with spin-dependent hopping on various lattices, and comment on the applicability to magnetically ordered materials like the iridates. [Preview Abstract] |
Friday, March 6, 2015 11:39AM - 11:51AM |
Z32.00003: Sub-gap optical conductivity in the Mott insulator in one-dimensional Hubbard model with randomness Cheng-Ju Lin, Olexei Motrunich We demonstrate a non-zero optical conductivity within the Mott gap in the one-dimensional Hubbard model with randomly distributed onsite potential. The effective Hamiltonian in the spin sector is described by the random exchange coupling spin-$\frac{1}{2}$ antiferromagnetic Heisenberg model, which is in the random-singlet phase. An electric field couples to the electric polarization operator, and we first find its expression in terms of the spin variables in the Mott insulator regime. We then apply the decimation renormalization-group analysis pioneered by Dasgupta, Ma and Fisher to keep track of the polarization operator. Via Kubo formula, we find the optical conductivity to be $\sigma(\omega) \sim \frac{\omega^2}{(\ln \omega)^{4-2\psi}}$ at low frequencies, where $\psi=(1+\sqrt 5)/4$. [Preview Abstract] |
Friday, March 6, 2015 11:51AM - 12:03PM |
Z32.00004: A 1D$_s$$\times$1D$_c$ Heisenberg-Kondo Lattice compound Nb$_{12}$O$_{29}$ Warren Pickett, Kwan-woo Lee Local moments embedded in conducting systems form a rich platform for unusual phases, with phenomena including Kondo, heavy fermion, and non-Fermi liquid physics. Using first principles based methods and the refined crystal structure based on columns of 3$\times$4 planar units of NbO$_6$ octahedra, we determine that mixed valent Nb$_{12}$O$_{29}$ displays tightly bound local moments forming spin chains along one direction criss-crossed by conducting ``nanowires'' in the perpendicular direction. Just how local moments -- very rare for Nb -- emerge and coexist with itinerant electrons, an enigma for decades in this system, is elucidated based on the local structure of the NbO$_6$ octahedra and orbital+spin ordering. The resulting 1D$_s$$\times$1D$_c$ Heisenberg-Kondo lattice ($s$=spin, $c$=charge) picture will be discussed. [Preview Abstract] |
Friday, March 6, 2015 12:03PM - 12:15PM |
Z32.00005: Competition between heavy-fermion and Kondo interaction in isoelectronic A-site ordered perovskites Derek Meyers, S. Middey, J.-G. Cheng, S. Mukherjee, B.A. Gray, Y. Cao, J.-S. Zhou, J.B. Goodenough, Y. Choi, D. Haskel, J.W. Freeland, T. Saha-Dasgupta, J. Chakhalian With current research efforts shifting towards the 4d and 5d transition metal oxides, understanding the evolution of the electronic and magnetic structure as one moves away from 3d materials is of critical importance. Here weX-ray spectroscopy and electronic structure calculations on A-site ordered perovskites with Cu in thesite and the B-sites descending along the 9th group of the periodic table to elucidate the emerging propertiesd-orbitals change from partially filled 3d, 4d, to 5d. The results show that when descending from Co to Ircharge transfers from the cuprate like Zhang-Rice state on Cu to the t2g orbital of the B site. As the Cuorbital occupation approaches the Cu2$+$ limit, a mixed-valence state in CaCu3Rh4O12 and heavy fermionin CaCu3Ir4O12 are obtained. The investigated d-electron compounds are mapped onto the Doniach phaseof the competing RKKY and Kondo interactions developed for f -electron systems. [Preview Abstract] |
Friday, March 6, 2015 12:15PM - 12:51PM |
Z32.00006: Nonlinear phononics for coherent light-control of transition metal oxides Invited Speaker: Antoine Georges |
Friday, March 6, 2015 12:51PM - 1:03PM |
Z32.00007: Stability of the AFM phase in the three-band Hubbard-Holstein model Edwin Huang, Steve Johnston, Yvonne Kung, Brian Moritz, Tom Devereaux The interplay between electron-electron interactions and electron-phonon coupling in cuprates can be explored via the Hubbard-Holstein model. Here, we use determinant quantum Monte Carlo simulations to study the three-band version of the model with electron coupling to c-axis optical oxygen vibrations. The model exhibits competition between an antiferromagnetic phase and a charge density wave phase. The corresponding phase diagram is compared against that from existing single-band Hubbard-Holstein results. Finally we investigate the evolution of the phase diagram due to changes in doping and temperature. [Preview Abstract] |
Friday, March 6, 2015 1:03PM - 1:15PM |
Z32.00008: Geometrical Effects in Orbital Magnetism Yang Gao, Shengyuan Yang, Qian Niu Within the wave-packet semi classical approach, the Bloch electron energy is derived to second order in the magnetic field and classified into gauge-invariant terms with clear physical meaning, yielding a fresh of the complex behavior of orbital magnetism. The Berry curvature and quantum metric of the Bloch states rise to a geometrical magnetic susceptibility, which can be dominant when bands are filled up to a small energy gap.is also an energy polarization term, which can compete with the Peierls-Landau and Pauli magnetism on a Fermi surface. These, and an additional Langevin susceptibility, can be calculated from each single band, leaving the Van Vleck susceptibility the only term truly from interband coupling. [Preview Abstract] |
Friday, March 6, 2015 1:15PM - 1:27PM |
Z32.00009: Effective transient states for nonequilibrium charge density wave systems under ultrafast control pulses Bin Hwang, Jenni Portman, Phillip Duxbury A central challenge for implementing Mott-insulator transition in nonequilibruim ~time-dependent charge density wave systems is finding an effective pulse to achieve the goal. Effective ultra laser pulses have been found for the transient states in nonequilibruim~~time-dependent charge density wave systems based on a promising optimal-control method. ~Intense ultrafast laser pulses allow the preparation of transient states of~~matter exhibiting strong non-equilibrium between electrons and lattice. By~controlling the laser pulse, we are able to change the transient states of these~quantum systems. The optical and structural properties as well as the temporal~evolution of such states provide insight into the mutual dependence of electronic~and atomic structure.~ We approach the problem by showing examples from charge-density-wave~systems. Nonequilibrium techniques can be used to qualitatively describe the common short-time experimental features. Through simulations based~on non-equilibrium Green's function formalism we show how to achieve effective transient states for nonequilibrium systems under ultrafast control pulses. [Preview Abstract] |
Friday, March 6, 2015 1:27PM - 1:39PM |
Z32.00010: Interplay of 3$d$-5$d$ interactions in high-$T_{\mathrm{C}}$ osmium-based double perovskites A.E. Taylor, S. Calder, R. Morrow, P.M. Woodward, J.Q. Yan, B. Winn, M.D. Lumsden, A.D. Christianson In 3d-5d systems the strongly magnetic 3d orbitals and extended 5d orbitals with enhanced spin-orbit coupling lead to a range of high $T_{\mathrm{C}}$ magnetic states and novel behavior not present in systems consisting solely of 3d or 5d ions. The two distinct octahedral sites in double perovskites $A_{2}BB$'O$_6$ allow an ordered 3d-5d structure to form, providing a variety of systems to be investigated. Unravelling the interactions controlling these systems, however, is an open challenge. The highest known $T_{\mathrm{C}}$ in such a system, 725K, is found in insulator Sr$_2$CrOsO$_6$. This questions the theory for high-$T_{\mathrm{C}}$s in systems such as $T_{\mathrm{C}}$=400K Sr$_2$FeReO$_6$ which relies on half-metallic behavior. To unravel the nature of the interactions in 3d-5d systems, we have studied the series of compounds Sr$_2X$OsO$_6$. We have utilized elastic and inelastic neutron scattering to probe the spin states in the systems, and therefore test predictions that the magnetic interactions are controlled by a frustrated AFM Heisenberg model [1]. By studying the series, we are able to relate changes in the spin wave spectrum to dramatic changes in the magnetic order from $T_{\mathrm{N}} = 95$K antiferromagnetism to $T_{\mathrm{C}}=725$K ferrimagnetism.\\[4pt] [1] O. N. Meetei et al, PRL 110, 087203(2013) [Preview Abstract] |
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