Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session Y19: 2D Quantum MagnetismFocus
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Sponsoring Units: GMAG DMP Chair: John Singleton, Los Alamos Natl Lab Room: LACC 308A |
Friday, March 9, 2018 11:15AM - 11:27AM |
Y19.00001: Haldane phase and magnetic ordering in the spin-$1$ anisotropic bilinear-biquadratic system on the square lattice Shoushu Gong, Wenjun Hu, Hsin-Hua Lai, Andriy Nevidomskyy, Qimiao Si, Kun Yang To investigate possible symmetry protected topological Haldane phase in two dimensions, we study a spin-$1$ bilinear-biquadratic model on the square lattice with spacing anisotropic interactions by combining analytic analysis and density matrix renormalization group. In the absence of interchain couplings, the system reduces to the decoupled Haldane chains when the biquadratic coupling $K_x$ ($K_x > 0$) is smaller than the bilinear coupling $J_x$ ($J_x > 0$). By switching on the interchain couplings $J_y, K_y$ with fixed coupling ratio $K_x/J_x = K_y/J_y$, we find that for $K_x/J_x \lesssim 0.5$, the Haldane phase of the decoupled chains extends to finite interchain couplings with $J_y$ up to about $0.4$, |
Friday, March 9, 2018 11:27AM - 11:39AM |
Y19.00002: Charge-density-wave, non-collinear magnetic structure and magneto-transport properties of the single crystalline EuAg$_4$As$_2$ Ni Ni, Huibo Cao, Chaowei Hu, Xin Gui, Weiwei Xie, Bing Shen Layered materials with exotic ground states have attracted a lot of research interest due to the possible competition or interplay among these orders. In this talk, we will discuss the growth and characterization of a layered silver pnictide material, EuAg$_4$As$_2$. Two-phase transitions, one is around 120 K and the other is around 15 K, are revealed by the resistivity, susceptibility, and heat capacity measurements. Single crystal X-ray diffraction data suggests the high-temperature phase transition is of an incommensurate charge density wave type while the single crystal neutron diffraction measurements show the low-temperature phase transition is from a paramagnetic to a non-collinear antiferromagnetic phase transition. We will also discuss the effect of this non-collinear antiferromagnetism on the magnetotransport in EuAg$_4$As$_2$. |
Friday, March 9, 2018 11:39AM - 11:51AM |
Y19.00003: Phase Transition of SU(N)×U(1) Theory with m Fundamental Bosons Ankur Das The phase transition in the case of Ginzburg-Landau theory is well studied in both the ε-exapansion and also in the large boson number expansion. The natural question that comes next is what happens if there is also a non-abelian SU(N) gauge field is present. This question is also important as it has been found that in SU(m) anti-ferromagnets on a square lattice with spins that sit at A and B sub lattices are in the representation described by the Young tableau with N rows in one sub-lattice and m − N in other. Then under the Schwinger boson representation and in the Large-m limit the theory can be described as a SU(N)×U(1) theory with m species of fundamental bosons. The phases for N=1 are known. Here, we study the problem for general N, calculate the beta function, and find a stable fixed point in the zero mass plane for m>mcrit, indicating a second order phase transition. The critical exponents are calculated in the 4-d expansion and in the large-m expansion. |
Friday, March 9, 2018 11:51AM - 12:03PM |
Y19.00004: Nonsymmorphic symmetry, zone-boundary Dirac line node and magnetic instability in Sr2IrO4 Jin-Hong Park, Seung Hun Lee, Hosub Jin, Bohm-Jung Yang Peierls distortion is a robust instability occurred in a partially-filled one-dimensional (1D) band with its susceptibility diverging, which is attributed to Fermi surface topology in 1D. Searching for two dimensional analog of Peierls instability is elusive since the topology of Fermi surface in higher than 1D experiences the deficit of nesting, in turn, and exhibits to weak susceptibility. In this talk, we present that such a difficulty can be overcome by non-symmorphic symmetry-protected Dirac line node (DLN) along Brillouin zone boundary in Sr2IrO4 whose space group is of this kind. Depending on the rotation angle of IrO6 octahedron, the susceptibility grows fast and diverges at a critical angle where DLN becomes flat. The infinitesimal Hubbard U interaction is enough to develop the magnetism in Iridates 214 near the critical rotation angle. This provides a unified viewpoint on magnetic instability in Sr2IrO4, originating from the cooperation between non-symmorphic crystal symmetry and electron correlation. |
Friday, March 9, 2018 12:03PM - 12:15PM |
Y19.00005: Effective interactions between local hopping modulations on the square lattices Huu Do, Kevin Beach
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Friday, March 9, 2018 12:15PM - 12:27PM |
Y19.00006: Coulomb interaction effects in the spin susceptibility of an organic Dirac fermion system Genki Matsuno, Akito Kobayashi In an organic conductor α-(BEDT-TTF)2I3, a two-dimensional correlated Dirac electron system is realized under hydrostatic pressure. Thanks to the sublattice-selective NMR measurement and theoretical analysis, it has been revealed that the magnetization is affected not only by on-site Coulomb interaction but also by inter-site Coulomb interaction. The random phase approximation (RPA) analysis based on the Hubbard model clarified that the on-site Coulomb repulsion causes the ferri magnetic polarization. On the other hand, the renormalization group approach based on 2x2 Wyel Hamiltonian showed that the inter-site long-range Coulomb interaction induces the fermi velocity renormalization. However, we noticed that these two correlation effects are competitive since the ferri magnetism is stabilized by inter-band thermal excitations, which are supsressed by the velocity renormalization. |
Friday, March 9, 2018 12:27PM - 12:39PM |
Y19.00007: Magnon decay in charge-ordered RbFe2+Fe3+F6 Manila Songvilay, Chris Stock, Efrain Rodriguez, Mark Green, Chris Stockdale, Helen Walker, Jose Rodriguez RbFe2+Fe3+F6 is a charge-ordered antiferromagnet, belonging to the family of mixed-metal fluorides AM2+M3+F6. This compound has a structure related to the well-known pyrochlores A2B2X6X'. RbFe2+Fe3+F6 displays a charge ordering on the iron sites, originating from their two different valences. Although it is usually presented as a pyrochlore system, its structure can also be described as interpenetrating chains of corner-shared Fe3+F6 and Fe2+F6 octahedra, running along the b and a axes respectively. |
Friday, March 9, 2018 12:39PM - 12:51PM |
Y19.00008: Magnetic Phase Diagram of Two-dimensional Square Metal-Organic Frameworks under Electrostatic Gating Yun-Peng Wang, Xiangguo Li, Shuanglong Liu, Hai-Ping Cheng Magnetism and magnetic phase transition induced by electrostatic gating of two-dimensional square metal-organic framework compounds was theoretically investigated. Results show that electrostatic gating can trigger phase transitions between homogeneous ferromagnetic and various spin-textured antiferromagnetic states. Hybridizations between transition-metal d-orbitals and conjugated π-orbitals in organic framework is evidenced by the electronic structure and Wannier function analysis. For compounds containing transition metal ions other than Mn, electronic structure around the Fermi energy is only slightly spin-splitted due to weak d-π hybridization and the magnetic interaction is of the Ruderman-Kittel-Kasuya-Yosida type. Mn-containing compounds exhibit strong d-π hybridization that drives spin-minority bands partially occupied, and the double-exchange model was adopted to understand the phase diagram in terms of carrier density. |
Friday, March 9, 2018 12:51PM - 1:03PM |
Y19.00009: Temperature dependence of an SU(4) to SU(2) Kondo crossover in a half-filling carbon nanotube quantum dot Yoshimichi Teratani, Akira Oguri In a carbon nanotube quantum dot, an SU(4) Kondo effect occurs owing to four-fold degenerate levels. An external magnetic field lifts the degeneracy and induces a new type of crossover from the SU(4) to SU(2) Kondo state which is observed at half-filling [1]. This crossover can be explained if two energy levels among the four still remain unlifted as a result of a matching of the spin and orbital Zeeman splittings [2]. We calculate the conductance G at finite temperatures T using the numerical renormalization group. The results of conductance nicely agree with the experimental results in a wide range of the gate voltages. Furthermore, at half-filling, the profile of G vs T relation varies from the SU(4) to the typical SU(2) form as magnetic field B increases. The Kondo temperature, at which G shows the log T dependence, also decreases as B increases. We also discuss how the spectral function evolves during the crossover. |
Friday, March 9, 2018 1:03PM - 1:15PM |
Y19.00010: Controlling Spin Interactions of Magnetic Molecules on Au(111) by Studied with Scanning Tunneling Spectroscopy Min Hui Chang, Yun Hee Chang, Na Young Kim, Howon Kim, Un Seung Jeon, Yong-Hyun Kim, Se-Jong Kahng Controlling spin interactions of magnetic molecules at the single molecule level is essential for spintronic molecular device applications. The exchange coupling between magnetic-molecules and metallic substrates gives rise to the Kondo resonances at the Fermi level. Controlling the Kondo resonances has been demonstrated with small molecule bindings, but not with adsorption of metal atoms to magnetic-molecules. Here, we demonstrate that Kondo resonances of Co-porphyrin on Au(111) can be controlled by adsorption of metal atoms, and be sensed using scanning tunneling microscopy and spectroscopy (STM and STS). Bare Co-porphyrin showed a clear zero-bias peak, a signature of Kondo resonances in STS, whereas Co-porphyrin adsorbed metal atoms showed modified zero-bias resonances, with reduced full width half maximum or Kondo temperature. Our density functional theory calculation results explain it with spatial redistribution of unpaired spins in d-orbitals of Co-porphyrin by the adsorption of metal atoms. Our study shows that the spin-state of metallo-porphyrin can be modified in multiple ways by the adsorption of additional metal atoms, and be probed through Kondo resonances with STS. |
Friday, March 9, 2018 1:15PM - 1:27PM |
Y19.00011: Ultrafast magnetism within time dependent density functional theory Jacopo Simoni, Maria Stamenova, Stefano Sanvito The search for solutions to increase the speed of manipulation of magnetic bits is a very important issue in modern information technology. |
Friday, March 9, 2018 1:27PM - 1:39PM |
Y19.00012: Electric-magneto-optical Kerr effect in a hybrid organic-inorganic perovskite Feng-Ren Fan, Hua Wu, Dmitrii Nabok, Shunbo Hu, Wei Ren, Claudia Draxl, Alessandro Stroppa Hybrid organic-inorganic compounds attract a lot of interest for their flexible structures and multifunctional properties. For example, they can have coexisting magnetism and ferroelectricity whose possible coupling gives rise to magnetoelectricity. Here using first principles computations, we show that, in a perovskite metal-organic framework (MOF), the magnetic and electric orders are further coupled to optical excitations, leading to an Electric tuning of the Magneto-optical Kerr effect (EMOKE). Moreover, the Kerr angle can be switched by reversal of both ferroelectric and magnetic polarization only. The interplay between the Kerr angle and the organic-inorganic components of MOFs offers surprising unprecedented tools for engineering MOKE in complex compounds. Note that this work may be relevant to acentric magnetic systems in general, e.g., multiferroics. |
Friday, March 9, 2018 1:39PM - 1:51PM |
Y19.00013: Axion-Higgs interplay and anomalous magnetic phase diagram in TlCuCl3 Gaurav Gupta, Kapildeb Dolui, Abhinav Mishra, D Sama, Tanmoy Das TlCuCl3 has been widely studied due to its peculiar magnetic phase diagram, observation of magnetic Higgs mode, BE condensation of the magnons etc. We study its peculiar magnetic phase, starting from the DFT band structure. (1) We discover that there exists a Su-Schrieffer-Heeger (SSH) like Cu-chain along the z-direction. We construct a 3D version of the SSH model. (2) As an AFM order sets in, we show that the system naturally transforms into a topological axion insulator. (3) Finally, we present a Chern-Simon-Ginzburg-Landau theory for the competition and coexistence of axion, Higgs and Goldstone modes, and present an anomalous magnetic phase diagram described in terms of topological axion angle. |
Friday, March 9, 2018 1:51PM - 2:03PM |
Y19.00014: Thermal driven topology in chiral magnets Wentao Hou, Jie-Xiang Yu, Morgan Daly, Jiadong Zang Chiral magnets give rise to the anti-symmetric Dzyaloshinskii-Moriya (DM) interaction, which induces topological nontrivial textures such as magnetic skyrmions. The topology is characterized by integer values of the topological charge. In our work[1], we performed the Monte-Carlo calculation of a two-dimensional model of the chiral magnet. A surprising upturn of the topological charge is identified at high fields and high temperatures. This upturn is closely related to thermal fluctuations at the atomic scale, and is explained by a simple physical picture based on triangulation of the lattice. This emergent topology is also explained well by a field-theoretic analysis using CP1 formalism. It is predicted that this phenomenon can be observed experimentally through the thermal Hall effect. [1] W. T. Hou, J. X. Yu, M. Daly and J. Zang, Phy. Rev. B 96, 140403 (2017). |
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