Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session H45: Charge Order |
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Sponsoring Units: DCMP Chair: Eduardo Da Silva Neto, Univ of California - Davis Room: LACC 505 |
Tuesday, March 6, 2018 2:30PM - 2:42PM |
H45.00001: STEM Studies of Charge and Orbital Ordering in La_{0.6}Sr_{2.4}Mn_{2}O_{7} Manganite Qiang Zheng, Nathaniel Schreiber, Hong Zheng, Jiaqiang Yan, Michael McGuire, John Mitchell, Miaofang Chi, Brian Sales Charge and orbital ordering typically occurs in perovskite-related oxides, and has been demonstrated to induce various interesting physical phenomena. La_{2−2x}Sr_{1+2x}Mn_{2}O_{7} represents one of the most interesting manganites where its charge and orbital ordering can be tuned by varying x. Specifically, no long-range magnetic order of any type was found using neutron powder diffraction for 0.66 ≤ x ≤ 0.72 in polycrystalline samples. In this study, we perform systematic scanning transmission electron microscopy (STEM) studies of charge and orbital ordering and local nano-scale phase competition in a La_{0.6}Sr_{2.4}Mn_{2}O_{7} (x = 0.7) single crystal. By combining lattice strain quantification and valence state mapping at atomic scale for this crystal, we show that charge and orbital ordering at short-ranges can be probed using real-space imaging and spectroscopy. Charge ordering stripes of Mn^{3+} and Mn^{4+} are directly visualized by electron-energy loss spectroscopy and found to be spatially correlated with periodic picometer-level shear deformations via orbital ordering in Mn^{3+} stripes. |
Tuesday, March 6, 2018 2:42PM - 2:54PM |
H45.00002: Atomic-Scale Surface Strain and Charge Density Wave States in TbTe_{3} Michael Boyer, Ling Fu, Aaron Kraft, Bishnu Sharma, Manoj Singh, Philip Walmsley, Ian Fisher In the bulk of TbTe_{3}, a unidirectional charge density wave (CDW) state is established along the c-crystal axis below ~336 K. Surprisingly, in our recent near-room temperature scanning tunneling microscopy (STM) measurements [1], we detect spatially-separated perpendicular unidirectional CDWs established along both the a- and c-crystal axes with no directional preference for the in-plane crystal axes (a or c). Our measurements indicate that surface strain may play a role in driving the observed CDW orders. Here we present our work on quantifying atomic-scale strain at the surface of TbTe_{3}. We then discuss connections between surface strain and the locally observed CDW order. |
Tuesday, March 6, 2018 2:54PM - 3:06PM |
H45.00003: Charge order in a frustrated two-dimensional atom lattice at a semiconductor surface Stephan Rachel, Florian Adler, Manuel Laubach, Andrzej Fleszar, Julian Maklar, Joerg Schaefer, Ralph Claessen Adatom systems deposited on Si(111) substrates have attracted much attention recently. Surface coverage of a 1/3 monolayer leads to √3×√3 reconstruction, resulting in a remarkable realization of an isotropic triangular lattice Hubbard model. |
Tuesday, March 6, 2018 3:06PM - 3:18PM |
H45.00004: Nonequilibrium Transport in La_{1.875}Ba_{0.125}CuO_{4} (LBCO) Near the Onset of the Charge Order (CO) and Structural Transition Lily Stanley, Paul Baity, Dragana Popovic, John Tranquada, Genda Gu The dynamics of charge-ordered states in underdoped cuprates is one of the key issues in the field. Recent work on a striped La_{1.48}Nd_{0.4}Sr_{0.12}CuO_{4} (LNSCO) revealed several nonequilibrium effects as evidence for collective dynamics and strong pinning of domains in the CO phase [1]. Since the CO in LNSCO is stabilized by the structural LTO-LTT transition, we report a similar study on LBCO to further investigate the interplay of charge and structure. In LBCO, the LTT domain pattern is known to be determined by the pattern of the LTO twin boundaries formed at the HTT-LTO transition. Hence, we use protocols where the sample is warmed up into the LTO phase (above ~54 K) or into the HTT phase (above ~235 K) before measuring the c-axis resistance in the region of the CO and LTO-LTT transition. As in LNSCO, we find evidence of metastable states and collective dynamics in the form of avalanches. We discuss the protocol dependence of such behavior, and further report the effects of a magnetic field. [1] P. G. Baity et al., arXiv:1609.02591v2 [cond-mat] (2016). |
Tuesday, March 6, 2018 3:18PM - 3:30PM |
H45.00005: Emergent Charge Order Near the Doping-Induced Mott-Insulating Quantum Phase Transition in Sr_{3}Ru_{2}O_{7} Justin Leshen, Mariam Kavai, Ioannis Giannakis, Yoshio Kaneko, Yoshinori Tokura, Shantanu Mukherjee, Wei-Cheng Lee, Pegor Aynajian Search for novel electronically ordered states of matter emerging near quantum phase transitions (QPT) is an intriguing frontier of condensed matter physics. Here we investigate the double layered Sr_{3}(Ru_{1-x}Mn_{x})_{2}O_{7} and its doping-induced quantum phase transition (QPT) from a metal to an antiferromagnetic (AFM) Mott insulator. Using spectroscopic imaging with the scanning tunneling microscope (STM), we visualize the evolution of the electronic states in real- and momentum-space. We find a pseudogap phase that develops with doping to form a weak Mott insulating (Δ ~ 100meV) state. Near the QPT, we discover a spatial electronic reorganization into a commensurate checkerboard charge order. These findings share close resemblance to the well-established universal charge order in the pseudogap phase of cuprates. Our experiments and complementary tight-binding model calculations provide insights into the origin and ubiquity of the incipient charge order that emanates from doped Mott insulators. |
Tuesday, March 6, 2018 3:30PM - 3:42PM |
H45.00006: ^{13}C NMR Study on charge ordered insulator, θ-(BEDT-TTF)_{2}TlCo(SCN)_{4} Kazuya Miyagawa, Takuro Sato, Humuro Hasahimoto, Hatsumi Mori, Kazushi Kanoda, Akira Ueda The BEDT-TTF salts with θ-type molecular arrangement, θ-(BEDT-TTF)_{2}X, which have a triangular lattice show a wide verity of electronic states according to X. X=RbZn(SCN)_{4} salt and title compound undergo a transition from a conducting state to a charge ordered (CO) insulating state[1] due to large inter-site Coulomb interaction. On the other hand, X=CsZn(SCN)_{4} salt does not show CO transition but has inhomogeneous charge distribution. It is believed that this difference comes from competition between various charge patterns in a triangular lattice. We measure ^{13}C NMR of X=TlCo(SCN)_{4} salt. Below 235 K, the spectra and 1/T_{1} give microscopic evidence of appearance of CO state. The 1/T_{1} below transition temperature gives the ratio of charge rich site and poor site is at least 10. This is larger than X=RbZn(SCN)_{4} salt. Moreover, we observed that slow dynamics above transition temperature like as X=RbZn(SCN)_{4} and CsZn(SCN)_{4} by comparing line width and 1/T_{2}. While the increase of 1/T_{2}, different from two salts, it does not take a peak since CO transition occurs during slowing down of charge fluctuations. |
Tuesday, March 6, 2018 3:42PM - 3:54PM |
H45.00007: Charge frustration in the mixed-valent iron oxide β-NaFe_{2}O_{3} with a double triangular layer consisting of Fe_{4} tetrahedra Shintaro Kobayashi, Hiroaki Ueda, Chishiro Michioka, Kazuyoshi Yoshimura, Hiroshi Sawa We have investigated physical properties of β-NaFe_{2}O_{3} with mixed-valent Fe^{2.5+} ions. This compound has double triangular layers (W layers) of Fe ions similar to LuFe_{2}O_{4}, and however, the coordination number of Fe ions of these two compounds is different; the coordination number is six and five for β-NaFe_{2}O_{3} and LuFe_{2}O_{4}, respectively. The W layers consist of the two-dimensional network of almost regular Fe_{4} tetrahedra. Thus, charge frustration is expected to be large in β-NaFe_{2}O_{3}. However, there are no reports on physical properties of β-NaFe_{2}O_{3} to our knowledge_{,} although there are many reports on the synthesis of this compound. |
Tuesday, March 6, 2018 3:54PM - 4:06PM |
H45.00008: Charge order and non-local correlations in the doped two-dimensional extended Hubbard model. Hanna Terletska, Tianran Chen, Joseph Paki, Emanuel Gull Various strongly correlated systems reveal exotic phases of matter away from half-filling. To explore how doping, non-local inter-site interactions, and strong correlations affect the charge order phase in two dimensions, we perform a thorough study of the extended Hubbard model at finite temperature and doping at local interactions strength below the Mott limit. We perform our analysis using the cluster dynamical mean-field theory on a cluster of size 8. Our results show that doping leads to the melting of the charge order phase at relatively small doping (15-20%). Also, we find that the interplay of the local and non-local interactions leads to a variety of phase transitions in this model. In particular, we find that under doping, a half-filled charge order insulator with vanishing compressibility first melts into a charge ordered metal. We explore the energetics and the non-local correlations change in and outside of the charge order phase as function of doping. |
Tuesday, March 6, 2018 4:06PM - 4:18PM |
H45.00009: Effect of phonon dispersion on the competition between pairing and charge order Wei-ting Chiu, Natanael De Carvalho Costa, Thomas Blommel, George Batrouni, Richard Scalettar The Holstein Model (HM) describes the interaction between fermions and a collection of local |
Tuesday, March 6, 2018 4:18PM - 4:30PM |
H45.00010: Current Induced Metal-Insulator Transition in 1D Charge Density Wave Giuliano Chiriaco, Andrew Millis Nakamura, Maeno and co-workers (Scientific Reports, 2013) reported that a modest electric field (∼40 V/cm) suppresses the metal insulator transition in Ca_{2-x}Sr_{x}RuO_{4}, so that the metallic phase persists down to temperatures well below the equilibrium transition temperature. They further argued that this effect is an intrinsic nonequilibrium correlation effect, due neither to Joule heating nor filamentary conduction. We investigate theoretically this issue by analysing the case of a 1D charge density wave model, using a Hartree-Fock/Boltzmann equation formalism which includes intraband and interband (up to quadratic order) relaxation processes. We find that even modest fields for which Zener tunnelling is negligible can have a strong effect on the distribution function, increasing the number of carriers in the conduction band and thereby, reducing the gap and ultimately driving a transition from insulating to metal phase. A phase diagram is derived and analysed. |
Tuesday, March 6, 2018 4:30PM - 4:42PM |
H45.00011: Light induced nonequilibrium dynamics in a charge ordering system -Role of inhomogeneity- Hitoshi Seo, Yasuhiro Tanaka, Sumio Ishihara We theoretically study early-stage nonequilibrium dynamics of a charge ordering (CO) system as a prototypical example of strongly correlated electrons showing photo-induced phase transition (PIPT). Our aim is to reconcile two different pictures of cooperative PIPT, i.e., spatially uniform excitation by laser light irradiation vs inhomogeneous growth of domains. To investigate this problem, we consider the one-dimensional interacting spinless fermion model as a basic model for CO owing to correlation effect, and apply Hartree-Fock real-time simulation by the time-dependent Schrödinger equation. We compare two cases as the initial state before light irradiation: a uniform CO state and a one-kink state imbedded in the bulk CO. When a short laser pulse is applied to the system, in the former case, we find that the reduction of CO amplitude shows a resonant behavior for frequencies near the half of the CO gap. In clear contrast, the latter one-kink state undergoes a significantly distinct process: As time evolves, an inhomogeneous region grows because of kink generations and motions, and in some cases, results in PIPT with CO melting and destruction. |
Tuesday, March 6, 2018 4:42PM - 4:54PM |
H45.00012: Distinguishing XY from Ising electron nematics Sayan Basak, Erica Carlson Electron nematic phases, which break the rotational symmetry of the host crystal while retaining liquidity, have been observed in a variety of systems, including strontium ruthenates, iron superconductors, cuprate superconductors, the (111) surface of bismuth, and high fractional Landau levels. Depending upon interactions with the lattice, the nematic may either be in the XY or the Ising universality class. We propose new experimental tests that can reveal the universality class, based on hysteresis: Upon cycling an applied orienting field, a 2D XY electron nematic will show no hysteresis, whereas an Ising nematic will show robust hysteresis. We discuss this in the context of ultraclean GaAs-AlGaAs heterojunctions, in which high Landau levels near half-integral filling break rotational symmetry. This leads to a temperature dependence of the transport anisotropy, which is better described by an Ising model than an XY model, indicating that this electron nematic is in the Ising universality class. The hysteresis test we propose can be used to test this hypothesis.[1] |
Tuesday, March 6, 2018 4:54PM - 5:06PM |
H45.00013: Observation of glass phase in three-dimensional Coulomb glass model Amin Barzegar, Wenlong Wang, Juan Carlos Andresen, Helmut Katzgraber Despite experimental results and mean-field theoretical calculations that predict the existence of a stable glass phase for electrons in a random potential, a thermodynamic Coulomb glass phase has remained elusive in numerical studies to date. Here we demonstrate that a Coulomb glass phase might exist at extremely low temperatures when studying the four-replica finite-size spin-glass correlation length using population annealing Monte Carlo. Our simulations also find a charge ordering phase for small enough random potentials. |
Tuesday, March 6, 2018 5:06PM - 5:18PM |
H45.00014: Elimination of Large Scale Electron Phase Separation in Full Chemically Ordered Manganites Tian Miao, Hanxuan Lin, Hao Liu, Qian Shi, Yang Yu, Peng Cai, Yinyan Zhu, Lifeng Yin, Jian Shen Chemical doping in strong correlated oxide system leads to novel properties such as superconductivity，multiferroics , colossal magnetoresistance. Theoretically, cation disorder, inevitably introduced by chemical doping, is believed to play an important role in some cases, such as the large length-scale electronic phase separation (EPS) in manganites. However, the real influence of the chemical doping induced disorder on physical properties of correlated oxides remains unclear experimentally. In this work, using layer-by-layer superlattice growth technique, we fabricate full chemically ordered manganites. The physical properties of the chemically ordered manganites are dramatically different from the their conventional, randomly doped counterpart. The electronic phase separation phenomena has also been observed to disappear in the ordered systems. |
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