Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session A07: Charge OrderFocus
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Hide Abstracts |
Sponsoring Units: DCMP Chair: Adriana Moreo, University of Tennessee Room: BCEC 109B |
Monday, March 4, 2019 8:00AM - 8:12AM |
A07.00001: Honeycomb Lattice-Type CDW associated with Interlayer Cu Ions Ordering in 1T-CuxTiSe2 Shunsuke Kitou, Shintaro Kobayashi, Tatsuya Kaneko, Naoyuki Katayama, Seiji Yunoki, Toshikazu Nakamura, Hiroshi Sawa The electronic state in 1T-TiSe2, which has attracted attention as an excitonic insulator, can be changed by electronic doping through Cu+ intercalation. Indeed, the superconductivity was reported in CuxTiSe2 on 0.04 ≤ x ≤ 0.10 [1]. We succeeded in synthesis of single crystal samples of CuxTiSe2 (x = 0 ~ 0.35) and performed physical property measurements, synchrotron x-ray diffraction experiments, and density-functional-theory calculations. It was found that x = 1/4 and 1/3 were magical numbers in this system and disorder-order transitions were caused by the interaction among Cu atoms. Furthermore, in x = 1/3, a hybrid-type phase transition caused by the commensurate connection between Cu-ordering and a new honeycomb lattice-type charge-density-wave in TiSe2 layers was realized. |
Monday, March 4, 2019 8:12AM - 8:24AM |
A07.00002: Charge disproportionation, mixed valence, and Janus effect in multiorbital systems: A tale of two insulators Aldo Isidori, Maja Berovic, Laura Fanfarillo, Luca De Medici, Michele Fabrizio, Massimo Capone Multiorbital Hubbard models host strongly correlated 'Hund's metals' even for interactions much stronger than the bandwidth. We characterize this interaction-resilient metal as a mixed-valence state. In particular it can be pictured as a bridge between two strongly correlated insulators: a high-spin Mott insulator and a charge-disproportionated insulator which is stabilized by a very large Hund's coupling. This picture is confirmed comparing models with negative and positive Hund's coupling for different fillings. Our results provide a characterization of the Hund's metal state and connect its presence with charge disproportionation, which has indeed been observed in chromates and proposed to play a role in iron-based superconductors. |
Monday, March 4, 2019 8:24AM - 8:36AM |
A07.00003: Unraveling spin and charge dynamics in two-leg spin ladders using resonant inelastic x-ray scattering Umesh Kumar, Alberto Nocera, Elbio R Dagotto, Steven Johnston Resonant inelastic x-ray scattering (RIXS) has become an important tool to study the spin and charge excitations in materials. We investigate the RIXS spectra of undoped and doped antiferromagnetic spin-ladder cuprate in both the non-spin conserving (NSC) and spin-conserving (SC) channels at the Cu L3 -edge. The spectra are rich and host many exotic excitations. In the undoped NSC-channel, we identify one-triplon, triplet two-triplon excitations in the strong rung coupling limit and confined spinons in the weak rung coupling limit. In the doped NSC-channel, we identify a new dispersive quasiparticle-like spectral features composed of bound 'charge and spin-1/2' in strong rung coupling limit in addition to the excitations branches already present in the undoped case. The NSC-channel can be well described by S(q, ω). On the other hand, SC-channel is unique to RIXS and reveals new features. In the undoped SC channel, we identify singlet two-triplon for the strong rung coupling and confined spinons for the weak rung coupling. In the doped SC-channel, RIXS probes the charge excitations instead of spin-excitations, and we identify gapless and gapped charge excitations in the spectra. |
Monday, March 4, 2019 8:36AM - 8:48AM |
A07.00004: Stripes and Nematicity in a Hole-Doped Three-Orbital Spin-Fermion Model for Superconducting Cuprates Adriana Moreo Numerical studies of a spin-fermion model that captures the charge-transfer properties |
Monday, March 4, 2019 8:48AM - 9:00AM |
A07.00005: New long-lived metastable state mediated by mode-selective electron-phonon coupling in 1T-TaSe2 Wenjing You, Xun Shi, Yingchao Zhang, Zhensheng Tao, Peter Oppeneer, Xianxin Wu, Ronny Thomale, Kai Rossnagel, Michael Bauer, Henry C Kapteyn, Margaret Mary Murnane Quantum materials represent one of the most promising frontiers in the quest for faster, lightweight, energy efficient technologies. However, their inherent complexity and rich phase landscape make them challenging to understand or manipulate in useful ways. Here we present a new ultrafast electron calorimetry technique that can systematically uncover new phases of quantum matter. Using time- and angle-resolved photoemission spectroscopy, we measure the dynamic electron temperature, band structure and heat capacity. We then show that this is a very sensitive probe of phase changes in materials, because electrons react very quickly, and moreover generally are the smallest component of the total heat capacity. This allows us to uncover a new long-lived metastable state in the charge density wave material 1T-TaSe2, that is distinct from all of the known equilibrium phases: it is characterized by a significantly reduced effective heat capacity that is only 30% of the normal value, due to selective electron-phonon coupling to a subset of phonon modes. As a result, significantly less energy is required to melt the charge order and transform the state of the material than under thermal equilibrium conditions. |
Monday, March 4, 2019 9:00AM - 9:12AM |
A07.00006: Observation of M2 phase coming from the charge density wave for the insulator-to-metal transition in VO2. Jin-Cheol Cho, Tetiana Slusar, Hyun-Tak Kim In strained VO2/AlN/Si films, insulator-to-metal transition (IMT) upshifted for TIMT ≈ 350 K higher than the bulk value (TIMT ≈ 340 K) [1]. Due to the strain, the intermediate monoclinic phase, known as the M2 phase, was clearly seen through the Raman phonon mode near 650 cm-1 [2]. The M2 phase has two substructures of both the charge density wave (CDW) responsible for the Peierls insulator and zig-zag chain for the Mott insulator [3]. However, the mechanism of the upshifted TIMT does not yet revealed. |
Monday, March 4, 2019 9:12AM - 9:24AM |
A07.00007: Ultrafast recovery of charge density wave order controlled in a pump-pump-probe free electron laser experiment Oleg Gorobtsov, Nelson Hua, Sheena Patel, Anatoly Shabalin, Diling Zhu, Eric Fullerton, Oleg Shpyrko, Andrej Singer Understanding and controlling charge density wave (CDW) order in metals can lead to better command of the materials’ superconducting properties and give dynamical access to hidden electronic states. In previous experiments at a free electron laser (FEL) LCLS, we demonstrated our capability to enhance charge density wave in thin chromium films by photoexcitation and measure its amplitude with an x-ray probe pulse with a precision of tens of femtoseconds. We now use two optical pump pulses, with x-ray FEL pulse providing feedback, to fine-tune the state of the material. Precise control over the state and high temporal resolution open the way to measurements of out-of-equilibrium states of the materials. We discover that recovery time of the charge density wave order decreases with the amplitude of the excited "frozen" acoustic phonon. We observe the effect of incoherent addition between two photoexcitations. |
Monday, March 4, 2019 9:24AM - 9:36AM |
A07.00008: Ultrafast probing of collective mode of the charge order in La1.875Ba0.125CuO4 Emre Ergecen, Mehmet B Yilmaz, Batyr Ilyas, Genda Gu, Nuh Gedik The phase diagram of cuprate superconductors exhibits a plethora of intertwined orders, such as pseudogap, charge order and pair density wave. In particular, many cuprate families display a charge order near the 1/8 doping that coexist with superconductivity. Recent scattering studies have demonstrated that suppressing the superconductivity can increase the strength of coexisting charge order. However, little is known about the collective modes of the charge order and its interaction with other phases. Here, we perform time resolved transient reflectivity measurements on La1.875Ba0.125CuO4 (LBCO) and La1.885Ba0.115CuO4 (LBCO). We find a short-lived oscillatory signal, which turns on near the charge ordering temperature consistent with the amplitude mode of the charge order. We will comment on the implications of these measurements on the coupling between two dimensional superconductivity and stripe phase in LBCO. |
Monday, March 4, 2019 9:36AM - 9:48AM |
A07.00009: The role of non-local correlations in the valence band spectra in NiO Byungkyun Kang, Sangkook Choi, Patrick Semon, Andrey Kutepov, Van Dam Hubertus, Gabriel Kotliar As an archetypical strongly-correlated material, late-transition metal NiO has been attracted for number of decades. The interesting electronic properties of charge transfer insulator and low energy Zhang-Rice bound state are attributed to Ni 3d and O 2p hybridization along with strong Coulomb interactions of Ni 3d. However, the rich physics may still raise unclear physical properties in NiO. One example is the second peak from the Fermi level in X-ray photoemission spectra which is enhanced below Neel temperature. By Using recently developed LQSGW + DMFT along with charge self-consistent LDA+DMFT, we will discuss the role of non-local correlation in the formation of the second peak and their temperature dependence. |
Monday, March 4, 2019 9:48AM - 10:00AM |
A07.00010: Magnetotransport in H || c of La1.875Ba0.125CuO4 near the charge order (CO) transition Lily Stanley, Paul G. Baity, Dragana Popovic, John Tranquada, Genda Gu The nature of the dynamics of charge-ordered states in underdoped cuprates has been of great recent interest. Our work on La2-xBaxCuO4 with x=0.125 (LBCO) in zero magnetic field (H) reveals the presence of dynamic behavior within the charge-ordered state in the form of avalanches, similar to that in La1.48Nd0.4Sr0.12CuO4 (LNSCO). In LNSCO, avalanches were also observed to be asymmetrically driven by H around the concurrent CO and structural transition with an additional onset of negative magnetoresistance (MR), which was attributed to the emergence of CO [1]. In La1.7Eu0.2Sr0.12CuO4 (LESCO) negative MR, albeit with no avalanches, was observed at the onset of CO but not at the higher temperatures around the structural transition [1]. The presence of avalanches and overlap of the CO and structural transitions in LBCO present the opportunity to clarify the role of the LNSCO Nd3+ moments and the origin of the negative MR. Therefore, we report the H = 0 findings and the study of H || c magnetoresistance of LBCO near the CO transition. |
Monday, March 4, 2019 10:00AM - 10:12AM |
A07.00011: Precision measurement of charge-order formation by coherent Resonant X-ray Scattering Li Yue, Jiarui Li, Claudio Mazzoli, Riccardo Comin, Yuan Li We report experimental research on the spontaneous formation of charge order and its relationship with disorder pinning effects. By studying a prototypical charge-density-wave material, ZrTe3, with high-precision resonant elastic X-ray scattering (REXS), we observe a clear temperature evolution of the ordering wave vector, along with a drastic increase in the correlation length, upon the development of the long-range charge order below T ≈ 63 K. These results are attributed to band-structure changes near the Fermi level due to the opening of the charge-ordering gap. By further utilizing a coherent X-ray beam, we are able to reveal unprecedented details in the mesoscopic dynamics of the charge order by X-ray photon correlation spectroscopy (XPCS), the results of which can be most naturally explained by the combined effects of thermal activation and disorder pinning. Our results provide empirical insights for understanding charge-order phenomena in correlated-electron systems such as the high-Tc cuprates. |
Monday, March 4, 2019 10:12AM - 10:24AM |
A07.00012: ABSTRACT WITHDRAWN
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Monday, March 4, 2019 10:24AM - 10:36AM |
A07.00013: Femtosecond electron imaging of a transformation between different symmetry broken ground states of 2D charge density wave near a nonthermal critical point Faran Zhou, Joseph Williams, Christos Malliakas, Mercouri Kanatzidis, Chong-yu Ruan We study the atomic scale dynamics of a CDW phase transition from a stripe phase into a new topological phase in rare-earth tritelluride compound. Such a new state is a hidden ground state not allowed thermodynamically, but is driven to form after an interaction quench by an intense infrared laser pulse. With femtosecond electron-based scattering, we capture the entire course of this transformation and show an emergent self-organization that defines a nonthermal critical point substantially different from a thermal critical point. The dynamical stabilization after the quench is achieved through the inherent underpinning symmetry that allows the development of the long-range coherence simultaneously for different broken symmetry states at far from equilibrium. |
Monday, March 4, 2019 10:36AM - 10:48AM |
A07.00014: Charge Density Wave Order in the Half-Filled Three Dimensional Holstein Model Benjamin Cohen-Stead, Chuang Chen, Zi Yang Meng, Richard Theodore Scalettar The Holstein Model (HM) is a tight-binding Hamiltonian describing electrons coupled to local phonon degrees of freedom. The electron phonon interaction gives rise to charge density wave (CDW) order at half-filling and superconducting (SC) order away from half-filling. The HM has been a recent focus for Determinant Quantum Monte Carlo (DQMC) simulation studies. However, the cubic scaling with system size, and long autocorrelation times, have restricted simulations to one and two dimensional systems. Here we demonstrate that the recent development of Self-Learning Monte Carlo (SLMC)[1,2] has made it possible to significantly reduce autocorrelation times, thereby allowing for simulation studies of the Holstein model on a fully three-dimensional cubic lattice at half-filling. SLMC is able to control autocorrelation times by learning an effective model that is used to propose more effective monte carlo moves, while still satisfying detailed-balance. SLMC allows us to not only access larger system sizes, but also slower phonon modes where the phonon frequency ω is less than the inter-site hopping parameter t. |
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