Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session F29: Strongly Correlated Systems, Including Quantum Fluids and Solids III |
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Sponsoring Units: DCMP Chair: Valentin Crépel, Flatiron Institute (CCQ) Room: Room 221 |
Tuesday, March 7, 2023 8:00AM - 8:12AM |
F29.00001: Phonon dispersion and self energy evolution in S-doped quasi-1D Ta2NiSe5 Zhibo Kang, Ayman H Said, Ahmet Alatas, Weichen Tang, Jacob Ruff, Xiang Chen, Robert J Birgeneau, Steven G Louie, Yao Wang, Yu He Ta2NiSe5 is considered as an excitonic insulator candidate where Coulomb interaction between electrons and holes leads to an ostensible exciton condensation. However, phonons are considered to play an important role [1]. Using inelastic x-ray scattering, an anomalous shortening of the phonon lifetime near Brillouin zone center is observed, indicating the instability of the phonons. Combining the electronic density of state extracted from angle-resolved photoemission spectra with the imaginary part of phonon self energy, the electron-phonon coupling strength is estimated to fall in a strong coupling regime. We also report structural hardening with S-doping indicated in the low-energy phonon spectra. In this process, rapidly dwindling electron phonon coupling is seen to accompany the precipitous drop of the structural transition temperature. |
Tuesday, March 7, 2023 8:12AM - 8:24AM |
F29.00002: Active learning approach to quantum embedding simulations of strongly correlated matter Marius S Frank, Denis Artiukhin, Tsung-Han Lee, Gargee Bhattacharyya, Cole M Miles, Yong-Xin Yao, Kipton M Barros, Ove Christiansen, Nicola Lanata We present a new method for solving efficiently quantum embedding (QE) simulations of strongly correlated matter, based on probabilistic machine learning (ML). Our strategy consists in training a machine for bypassing the most computationally expensive components of QE algorithms, which is the calculation of the ground-state density matrix of the so-called “embedding Hamiltonian” (EH). Rather than pre-training our machine, as in previous work [1], our method actively trains the ML algorithm on the fly. This allows us to reduce substantially the number of necessary training data, by computing only data corresponding to physically relevant embeddings. We benchmark our method on the recently developed ghost Gutzwiller approximation (g-GA) [2-4], showing that our ML algorithm efficiently exploits previously acquired data for reducing the computational cost of new computations, providing us with very reliable and accurate predictions. |
Tuesday, March 7, 2023 8:24AM - 8:36AM |
F29.00003: Anomalous magneto-transport at low-density in a quasi-1d conductor Giacomo Morpurgo, Christophe Berthod, Thierry Giamarchi Among the various 2D magnetic semiconductors that have been recently discovered and investigated, CrSBr has shown unexpected transport properties under field-effect doping. In particular, the absence of Hall effect and a large anisotropy of the conductivity indicate quasi-1D behavior and possibly strong disorder [1]. |
Tuesday, March 7, 2023 8:36AM - 8:48AM |
F29.00004: Large Rashba spin-orbit-coupling for metallic oxide films Hikaru Okuma, Yumiko Katayama, Kazunori Ueno Oxide interface with large Rashba spin-orbit-coupling (SOC) is hopeful material for spintronic applications owing to the remarkable high spin to charge currents conversion, which promises a substantial reduction of power consumption in spintronic devices. Therefore, there has been a lot of effort spent finding oxide semiconductor heterostructures with large Rashba SOC, such as SrTiO3 and KTaO3 based interfaces. Furthermore, there have been several reports on Rashba SOC for metallic oxide ultrathin films, such as SrIrO3 and La2/3Sr1/3MnO3, although Rashba SOC was even smaller for these materials than for semiconductor heterostructures. Here, we discover metallic ultrathin oxides SrNbO3 with Rashba SOC, which is largest in the values reported for other metallic oxides and is comparable to the value of LaAlO3/SrTiO3. Ultrathin films are advantageous over interfaces because information about the electronic structure and local density of states can be directly obtained by using angle-resolved photoemission and scanning tunneling spectroscopy, respectively. It is expected that Rashba SOC of metallic oxides would be further enhanced by breaking the spatial inversion symmetry such as fabricating heterostructures and applying vertical electric field. |
Tuesday, March 7, 2023 8:48AM - 9:00AM |
F29.00005: Resolving emergent structure states in 2D transition metal dichalcogenids by total x-ray scattering Valeri Petkov Materials exhibiting reduced dimensionality and strongly interacting charge and lattice degrees of freedom can appear in various crystal structure states that harbor fascinating quantum phenomena. The complexity of the states, however, often makes it challenging to understand the nature of the phenomena, impeding their exploration for practical applications. Typical examples are the emergence of charge density waves (CDWs), Mott insulator and Wyel semimetal phases in transition metal dichalcogenides. We will show that the problem can be solved by total x-ray scattering experiments and 3D structure modeling. Examples will include results of our recent studies on the genesis of CDWs in 2H-TaSe2 [1], nature of metal-to-insulator transition in 1T-TaS2 [2], and local structure memory effects in the Wyel semimetal MoTe2 [3]. |
Tuesday, March 7, 2023 9:00AM - 9:12AM |
F29.00006: Real-space Imaging of Periodic Nano-Textures in Epitaxial Ca2RuO4 Thin Films via Inversion of Diffraction Data Ziming Shao, Noah Schnitzer, Jacob Ruf, Oleg Gorobtsov, Berit H Goodge, Hari P Nair, Jacob Ruff, Darrell G Schlom, Kyle M Shen, Lena F Kourkoutis, Andrej Singer Coherent X-ray diffraction imaging (CXDI) is a lensless imaging technique by directly inverting the oversampled diffraction pattern into real-space images. Because of its non-destructive nature and ability to image sub-picometer atomic-lattice displacements with nanometer resolutions, CXDI has been applied to visualize biological cells, strain in nanocrystals, and recently operando changes in energy materials. Yet, it is limited to objects spatially confined in all three dimensions. Here, we will demonstrate the extension of CXDI to mapping periodic lattice distortions in an extended object. By combining the conventional CXDI iterative computation and an unsupervised machine learning clustering algorithm, we imaged the periodic nanotextures in epitaxially strained Ca2RuO4 thin films grown on LaAlO3 substrate via the inversion of its diffraction pattern. The result reveals the formation of striped periodic nanodomains during the Ca2RuO4 structural L-Pbca to S-Pbca phase transition upon cooling, which is confirmed by cryogenic scanning transmission electron microscopy. Our model-independent imaging approach promises to facilitate the understanding of low-dimensional quantum materials where periodic nano-textures are ubiquitous. |
Tuesday, March 7, 2023 9:12AM - 9:24AM |
F29.00007: Real Space and Momentum Space Cluster Methods for Strongly Disordered Systems Patrick S Wong, Ka-Ming Tam, Juana Moreno, Liviu Chioncel, Yang Wang, Tom Berlijn, Hanna Terletska The Anderson localization (AL) of electrons in disordered media continues to receive increasing interest due to the strong impact of the disorder on quantum materials. However, despite extensive studies, numerical simulations of the influence of strong disorder remains challenging. We have recently developed two kinds of cluster embedding methods to study strong disorder effects. This includes the real space cluster extension of the typical medium theory (cluster-TMT) [1] and the momentum-space cluster DCA (TM-DCA) to study Anderson localization [2]. Applying the developed methods to the Anderson tight-binding model with different types of disorder distributions, we demonstrate that both cluster methods successfully capture the localization phenomena in all disorder regimes as cluster size increases. However, we have found different accuracy and cluster size convergence of developed embedding frameworks. From a general perspective, our developed methodology offers the potential to study Anderson localization in real materials within quantum embedding theories. |
Tuesday, March 7, 2023 9:24AM - 9:36AM |
F29.00008: Free energy and specific heat near a quantum critical point of a metal Andrey V Chubukov In this talk I analyze in detail free energy and specific heat of a metal at the verge of a collective instability towards particle-hole order (Ising-nematic order, antiferromagnetism, etc), and of an electron-phonon system in a situation, when the effective Debye frequency of an optical phonon vanishes due to renormalization from fermions. In both cases, the low-energy model consists of fermions with Luttinger Fermi surface, coupled by Yukawa-type interaction to a massless boson, which either represents a critical fluctuation of a particle-hole order parameter, bilinear in fermions, or is an Einstein phonon with vanishing dressed Debye frequency. The key motivation for this study is to understand the interplay between contributions to the specific heat from fermions, which display non-Fermi liquid behavior near a quantum-criγtical point with and Σ(ω) ~ ωγ and massless collective bosons. I discuss three cases: Ising-nematic critical point (γ =1/3), antiferromagnetic quantum critical point (an effective γ =0+) and electron-phonon problem (γ =2). I argue that in all three cases the specific heat is positive at the critical point. For Ising-nematic and antiferromagnetic cases, fermionic and bosonic contributions are comparable in magnitude. Each contains contributions from the upper theory cutoff, but this dependence cancels out in the total specific heat. For electron-phonon problem, the electronic contribution is negative and scales as 1/T, but the bosonic one is positive, temperature-independent, and is larger than the fermionic one in the T-range where Eliasberg theory is valid. I compare the results with recent analytical and numerical studies of the specific heat, particularly the one, which argued that the negative electronic contribution to the specific heat indicates that the normal state is unstable. I will argue instead that it is stable. I also discuss how the expressions for the specific heat vary upon deviation from a quantum-critical point. |
Tuesday, March 7, 2023 9:36AM - 9:48AM |
F29.00009: Nature of the anomalous 4/13 fractional quantum Hall effect in graphene Ajit Coimbatore Balram Extensive fractional quantum Hall effect (FQHE) has been observed in graphene-based materials. Some of the observed fractions are anomalous in that FQHE has not been established at these fractions in conventional GaAs systems. One such fraction is 4/13, where incompressibility has recently been reported in graphene [Kumar et al., Nat. Comm. 9, 2776 (2018)]. We propose a partonic wave function at 4/13 and show it to be a viable candidate to describe the Coulomb ground state. Using the effective edge theory, we make predictions for experimentally measurable properties of the state. |
Tuesday, March 7, 2023 9:48AM - 10:00AM |
F29.00010: Fluctuating the magnetic slave-boson mean-field: analysis of charge modulations in an antiferromagnetic background Jannis Seufert, David Riegler, Michael Klett, Ronny Thomale The richness of the cuprate phase diagram and the intricate relations between the different types of order call for computationally cheap and stable methods that also allow for the inspection of symmetry-broken ground states. Aiming at the single-orbital Hubbard Hamiltonian as a minimal cuprate model, we present a fluctuation analysis around magnetic saddle points in the spin-rotation invariant Kotliar-Ruckenstein slave-boson approach. We derive the effective second-order field theory on top of an antiferromagnetic parent state. Spin and charge correlation functions are analyzed for the stability of the phase diagram and the magnon spectra are discussed. Further, we find different signatures of charge order at intermediate to high interaction strengths. |
Tuesday, March 7, 2023 10:00AM - 10:12AM |
F29.00011: Zoology of charge-orders in the electron-doped cuprates David Riegler, Jannis Seufert, Michael Klett, Ronny Thomale Since the discovery of unconventional superconductivity in 1986, the high-Tc cuprates have attracted many scientists to study these strongly correlated materials. Besides the superconducting dome, the cuprates feature a plethora of other phases involving spin- and charge-order that have gotten into focus in order to decipher the superconducting pairing mechanism. Based on the one-band Hubbard model, we analyze combined spin- and charge order in the electron-doped cuprates by means of Gaussian fluctuations around an antiferromagnetic slave-boson mean-field parent state. We detect nesting-induced charge-order in good agreement with experimental RXS data in the electron-doped cuprate Nd2-xCexCuO4, and identify another type of charge-order for which experimental evidence is yet lacking. |
Tuesday, March 7, 2023 10:12AM - 10:24AM |
F29.00012: Development of ab initio method for exciton condensation and its application to TiSe2 Hsiao-Yi Chen, Takuya Nomoto, Ryotaro Arita Exciton condensation indicating the spontaneous formation of electron-hole pair can cause the phase transition from a semimetal to an excitonic insulator by gap opening at the Fermi surface. While the idea of this excitonic insulator has been proposed for decades, current theoretical approaches can only provide qualitative descriptions, and a quantitative predicting tool is still missing. To shed insight on this problem, we developed an ab initio method based on the finite-temperature density functional theory and many-body perturbation theory to compute the exciton condensation critical behavior. Applying our approach to the monolayer TiSe2, we find a lattice distortion accompanied by the formation of the excitonic gap via electron-phonon coupling without phonon softening, proving that the exciton condensation is the origin of the charge-density-wave state observed in this compound. |
Tuesday, March 7, 2023 10:24AM - 10:36AM |
F29.00013: Probing symmetry breaking of the fractionally filled Landau level with a scanning tunneling microscope Gelareh Farahi, Xiaomeng Liu, Cheng-Li Chiu, Zlatko Papic, Kenji Watanabe, Takashi Taniguchi, Michael P Zaletel, Ali Yazdani In monolayer graphene, the spin and valley degeneracy lead to a fourfold isospin degeneracy of the macroscopically degenerate Landau levels. The partially filled landau level in particular hosts a myriad of exotic phases such as the fractional quantum hall states[1], Wigner crystals and skyrmion solids[2]. Understanding the spin and valley symmetries of the electronic wavefunctions is thus crucial in characterizing the ground states and excitations. Exploiting the valley-sublattice equivalence in the zeroth Landau level (zLL), we previously employed gate-tunable scanning tunneling microscopy and spectroscopy (STM-STS) to quantify the valley symmetry of the ground state at integer fillings of the zLL [3], whereas the spectral features at fractional fillings were more susceptible to the tip-sample work function mismatch. In this work, we show that through careful characterization of the spectral features we can reproducibly make STM tips that have minimal effect on the electronic states at partial fillings, enabling us to underpin the valley order of the fractionally filled zLL in a pristine monolayer graphene device. We resolve the spectral features attributed to Haldane pseudopotentials[4], showing remarkable agreement with the exact diagonalization calculations. Moreover, we detect a magnetic field dependent isospin transition near nu = -2/3 marked by a sharp decrease in sublattice polarization of the ground state. We then probe the energy dependence of the valley polarization in fractional excitations beyond the theoretically accessible regime which exhibits excellent particle-hole symmetry. Our findings establish STS as a robust technique to probe the intricate charge ordering of highly interacting electron systems. |
Tuesday, March 7, 2023 10:36AM - 10:48AM |
F29.00014: An oxygen vacancy memristor ruled by electron correlations Vincent Humbert Resistive switching effects offer new opportunities in the field of conventional memories as well as in the booming area of neuromorphic computing. The tunneling electroresistance, usually observed in ferroelectric tunnel junctions, allows for large and fast resistance variations triggered by voltage pulses. We have recently demonstrated that similar tunnel resistance switching effects can be produced in judiciously chosen metal/oxide junctions by an electrochemical (redox) mechanism (1). |
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