Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session L37: Correlated Electrons in Cuprates and TitanatesFocus Live
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Sponsoring Units: GMAG DMP DCOMP DCMP Chair: Stephan Rosenkranz, Argonne National Laboratory |
Wednesday, March 17, 2021 8:00AM - 8:12AM Live |
L37.00001: Phonon Hall Viscosity and Berry Phase in Magnetic Insulators Mengxing Ye, Leon Balents Phonon Hall viscosity may generate the Berry phase of phonons, and be observed experimentally in acoustic Faraday effect and thermal Hall transport. We present a systematic procedure to obtain the phonon Hall viscosity induced by phonon-magnon interaction in magnetic insulators under an external magnetic field. We first obtain a general symmetry criterion that leads to non-zero phonon Berry phase, and clarify the interplay between lattice symmetry, spin-orbit-coupling, external magnetic field and magnetic ordering. Next, by constructing the general symmetry allowed effective action that describes the spin dynamics and spin-lattice coupling, and then integrating out the spin fluctuations, the phonon Hall viscosity terms in the phonon effective action that break time-reversal symmetry can be obtained. The analysis of the square lattice antiferromagnet for a cuprate Mott insulator, Sr2CuO2Cl2, is presented explicitly, and the procedure described here can be readily generalized to other magnetic insulators. |
Wednesday, March 17, 2021 8:12AM - 8:24AM Live |
L37.00002: Cavity Probes and Control of Antiferromagnetic Fluctuations in a Mott Insulator Jonathan Curtis, Andrey Grankin, Nicholas Poniatowski, Prineha Narang, Victor Galitski, Eugene Demler We present a mechanism for coupling the electromagnetic field of a THz cavity to the antiferromagnetic order in a simplified model of an undoped cuprate Mott insulator. In addition to the direct magnetic-dipole coupling between spins and the magnetic component of the near-field radiation, we also consider a more elaborate magnetoelectric coupling which couples various spin-exchange processes to the electric field. We show how these terms can lead to the formation of Neel magnon-polariton resonances, as well as allow for the optical parametric driving of spin-waves. We identify clear experimental signatures to look for in a proposed setup. Finally, we conclude by speculating about the fate of charge carriers doped into the system in the presence of our coupling scheme. |
Wednesday, March 17, 2021 8:24AM - 8:36AM Live |
L37.00003: Ultrafast magnetic dynamics in insulating YBa2Cu3O6.1 revealed by time resolved two-magnon Raman scattering Dmitry Reznik, Jhih-An Yang, Nick Pellatz, Thomas Wang, Rahul Nandkishore Measurement and control of magnetic order and correlations in real time is a rapidly developing scientific area relevant for magnetic memory and spintronics. In these experi- ments an ultrashort laser pulse (pump) is first absorbed by excitations carrying electric dipole moment. These then give their energy to the magnetic subsystem monitored by a time- resolved probe. A lot of progress has been made in investigations of ferromagnets but antiferromagnets are more challenging. Here, we introduce time-resolved two-magnon Raman scattering as a real time probe of magnetic correlations especially well-suited for antiferromagnets. Its application to the antiferromagnetic charge transfer insulator YBa2Cu3O6.1 revealed rapid demagnetization within 90 fs of photoexcitation. The relaxation back to thermal equilibrium is characterized by much slower timescales. We interpret these results in terms of slow relaxation of the charge sector and rapid equilibration of the magnetic sector to a prethermal state characterized by parameters that change slowly as the charge sector relaxes. |
Wednesday, March 17, 2021 8:36AM - 9:12AM Live |
L37.00004: Unveiling the Normal State of Cuprates with Charge and Spin Orders Invited Speaker: Dragana Popovic In underdoped cuprates, the relationship between the pseudogap, superconductivity, and charge and spin ordering has been of key interest. Since high magnetic fields are commonly used to suppress superconductivity and probe the nature of this unusual normal state, one of the central issues is to understand the interplay of superconductivity with charge and spin orders in the limit of high magnetic fields. Time permitting, this talk will describe the main results of the comprehensive series of experiments [1-4] performed using several complementary electrical transport techniques on underdoped La-214 cuprates in which charge and spin orders appear in the form of stripes near x~1/8 doping. Our results a) establish a robust phase diagram for superconducting vortices in underdoped cuprates, b) provide much-needed transport signatures of the elusive pair-density wave state in stripe-ordered cuprates in the regime where superconductivity is destroyed by quantum phase fluctuations, and c) reveal striking, novel properties of the normal state of cuprates. The broader relevance of our findings to cuprate physics will be also discussed. |
Wednesday, March 17, 2021 9:12AM - 9:24AM Live |
L37.00005: Super Van Hove singularities in cuprate high-Tc superconductors Robert Markiewicz, Bahadur Singh, Christopher Lane, Arun Kumar Bansil Two-dimensional (2D) Van Hove singularities (VHSs) associated with the saddle point extrema of the energy dispersions usually yield logarithmic divergences in the density of states (DOS). However, recent studies find that the VHSs associated with higher-order saddle-points yield faster-than-logarithmic divergences which can amplify electron correlation effects and create exotic states such as the supermetals in 2D materials.[1] Here we discuss the existence of high-order VHSs in the cuprate high-Tc superconductors and show how these VHSs are the result of the effective electronic dimensionality of the material being smaller than the dimensionality of the crystal lattice.[2] The presence of high-order VHSs is found to be correlated with the occurrence of higher Tc’s in the cuprates. We also comment on the role of higher-order VHSs in generating complex intertwined magnetic, charge-order, and superconducting phases. |
Wednesday, March 17, 2021 9:24AM - 9:36AM Live |
L37.00006: An ab initio Study of Oxygen Vacancies in Ba2CuO4-δ Matthew Matzelle, Christopher Lane, Ruihua He, Robert Markiewicz, Arun Bansil Oxygen vacancies have been shown to play a key role in the emergence of superconductivity in the recently discovered superconductor Ba2CuO4-δ. Interestingly, the amount of holes contributed by these vacancies is found to lie outside the typical superconducting dome of other cuprates. There is also considerable debate as to whether the vacancies reside in the CuO2 plane or at the apical sites and what spatial configuration they occupy. Using state-of-the-art ab initio techniques, we systematically examine the energy landscape and electronic structure of oxygen vacancies in Ba2CuO4-δ. A number of different configurations involving single and multiple vacancies in apical and planar positions are considered. Planar vacancies are found to yield lower energies and display exotic band structures. Finally, we will briefly connect our results to recent experiments. |
Wednesday, March 17, 2021 9:36AM - 9:48AM Live |
L37.00007: A large modulation of electron-phonon coupling and an emergent superconducting dome in doped strong ferroelectrics Jiaji Ma, Ruihan Yang, Hanghui Chen We use first-principles methods to study doped strong ferroelectrics (taking BaTiO3 as a prototype). Contrary to Anderson/Blount’s weakly coupled electron mechanism for “ferroelectric-like metals”, we find a strong coupling between itinerant electrons and soft polar phonons in doped BaTiO3. As a consequence, across a polar-to-centrosymmetric phase transition in doped BaTiO3, the total electron-phonon coupling is increased to about 0.6 around the critical concentration, which is sufficient to induce phonon-mediated superconductivity of about 2 K. Lowering the crystal symmetry of doped BaTiO3 by imposing epitaxial strain can further increase the superconducting temperature via a sizable coupling between itinerant electrons and acoustic phonons. Our work demonstrates a viable approach to modulating electron-phonon coupling and inducing phonon-mediated superconductivity in doped strong ferroelectrics and potentially in polar metals. Our results also show that the weakly coupled electron mechanism for “ferroelectric-like metals” is not necessarily present in doped strong ferroelectrics. |
Wednesday, March 17, 2021 9:48AM - 10:00AM Live |
L37.00008: The Pockels Response in Low-Temperature Rhombohedral BaTiO3 Therese Paoletta, Alexander Demkov The linear electro-optic (EO), or Pockels, effect can bridge upcoming optical technology with conventional silicon devices. Si-integrated barium titanate (BTO) is a promising material for EO modulators in silicon photonics, but little is known about its low-temperature phases. Understanding the lowest-temperature phase (rhombohedral) is critical for certain fields, such as optical quantum computing, that require cryogenic conditions. In this talk, we report a first principles analysis built on density functional perturbation theory, exploring the origins of a strong Pockels response by examining the components that make up the ionic contribution to the electro-optic tensor. We identify the phonon modes dominating the response and establish their relation to the electronic structure and optical properties. We also consider the role strain plays in enhancing the response. |
Wednesday, March 17, 2021 10:00AM - 10:12AM Live |
L37.00009: First-principles and Group-theoretical Analysis of the Magnetic Order in the Rare Earth Titanates Dominique Gautreau, Zhentao Wang, Rafael Fernandes, Turan Birol The low-temperature magnetic order in the rare earth titanate perovskites (RTiO3) transitions from ferromagnetic (FM) to antiferromagnetic (G-AFM) as the rare earth atom varies from Y to La. The nature of this transition, and in particular how this transition is intertwined with the structural distortions (which vary as a function of rare earth ion size) is unclear. We present a combined first-principles, group theoretical, and phenomenological analysis to elucidate the nature of the magnetic phases in strained (biaxial and uniaxial) and doped compounds. We discuss the competition between multiple magnetic phases and the sensitive dependence on the exchange anisotropies, as investigated using a next-nearest neighbor Heisenberg model fitted to first-principles calculations. We further present a general phenomenological theory based on a group theoretical analysis of the octahedral rotations, which couple different magnetic orders, and discuss its implication on the nature of the FM-AFM transition. |
Wednesday, March 17, 2021 10:12AM - 10:24AM Live |
L37.00010: Influence of structural distortions on the magnetic order of rare-earth titanates Ana Najev, Damjan Pelc, Sajna Hameed, Dominique Gautreau, Joseph Joe, Zhentao Wang, Miroslav Pozek, Turan Birol, Rafael Fernandes, Martin Greven Perovskite oxides feature fundamentally and technologically alluring properties such as magnetism, superconductivity and colossal magnetoresistance. How structural distortions and disorder influence the electron system in these materials is an important open question. Rare-earth titanates show promise in shedding new light on this problem through the study of their magnetic ground states, which are controlled by distortions induced by different-sized rare-earth ions. The compounds exhibit an interplay among charge, orbital, spin and lattice degrees of freedom, which produces a complex phase diagram that includes ferromagnetic and antiferromagnetic phases (e.g., in Y1-xLaxTiO3) and metal-insulator transitions (e.g., Y1-xCaxTiO3, La1-xSrxTiO3). Using a custom-made uniaxial pressure cell, we have been able to modify the structural distortions and tune the magnetism of rare-earth titanates in a wide range. We compare the results to ab initio calculations and discuss implications for the nature of the ground state and magnetic transitions in these systems. |
Wednesday, March 17, 2021 10:24AM - 10:36AM On Demand |
L37.00011: The effect of electronically-induced lattice distortions on the structural distortions in layered lanthanum cuprates. Christopher Keegan, Mark Senn, Nicholas Bristowe, Arash A Mostofi The Jahn-Teller active La(2-x)Ba(x)CuO4 system undergoes a phase transition from a low-temperature orthorhombic (LTO) to a low-temperature tetragonal (LTT) phase at doping values centred around x = 0.125. The LTT phase correlates with a dramatic suppression of superconductivity, neither of which are observed in the Sr-doped lanthanum cuprate. In this work we use density-functional theory calculations to understand the extent to which structural distortions arising from the Jahn-Teller effect induce a symmetry-breaking distortion in the Ba-doped system but not in the Sr-doped system. We find that the relative stability of the LTT and LTO phases is sensitive to the magnitude of the Jahn-Teller distortion and the average A-site ionic radius, which helps explain the differences between the phase diagrams of the Ba- and Sr-doped systems. |
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