Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session D70: Novel 5d MaterialsFocus Recordings Available

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Sponsoring Units: DMP DCMP Chair: Gavin Hester, Purdue University Room: Hyatt Regency Hotel Jackson Park B 
Monday, March 14, 2022 3:00PM  3:36PM 
D70.00001: Discovery of Honeycomb and KagomÃ© Quantum Magnets Invited Speaker: Tyrel M McQueen In this talk, I will present recent results on the discovery of kagome and honeycomb quantum magnets. Particular focus will be placed on the development of cobalt and rare earth based honeycomb materials, and the similarities and differences between integer and halfinteger spin ions. The discovery of bidirectional twisting in MgCo_{6}Ge_{6} will also be discussed and put in context. If time permits, I will also report on emerging materials discoveries that have the potential to reveal Kitaev spin liquid ground states. 
Monday, March 14, 2022 3:36PM  3:48PM 
D70.00002: Nuclearmagnetic resonance studies of double perovskite Mott insulating Ba_{2}LiOsO_{6} Erick Garcia, Rong Cong, Calvin C Bales, Samuele Sanna, Arneil P Reyes, Jiaqiang Yan, Vesna F Mitrovic Double perovskites with 5d transition metal ions offer a flexible environment to study the interplay of comparable electron correlations and spinorbit coupling. Mott insulating osmium compounds present an opportunity to study the resulting delicate emergent phases from such competing interactions. Here, we present detailed nuclear magnetic resonance (NMR) measurements on Ba_{2}LiOsO_{6} single crystals. The nature of its magnetic transition at low temperature and its metamagnetic transition at 6 T will be discussed. The results are compared to the isostructural compound Ba_{2}NaOsO_{6}. 
Monday, March 14, 2022 3:48PM  4:24PM 
D70.00003: Untangling the structural, magnetic dipole, and charge multipolar orders in Ba2MgReO6 and Cs2TaCl6 Invited Speaker: Aria Mansouri Tehrani We present densityfunctional calculations of hidden multipolar orders in 5d transitionmetal double perovskites, using Ba2MgReO6 and Cs2TaCl6 as examples. Recent studies have suggested the existence of unconventional types of ordering, not detectable using typical probes, in these 5d double perovskites, stemming from the interplay of spinorbit coupling, crystalfield splitting, and electronelectron repulsion. These "hidden orders" are formed from ordered anisotropies in the electronic charge and magnetization density distributions that can be described within multipole expansions beyond the usual dipolar distributions and include ordered charge quadrupoles and magnetic octupoles, as well as higherorder multipoles. 
Monday, March 14, 2022 4:24PM  4:36PM 
D70.00004: Highpressure synthesis, crystal structure, and physical properties of perovskite KOsO_{3} Jie Chen, Hongze Li, Jiaming He, Jianshi Zhou The syntheses of LiOsO_{3} and NaOsO_{3} have brought some fresh input to the longstanding dialogs of ferroelectric metal and the metalinsulator transition. The LiOsO_{3} with the LiNbO_{3}type structure has been believed to be the best candidate for the ferroelectric metal proposed by Anderson and Blount [1]. Whether the metalinsulator transition in the orthorhombic perovskite NaOsO_{3} [2] can be attributed to either a Mott transition or a Slater transition is still controversial [3,4]. KOsO_{3} in this family has been synthesized under a highpressure and hightemperature condition for the first time. As the geometric tolerance factor is close to 1, the perovskite KOsO_{3} crystallizes in a cubic structure (Pm3m). The cubic phase remains stable for a large range of the Na doping in K_{1x}Na_{x}OsO_{3}. The perovskite KOsO_{3} and the Nadoped KOsO_{3} samples were characterized by the measurements of magnetic susceptibilities, thermoelectric power, and specific heat. In the talk, we will present the measurement results and the magnetic structure by neutron diffraction. 
Monday, March 14, 2022 4:36PM  4:48PM 
D70.00005: Octupolar order and Ising quantum criticality tuned by strain and dimensionality: Application to $d$orbital Mott insulators Sreekar Voleti, Arijit Haldar, Arun Paramekanti Recent experiments have discovered multipolar orders in a variety of $d$orbital Mott insulators. Motivated by uncovering the exchange interactions which underlie octupolar order proposed in the Osmate ($5d^2$) double perovskites, we study a twosite model using exact diagonalization on a fiveorbital Hamiltonian, incorporating spinorbit coupling (SOC) and interactions, and including both intraorbital and interorbital hopping. Using an exact SchriefferWolff transformation, we then extract an effective pseudospin Hamiltonian for the nonKramers doublets, uncovering dominant ferrooctupolar coupling driven by the interplay of two distinct intraorbital hopping terms. Our work highlights the importance of higher order contributions to the exchange couplings coming from the small gap between the nonKramers doublet and excited triplets in these systems. Using classical Monte Carlo simulations on the facecentered cubic lattice, we obtain a ferrooctupolar transition temperature ($T_c$) which is in good agreement with experiments on the osmate double perovskites. We also explore the impact of uniaxial strain and dimensional tuning via ultrathin films, which are shown to induce a transverse field on the Ising octupolar order. This suppresses $T_c$ and potentially allows one to access octupolar Ising quantum critical points. We discuss possible implications of our results for a broader class of materials which may host such nonKramers doublet ions. 
Monday, March 14, 2022 4:48PM  5:00PM 
D70.00006: Magnetization dynamics fingerprints of an excitonic condensate (t_{2g})^{4} magnet Nitin Kaushal, Jacek Herbrych, Gonzalo Alvarez, Elbio R Dagotto The competition between spinorbit coupling λ and electronelectron interaction U leads to a plethora of novel states of matter, extensively studied in materials such as ruthenates and iridates. Recent theoretical studies predicted that excitonic magnets  the antiferromagnetic state due to the condensation of excitons (bounded electronhole pairs)  can be found in the groundstate of spinorbitcoupled (t_{2g})^{4} Hubbard models [1,2]. We present a detailed study of the magnetic excitations in that excitonic magnet, employing onedimensional chains (via density matrix renormalization group) and small twodimensional clusters (via Lanczos). First we show that the lowenergy spectrum is dominated by a dispersive (acoustic) magnonic mode, with extra features arising from the λ=0 state in the phase diagram. Second, and more importantly, we found a novel magnetic excitation forming a highenergy optical mode with the highest intensity at wavevector q→0 . These unique fingerprints of the excitonic magnet are important in the analysis of neutron and RIXS experiments. 
Monday, March 14, 2022 5:00PM  5:12PM 
D70.00007: Small polaron formation in 5d spinorbit coupled omsates Lorenzo Celiberti, Dario Fiore Mosca, Anna Tassetti, Paola Caterina Forino, Roberto De Renzi, Giuseppe Allodi, Vesna F Mitrovic, Erick Garcia, Rong Cong, Patrick Woodward, Samuele Sanna, Cesare Franchini Small polarons (SP) have been thoroughly investigated in 3d transition metal oxides [1]. However, very little is known about these quasiparticles in 5d systems, since the more delocalised nature of the 5d orbitals reduces the strength of the Electronic Correlation (EC), making SP formation in these compounds rather unexpected. The spinorbit coupled DiracMott insulator Ba_{2}NaOsO_{6} (BNOO) represents a candidate material for enabling polaron formation in a relativistic background, due to the relatively large EC (U ~ 3 eV) and JahnTeller activity [2]. We verify this hypothesis by combining first principles calculations with nuclear magnetic resonance (NMR) and muons measurements. We find that excess electrons injected into BNOO through chemical doping are trapped in Os sites and distort the local phonon field, typical hallmark of SP formation. SP are subjected to thermally activated hopping, revealed by anomalous peaks in the spinlattice and spinspin relaxation rates, attributed to fluctuation of the electric field gradients driven by a chargerelated time dependent perturbation. 
Monday, March 14, 2022 5:12PM  5:24PM 
D70.00008: Ferrooctupolar order in d^{2} double perovskites of Osmium from first principles Dario Fiore Mosca, Cesare Franchini, Leonid V Pourovskii Conflicting interpretations of experimental data preclude the understanding of the quantum magnetic state of spinorbit coupled d^{2} double perovskites. Whether the ground state is a JanhTellerdistorted order of quadrupoles or the hitherto elusive octupolar order remains debated. We resolve this uncertainty through direct calculations of allrank intersite exchange interactions and inelastic neutron scattering crosssection for the d^{2} double perovskite series Ba_{2}MOsO_{6} (M= Ca, Mg, Zn). Using advanced manybody first principles methods we show that the ground state is formed by ferroordered octupoles and is dominated by superexchange interactions within the groundstate E_{g} doublet. Computed ordering temperature of the single secondorder phase transition is consistent with experimentally observed materialdependent trends. We further investigate the electronic, structural and magnetic properties of such compounds by purely Density Functional Theory (DFT) calculations with a new approach that consists in the constrain of the onsite density matrix, as obtained via DFT + Dynamical Mean Field Theory calculations. We prove that this method is able to reproduce the ferrooctupolar order and we compare this result to conventional DFT dipolar solutions. 
Monday, March 14, 2022 5:24PM  6:00PM 
D70.00009: Flatband ferroelectricity first discovered in HfO_{2} Invited Speaker: Jun Hee Lee Ferroelectricity has been known to originate from the lowestenergy Gammaphonon of a dispersed band. Therefore, ferroelectricity is believed since it’s discovery in 1920 that at least finitesized domains (10~100nm) that has the Gamma characteristics are required to stabilize and switch the ferroelectric dipoles. Here, we break the 100years belief by introducing flatband physics into the history of ferroelectricity. We discovered that, for the first time, flat bands in polar phonon exist surprisingly in ferroelectric HfO_{2} and showed that they induce irreducibly localized dipoles of a few angstroms width which is the recordhigh small. More strikingly, these extremely localized dipoles are individually switchable by local electric fields and thus now one can circumvent the formation of the conventionally large domains for the ferroelectric switching. We can directly switch the ultimatelysmall unitcellscale dipoles and finally pave a way to achieve densest memory devices in the commercial ferroelectric compatible with Sitechnology [1]. 
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