Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session K43: Spin Orbit Physics in Oxides IIIFocus
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Sponsoring Units: GMAG DMP DCOMP Chair: Jack Simonson, Farmingdale State College Room: 390 |
Wednesday, March 15, 2017 8:00AM - 8:12AM |
K43.00001: Local structural aspects of metal-metal transition in IrTe$_{\mathrm{2}}$ from x-ray PDF Runze Yu, Milinda Abeykoon, Haidong Zhou, Weiguo Yin, Emil S. Bozin Evolution of local atomic structure across the metal-metal transition in IrTe$_{\mathrm{2}}$ is explored by pair distribution function (PDF) analysis of x-ray total scattering data over 80 K \textless T \textless 300 K range. Local and average structures are found to be in accord at all temperatures conforming to P-1 and P-3m1 symmetry at low and high temperature, respectively. We find no evidence of short-range Ir-dimers surviving into the high-T regime, in stark contrast to the earlier EXAFS study proposing Ir-dimer order-disorder mechanism. Phase fraction obtained from explicit 2-phase structural modeling displays hysteretic behavior across the transition, in agreement with electronic transport measurements, indicative of a strong tie between the lattice and electronic configurations. Bond valence methodology applied to structural parameters further indicates significant bond charge disproportionation in association with the transition. [Preview Abstract] |
Wednesday, March 15, 2017 8:12AM - 8:24AM |
K43.00002: Simultaneous Metal-Insulator and Antiferromagnetic Transitions in Orthorhombic Perovskite Iridate Sr0.94Ir0.78O2.68 Single Crystals H. Zheng, J. Terzic, F. Ye, X. G. Wan, D. Wang, J. Wang, X. P. Wang, P. Schlottmann, S. J. Yuan, G. Cao We report results of our investigation of bulk single-crystal Sr0.94Ir0.78O2.68 or Ir-deficient, orthorhombic perovskite SrIrO3. It retains the same crystal structure as stoichiometric SrIrO3 but exhibits a sharp, simultaneous antiferromagnetic (AFM) and metal-insulator (MI) transition occurring in the basal-plane resistivity at 185 K. All results including our first-principles calculations underscore a delicacy of the paramagnetic, metallic state in SrIrO3 that is in close proximity to an AFM insulating state. [Preview Abstract] |
Wednesday, March 15, 2017 8:24AM - 8:36AM |
K43.00003: The nature and origin of electronic gap in perovskite and post-perovskite CaIrO$_{\mathrm{3}}$ Vijeta Singh, jiji pulikkotil Accumulated experimental data and theoretical studies derive little consensus on the insulating ground state of CaIrO$_{\mathrm{3}}$. While in post-perovskite CaIrO$_{\mathrm{3}}$, the origin of the electronic gap is associated with Coulomb correlations, Spin-orbit coupling, long range antiferromagnetic ordering of the Ir ions and/or as a cooperative effect, perovskite CaIrO$_{\mathrm{3}}$ is found to be a semi-metal. Using comprehensive calculations, based on density functional theory, we find that post-perovskite CaIrO$_{\mathrm{3}}$ is a slater-type antiferromagnetic insulator, while its orthorhombic perovskite counterpart is a semi-metal. We owe the discrepancies in the theoretical calculations, to the choice of the exchange correlation potential. Our mBJ calculations correctly reproduce the experimental observed properties of pPv- CaIrO$_{\mathrm{3}}$, such as the magnitude of the Ir moment and electronic gap, large crystalline anisotropy etc. On the other hand, the transport properties calculated using BTE in CSTA for pv- CaIrO$_{\mathrm{3}}$ clearly shows the semi-metallic characteristics of the system. [Preview Abstract] |
Wednesday, March 15, 2017 8:36AM - 9:12AM |
K43.00004: Competing electronic instabilities in the bilayer spin-orbit Mott insulator Sr$_{\mathrm{3}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7}}$ Invited Speaker: Stephen Wilson Destabilizing the spin-orbit Mott state is central to unveiling many of the unconventional electronic states predicted to reside in close proximity, ranging from correlated topological states to high-temperature superconductivity. In particular, carrier substitution into the spin-orbit Mott states manifest in Ruddlesden-Popper (R.P.) strontium iridates is predicted to parallel doping their more strongly correlated cuprate cousins, potentially revealing rich phase diagrams featuring an interplay of competing charge density wave, pseudogap, and superconducting states. Cleanly doping the more strongly insulating R.P. iridates however has proven challenging due to both to the larger carrier densities required to globally quench the Mott state and the limited chemical solubility of traditional dopants. In contrast, the weakly insulating phase of the bilayer R.P. system Sr$_{\mathrm{3}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7}}$ resides close the limit of the spin-orbit Mott state's stability and can be driven into a homogenous metallic state via electron (La) doping, providing an ideal platform for searching for competing instabilities. In this talk, I will present our recent work exploring the magnetic and coupled electronic/structural responses of (Sr$_{\mathrm{1-x}}$La$_{\mathrm{x}})_{\mathrm{3}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7}}$ to electron-doping. Data consistent with the formation of spin dimer and charge density wave states coincident with the emergence of the metallic phase will be presented. These features, when combined with the observation of a pseudogap-like state in this compound, provide an intriguing parallel to the canonical phase diagrams of the cuprates and demonstrate an equally rich electronic phase space in correlated R.P. iridates. [Preview Abstract] |
Wednesday, March 15, 2017 9:12AM - 9:48AM |
K43.00005: Magnetism and transport in defected and doped pyrochlore iridates Invited Speaker: Shixiong Zhang Pyrochlore iridates A2Ir2O7 (A-227, where A$=$Y, Bi and rare earth elements) host a variety of novel magnetic and electronic ground states that arise from the interplay of electron correlation, spin-orbit coupling and geometric frustration. In many of the insulating A-227 single crystals, the Ir4$+$ moments form a long-range, all-in/all-out antiferromagnetic order at low temperatures. In this talk, we will discuss some unusual magnetic properties of the defected and doped A-227 compounds, in which Ir5$+$ ions coexist with the nominal Ir4$+$. In particular, a cooling field dependent shift of magnetic hysteresis loop is observed below the antiferromagnetic ordering temperature. Possible origins of this exchange-bias-like phenomenon will be discussed. We will also present magneto-transport studies of pyrochlore thin films that are grown by pulsed laser deposition. In particular, we will discuss the influence of oxygen vacancies on the transport properties. [Preview Abstract] |
Wednesday, March 15, 2017 9:48AM - 10:00AM |
K43.00006: Evolution of Structural and Electronic Phase Behavior in Sr$_3$(Ir$_{1-x}$Mn$_x$)$_2$O$_7$ Julian Schmehr, Tom Hogan, Wei Tian, Stephen Wilson Sr$_3$Ir$_2$O$_7$ is a rare example of a spin-orbit coupling (SOC) induced $J_{eff}=1/2$ Mott antiferromagnet. Here, we present an investigation of the evolution of the electronic and structural properties of Sr$_3$(Ir$_{1-x}$Mn$_x$)$_2$O$_7$, with $x$ up to 44\%. Sr$_3$Mn$_2$O$_7$ is an antiferromagnetic insulator due to exchange splitting of the $t_{2g}$ orbitals\footnote{J.F. Mitchell \emph{et al.}, \emph{J. Appl. Phys.} {\bf 85}, 4352 (1999)}. Nevertheless, hole-doping the B-site of Sr$_3$Ir$_2$O$_7$ with Mn should substantially renormalize the SOC required for the appearance of the Mott state. Our results from neutron diffraction and magnetic susceptibility show a suppression of the magnetic ordering temperature without a substantial increase in the ordered moment. While all measured samples remained insulating, the inflection in the resistivity at $T_N$ is rapidly suppressed upon Mn substitution. Additionally, the monoclinic lattice distortion observed in Sr$_3$Ir$_2$O$_7$ is also substantially reduced. Mn-doping therefore represents an intriguing new pathway for the suppression of the Mott state, while also allowing for an investigation of the interplay between nuclear structure and electronic properties in the Ruddlesden-Popper iridates. [Preview Abstract] |
Wednesday, March 15, 2017 10:00AM - 10:12AM |
K43.00007: Abstract Withdrawn
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Wednesday, March 15, 2017 10:12AM - 10:24AM |
K43.00008: A charge density wave-like instability in a doped spin-orbit assisted weak Mott insulator Hao Chu, Liuyan Zhao, Alberto de la Torre, Tom Hogan, Stephen Wilson, David Hsieh Layered perovskite iridates realize a rare class of Mott insulators that are predicted to be strongly spin-orbit coupled analogues of the parent state of cuprate high-temperature superconductors. Recent discoveries of pseudogap, magnetic multipolar ordered and possible d-wave superconducting phases in doped Sr$_{\mathrm{2}}$IrO$_{\mathrm{4}}$ have reinforced this analogy among the single layer variants. However, unlike the bilayer cuprates, no electronic instabilities have been reported in the doped bilayer iridate Sr$_{\mathrm{3}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7}}$. In this talk I will show that Sr$_{\mathrm{3}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7}}$ realizes a weak Mott state with no cuprate analogue by using ultrafast time-resolved optical reflectivity to uncover an intimate connection between its insulating gap and antiferromagnetism. However, a subtle charge density wave like Fermi surface instability is detected in metallic electron doped Sr$_{\mathrm{3}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7}}$ at temperatures (T$_{\mathrm{DW}})$ close to 200 K via the coherent oscillations of its collective modes, which is reminiscent of that observed in cuprates. The absence of any signatures of a new spatial periodicity below TDW from diffraction, scanning tunneling and photoemission based probes suggests an unconventional and possibly short-ranged nature of this density wave order. [Preview Abstract] |
Wednesday, March 15, 2017 10:24AM - 10:36AM |
K43.00009: Spin-orbital decoupling and orbital order in cubic $5d$ double perovskites Christopher Svoboda, Mohit Randeria, Nandini Trivedi Mott insulating $5d^1$ and $5d^2$ double perovskites $\mathrm{A}_2 \mathrm{B}\mathrm{B}^\prime \mathrm{O}_6$ (where $\mathrm{A}$ is an alkaline earth, $\mathrm{B}$ a nonmagnetic metal, and $\mathrm{B}^\prime$ the $5d$ transition metal) are expected to be described by models with $j=3/2$ and $j=2$ ions respectively, when spin-orbit coupling dominates. However, this picture is at odds with susceptibility measurements for both cubic and distorted compounds which show effective moments that are too large to be explained by the $j_{\rm eff}$ picture. Motivated by this puzzle, we derive spin-orbital models with unquenched orbital degrees of freedom for $5d^1$ and $5d^2$ double perovskites and analyze them at finite temperature using mean field theory. At high temperatures, the onset of orbital order partially decouples the spin and orbital degrees of freedom leading to enhanced Curie moments, which would be impossible to explain using $j_{\rm eff}$ models. The orbital order that sets in below $T_o$ plays a crucial role in determining the magnetic phases that occur below a $T_c$, which can be much lower than $T_o$. [Preview Abstract] |
Wednesday, March 15, 2017 10:36AM - 10:48AM |
K43.00010: Breakdown of the spin-orbit imposed Jeff $=$ 0 singlet state in double-perovskite iridates with Ir5$+$(5d4) ions Jasminka Terzic, Hao Zheng, Feng Ye, Pedro Schlottmann, Hengdi Zhao, Shujuan Yuan, Gang Cao The strong spin-orbit interaction is expected to impose a nonmagnetic singlet ground state, Jeff $=$ 0, in iridates having pentavalent Ir5$+$(5d4) ions. We report an exotic magnetic ground state in single-crystal double-perovskite Ba2YIrO6 and Sr doped Ba2YIrO6 with Ir5$+$(5d4) ions. The magnetic state fits no descriptions of the spin-alone S$=$1 state in materials with d4 ions as well as the Jeff $=$ 0 singlet state but appears to be situated intermediate between them. The emergence of the magnetic ground state is extraordinary because its occurrence contradicts the highly anticipated Jeff $=$ 0 singlet ground state in presence of the strong spin-orbit interaction and highlights the unusual interplay between the strong spin-orbit interaction, electron-electron correlations and electron hopping. [Preview Abstract] |
Wednesday, March 15, 2017 10:48AM - 11:00AM |
K43.00011: Behavior of Magnetic Domains in Pyrochlore Iridates Tian Liang, Ryoma Kaneko, Eric Yue Ma, Kentaro Ueda, Yongtao Cui, Yongliang Yang, Yoshinori Tokura, Zhi-Xun Shen Pyrochlore Iridates have attracted considerable attention recently. Electrons in the pyrochore iridates experience a large interaction energy in addition to a strong spin-orbit interaction. Both features make the iridates promising platforms for realizing novel states such as the Topological Mott Insulator. The pyrochlore iridate Nd$_2$Ir$_2$O$_7$ shows metal insulator transition at $T_N \sim$ 32 K below which magnetically ordered state develops. Torque magnetometry reveals that the hysteresis behavior of the magnetic domains of Nd$_2$Ir$_2$O$_7$ depends on the direction of applied magnetic field. Interestingly, for some direction of applied magnetic field, the domains are frozen at low temperatures, but become mobile at high temperatures, showing large hysteresis curves only at elevated temperatures. We compare these results with the metallic domain walls observed in Nd$_2$Ir$_2$O$_7$ by microwave impedance microscopy (MIM) and discuss the implications. [Preview Abstract] |
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