Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session A4: Focus Session: Emergent Properties in Bulk Complex Oxides: Iridates I |
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Sponsoring Units: GMAG DMP Chair: L. Andrew Wray, SLAC/Lawrence Berkeley National Laboratory Room: 112/110 |
Monday, March 3, 2014 8:00AM - 8:12AM |
A4.00001: Electronic structure of Rh and Ru doped Sr$_2$IrO$_4$ Shalinee Chikara, Gilberto Fabbris, Jasminka Terzic, Tongfei Qi, Kamal Butrouna, Larissa Veiga, Narcizo Souza Neto, Gang Cao, Daniel Haskel Sr$_2$IrO$_4$ is a spin-orbit interaction(SOI) assisted insulator. It has been proposed that the weaker SOI in the $4d$-substituted Sr$_2$Ir$_{\mathrm{1-x}}$(Ru, Rh)$_{\mathrm{x}}$O$_4$ closes the insulating gap, rendering it a paramagnetic metal. Rh(${4d}^5$) is isoelectronic to Ir(${5d}^5$) whereas Ru(${4d}^4$) has one less electron in the $4d$-band. The AFM-I/PM-M transition takes place at lower $x$ for Ru than Rh, presumably due to the effect of hole doping. X-ray absorption near edge structure (XANES) and x-ray magnetic circular dichroism (XMCD) measurements at the Ir $ L_{2,3}$ edges show that $\langle\mathbf{L}.\mathbf{S} \rangle $ is non-zero and independent of $x$. This is indicative of a strong local $5d$ spin orbit interaction that is rather insensitive to the $4d$ doping. In contrast, measurements at the $ L_{2,3}$ edges of Ru and Rh show $\langle\mathbf{L}.\mathbf{S} \rangle \approx 0 $ for all $x$. The results point to the importance of local $4d/5d - 2p$ hybridization as opposed to $4d-5d$ band formation in the Rh and Ru doped Sr$_2$IrO$_4$. [Preview Abstract] |
Monday, March 3, 2014 8:12AM - 8:24AM |
A4.00002: Iridate compound produces extraordinarily high coercive magnetic field Vivien Zapf, Craig Topping, Jae-Wook Kim, Eun-Deok Mun, Paul Goddard, Saman Ghannadzadeh, Xuan Luo, Sang-Wook Cheong, John Singleton We present a data on an iridate compound that shows an extraordinarily large magnetic hysteresis loop. The coercive magnetic field exceeds 40 Tesla in single-crystal samples. The hysteresis coexists with a linear background, and the total remanent magnetization is about half a Bohr magneton. We will discuss the emergence of these properties from the interplay of spin-orbit coupling, magnetic exchange and possible frustration. The single crystalline material exhibits a magnetic hysteresis loop for one orientation of the magnetic field and a smooth linear increase in the magnetization with field for the other. Measurements were conducted in 65 T short-pulse magnets and the 60 Tesla shaped-pulse magnet at the National High Magnetic Field Lab in Los Alamos. We do not observe any dependence of the magnetic hysteresis on magnetic field sweep rate. Compounds containing Ir4$+$ have attracted attention recently due to strong spin-orbit coupling that competes with crystal-electric field and exchange interactions. This competition can result in non-Hund's-rule ground states with unusual properties. [Preview Abstract] |
Monday, March 3, 2014 8:24AM - 8:36AM |
A4.00003: Magnetic and structural behaviors in (Sr$_{\mathrm{1-x}}$La$_{\mathrm{x}})_{2}$IrO$_{4}$ Xiang Chen, Tom Hogan, Chetan Dhital, Zhensong Ren, Mani Pokharel, Mengliang Yao, Cyril Opeil, Stephen Wilson There has been a considerable amount of interest recently in exploring the compound Sr$_{2}$IrO$_{4}$ due to its similarity to the high-T$_{\mathrm{c}}$ superconducting parent compound La$_{2}$CuO$_{4}$ and the possible realization of a parallel unconventional superconducting state by electron-doping. There has since been renewed effort attempting to doped electrons into prototypical spin-orbit driven Mott phases such as Sr$_{2}$IrO$_{4}$ (Sr-214), where La-substitution within (Sr$_{\mathrm{1-x}}$La$_{\mathrm{x}})_{2}$IrO$_{4}$ remains one of the more promising avenues. Here we present a combined transport, magnetization, and diffraction study revisiting the mechanism and effect of doping in this compound. We will focus on how the evolution of known structural and electronic order parameters in the parent Sr$_{2}$IrO$_{4}$ evolve upon La-substitution. [Preview Abstract] |
Monday, March 3, 2014 8:36AM - 8:48AM |
A4.00004: Electronic Structure and Magnetism of Ir based Oxides Indra Dasgupta, Swarup Panda We have investigated in details the electronic structure of several Ir based oxides where in addition to crystal field and Coulomb repulsion, the spin-orbit coupling (SOC) plays an important role. We shall first consider two Ir based oxides with 4+ (d$^{5}$) charge state of Ir, namely the insulating double perovskite Sr$_{2}$CeIrO$_{6}$ and the metallic rutile IrO$_{2}$, and examine the validity of the novel spin-orbital entangled J$_{eff}$=1/2 states for the description of their electronic structure. In particular, explore in details whether the J$_{eff}$=1/2 state survives for the itinerant metallic IrO$_{2}$. Finally we shall also present our electronic structure calculations on 6H perovskite type iridates where different charge state of Ir (5+, 4.5+, and 4+) may be realized. We show in addition to SOC, the strong intra-dimer hopping play a crucial role for the magnetic ground state and the insulating property of these systems. We shall compare our results with available experiments. [Preview Abstract] |
Monday, March 3, 2014 8:48AM - 9:00AM |
A4.00005: Anisotropic magnetoresistance in Sr$_{2}$IrO$_{4}$ C. Wang, H. Seinige, G. Cao, J.-S. Zhou, J.B. Goodenough, M. Tsoi We report the first measurements of the point-contact magnetoresistance (MR) of antiferromagnetic semiconductor Sr$_{2}$IrO$_{4}$. The point-contact technique allows to probe very small volumes associated with point contacts and, therefore, looks for electronic transport on a microscopic scale. Point-contact measurements with single crystals of Sr$_{2}$IrO$_{4}$ were intended to see if the additional local resistance associated with a small contact area between a sharpened Cu tip and the antiferromagnet shows MR such as that seen in bulk crystals. The Sr$_{2}$IrO$_{4}$ crystals were grown by the flux method. Point-contact measurements at liquid nitrogen temperature revealed large MRs (up to 8{\%}) for modest magnetic fields (250 mT) applied within IrO$_{2}$ (ab) plane. The angular dependence of MR shows a crossover from four-fold to two-fold symmetry with an increasing magnetic field which may be tentatively attributed to the field-induced changes of antiferromagnetic order within IrO$_{2}$ planes. The observed MR can be potentially used to sense the antiferromagnetic order in spintronic applications. [Preview Abstract] |
Monday, March 3, 2014 9:00AM - 9:12AM |
A4.00006: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 9:12AM - 9:48AM |
A4.00007: Electronic Phase Separation and Magnetic Phase Behavior in the Ru-doped Spin-Orbit Mott Insulator Sr$_3$Ir$_2$O$_7$ Invited Speaker: Chetan Dhital Iridium-based 5d transition metal oxides host rather unusual electronic/magnetic ground states due to strong interplay between electronic correlation, lattice structure and spin-orbit interactions. Out of the many oxides containing iridium, the Ruddelsden-Popper (RP) series [Sr$_{n+1}$Ir$_n$O$_{3n+1}$] oxides are some of the most interesting systems to study both from the point of view of physics as well as from potential applications. Sr$_3$Ir$_2$O$_7$ (n=2) and Sr$_2$IrO$_4$ (n=1) are two representative candidates of this series. One way of experiencing the strength and relevance of electronic correlation in any condensed matter system is by doping charge carriers. The presence of electronic correlations in the host system determines the fate of the dopant and hence stabilizes a new electronic/magnetic ground state. I will discuss about importance of electronic correlations in one such doped system Sr$_3$ (Ir$_{1-x}$Ru$_x$)$_2$O$_7$ using combined neutron scattering, electric transport and magnetization techniques. Our findings demonstrate that correlation effects felt by carriers introduced within in a $5d$ Mott phase remain robust enough to drive electron localization, a key ingredient in emergent phenomena such as high temperature superconductivity and enhanced ferroic behavior.\\[4pt] [1] Dhital, Chetan, et al. ``Spin ordering and electronic texture in the bilayer iridate Sr$_3$Ir$_2$O$_7$.'' \textit{Physical Review B} 86.10 (2012): 100401.\\[0pt] [2] Dhital, Chetan, et al. ``Neutron scattering study of correlated phase behavior in Sr$_2$IrO$_4$.'' \textit{Physical Review B} 87.14 (2013): 144405.\\[0pt] [3] Dhital, Chetan, et al. ``Electronic phase separation in the doped spin-orbit driven Mott phase of Sr$_3$(Ir$_{1-x}$Ru$_x$)$_2$O$_7$.'' \textit{arXiv preprint arXiv:1311.0783} (2013). [Preview Abstract] |
Monday, March 3, 2014 9:48AM - 10:00AM |
A4.00008: Evolution of Magnetism in Single-Crystal Honeycomb Iridates Jasminka Terzic, T.F. Qi, L. Li, V.S. Cao, S.J. Yuan, M. Tovar, G. Murthy, R.K. Kaul, G. Cao We report the successful synthesis of single-crystals of the layered iridate, (Na$_{1-x}$Li$_x$)$_2$IrO$_3$, 0 $\le$ x $\le$ 0.90, and a thorough study of its structural, magnetic, thermal and transport properties. The new compound allows a controlled interpolation between Na$_2$IrO$_3$ and Li$_2$IrO$_3$, while maintaining the novel quantum magnetism of the honeycomb Ir4$+$ planes. The measured phase diagram demonstrates a suppression of the Neel temperature at an intermediate x indicating that the magnetic order in Na$_2$IrO$_3$ and Li$_2$IrO$_3$ are distinct. X-ray data shows that for x$=$0.70 when the Neel temperature is suppressed the most, the honeycomb structure is least distorted, suggesting at this intermediate doping that the material is closest to the spin liquid that has been sought after in Na$_2$IrO$_3$ and Li$_2$IrO$_3$. By analyzing our magnetic data with a single-ion theoretical model we also show that the trigonal splitting, on the Ir4$+$ ions changes sign from Na$_2$IrO$_3$ to Li$_2$IrO$_3$. [Preview Abstract] |
Monday, March 3, 2014 10:00AM - 10:12AM |
A4.00009: Novel magnetism of Ir5$+$ ions in the double perovskite Sr2YIrO6 Gang Cao, T.F. Qi, La Li, J. Terzic, S.J. Yuan, L.E. DeLong, G. Murthy, R.K. Kaul We synthesize and study single crystals of a new double-perovskite Sr2YIrO6. Despite two strongly unfavorable conditions for magnetic order, namely, pentavalent Ir5$+$(5d4) ions which are anticipated to have J$=$0 singlet ground states in the strong spin-orbit coupling (SOC) limit, and geometric frustration in a face centered cubic structure formed by the Ir5$+$ ions, we observe this iridate to undergo a novel magnetic transition at temperatures below 1.3 K. We provide compelling experimental and theoretical evidence that the origin of magnetism is in an unusual interplay between strong non-cubic crystal fields, local exchange interactions and ``intermediate-strength'' SOC. Sr2YIrO6 provides a rare example of the failed dominance of SOC in the iridates. [Preview Abstract] |
Monday, March 3, 2014 10:12AM - 10:24AM |
A4.00010: Hallmarks of Metal Insulator transition in Doped Sr$_{2}$IrO$_{4}$ Yue Cao, Qiang Wang, Rajendra Dhaka, Justin Waugh, Theodore Reber, Haoxiang Li, Stephen Parham, Xiaoqing Zhou, Seung Ryong Park, Tongfei Qi, Oleksandr Korneta, Nicholas Plumb, Aaron Bostwick, Eli Rotenberg, Jonathan Denlinger, Michael Hermele, Gang Cao, Daniel Dessau How Mott insulators acquire metallicity upon the introduction of extra carriers lies at the heart of correlated electron physics. The evolution of the electronic structure and low energy dynamics in the ultra-low doped region where the Mottness begins to break down is a critical place to study this physics. We report ARPES studies of the Rh and La doped Sr$_{2}$IrO$_{4}$ and show the appearance and evolution of a pseudogap and Fermi arcs. Further more we present evidence how the Mott gap breaks down with a profound change in the band structure. The experimental results in the doped iridates resemble those observed in the cuprate systems, which are prototype Mott insulators, and suggest we could establish a series of signatures that occur in the metal insulator transition. [Preview Abstract] |
Monday, March 3, 2014 10:24AM - 10:36AM |
A4.00011: Destruction of J$_{\mathrm{eff}}=$1/2 Mott Phase by A-site doping in (Sr$_{\mathrm{1-x}}$La$_{\mathrm{x}})_{3}$Ir$_{2}$O$_{7}$ Tom Hogan, Chetan Dhital, Zahra Yamani, Cyril Opeil, Stephen Wilson Recent theoretical progress in describing the insulating behavior of the n$=$1 and n$=$2 Ruddlesden-Popper (RP) series iridates (Sr$_{2}$IrO$_{4}$ and Sr$_{3}$Ir$_{2}$O$_{7})$ has proposed a novel J$_{\mathrm{eff}}=$1/2 Mott ground state. This new Mott phase theoretically arises from the splitting of the Ir 5d orbitals by the crystal field combined with further splitting of the t$_{\mathrm{2g}}$ manifold by relativistic spin-orbit coupling which then combines with a modest U to form a Mott insulating phase. Our group's previous work in Ir-site substitution of Sr$_{3}$Ir$_{2}$O$_{7}$ (Sr-327) has revealed a rich interplay of correlated effects, presenting a strong argument that correlation physics plays a dominant role in the ground state of this material. While doping the transition metal B-site with Ru$^{4+}$ induces a percolative metal-insulator transition (MIT) with doped-holes remaining localized, it is known that the A-site doping of electrons results in a very abrupt MIT realized with only a small percentage level of doping ($\sim$ 3{\%}). Here we present a combined transport and diffraction study exploring the evolution of electronic and structural properties in electron-doped (Sr$_{\mathrm{1-x}}$La$_{\mathrm{x}})_{3}$Ir$_{2}$O$_{7}$ as it traverses the MIT in its electronic phase diagram. Elastic neutron scattering experiments alongside DC magnetization and electronic transport data will be presented exploring the ordering temperature, moment size, and the extent of any structural distortions present, as a function of dopant concentration. [Preview Abstract] |
Monday, March 3, 2014 10:36AM - 10:48AM |
A4.00012: Influence of non-magnetic dilution in honeycomb-lattice iridates A$_2$IrO$_3$ (A=Na,Li) Soham Manni, Philipp Gegenwart Honeycomb-lattice iridates A$_2$IrO$_3$ (A= Na,Li) display a spin-orbit Mott insulating state [1,2] and have been proposed as experimental realizations for the Kitaev-Heisenberg(KH) model[1] or a novel kind of quasi-molecular orbital(QMO) system [3]. Recently it has been proposed, that dilution of the Ir$^{4+}$ moments could be used to investigate the importance of next neighbor interactions (HK model) versus further next neighbor interactions (J1-J2-J3 model)[4]. We have synthesized A$_2$(Ir$_{1-x}$Ti$_x$)O$_3$ single- and polycrystals for the Na and Li system, respectively and investigated their magnetic and thermodynamic properties. Even very low Ti$^{4+}$ substitution leads to spin glassy behavior and spin glass temperature (T$_g$) is steeply suppressed towards the percolation threshold. This confirms that frustrated nearest-neighbor interactions are the most important factor to set up the magnetism in A$_2$IrO$_3$.\\[4pt] [1] Y.Singh et.al. - PRL 108, 127203 (2012).\\[0pt] [2] H. Gretarsson et.al. - PRL 110, 076402 (2013).\\[0pt] [3] I. Mazin et.al. - PRL 109, 197201 (2012).\\[0pt] [4] Eric C. Andrade et.al. - arxiv 1309.2951. [Preview Abstract] |
Monday, March 3, 2014 10:48AM - 11:00AM |
A4.00013: Evolution of magnetic structure in the square lattice iridate Sr$_{2}$Ir$_{\mathrm{1-x}}$Rh$_{\mathrm{x}}$O$_{4}$ Feng Ye, Songxue Chi, Masaaki Matsuda, Xiaoping Wang, Christina Hoffmann, Bryan Chakoumakos, Jaime Fernandez-Baca, Tongfei Qi, Gang Cao 5$d$ based iridates have continuously provides a fertile playground for the studies of novel physics driven by spin-orbit interaction (SOI) that rigorously competes with other relevant energies, particularly the on-site Coulomb interaction U. Using single crystal neutron diffraction and polarized neutron scattering analysis, we have investigated the evolution of spin and crystal structures in the doped Sr$_{2}$Ir$_{\mathrm{1-x}}$Rh$_{\mathrm{x}}$O$_{4}$(0$\le $x$\le $0.20). The parent Sr$_{2}$IrO$_{\mathrm{4}}$ shows canted antiferromagnetic structure with spin lies in the basal plane. The spin orientation closely follows the rotation of the IrO$_{6}$ octahedra with total ordered moment of 0.21 $\mu_{\mathrm{B}}$/Ir. A small amount of Rh ions doped at the Ir sites drastically reduces the magnetic transition and modifies the spin configuration. The neutron scattering results provide experimental insights into the magnetic and crystal structure crucial to the understanding this prototype iridates. [Preview Abstract] |
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