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Search Results: 1 - 10 of 297496 matches for " J. Chakhalian "
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Thin Film Substrates from the Raman spectroscopy point of view
L. Gasparov,T. Jegorel,L. Loetgering,S. Middey,J. Chakhalian
Physics , 2013, DOI: 10.1002/jrs.4487
Abstract: We have investigated ten standard single crystal substrates of complex oxides on the account of their applicability in the Raman spectroscopy based thin film research. In this study we suggest a spectra normalization procedure that utilizes a comparison of the substrate Raman spectra to those of well-established Raman reference materials. We demonstrate that MgO, LaGaO3, (LaAlO3)_0.3(Sr2AlTaO6)_0.7 (LSAT), DyScO3, YAlO3, and LaAlO3 can be of potential use for a Raman based thin film research. At the same time TiO2 (rutile), NdGaO3, SrLaAlO4, and SrTiO3 single crystals exhibit multiple phonon modes accompanied by strong Raman background that substantially hinder the Raman based thin film experiments.
Depth-Resolved Subsurface Defects in Chemically Etched SrTiO3
Jun Zhang,D. Doutt,T. Merz,J. Chakhalian,M. Kareev,J. Liu,L. J. Brillson
Physics , 2009, DOI: 10.1063/1.3093671
Abstract: Depth-resolved cathodoluminescence spectroscopy of atomically flat TiO2-terminated SrTiO3 single crystal surfaces reveals dramatic differences in native point defects produced by conventional etching with buffered HF (BHF) and an alternative procedure using HCl-HNO3 acidic solution (HCLNO), which produces three times fewer oxygen vacancies before and nearly an order of magnitude fewer after pure oxygen annealing. BHF-produced defect densities extend hundreds of nm below the surface, whereas the lower HCLNO-treated densities extend less than 50 nm. This "Arkansas" HCLNO etch and anneal method avoids HF handling and provides high quality SrTiO3 surfaces with low native defect density for complex oxide heterostructure growth
Magnetism in purple bronze Li$_{0.9}$Mo$_6$O$_{17}$
J. Chakhalian,Z. Salman,J. Brewer,A. Froese,J. He,D. Mandrus,R. Jin
Physics , 2004, DOI: 10.1016/j.physb.2005.01.402
Abstract: Muon spin relaxation measurements around the 25 K metal-insulator transition in Li$_{0.9}$Mo$_6$O$_{17}$ elucidate a profound role of disorder as a possible mechanism for this transition. The relaxation rate $1/T_1$ and the muon Knight shift are incompatible with the transition to a SDW state and thus exclude it.
Local Electronic and Magnetic Studies of an Artificial La2FeCrO6 Double Perovskite
Benjamin Gray,Ho Nyung Lee,Jian Liu,J. Chakhalian,J. W. Freeland
Physics , 2010, DOI: 10.1063/1.3455323
Abstract: Through the utilization of element-resolved polarized x-ray probes, the electronic and magnetic state of an artificial La2FeCrO6 double perovskite were explored. Applying unit-cell level control of thin film growth on SrTiO3 (111), the rock salt double perovskite structure can be created for this system, which does not have an ordered perovskite phase in the bulk. We find that the Fe and Cr are in the proper 3+ valence state, but, contrary to previous studies, the element-resolved magnetic studies find the moments in field are small and show no evidence of a sizable magnetic moment in the remanent state.
Effect of polar discontinuity on the growth of LaNiO3/LaAlO3 superlattices
Jian Liu,M. Kareev,S. Prosandeev,B. Gray,P. Ryan,J. W. Freeland,J. Chakhalian
Physics , 2010, DOI: 10.1063/1.3371690
Abstract: We have conducted a detailed microscopic investigation of [LaNiO3(1 u.c.)/LaAlO3(1 u.c.)]N superlattices grown on (001) SrTiO3 and LaAlO3 to explore the influence of polar mismatch on the resulting electronic and structural properties. Our data demonstrate that the initial growth on the non-polar SrTiO3 surface leads to a rough morphology and unusual 2+ valence of Ni in the first LaNiO3 layer, which is not observed after growth on the polar surface of LaAlO3. A newly devised model suggests that the polar mismatch can be resolved if the perovskite layers grow with an excess of LaO, which also accounts for the observed electronic, chemical, and structural effects.
On Magnetic Interlayer Coupling and Proximity Effect in a La$_{0.67}$Ca$_{0.33}$MnO$_3$(10 nm)/YBa$_2$Cu$_3$O$_7$(10 nm) Superlattice
J. W. Freeland,J. Chakhalian,G. Cristiani,H. -U. Habermeier,B. Keimer
Physics , 2007, DOI: 10.1063/1.2747678
Abstract: We present a study of interlayer coupling and proximity effects in a La$_{0.66}$Ca$_{0.33}$MnO$_3$(10 nm)/YBa$_2$Cu$_3$O$_7$(10 nm) superlattice. Using element-sensitive x-ray probes, the magnetic state of Mn can be probed without seeing the strong diamagnetism of the superconductor, which makes this approach ideal to study changes in the magnetic properties across the superconducting transition. By a combined experiment using {\it in situ} transport measurements during polarized soft x-ray measurements, we were able to see no noticeable influence of the superconducting state on the magnetic properties and no evidence for magnetic coupling across a 10 nm YBCO layer.
Metal-insulator transition and orbital reconstruction in Mott quantum wells of NdNiO$_{3}$
Jian Liu,M. Kareev,D. Meyers,B. Gray,P. Ryan,J. W. Freeland,J. Chakhalian
Physics , 2012, DOI: 10.1103/PhysRevLett.109.107402
Abstract: The metal-insulator transition (MIT) and the underlying electronic and orbital structure in $e_{g}^{1}$ quantum wells based on NdNiO$_{3}$ was investigated by d.c. transport and resonant soft x-ray absorption spectroscopy. By comparing quantum wells of the same dimension but with two different confinement structures, we explicitly demonstrate that the quantum well boundary condition of correlated electrons is critical to selecting the many-body ground state. In particular, the long-range orderings and the MIT are found to be strongly enhanced under quantum confinement by sandwiching NdNiO$_{3}$ with the wide-gap dielectric LaAlO$_{3}$, while they are suppressed when one of the interfaces is replaced by a surface (interface with vacuum). Resonant spectroscopy reveals that the reduced charge fluctuations in the sandwich structure are supported by the enhanced propensity to charge ordering due to the suppressed $e_g$ orbital splitting when interfaced with the confining LaAlO$_{3}$ layer.
Metallic Conductance at the Interface of Tri-color Titanate Superlattices
M. Kareev,Yanwei Cao,Xiaoran Liu,S. Middey,D. Meyers,J. Chakhalian
Physics , 2013, DOI: 10.1063/1.4841955
Abstract: Ultra-thin tri-color (tri-layer) titanate superlattices ([3u.c. LaTiO3/2u.c. SrTiO3/3u.c. YTiO3], u.c. = unit cells) were grown in a layer-by-layer way on single crystal TbScO3 (110) substrates by pulsed laser deposition. High sample quality and electronic structure were characterized by the combination of in-situ photoelectron and ex-situ structure and surface morphology probes. Temperature-dependent sheet resistance indicates the presence of metallic interfaces in both [3u.c. LaTiO3/2u.c. SrTiO3] bi-layers and all the tri-color structures, whereas a [3u.c. YTiO3/2u.c. SrTiO3] bi-layer shows insulating behavior. Considering that in the bulk YTiO3 is ferromagnetic below 30 K, the tri-color titanate superlattices provide an opportunity to induce tunable spin- polarization into the two-dimensional electron gas (2DEG) with Mott carriers.
Emergent properties hidden in plane view: Strong electronic correlations at oxide interfaces
Jak Chakhalian,John W. Freeland,Andrew J. Millis,Christos Panagopoulos,James M. Rondinelli
Physics , 2014, DOI: 10.1103/RevModPhys.86.1189
Abstract: Finding new collective electronic states in materials is one of the fundamental goals of condensed matter physics. Atomic-scale superlattices formed from transition metal oxides are a particularly appealing hunting ground for new physics. In bulk form, transition metal oxides exhibit a remarkable range of magnetic, superconducting, and multiferroic phases that are of great scientific interest and are potentially capable of providing innovative energy, security, electronics and medical technology platforms. In superlattices new states may emerge at the interfaces where dissimilar materials meet. Here we illustrate the essential features that make transition metal oxide-based heterostructures an appealing discovery platform for emergent properties with a few selected examples, showing how charge redistributes, magnetism and orbital polarization arises and ferroelectric order emerges from heterostructures comprised of oxide components with nominally contradictory behavior with the aim providing insight into the creation and control of novel behavior at oxide interfaces by suitable mechanical, electrical or optical boundary conditions and excitations.
Metallic interface in non-SrTiO3 based titanate superlattice
Xiaoran Liu,D. Choudhury,Yanwei Cao,M. Kareev,S. Middey,J. Chakhalian
Physics , 2015, DOI: 10.1063/1.4935550
Abstract: We report on the fabrication of all perovskite Mott insulator/band insulator YTiO3/CaTiO3 superlattices by pulsed laser deposition. The combination of in situ reflection high energy electron diffraction, X-ray diffraction, and X-ray reflectivity confirms the high quality of the films grown in a layer-by-layer mode. Electrical transport measurements reveal that a non-SrTiO3 based two dimensional electron gas system has formed at the YTiO3/CaTiO3 interface. These studies offer another route in the pursuit of complex oxide two-dimensional electron gas systems, which allows to obtain greater insights into the exotic many-body phenomena at such interfaces.
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