Abstract

Oxide thin films and interfaces have attracted considerable interestnot only because of the rich physics it can host but also because ofthe possibility of integrating materials with different properties toachieve new multifunctionality that can be used for future generationof high speed, low power consuming and small size spintronics devices.Recently discovered topologically protected non-trivial magnetic spinstructures namely “skyrmions” have shown their potential for low powerconsuming, small size and high speed spintronics devices. So far,formation of skyrmionic crystals have been observed in chiralnoncentrosymmetric B20-type compounds mediated by the Dzyaloshinskii-Moriya (D-M)interaction. On the other hand, in centrosymmetriccrystals without D-M interaction, such nontrivial spin structure hasbeen proposed to occur, yet compelling evidence has remained to bepresented. We have shown the emergence of such non-trivial spintexture in centrosymmetric simple cubic perovskite SrFeO3 thin filmsthrough the combine methods of topological hall effect andresonant soft x-ray diffraction measurements. On the other hand, wehave observed that isoelectronic BaFeO3 is an unusual ferromagneticinsulator. A systematic doping of Sr in Ba – site give rise toinsulator-metal to ferromagnetic-skyrmionic transition, throughpossible skyrmionic-insulating phase. Using controlledSr0.5Ba0.5FeO3-La0.7Sr0.3MnO3 interface we have shown the possibility ofinducing non-trivial spin structure in ferromagnetic La0.7Sr0.3MnO3 layer,that has been detected by the topological transport through thatinterface. In this presentation I will talk about:1. A unique example of magnetic skyrmionic crystal formation in acentrosymmetric perovskite oxide and its detection through“Topological Hall Effect (THE)”.2. BaFeO3 to SrFeO3 : Ferromagnetic insulator to skyrmionic metaltransition.3. Topological transport at Sr0.5Ba0.5FeO3-La0.7Sr0.3MnO3 interface.Double perovskite oxide film and interface.

Abstract

With the success of Planck experiment we have extracted almost all information in the primary temperature anisotropies of CMB. Since Silk damping erases almost all primary perturbations on scales smaller than the Planck/SPT/ACT resolution, it is not possible to make significant progress by further improvement in resolution and we must look elsewhere as far as the initial conditions of the Universe are concerned. The informationerased by Silk damping from the anisotropies ends up as spectral deviations from a blackbody in the CMB spectrum. CMB spectral deviations (mu-type and i-type) can thus gives us new information about the primordial power spectrum on very small scales (ell ~ 10^5-10^8, corresponding to conventional anisotropy experiment with angular resolution of 6 milli-arcsec) which cannot be measured directly. In terms of inflation or initial conditions, these measurements will increase our view of inflation from 7 e-folds accessible at present from the observations of CMB anisotropies and large-scale structure to more than 17 e-folds. I will briefly review the physics behind the spectral features and discuss what information can be gained from their measurement with experiments such as Pixie and PRISM.

Abstract

The last decade has witnessed explosive growth of research on various oxide heterostructures, resulting in the discovery of exciting interfacial phenomena. However, it remains elusive hitherto to control and subsequently measure oxygen sub-lattice in oxide thin films/heterostructures that plays a pivotal role in the structure-property affairs. Specifically, the crystallographic mismatch, violation of local charge neutrality and the difference in chemical potentials between the constituents belonging to thin films/heterostrutures, strongly modify the atomic/electronic structure by – (i) electronic and/or atomic reconstruction (ii) formation of oxygen and/or cation vacancies as well as (iii) large atomic displacements. In this talk, I will present our recent results on ultrathin cuprate layers that undergo profound change in the oxygen sub-lattice structure giving rise to novel structural and electronic properties. In the first half, I will discuss about the infinite-layer SrCuO2, which in the bulk-form, has each Cu2+ ion coordinated by four planar O2- ions. However, for ultrathin layers, we find atransformation from bulk-planar to chain-type structure having apical oxygen via atomic rearrangement [1,2]. This phenomena turns out to be a direct consequence of electrostatic instability associated with the polar nature of SrCuO2. We illustrate that the geometry of CuO4 plaquette in polar cuprates can precisely be controlled from in-plane to out-of-plane upon reducing the film thickness at the sub-unit cell level and this opens possibilities to design structures that have specific functions, e.g. current-carrying layers, charge reservoirs and scaffolding layers. In the second half, I will discuss about CuO, which unlike other 3d transition metal monoxides is found in a low symmetry distorted monoclinic structure rather than rocksalt structure. We demonstrate direct evidence of strain-induced structural transformation from monoclinic to tetragonal phase for ultrathin CuO films grown on SrTiO3 [3]. The experimental confirmation of the high symmetry structure of CuO opens up new avenues to explore electronic and magnetic properties in the context of high Tcsuperconductivity.References:1. D. Samal, G. Koster, et al., Phys. Rev. Lett., 111, 096102 (2013)2. B. Kuiper, D. Samal, G. Koster, et al., Control of oxygen sub-lattice structure in ultrathinSrCuO2 films studied by X-ray photoelectron diffraction (APL materials, 2013 in press)3. D. Samal, G. Koster, et al., Direct structural and spectroscopic investigation of ultrathinfilms of tetragonal CuO: Six-fold co-ordinated copper (Under review)

Abstract

Alloys are mixtures of two or more metals. Alloys in which the positionsof the atoms form an approximate crystal structure, but where the patternformed by considering the chemical elements to which the atoms belong isnot periodic, are of fundamental importance to metallurgy andnanotechnology. Atoms belonging to the same element in such ‘disorderedalloys’ will exhibit a variety of environments. For example, in an alloyconsisting of two elements A and B, the environment of an A atom couldconsist entirely of A atoms, entirely of B atoms, or a mixture of both.Differences in the environments of A atoms leads to differences in theelectronic structures ‘within’ these atoms, which can be detectedexperimentally using core-level X-ray photoelectron spectroscopy(CL-XPS). Therefore the prospect exists of using CL-XPS to probe specificatomic environments in alloys. One possible application of this is tonon-destructively characterise alloy-based nanomaterials and nanodeviceson the atomic scale. However, to make this a reality one must understandthe relationship between an atom’s environment, its electronic structure,and the binding energies of its core levels. I will describe a simple model for the distribution of core level bindingenergies in alloys, and apply it to a variety of disordered alloys, withthe aim of elucidating the relationship between atomic environment andcore level binding energies in alloys. The model reveals a number ofinteresting phenomena which must be taken into account when interpretingthe CL-XPS spectra of these systems. These include anomalously large’disorder broadenings’ of spectra in alloys exhibiting inhomogeneousconcentration profiles; and a counterintuitive relationship between anatom’s core level binding energies, and its local and globalconcentration of ‘unlike’ atoms: increasing the local concentrationalters the core level binding energies in the opposite direction toincreasing the global concentration.

Abstract

Observations of large elliptic flow and suppressed particle production atthe Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (USA) have provided strong evidence, that a de-conned phase of matterconsisting of quarks and gluons commonly known as the Quark Gluon Plasma(QGP) is produced in very high energy nucleus-nucleus collisions. The pro-duction of the QGP is now further explored at the Large Hadron Collider(LHC) at CERN which produces Pb on Pb collisions at 2.76 TeV.At this unprecedented large collision energy, large momentum transferprocesses’ cross sections are signicantly enhanced. It has thus become pos-sible to carry out detailed and robust measurements of jet medium inter-actions. I will present a summary of key results obtained by the ALICEcollaboration in measurements of ow and jet production. My main focuswill be on measurements of charged particle jet production cross sections andjet shapes in proton-proton collisions at 7 TeV. Measured jet production crosssection, charged particle multiplicity in the leading jet, transverse momen-tum distribution about the jet axis, and jet size are compared to predictionsfrom various Monte Carlo models.