Abstract

In this lecture I first discuss the fundamentals of self-organizedformation of nanoscale dot and ripple patterns due to ion-inducedperturbation of a surface layer which exhibits a certain ion-inducedviscosity. Viscous flow is the smoothing mechanism and ion-inducederosion and subsurface mass transport in the collision cascade is theroughening mechanism.Examples of ripple pattern formation on Si, SiO_2 and a-C surfaces anddifferent incident ions are presented. The experimental observations arethen compared to predictions made by simple theoretical models. Theparameters needed in the theoretical models are obtained from binarycollision Monte Carlo Simulations (SDTRIM) or molecular dynamicssimulation. In this context the crater function concept is exemplified.The important role of metal impurities on pattern formation ishighlighted with several examples. It is shown that silicide or carbideformation is now the driving force for pattern formation. Co-depositionof metal impurities from multiply sources allow the design of dotpatterns with predefined symmetry.Finally I discuss the dynamic behavior of ion induced patterns, inparticular the propagation of ripples across the surface. Recentexperiments on ripple propagation will be compared with theoreticalpredictions with some surprising results.

Abstract

We analyze the dynamics of overlapping antiparallel treadmillingmicrotubules in the presence of crosslinking processive motor proteinsthat counterbalance an external force. We show that coupling the force-dependent velocity of motors and the kinetics of motor exchange with abath in the presence of treadmilling leads generically to oscillatorybehavior. In addition, we show that coupling the polymerization kineticsto the external force through the kinetics of the crosslinking motors canstabilize the oscillatory instability into finite-amplitude nonlinearoscillations and may lead to other scenarios, including bistability. Reference : (2012) EPL 98 68005

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)