Conference Photos - WE Heraeus Seminar

April 19 - 23, 2015, Bad Honnef, Germany

Conference Poster A2 and Report

PPNEC_A2.pdf

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HeraeusBericht587.pdf

WE Heraeus Seminar Program 2015

Poster List - Alphabetical Order

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Mirco Ackermann*

Universität Zürich, Switzerland

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Statistics of the Transition Matrix in samples
showing Anderson Localization

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In three dimensions, Anderson localization has been shown to occur for light and
ultrasound through time of flight and time dependent mean square width
measurements [1–3]. For ultrasound, additional statistical evidence of localization
exists, based on the intensity distribution of the speckles. In localizing samples, the
speckle intensity deviates from the Rayleigh law [1 and 4]. A first aim of this project is
to measure such a distribution for light. Further, we want to measure the transmission
matrix (TM) of localizing and non-localizing samples and compare statistical
properties such as the singular value decomposition of the TM to gain further
understanding how strong localization changes the transport of
waves.

[1] H. Hu, Nature Physics, 4, 945 (2008)

[2] C. M. Aegerter, EPL, 75, 562, (2006)

[3] T. Sperling, Nat Photon, 7, 48 (2013)

[4] T. M. Niewenhuizen, PRL, 74, 2674 (1995)

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K. Annou*, D. Bara and D. Bennaceur-Doumaz

Centre de Développement des Technologies Avancées, Baba Hassen, Algiers, Algérie

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Cairns-Gurevich equation for soliton in plasma expansion into vacuum

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Plasma expansion and soliton formation in laser created plasma are addressed. Nonlinear acoustic waves in plasmas where the combined effect of trapped and nonthermal electrons are dealt with, in plasma expansion are studied. Using the perturbation method, a modified Korteweg-de Vries equation (mKdV) that describes the ion acoustic waves is derived. The plasma is modeled by a Cairns distribution function for nonthermal electrons combined with Gurevich distribution function for the trapped electrons. It is found that parameters taken into account have significant effects on the properties of nonlinear waves as well as on plasma expansion into vacuum. We point out, that this work has been motivated by space and laboratory plasma observations of plasmas containing energetic particles, combined with trapped particles. Furthermore, this study is of interest in the context of the investigation of mono-energetic ion beams from intense laser interactions with plasmas.

[1] L.N. Hau and W.-Z. Fu, Phys. Plasmas 14, 110702 (2007).

[2] M. P. Leubner, Phys. Plasmas 11, 1308 (2004).

[3] Y. Huang, Y. Bi, X. Duan, X. Lan, N. Wang, X. Tang, and Y. He, Appl. Phys. Lett. 92, 141504 (2008).

[4] T. E. Itina, J. Hermann, P. Delaporte, and M. Sentis, Phys. Rev. E 66, 066406 (2002).

[5] E. C. Shoub, Astrophys. J. 266, 339 (1983).

[6] A. A. Plyutto, Sov. Phys. JETP 12, 1106 (1961).

[7] G. Hairapetian and R. L. Stenzel, Phys. Rev. Lett. 61, 1607 (1988).

[8] G. Hairapetian and R. L. Stenzel, Phys. Fluids B 3, 899 (1991).

[9] G. Williams, F. Verheest, M.A. Hellberg, M.G. Anowar, and I. Kourakis. Phys.Plasmas 21, 092103 (2014).

[10] K. Annou and R. Annou, Pramana – J. Phys. 78, (2012).

[11] K. Annou and R. Annou, Phys. Plasmas 19, 043705 (2012).

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M. Ayoub*, J. Imbrock, J. Hanisch, and C. Denz

Institute of Applied Physics and Center for Nonlinear Science (CeNoS)

University of Muenster, Corrensstraße 2/4, 48149 Muenster, Germany

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Frequency Conversion in Disordered Nonlinear Photonic Structures

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Nonlinear disordered photonic structures possess a random distribution of ferroelectric domains which can be used for broadband frequency conversion. The spatial randomness strongly affects all relevant parameters in the quasi-phase matching process such as polarization, propagation, coherence, etc. The current investigations are devoted to visualize nonlinearly these disordered ferroelectric domains using so-called Čerenkov SHG microscopy (ČSHGM), in their static as well as dynamic form [1] (see Fig. 1a, b).

Fig. 1: (a, b) ČSHGM images of two different domain size statistics in SBN; (c, d) SHG polarization analysis corresponding the statistics status in (a, b).

Recently, several effects associated with changing the degree of the domain disorder have been discussed. Primarily interesting is the effect of spatial disorder on the polarization properties of frequency conversion [2]. Thus, for different statistics of domain sizes, measured by ČSHGM, the polarization properties of the allowed parametric have been analyzed [3] (see e.g. Fig. 1c, d). As an example, the measurements of the polarization in strontium barium niobate (SBN), as a ferroelectric medium of 4mm symmetry were investigated to determine the relative strengths of non-zero components of the second-order susceptibility tensor, d32 and d33 for the frequency doubling process and the incoherent interplay between d24, d31, and d33, for the frequency tripling process. The results show that changing of the domain distributions redistribute the corresponding Fourier coefficients, which in turn effectively weight the contribution of different possible processes.

[1] Y. Sheng et al., Opt. Exp. 18, 16539 (2010)

[2] J. Trull et al. Opt. Exp. 15, 15868 (2007)

[3] M. Ayoub et al., in preparation (2015)

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Sebastian Brodbeck*°, H. Suchomel°, M. Amthor°, A. Wolf°, M. Kamp°,
C. Schneider°, and S. Höfling°^

°Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen-Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany

^SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews, KY 16 9SS, United Kingdom

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Electro-optical tuning of exciton-polariton condensates

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We investigate exciton-polariton condensates in electrically contacted, doped microcavities under the influence of external bias. Shifts of the polariton emission of hundreds of µeV are observed with increasing electric field both below and above condensation threshold. In the conventional micropillar geometry, we observe a blueshift due to carrier tunneling and field screening effects as reported previously [1].

By choosing a semi-planar device geometry where the quantum wells are not etched through, we significantly extend the range of electric fields and instead observe a redshift of the polariton emission. We attribute this different tuning behavior to carrier spreading in the unetched quantum wells and consequently reduced field screening. The polariton redshift is in good agreement with the shift calculated from the experimentally determined exciton Stark shift and the bias-dependency of the Rabi splitting [2].

Fig. 1: Photoluminescence spectra above condensation threshold for the micropillar sample (a) exhibiting a blueshift with increasing nominal electric field F and for the semi-planar sample (b) exhibiting a redshift. The left half of each spectrum is recorded at zero electric field and the right half at F~150kV/cm.

[1] P. Tsotsis et al., Phys. Rev. Appl. 2, 014002 (2014)

[2] S. Brodbeck et al., “Impact of lateral carrier confinement on electro-optical tuning properties of polariton condensates”, submitted
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Bruno Gompf*, Katharina Junge, Audrey Berrier, and Martin Dressel

I. Physikalisches Institut, Universität Stuttgart

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Müller-Matrix ellipsometric investigations on strongly scattering granular films

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Ellipsometric measurements are usually described in the framework of Fresnel’s equations, whereas the scattering of light on spherical particles is described by Mie-theory. But what happens when strongly scattering dielectric Mie-particles form a thin film? For our eyes transparent samples with dielectric inclusions appear white. On the one hand one expect diffuse reflection close to that of a Lambertian surface, on the other hand new phenomena can arise, like the appearance of a coherent backscattering peak or Anderson localization, i.e. the complete trapping of light in the medium. Even though we are surrounded by white surfaces in daily life, up to now only few systematic Müller-Matrix (MM) investigations on strongly scattering samples have been published.

We present a systematic investigation of granular Zn0 films of different thickness composed of nanoparticles with 300nm diameter on glass. On these samples we perform MM ellipsometry as well as MM scatterometry over a broad angular range (20° to 90°) at different wavelengths ranging from the UV up to the near infrared. Although the samples are extremely rough, they exhibit a strong reflection peak additionally to the broad incoherent background due to subsurface scattering. The peak intensity depends on the wavelength and on the incident polarization with a Brewster-angle corresponding to a negative effective neff of the granular film. In principle non-depolarizing samples can be described by 7 independent optical parameters and homogenous depolarizing samples by 10. In contrast white samples are inherently inhomogeneous. Therefore a careful analysis of the measured MMs is necessary. To reveal the physics behind the different scattering phenomena we analyze the measured MMs by matrix decomposition. We found that the degree of polarization strongly depends on wavelength and that the depolarization of the off-specular incoherent background cannot simply be described by a perfect depolarizer.

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Y. H. Goolam Hossen*, F. Petruccione, I. Sinayskiy

School of Chemistry & Physics, UKZN, Durban, South Africa

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Analysis of open quantum walks with non-reversal and non-repeating properties

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Given that the path of a particle is non-reversal, its quantum trajectory is analysed using the formalism of Open Quantum Walk (OQW) on finite graphs [1]. The non-reversal OQW is established on a line to which a memory is associated so that the particle cannot step back. Its spread is compared with that of the OQW. The principle is then extended to a two-dimensional lattice whereby the particle can move in one of the four cardinal directions to a new site or stay on the same spot. The probability distribution of the 2D non-reversal OQW varies with respect to the parameters of the coin operators employed. In order to make the walk more interesting, the particle is made to change direction in every step that it moves. This condition is referred as the non-repeating behaviour. Finally, the OQW with both non-reversal and non-repeating properties is compared with the spread of the ordinary OQW, the unitary quantum Self-Avoiding Walks (SAWs) [2,3] and the classical SAWs.

[1] Attal et al, J Stat Phys 147:832–852 (2012)

[2] Machida et al, arXiv: quant-ph /1307.6288v2 (2013)

[3] Proctor et al, Phys. Rev. A 89, 042332 (2014)

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Harald R. Haakh*^, Sanli Faez^°, and Vahid Sandoghdar^

^Max-Planck-Institute for the Science of Light, Erlangen, Germany

°Institute of Physics, University of Leiden, Leiden, Netherlands

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Polaritonic phase diagram for ensembles of quantum scatterers in a waveguide

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The propagation of light in photonic crystal waveguides coupled to individual quantum emitters has moved to the focus of experiment and theory [1-3] lately, with prospects of strong many body coupling outside the regime of cavity QED [3,4]. Recent demonstrations of efficient coherent coupling between quantum scatterers and guided modes of an optical fiber [5] suggest a novel versatile platform for the study of polariton formation and optical transport in reduced dimensions. We present a theoretical characterization of the polariton modes formed in this system (Fig 1), indicating the presence of several phases dominated by either localized or extended states and obtain a full phase diagram. A rigorous theoretical treatment based many-body Green's functions [6-8] allows for a careful analysis of the role of nonradiative near-field coupling, density, and disorder. We link the different phases to the optical transport properties and the spectral response of the waveguide. The results can be immediately transferred to, e.g., NV centers in diamond [9] or quantum dots in silicon waveguides [2,3,10].

[1] J. Topolancik, B. Ilic, and F. Vollmer, Phys Rev. Lett. 99, 253901 (2007).

[2] L. Sapienza H. Thyrrestrup, S. Stobbe, P. Garcia, S. Smolka, and P. Lodahl, Science 327, 1352 (2010).

[3] H. Thyrrestrup, S. Smolka, L. Sapienza, and P. Lodahl, Phys. Rev. Lett 108, 113901 (2012).

[4] A. Cazé and R. Carminati, Phys. Rev. Lett. 111, 053901 (2013).

[5] S. Faez, P. Türschmann, H. R. Haakh, S Götzinger, and V. Sandoghdar, Phys. Rev. Lett. 111, 053901 (2013).

[6] M. Rusek, A. Orlowski and J. Mostowski J Phys. Rev. E 53, 4122 (1996).

[7] M. Rusek, J. Mostowski and A. Orlowski A Phys. Rev. A 61 022704 (2000).

[8] S. Skipetrov and A. Goetschy, J. Phys. A, 44, 065102 (2010).

[9] T. Babinec, B. Hausmann, M. Khan, Y. Zhang, J. Maze, P. Hemmer, and M. Loncar, Nature Nanotech. 5, 195 (2010).

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Craig Hamilton*

University of Prague, Czech Republic

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Armen Hayrapetyan*

Max Planck Institute of Complex Systems, Dresden

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Patrik Hlobil*

Institute of Condensedd Matter Theory, KIT

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Andrey Iljin*

Department of Crystals, Institute of Physics, National Academy of Sciences of Ukraine, Kiev, Ukraine

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Eli Levy*

Department of Physics, Technion, Haifa, Israel

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Pritam Pai*

Physikalisches Institut, Universität Bonn

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Elena Redchenko*

Elena, Moscow Institute of Physics and Technology, Russia

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Andreas Sinner*, Klaus Ziegler

Universität Augsburg, Institut für Physik

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Two-parameter scaling theory of transport near a spectral node

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We investigate the finite-size scaling behavior of the conductivity in a two-dimensional Dirac electron gas within a chiral sigma model. Based on the fact that the conductivity is a function of system size times scattering rate, we obtain a two-parameter scaling flow toward a finite fixed point. The latter is the minimal conductivity of the infinite system. Depending on boundary conditions, we also observe unstable fixed points with conductivities much larger than the experimentally observed values, which may account for results found in some numerical simulations. By including a spectral gap we extend our scaling approach to describe a metal-insulator transition.

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Daniela Schneevoigt^, Frederik Bub^, Alexander Sprafke^*, Ralf B. Wehrspohn^°, André Hoffmann', Karsten Bittkau', Reinhard Carius', Samuel Wiesendanger'', and Carsten Rockstuhl'''

^Martin- Luther-Universität Halle-Wittenberg, Germany

°Fraunhofer IWM, Halle, Germany

'Forschungszentrum Jülich GmbH, Germany

''Friedrich-Schiller-Universität Jena, Germany

'''Karlsruher Institut für Technologie, Germany

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Opaline Photonic Crystals as Back Side Reflectors for Thin-Film Silicon Solar Cells

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3D photonic crystals, such as opaline structures, have the potential to increase the efficiency of solar cells by enabling advanced light management concepts. E.g., applied to the back side of a solar cell they provide various functions that can enhance the light path in the cell. Light in a specific spectral interval that is not absorbed during its first passage through the solar cell is strongly back reflected if the opal satisfies a Bragg condition. Light at other wavelengths might be diffracted back into the cell by the opal. By both means the probability of light absorption and thus the efficiency of the solar cell is increased. Here, we present the successful fabrication of large-area opaline structures at the back side of 1μm thick hydro- genated microcrystalline silicon (μc-Si:H) single junction solar cells via an automated spray coating process. The optical, structural, and electrical characteristics of these structures on different μc-Si:H textures were analyzed and the photovoltaic characteristics of the completely integrated system were evaluated and compared to simulations.

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P. Türschmann*^, S. Faez^, H. R. Haakh^, T. Utikal^, N. Rotenberg^, S. Götzinger^°, and V. Sandoghdar^°

^Max Planck Institute for the Science of Light (MPL), D-91058 Erlangen, Germany

°Department of Physics, Friedrich Alexander University Erlangen-Nürnberg, D-91058 Erlangen, Germany

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Single Molecules Coupled to a Dielectric Nanoguid

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An efficient interface between photons and a controlled number of individual quantum emitters would allow one to study fundamental many-body effects relying on cooperative phenomena and polaritonic excitations. Our experimental system consists of a glass capillary with a subwavelength and high refractive index core that is doped with dye molecules. The highly confined mode of such a nanoguide can deliver coupling efficiencies up to 18%. By combining high-resolution microscopy with extinction, fluorescence excitation and resonance fluorescence spectroscopy, we demonstrate the versatility of our geometry for reaching of high optical densities while maintaining a low background and addressability of each single emitter [1]. We discuss our experimental results, the prospects of our approach, as well as the ongoing efforts for achieving higher coupling efficiencies in a chip-compatible geometry.

[1] S. Faez, P. Türschmann, H.R. Haakh, S. Götzinger, and V. Sandoghdar, Phys. Rev. Lett. 113, 213601 (2014).

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