Thema: 
Towards the alloptical transistor – Fabrication, characterization and application of plasmonic nanostructures 
Datum: 
17.07.17 
Uhrzeit: 
16:15 
Ort: 
H6 
Vortragender: 

Universität Oldenburg 

Inhalt: 
They are ubiquitous and indispensable in our daily life: Electronic transistors are the key elements and the smallest processing units in our smartphones and computers  basically in every electronic device. Even though the miniaturization and optimization seems to be an ongoing and never ending process, the physical limit of the clock frequency of electronic transistors is about to be reached. Within my talk I will present the idea of an alloptical transistor, for which the limitation of the conventional, electronic switching speed might not be valid. This optical switch is based on the interaction of propagating, metalbound SurfacePlasmon Polariton (SPP) waves in confined metallic nanoantennas with single or few excitonic molecules. These metallic nanoantennas are able to localize farfield electromagnetic waves in volumes of a fraction of the wavelength [1]. Hence the interaction of light with organic or inorganic molecules can be enhanced by several orders of magnitude. Standard tools for fabricating plasmonic antenna structures with sub20 nm feature sizes are Electron Beam Lithography or Gabased Focused Ion Beam (FIB) Milling. These structures however show limited electric field localization. Within my talk, I will present new ideas to overcome this limitation and to fabricate plasmonic nanostructures with feature sizes of 6 nm and less by a combination of He and Ga ion beam milling. The superior ability to concentrate electric fields within these structures is demonstrated using linear and nonlinear confocal optical microscopy [2]. In a second step, twodimensional tapered metallic wires with Gaion beam written gratings are fabricated to efficiently guide light into the transistor core. Here, our emphasis is placed on an efficient coupling process from farfield propagating light to metalbound SPPs and on a dispersionreduced propagation of the SPP waves [3]. A future idea for the interaction of the fabricated plasmonic nanostructures with dye molecules is finally discussed. Within this proposed scheme, the switching speed and hence the clock rate of the optical transistor is only limited by the switching speed of the involved excitonic molecules, which can be on the order of less than 100 fs. [1] P. Bharadwaj, P. Deutsch, and L. Novotny, Optical Antennas. Adv. Opt. Photon., 1, 438 (2009) [2] H. Kollmann, M. Silies, et al., Nano Letters 14, 4778 (2014) [3] J. Yi, M. Silies, M. Silies et al., ACS Nano 4, 347 (2017) 
Ansprechpartner: 
Thema: 
Random field of gradients  Critical Phenomena and Scaling limits 
Datum: 
02.06.17 
Uhrzeit: 
16:15 
Ort: 
V2210/216 
Vortragender: 

University of Warwick 

Inhalt: 
Random fields of gradients are families of highly correlated random variables arising in the studies of e.g. random surfaces & interfaces and discrete Gaussian Free Fields (GFFs), random geometry, field theory, and elasticity theory. Recently their study has attained a lot of attention. There are several reasons for that. On one hand, these are approximations of critical systems and natural models for a macroscopic description of elastic systems as well as, in a different setting, for fluctuating phase interfaces. In addition, over continuum, the level lines of the GFF are connected to Schramm's SLE (an active field of modern mathematics for understanding critical phenomena) and the fields are natural spacetime analog of Brownian motions and as such a simple random object of widespread application and great intrinsic beauty. Gradient fields are likely to be an universal class of models combining probability, analysis and physics in the study of critical phenomena, and these massless fields are also a starting point for many constructions in field theory. A more recent connection are mathematical models for the CauchyBorn rule of materials, i.e., a microscopic approach to nonlinear elasticity. The latter class of models requires that interaction energies are nonconvex functions of the gradients. Open problems over the last decades include unicity of Gibbs measures and strict convexity of the free energy as well as scaling limits to the Gaussian Free Field and the decay behaviour of twopoint correlation functions. After giving a broad introduction to this recently active field of research we present in the talk Gaussian decay of correlations and the scaling to the Gaussian Free Field for a class of massless fields with nonconvex interaction using a recent renormalisation group approach. 
Ansprechpartner: 
Thema: 
Relativistic wideangle galaxy bispectrum on the lightcone: Allsky analysis 
Datum: 
18.07.17 
Uhrzeit: 
14:15 
Ort: 
D6135 
Vortragender: 

Argelander Institut für Astronomie, Bonn 

Inhalt: 
Given the important role that the galaxy bispectrum has recently acquired in cosmology and the scale and precision of forthcoming galaxy clustering observations, it is timely to derive the full expression of the largescale bispectrum going beyond approximated treatments which neglect integrated terms or higherorder bias terms or use the Limber approximation. On cosmological scales, relativistic effects that arise from observing on the past lightcone alter the observed galaxy number counts, therefore leaving their imprints on Npoint correlators at all orders. Working in spherical Bessel coordinates, in this talk I will show that it is possible to derive a compact expression for the power spectrum and bispectrum that encompasses all the physical effects at first and second order, including integrated (along the line of sight) terms. 
Ansprechpartner: 
Thema: 
Leitfähigkeitsänderungen von Nanoporen bei Translokation geladener Teilchen 
Datum: 
13.07.17 
Uhrzeit: 
14:15 
Ort: 
D5153 
Vortragender: 
Christian Nils Eidecker 
Universität Bielefeld 

Inhalt: 

Ansprechpartner: 
Thema: 
Nonorthogonality of eigenvectors from the HaagerupLarsen theorem 
Datum: 
01.06.17 
Uhrzeit: 
17:00 
Ort: 
D5153 
Vortragender: 
Wojciech Tarnowski 
Jagiellonian University Krakow 

Inhalt: 
Biunitarily invariant ensembles have been thoroughly studied in recent years from the point of view of statistics of eigenvalues. An enhanced symmetry of the probability distribution function allows us to expect that all spectral properties will be determined by the singular values only. Indeed, for large matrices, a mapping between onepoint densities is known as the HaagerupLarsen theorem. Recently, this mapping has been extended to all kpoint functions (KieburgKösters). During my talk, I will present a recent extension of the HaagerupLarsen theorem, which gives a simple mapping between the radial spectral cumulative distribution function and a certain onepoint eigenvector correlation function, built out of (nonorthogonal) left and right eigenvectors. I will discuss also its relation with the stability of the spectrum. 
Ansprechpartner: 
Thema: 
Matrix product ensembles of Hermitetype 
Datum: 
21.06.17 
Uhrzeit: 
16:00 
Ort: 
V3201 
Vortragender: 
DangZheng Liu 
Institute of Science and Technology Austria & University of Science and Technology of China 

Inhalt: 
We investigate spectral properties of a Hermitised random matrix product which, contrary to previous product ensembles, allows for eigenvalues on the full real line. We find an explicit expression of the joint probability density function as a biorthogonal ensemble. As an interesting example, we focus on the product of GUE and LUE matrices and provide explicit expressions both for the biorthogonal functions and the correlation kernel. Then a new doubleside kernel is found at the origin, which is slightly different from the Bessel kernel. This talk is based on joint work with P. J. Forrester and J. R. Ipsen. 
Ansprechpartner: 