Thema:

Spin Currents in Ferromagnet/Normal Metal Hybrid Structures

Datum:

21.05.12

Uhrzeit:

17:15

Ort:

H6

Vortragender:

Dr. Sebastian Gönnenwein

Walther-Meißner-Institut Garching

Inhalt:

A pure spin current – i.e., the directed flow of spin angular momentum – is a fascinating manifestation of spin physics in the solid state. In ferromagnet/normal metal hybrid bilayers, pure spin currents can be generated, e.g., by means of spin pumping [1], or via the application of thermal gradients [2]. Interestingly, both of these approaches hinge on non-equilibrium, “hot” magnetization states in the ferromagnet, and thus can be ascribed to the emerging field of spin caloritronics. In the talk, I will introduce and compare our recent experimental investigations of pure spin currents in ferromagnet/normal metal hybrid devices. We took advantage of the spin pumping process [3] as well as local thermal gradients [4] to induce pure spin currents in these hybrid structures, and exploited the inverse spin Hall effect to detect the spin current in the normal metal layer. Our results show that spin current generation is possible from both electrically conductive as well as electrically insulating ferromagnets (so-called magnetic insulators), with comparable efficiency. This opens interesting perspectives for the study and the exploitation of pure spin currents in particular in electrically insulating magnetic materials. [1] O. Mosendz et al., Phys. Rev. Lett. 104, 046601 (2010). [2] K. Uchida et al., Nature 455, 778 (2008). [3] F. D. Czeschka et al., Phys. Rev. Lett. 107, 046601 (2011). [4] M. Weiler et al., Phys. Rev. Lett. 108, 106602 (2012).

Ansprechpartner:

A. Thomas

Thema:

tba

Datum:

01.06.12

Uhrzeit:

16:15

Ort:

H11

Vortragender:

Reinhard F. Werner

Leibniz Universität Hannover

Inhalt:

Ansprechpartner:

M. Baake

Thema:

D mesons and charmonium states in hot isospin asymmetric strange hadronic matter

Datum:

22.05.12

Uhrzeit:

14:15

Ort:

D6-135

Vortragender:

Amruta Mishra

IIT Delhi

Inhalt:

We study the properties of D and \bar{D} mesons in hot isospin asymmetric strange hadronic matter, arising due to their interactions with the hadrons in the hyperonic medium. The interactions of D and \bar{D} mesons with these light hadrons are derived by generalizing the chiral SU(3) model used for the study of hyperonic matter to SU(4). The nucleons, hyperons, the scalar isoscalar meson, \sigma and the scalar-isovector meson, \delta as modified in the strange hadronic matter, modify the masses of D and \bar D mesons. We also study the mass modifications of the charmonium states J/\psi, \psi(3686) and \psi(3770) in the isospin asymmetric strange hadronic matter at finite temperatures and investigate the possibility of the decay of the charmonium states into D\bar D pairs in the hot hadronic medium. The mass modifications of these charmonium states arise due to their interaction with the gluon condensates of QCD, simulated by a scalar dilaton field introduced to incorporate the broken scale invariance of QCD within the effective chiral model. The strong dependence on density of the in-medium properties of the D, \bar D and the charmonium states, as well as the partial decay widths of charmonium states to D\bar D pairs, found in the present investigation, will be of direct relevance in observables like open charm enhancement as well as J/\psi suppression in the compressed baryonic matter (CBM) experiments at the future Facility for Antiproton and Ion Research, GSI, where the baryonic matter at high densities is planned to be produced.

Ansprechpartner:

H. Satz

Thema:

The pentagonal Cairo spin lattice

Datum:

24.05.12

Uhrzeit:

14:15

Ort:

D5-153

Vortragender:

Ioannis Rousochatzakis

IFW Dresden

Inhalt:

Ansprechpartner:

Jürgen Schnack

Thema:

Dimensions of trees with a unique infinite spine

Datum:

03.05.12

Uhrzeit:

16:15

Ort:

D5-153

Vortragender:

Sigurdur Stefansson

Nordita, Stockholm

Inhalt:

Consider a class of random rooted trees in which the trees have a unique self avoiding path from the root to infinity (an infinite spine). Such trees arise naturally in a number of models, examples being the uniform planar tree, critical Galton-Watson trees conditioned on survival and the uniform spanning tree on Z^2. I will discuss two common notions of dimension of random graphs, the spectral dimension and the Hausdorff dimension. The spectral dimension is defined by a relation to the probability that a simple random walk returns to its original position after large time t and the Hausdorff dimension is defined in terms of the volume growth of graph balls of large radius R. Using generating function techniques we develop a relation between the Hausdorff and spectral dimension of trees with a unique infinite spine. Furthermore, it is shown that if the finite outgrowths along the spine are independent and identically distributed, then both the Hausdorff and spectral dimension can be determined by the volume distribution of the outgrowths, provided that the probability of the height of the outgrowths exceeding n falls off fast enough.

Ansprechpartner:

Gernot Akemann

Thema:

Spherical ensembles of random matrices

Datum:

16.05.12

Uhrzeit:

16:15

Ort:

V3-201

Vortragender:

Anthony Mays

University of Melbourne

Inhalt:

Abstract: The Ginibre ensembles contain matrices with iid Gaussian entries (real, complex or real quaternion). The eigenvalues of these matrices are roughly uniformly distributed in a disk of radius square root of N, a consequence of the 'circular law'. However, if we take two Ginibre matrices A and B and form the product Y equals A inverse times B then the circular law no longer holds. Rather we find a 'spherical law': that the eigenvalues are roughly uniformly distributed on the surface of a sphere (under stereographic projection). In this talk I will discuss the calculation of the correlation functions for the real and complex spherical ensembles, drawing analogies to similar calculations in the Ginibre ensembles. We will also pay special attention to the problems presented by real ensembles.

Ansprechpartner:

Gernot Akemann