Thema:

Ultrafast heat transfer in nanoscale materials

Datum:

27.05.19

Uhrzeit:

16:15

Ort:

H6

Vortragender:

Prof. David Cahill

University of Illinois

Inhalt:

On the macroscopic lengths scales of conventional engineering systems, heat transfer by conduction is generally a slow process well-described by the heat diffusion equation. The characteristic time-scale of diffusion scales with the square of length; therefore, at nanometer length scales, heat conduction can involve processes that occur on time-scales of picoseconds, i.e., a few trillionth of a second. We use ultrafast pump-probe optical techniques to directly study a variety of unconventional heat transfer mechanisms that are critical in nanoscale devices and nanoscale materials. Our studies encompass a diverse variety of systems (metallic nanoparticles for photothermal medical therapies, phase change materials for solid-state memory, and heat-assisted magnetic recording) and physical mechanisms (the thermal conductance of interfaces between dissimilar materials, the non-equilibrium between thermal excitations of electrons, phonons, and magnons, and the cross-terms in the transport of heat, charge, and spin). In this talk I will highlight three recent examples: i) ultrafast thermal transport in the surroundings of plasmonic nanostructures; ii) limitations on ultrafast heating of metallic multilayers imposed by electron-phonon coupling; and iii) the generation of currents of magnetization by the spin-dependent Seebeck effect and extreme heat fluxes exceeding 100 GW m^{-2}.

Ansprechpartner:

T. Kuschel

Thema:

The Widom-Rowlinson model: metastability, mesoscopic and microscopic fluctuations for the critical droplet

Datum:

24.05.19

Uhrzeit:

16:15

Ort:

V3-204

Vortragender:

Elena Pulvirenti

University of Bonn

Inhalt:

In this talk I will discuss the Widom-Rowlinson model on a finite two dimensional torus subject to a stochastic dynamics in which particles are randomly created and annihilated inside the torus according to an infinite reservoir with a given chemical potential. We are interested in the metastable behaviour of the system at low temperature when the chemical potential is supercritical. In particular, we compute the asymptotics of the average time the system needs to condensate and we describe the shape of the critical droplet. Our results rely on a precise analysis of the microscopic and mesoscopic fluctuations of the surface of the critical droplet. This is a joint work in progress with F. den Hollander, S. Jansen, R. Kotecky.

Ansprechpartner:

M. Baake

Thema:

On the relation between low-scale leptogenesis and dark matter

Datum:

28.05.19

Uhrzeit:

14:15

Ort:

D6-135

Vortragender:

Mikko Laine

Univ. Bern

Inhalt:

There has been recent interest in leptogenesis induced by "light" right-handed neutrinos, with masses in the GeV range. Apart from accounting for the observed baryon asymmetry, this scenario may produce lepton asymmetries much larger than the baryon asymmetry. A possible consequence of the latter could be keV-scale sterile neutrino dark matter production through the resonantly enhanced Shi-Fuller mechanism. Making use of a "complete" theoretical framework, which tracks both helicity states of the right-handed neutrinos as well as their kinetic non-equilibrium, and solving numerically a set of non-linear evolution equations, we explore to what extent such a minimal scenario could represent a viable explanation for dark matter and baryogenesis.

Ansprechpartner:

D. Bödeker

Thema:

Matrix product states and matrix product operators

Datum:

13.06.19

Uhrzeit:

14:15

Ort:

D5-153

Vortragender:

Murod Bahohavinov

Bielefeld University

Inhalt:

Ansprechpartner:

Jürgen Schnack

Thema:

Critical behaviour and characteristic polynomials of non-Hermitian random matrices

Datum:

23.05.19

Uhrzeit:

16:15

Ort:

D5-153

Vortragender:

Nicholas Simm

University of Sussex

Inhalt:

I will discuss some recent developments regarding the normal matrix model. In particular my interest will be in certain critical models where the limiting support of the eigenvalues can radically change its topology by slightly adjusting an external parameter. I will discuss how aspects of the model can be explicitly mapped to the study of expectations of characteristic polynomials of non-Hermitian random matrices (e.g. Ginibre or truncated unitary). Many of these averages are related to Painlevé transcendents, and by exploiting this, a precise and non-trivial asymptotic expansion of partition functions can be calculated in the critical models. This is joint work with Alfredo Deaño (University of Kent).

Ansprechpartner:

Gernot Akemann

Thema:

The Laguerre Unitary Process

Datum:

12.06.19

Uhrzeit:

16:15

Ort:

V3-201

Vortragender:

Jesper Ipsen

University of Melbourne

Inhalt:

We define a new matrix-valued stochastic process with independent stationary increments from the Laguerre Unitary Ensemble, which in a certain sense may be considered a matrix generalisation of the gamma process. We show that eigenvalues of this matrix-valued process forms a spatiotemporal determinantal point process and give an explicit expression for the correlation kernel in terms of Laguerre polynomials. Furthermore, we show that in an appropriate long time scaling limit, this correlation kernel becomes identical to that of Dyson Brownian Motion.

Ansprechpartner:

Gernot Akemann