# Aktuelle Veranstaltungen

## Kolloquium

Thema:

### Ultrafast terahertz spectroscopy: probing and controlling fundamental motions of electrons, spins and ions

Datum:

08.05.17

Uhrzeit:

16:15

Ort:

H6

Vortragender:

Dr. Tobias Kampfrath

Fritz Haber Institut and FU Berlin

Inhalt:

The terahertz (THz) frequency range is attracting increasing interest for both applied and fundamental reasons. On one hand, bit rates in current information technology may soon approach the THz range. Therefore, it is warranted to study the behavior of materials at THz frequencies. This goal is also highly interesting from a scientific viewpoint because its low photon energy (4.1 meV at 1 THz) makes THz radiation an excellent probe of many elementary excitations of solids, for instance lattice vibrations (phonons), conduction electrons, excitons and spin waves. This talk is supposed to provide an introduction to THz spectroscopy of solids. It will show how ultrashort THz electromagnetic pulses (duration <1 ps) are used as ultrafast Ohmmeters and Amperemeters to gain insight into elementary motions of electrons and spins and their coupling to the crystal lattice. Part of these results has paved the way to a new class of broadband THz radiation sources. Finally, examples are provided to demonstrate that extremely strong THz fields (~MV/cm) can even be used to push matter into novel states.

Ansprechpartner:

M. Meinert

## Kolloquium Mathematische Physik

Thema:

### tba

Datum:

04.05.17

Uhrzeit:

16:15

Ort:

V2-210/216

Vortragender:

Mathieu Lewin

Université Paris Dauphine

Inhalt:

Ansprechpartner:

M. Baake

Thema:

Datum:

06.06.17

Uhrzeit:

14:15

Ort:

D6-135

Vortragender:

Bastian Brandt

Univ. Frankfurt

Inhalt:

Ansprechpartner:

W. Unger

Thema:

Datum:

06.04.17

Uhrzeit:

14:15

Ort:

D5-153

Vortragender:

TU Berlin

Inhalt:

Ansprechpartner:

Jürgen Schnack

## Seminar Mathematische Physik

Thema:

### Induced QCD

Datum:

02.02.17

Uhrzeit:

16:00

Ort:

D5-153

Vortragender:

Robert Lohmeyer

University of Regensburg

Inhalt:

We explore an alternative discretization of continuum SU(Nc) Yang-Mills theory on a Euclidean spacetime lattice, originally introduced by Budzcies and Zirnbauer. In this discretization the self-interactions of the gauge field are induced by a path integral over Nb auxiliary boson fields, which are coupled linearly to the gauge field. The main progress compared to earlier approaches is that Nb can be as small as Nc. In the main part of this talk we (i) extend the proof that the continuum limit of the new discretization reproduces Yang-Mills theory in two dimensions from gauge group U(Nc) to SU(Nc), (ii) derive refined bounds on Nb for non-integer values, and (iii) perform a perturbative calculation to match the bare parameter of the induced gauge theory to the standard lattice coupling. Furthermore, we will present some numerical evidence in support of the conjecture that the induced gauge theory reproduces Yang-Mills theory also in more than two dimensions.

Ansprechpartner:

Gernot Akemann

## Seminar AG Zufallsmatrizen

Thema:

### Radial statistics in the two-dimensional one-component plasma and associated phase transitions

Datum:

25.01.17

Uhrzeit:

14:15

Ort:

V3-201

Vortragender:

Pierpaolo Vivo

King's College London

Inhalt:

The two-dimensional one-component plasma is an ubiquitous model in statistical physics. For special values of the coupling constant $\beta q^2$ (where q is the particles charge and ? the inverse temperature), the model also corresponds to the eigenvalues distribution of normal matrix models. I will discuss several features of the system - in the limit of large number N of particles for generic values of the coupling constant. I show that the statistics of a certain class of radial observables produces a rich phase diagram: their asymptotic behaviour in terms of large deviation functions is calculated explicitly, including next-to-leading terms up to order 1/N. I will discuss a split-off phenomenon associated to atypical fluctuations of the edge density profile, and show explicitly that a failure of the fluid phase assumption of the plasma can break a genuine 1/N-expansion of the free energy. An outlook on the problem of spatially constrained Coulomb gas systems in any dimensions and universality of the associated third-order phase transition will also be offered.

Ansprechpartner:

Mario Kieburg

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