Thema: 
Ultrafast terahertz spectroscopy: probing and controlling fundamental motions of electrons, spins and ions 
Datum: 
08.05.17 
Uhrzeit: 
16:15 
Ort: 
H6 
Vortragender: 

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: 
Thema: 
Induced QCD 
Datum: 
06.06.17 
Uhrzeit: 
14:15 
Ort: 
D6135 
Vortragender: 

Univ. Frankfurt 

Inhalt: 

Ansprechpartner: 
Thema: 
Connecting Spin Hamiltonians from DFT Calculations to Experiment 
Datum: 
06.04.17 
Uhrzeit: 
14:15 
Ort: 
D5153 
Vortragender: 
Shadan Ghassemi 
TU Berlin 

Inhalt: 

Ansprechpartner: 
Thema: 
Induced QCD 
Datum: 
02.02.17 
Uhrzeit: 
16:00 
Ort: 
D5153 
Vortragender: 
Robert Lohmeyer 
University of Regensburg 

Inhalt: 
We explore an alternative discretization of continuum SU(Nc) YangMills theory on a Euclidean spacetime lattice, originally introduced by Budzcies and Zirnbauer. In this discretization the selfinteractions 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 YangMills theory in two dimensions from gauge group U(Nc) to SU(Nc), (ii) derive refined bounds on Nb for noninteger 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 YangMills theory also in more than two dimensions. 
Ansprechpartner: 
Thema: 
Radial statistics in the twodimensional onecomponent plasma and associated phase transitions 
Datum: 
25.01.17 
Uhrzeit: 
14:15 
Ort: 
V3201 
Vortragender: 
Pierpaolo Vivo 
King's College London 

Inhalt: 
The twodimensional onecomponent 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 nexttoleading terms up to order 1/N. I will discuss a splitoff 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/Nexpansion of the free energy. An outlook on the problem of spatially constrained Coulomb gas systems in any dimensions and universality of the associated thirdorder phase transition will also be offered. 
Ansprechpartner: 