# Condensed Matter Theory

The dates of the condensed matter theory seminar are announced via mailing lists. Anonye interested can join the lists here. Note that many people will automatically receive the announcement via institute lists.

These lists will also be used occasionally to broadcast seminar announcements that do not fall into the category. People interested in all three condensed matter seminars should sign up for this mailing list, which includes the three.

### Tuesday 8th December, 16:00, seminar room 26C401

**Hierarchical quantum master equations and driven long-term impurity dynamics**

**Rainer Härtle (Universität Göttingen)**

The hierarchical quantum master equation technique is a promising method to solve nonequilibrium impurity problems. It employs a hybridization expansion of the time evolution operator that is time-local. The numerical effort to evaluate the corresponding equations of motion scales linearly with the simulation time. A systematic truncation scheme reduces the numerical effort to a practical level such that convergence can be achieved if the temperature of the environment is not too low. Thus, numerically exact results can be obtained, which I will corroborate by a direct comparison with the continuous-time quantum Monte Carlo approach. As an example, I will discuss the nonequilibrium dynamics of interacting quantum dot systems. To highlight the strength of the method, I will focus on effects and phenomena that emerge on long time scales such as, for example, the steady-state magnetization or the slow build-up of nonequilibrium coherences.

### Tuesday 17th November, 16:00, seminar room 26 C 401

**Classical and quantum anisotropic Heisenberg antiferromagnets**

**Prof. Walter Selke**

XXZ antiferromagnetic Heisenberg models, with and without single-ion anisotropy term, in a magnetic field are studied for spin values 1/2 and 1 as well as in the classical limit for one-, two- and three-dimensional lattices, using, mainly, Monte Carlo and density matrix renormalization group techniques. The model displays interesting structures, such as spin-flop and biconical ("supersolid") phases as well as various multicritical phenomena, like critical end-points, bi- and tetracritical points. Coauthors include Martin Holtschneider, Ian P. McCulloch, David Peters, and Stefan Weßel.