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Ultracold polarons: from impurity atoms in a BEC to single holes in an anti-ferromagnetic Mott insulator

Fabian Grusdt, Harvard University

22.12.2016 at 12:15 

By doping a fermionic Mott insulator at half filling, it is believed that the anti-ferromagnetic (AFM) state is destroyed and a high-$T_c$ superconducting phase can be reached. To unravel the physics of the hole-doped regime, an important first step is to understand the behavior of a single hole in the AFM. In analogy with the polaron problem, where a mobile impurity interacts with a surrounding bath, one can expect a so-called magnetic polaron to form when a hole is introduced into the AFM. The analogy between these two problems will be the main topic of this talk. After providing an overview of the Bose polaron problem -- an impurity strongly interacting with a Bose-Einstein condensate -- it will be argued that the magnetic polaron is more than just a hole dressed by magnetic excitations. Instead, the strong correlations in this system require a different physical picture, which will be provided in the strong-coupling limit where the hole-hopping is much faster than spin-exchange interactions. Very recently, the Heisenberg AFM has become accessible for quantum-gas microscopes with ultracold fermions in optical lattices. A brief overview of recent experimental progress towards observing single holes and their correlations with the spin environment will also be given.

A 450, Theresienstr. 37