Punk Group

The research in our group is focused on properties of strongly correlated quantum matter. A thorough theoretical understanding of such systems is a necessary prerequisite for the development of new materials, which will likely build the foundation of future quantum technologies. Our aim is to identify, characterize and classify interesting and novel quantum phases of matter in paradigmatic examples of strongly correlated electron materials, such as high-Tc cuprate superconductors and frustrated antiferromagnets, as well as ultracold atomic gases.


High Temperature Superconductors

Understanding the properties of high-Tc cuprate superconductors in the pseudo-gap regime remains one of the outstanding questions in the field of strongly correlated electron systems. Recent measurements show that in-plane electronic transport in the pseudo-gap regime is plain-vanilla Fermi-liquid like, whereas several other experimental probes clearly demonstrate a drastic reduction of available electronic states close to the Fermi energy. One promising approach to explain these results is to assume that the ground-state of the is a so-called fractionalized Fermi liquid (FL*). This exotic state of matter has been proposed at first to understand properties of heavy-Fermion materials, where the relevant physical properties arise due to the interaction between a band of conduction electrons and localized f-electrons. Recently we developed a simple single band, which seems to capture several key properties of the metal.

[1]. One of our goals in the near future is to study this in detail.
[1] M. Punk, A. Allais, and S. Sachdev, "A quantum dimer model for the pseudogap metal", arxiv: 1501.00978

 


Spin-Liquids

Magnets with frustrated exchange interactions provide an ideal playground to study exotic quantum phases of matter. These systems can exhibit so-called quantum spin-liquid ground states, which display a variety of interesting physical phenomena such as fractionalized excitations and topological order. Several candidate materials which may host such quantum spin-liquid phases have been identified in recent years, but many theoretical aspects of spin-liquids are still poorly understood. For example, simple mean-field models for such phases often exist, but in many cases they do not capture essential features that are observed in experiments [2]. Trying to span the bridge between experiments and exotic theoretical models is one of our main motivations to work in this field.


[2] M. Punk, D. Chowdhury, and S. Sachdev, “Topological excitations and the dynamic structure factor of spin-liquids on the kagome lattice”, Nature Physics 10, 289-293 (2014).


Prof. Matthias Punk

Address:

Ludwig-Maximilian Universiät
Theresienstr. 37
D-80333 Munich
Germany

Group webpage