Welcome to this video presentation about the research I'm conducting in my group Molecular Materials.

This presentation is intended entirely for you, the online audience, as I'm standing here in front of an empty classroom

due to the still ongoing coronavirus lockdown.

My name is Philipp Hansmann, I'm a newly appointed professor here in Erlangen

and arrived basically two weeks before the virus lockdown hit our university,

which made of course starting my group a little bit more challenging

as well as giving the lecture here on the virtual platform instead of at the blackboard.

So while this has been challenging, I couldn't have been happier about my arrival in Erlangen.

I had so much help from colleagues, staff and students alike.

And I also found a very nice and well-working electronic platform for several occasions,

including this one here, which is a fantastic win-win concept in my opinion for us as group leaders

to reach out to you, presenting ourselves and projects,

and you in turn making a more informed decision about potential bachelor and master projects.

So let's get to the point and talk about my research,

which is in the field of theoretical condensed matter physics.

To be more specific, a large part of my research is devoted to systems that are correlated.

And to understand why correlated systems are interesting to study and rich,

I don't immediately have to go into the quantum world,

which we eventually of course have to do in solid state.

No, also in classical systems, correlation effects make interesting phenomena.

You know that from traffic, from the stock market, from behavior of large animal swarms,

from life itself probably, that correlation in systems give really rise to new phenomena.

And even though it's kind of unsatisfactory and kind of weird to joke in front of an empty classroom,

I kept this slide here because it nonetheless being a joke,

it conveys some kind of takeaway message I would like to give you,

and it introduces you into the concept of correlations.

So what I plot here is what I show here are pictures of European leaders

represented by these pictures and floating in space and time by these arrows.

If it were that there is no interaction between these entities,

the situation would be quite boring,

and any kind of equation of motion for a single entity could be solved independently from all the other entities.

Mathematically speaking, any kind of expectation value of a product of states

would just factorize into the product of expectation values.

But you know the European Union, we are famous for interactions,

short-range, long-range, retarded, repulsive, attractive,

we have all kinds of interactions in the European Union,

and this kind of interaction and the relation that evolves out of this interaction

makes the entities with relation cum relatio in Latin,

and that's where the origin of the word correlation comes from,

and this correlation is represented here by this unequality.

So I can no longer factorize expectation value of product states into products of expectation values.

A more physical motivating aspect of this is given here in this hypothetical,

still a joke, phase diagram where I plot some kind of hypothetical temperature and pressure dependence.

So what that means is that I can go to my system and make small perturbations from the outside.

I can tune the temperature, I can put a little bit of pressure here and there,

and what is really intrinsic to correlated systems is a huge reaction

and a reaction in directions which you cannot foresee,

and indeed the concept of emergence is essential to correlated systems.

States emerge literally in the case of our European Union,

which are completely beyond an interpretation by single entity understanding.