Repulsive Polarons

Yes, indeed this post is about repulsive polarons, but that does not mean that they are repulsive because they cause revulsion or anything of the sort. We are talking about quasiparticles which are predicted to occur when ‘impurity’ fermionic particles interact repulsively with a fermionic environment. And it turns out that these quasiparticles have now been detected.

Ok, “what is a quasiparticle?” I hear you say. Well, a quasiparticleis a perturbation or disturbance in a medium, whose behaviour is that of a particle and thus for all intent and purposes can be regarded as one. Their study is important in relationship to solid-state physics, condenses matter and nuclear physics as they help us in determining the properties of matter.

Rudolf Grimm (Innsbruck) and a team of physicists have experimentally realised the observation of a repulsive polaron in an ultracold quantum gas. The results have been publised in Nature.

Varios phenomena from condensed matter physics can be experimentally simulated using ultracold quantum gases. In these system, the control that can be achieved over the many-body interactions is grater and this is always helpful.

In order to observe repulsive polarons the physicists used an ultracold quantum gas of lithium and potassium atoms and they control the atomic interactions using electromagnetic fields and RF pulses. The potassium atoms are dirven into a state where they repulse the surrounding lithium atoms. This interaction can be seen as a particle with modified properties – a quasiparticel. Once the researchers analyse the energy spectrum of the system, they were able to demonstrate repulsive polarons.

The observation of these polarons is important as it demonstrates that they can indeed be observed. In condensed matter quasiparticles decay very quickly and this poses the problemof studying them. In this experiments, the researchers say, the polarons showed an almost ten times increased lifetime compared to earlier experiments in similar systems. This opens up the possibility of having a platform for a more detailed analysis of many-body systems that rely on repulsive interactions.