Prof. Dr. Gordon Callsen

Univ. Bremen, Institut für Festkörperphysik

Linking photonic and thermal properties of semiconductor nanostructures

This inaugural lecture will start with a brief summary of past research topics of Gordon Callsen, before outlining future research topics that will be pursued by the new research group (RG) Callsenat the University of Bremen. The aim of this lecture is not only to outlinefirst routes for future collaborations, but also, to raise a general fascination for the overall research topic as described in the following.

During the last decades, much research was devoted to the optical properties of semiconductor nanostructures, enabling fascinating insights into the underlying physics, which already entailed numerous real-world devices like light-emitting diodes, laser diodes, and various types of quantum light sources. However, the high level of sophistication reached for such photonic devices is often contrasted by scarce knowledge about the related thermal phenomena, ultimately limiting device functionality, efficiency, and longevity.Thus, it is the aim of the RG Callsen to fill this void by bridging the fields of nano-photonics andnano-thermometry based on a unique, hybrid spectroscopic approach that enablessimultaneous studies ofoptical and thermal material properties. Therefore, theenvisioned research has to answerthe fundamental and in physics often reoccurring question: How can we define and measure temperature?

Ultimately, the employedhybrid spectroscopywill either probe the temperature of the phonon or charge carrier bathalong with the optical material properties, which jointly provide access to the weighting in between the different contributions to thermal transportgiven by charge carriers, excitons, andthermal THz phonons. Clearly, such spectroscopy needs to spatially and temporally resolve the temperature field across nanostructures, which can be achieved by an optical setup recently developed at the University of Bremen.This optical setup will prove pivotal to an understanding of thetransportof thermal phonons and charge carriers, which also requests a thorough understanding of the related couplings. Eventually, this understanding will even pave the way to novel thermal designs and circuits that, e.g., manipulate the flow of heat by means of thermal crystals that can be linked to photonic structures.

In summary, it is the aim of the RG Callsen to pioneer an interlinked physical understanding of photonic and thermal material properties. Future mutual optimizations based on this understanding will not only benefit classical optical, electrical, and thermoelectric devices (e.g., light-emitting diodes, transistors, Seebeck generators), but even quantum light sources and related circuitry.