Research Profile

The various challenges in bringing modern approaches of condensed matter theory to real materials are the main motivation for our work. The research in my group is focused on the development of first-principles-based methods to study the electronic properties and transport physics of emerging materials.

 

Quantum Transport Simulations

The development of efficient methods and computational tools to simulate charge carrier transport, polaron transport, and spin transport in complex matter is a main direction of research in the group. This includes also transverse transport phenomena. 

 

Organic Semiconductors

This material class offers great potential for applications but also basic research. The atomic structure is precisely defined and changing a single atom may change the fundamental physical properties completely. Electronics based on molecular structures is therefore an obvious direction for science. Our research on electronic, optical and transport properties enjoys several collaborations.

Theory and Models

 

Polaron transport in organic semiconductors

The great challenge is the sizable electron-phonon coupling in these systems which need to be addressed non-perturbatively. Here I developed a transport theory in the past and my group is elaborating improvements and applies it to various interesting systems. The connection to a full first-principles parameterization makes it specific.
Further reading: Phys. Rev. B 2009, New. J. Phys. 2010, Phys. Stat. Sol B 2011, Adv. Funct. Mater 2015.

 

 

Spin physics and spin coherence

Here we are looking into the electron’s spin degree of freedom. Long spin coherence times are essential for any kind of spintronic application and possible relaxation mechanisms are studied. Further reading: Phys. Rev. Lett. 2012, Nature Phys. 2014, 2D Mater. 2015.

 

 

Non-equilibrium dynamics and localization

Transport phenomena at different lenghscales and timescales are under investigation here. Multiple quantum interferences are important when studying weak-localization/weak antilocalization phenomena. Further reading: EPL 2011, Phys. Rev. Lett. 2013, Phys. Rev. B 2011.

Simulations

From Theory to Numbers

In house developed codes are mainly used but also combined with open source or proprietary software particularly for ab initio part.

 

 

Transverse Transport Phenomena 

are unconventional responses in the sense that they are transverse to the external fields. Examples include Hall effects, Spin-Hall effects, or transverse thermoelectric effects (Nernst effect) etc. I have developed a linear-scaling approach to simulate such transverse transport on a large scale (millions of orbitals) which allows to have unprecedented insight into the underlying fundamental physics. Further reading: Phys. Rev. Lett. 2013, Phys. Rev. B 2015.

 

Ab Initio

The variety of materials need to be described on the ab initio level to simulate their specific properties. We use density functional theory and time-dependent density functional theory for the simulations of various electronic parameters and optical spectra. Further reading: Phys. Rev. Lett. 2005, Phys. Rev. B 2006, J. Comput. Chem. 2007. 

 

  

 

Ultrafast Dynamics and Localization

Transport phenomena from the femtosecond to the nanosecond timescale are being explored. We develop efficient linear-scaling approaches (order N) and implement them in our codes. Further reading: EPL 2011, Phys. Rev. Lett. 2013, Nano Lett. 2013, 2D Mater 2014. 

 

Spin Physics and Spin Coherence

Here we are looking into the electron’s spin degree of freedom. Long spin coherence times are essential for any kind of spintronic application. It is therefore of utmost importance to understand the physics behind spin relaxation mechanisms. Spin currents are under scrutiny. Further reading: Phys. Rev. Lett. 2012, Nature Phys. 2014, 2D Mater. 2015. 

 

 

Materials

Molecular Materials/Organic Semiconductors

These are very challenging materials because intramolecular and intermolecular forces differ strongly in size but have to be described accurately. Recent focus of our group is on organic molecules that are considered in (opto-) electronics applications. Further reading: Adv. Funct. Mater. (2015), J. Phys. Chem. C (2014). 

 

 

2D Materials

Graphene and its friends appear in many forms (CVD, mechanical exfoliated, liquid-phase exfoliated, epitaxial, etc.). We have been looking at them from the charge transport perspective including fundamental questions such as weak localization phenomena or quantum Hall effect. Further reading: EPL 94, 47006 (2011), Phys. Rev. Lett. 110, 086602 (2013), Phys. Rev. B 89, 161401(R) (2014). 

 

 

Topological Insulators

TIs and other novel forms of topological materials have a quite complex basis including heavy atoms (such as Bi etc.) and often large unit cells. We have been looking into more simple models such as the seminal Fu-Kane-Mele model and analyzed effects of disorder on the spin polarization of surface states. Further reading: Phys. Rev. Lett. 109, 266805 (2012).