Technical University Munich
Department of Physics
Research focus: quantum phase transitions, electronic order, topology of correlated systems
The systematic search for quantum order in bulk materials, comprising the synthesis of high-purity single crystals, the experimental exploration of their thermodynamic and transport properties under extreme conditions, as well as microscopic studies using advance neutron and x-ray scattering form the basis for harvesting quantum phenomena in real materials.
Quantum phase transitions
The notion of particle-like elementary excitations represents a cornerstone of present day condensed matter physics. The putative breakdown of this concept in the vicinity of so-called quantum phase transitions, driven by quantum rather than thermal fluctuations, has been attracting tremendous interest for many decades. In turn the materials properties in the vicinity of quantum phase transitions offer an important starting point for an understanding of a wide range of materials with anomalous normal state properties, as well as emergent novel electronic phases such as magnetically mediated superconductivity or partial spin and charge order.
- Formation of a Topological Non-Fermi Liquid in MnSi; Nature, 497, 231 (2013)
- Spin Dynamics and Spin Freezing at Ferromagnetic Quantum Phase Transitions, European Journal of Physics: Special Topics, 224, 1041 (2015)
Complex forms of electronic order
Complex forms of electronic order are intimately connected with the electronic structure and the topological character of the Fermi surface as well as their modification in the presence of strong quantum correlations. The experimental investigation of the electronic structure of materials with complex forms of electronic order permits to track the effects of many body quantum effects and their relationship with thermodynamic and transport properties close to and far from equilibrium.
- Spin-resolved Fermi surface of the localized ferromagnetic Heusler compound Cu2MnAl measured with spin-polarized positron annihilation, Phys. Rev. Lett., 115, 206404 (2015)
- Parasitic small-moment-antiferromagnetism and non-linear coupling of hidden order and antiferromagnetism in URu2Si2 observed by Larmor diffraction, Phys. Rev. Lett., 104, 106406 (2010)
- Superconducting phases of f-electron compounds, Rev. Mod. Phys., 81, 1551 (2009)
The notions of symmetry breaking and generalized rigidities have let to a remarkably comprehensive account of complex forms of magnetic order in condensed matter systems. In recent years a new facet of magnetism research receives increasing attention that concerns the topological character of magnetically ordered systems, notably those properties that remain unchanged under elastic deformations. Important examples include skyrmions, vortices and monopoles in chiral or frustrated magnets. These topological aspects of magnetic order are not only appealing from an esthetical and conceptual point of view, but offer strikingly simple explanations for materials properties that may seem to be surprising and hideously complicated at first sight.
- Universal Helimagnon and Skyrmion Excitations in Metallic, Semiconducting, and Insulating Chiral Magnets, Nature Materials 14, 478 (2015)
- Unwinding of a Skyrmion Lattice by Magnetic Monopoles, Science 340, 1076 (2013)
- First Order Metamagnetic Transition in Ho2Ti2O7 observed by Vibrating Coil Magnetometery at Milli- Kelvin Temperatures, Phys. Rev. Lett. 108, 257204 (2012)
- Spin Transfer Torques in MnSi at Ultra-low Current Densities, Science 330, 1648 (2010)
- Skyrmion Lattice in a Chiral Magnet, Science 323, 915 (2009)