The high-temperature superconductivity in iron-pnictides and –chalcogenides is based on the intricate interplay of crystal structure, electronic and magnetic states. The concerted study by scientists from different departments of the Max Planck Institute for Chemical Physics of Solids and from the Leibniz Institute for Solid State and Materials Research found for iron-telluride the remarkable result that hydrostatic pressure leads to the emergence of ferromagnetic order in a peculiar way.
Ultraclean metals show high conductivity with a high number of charge carriers, whereas semiconductors and semimetals with low charge carriers normally show a low conductivity. This scenario in semimetals can be changed if one can protect the carriers from scattering.
In the new iron-based superconductors (FeSC), superconductivity occurs close to an antiferromagnetic phase. This indicates that correlation effects may be important in these materials. Theoretical calculations predict that different from cuprates, besides the on-site Coulomb interaction also the on-site Hund exchange interaction plays an important role in the correlation effects of FeSCs. This would mean that a completely new state of correlated matter has appeared which has been termed “Hund’s metal”.
Graphite is a model system for the study of electrons in the so-called magnetic quantum limit. This quantum limit is attained when the magnetic field is strong enough to confine the charge carriers to their lowest Landau levels. It is expected that the model of the free electron gas fails beyond this limit since here electron interactions may play a significant role in determining the electronic ground state. Indeed, our thermodynamic studies in high magnetic field revealed that even electron-lattice interaction has to be taken into account in addition to electron-electron interaction.
The simple cubic structure of CeB6 does not change while intricate multipolar phenomena are developed upon a non-magnetic La substitution. However, phase diagrams of Ce1-xLaxB6 have been elusive for the last decades. Recently, detailed phase transitions in Ce1-xLaxB6 have been revealed by scientists of MPI-CPfS, TU-Dresden, and I. M. Frantsevich Institute. In addition, a simple feature which is likely to be observed in a multipolar heavy-fermion system has been found.
The premartensite phase of shape memory and magnetic shape memory alloys is believed to be a precursor state of the martensite phase with preserved austenite phase symmetry. The thermodynamic stability of the premartensite phase and its relation to the martensitic phase is still an unresolved issue, even though it is critical to the understanding of the functional properties of magnetic shape memory alloys.[mehr]
Steffen Wirth erhält die Fellowship für „seine grundlegenden Beiträge zu unserem Verständnis von stark korrelierten Elektronensystemen, insbesondere bei reduzierten Längenskalen, einschließlich des Kondo-Effekts und magnetischer Wechselwirkungen", wie es in der Ernennungsurkunde heißt.