Non-oxy delafossites: unconventional spin orbit entangled magnetism and electron transport
Layered chalcogenide (Ch) delafossites ABCh2, where A is a monovalent and B is a trivalent transition metal/rare earth ion, feature a wide variety of interesting phenomena, including superconductivity (NaxCoO2) , large thermoelectricity (Cu[Rh,Mg]O2) , multiferroicity (CuFeO2) , hydrodynamic electron flow (PdCoO2) [4,5] and spin-orbit driven frustration on a perfect triangular lattice (NaYbCh2) [6,7,8].
Most of the research done so far was on oxygen-based delafossites (DFs) whereas non-oxygen DFs (with S, Se or Te) are less investigated yet. The variation of the ionic radii of the mono- and trivalent- ions has only a little effect on the band structure and mainly tunes the lattice parameters whereas the choice of the chalcogenide ion itself has a strong impact on the band structure. For example, the oxy delafossite PdCoO2 has a quasi two-dimensional conductivity and the density of states at the Fermi level show minor chalcogenide 2p- electron admixture. In contrast to that in AgCrS2 or AgCrSe2 the larger spatial extended 3(4)p- states of S and Se promote the emergence of hybridized p- states at the Fermi level which finally leads to three-dimensional metallic or semi-metallic conductivity . This promotes correlation effects in general and together with the emergence of strong spin polarization unconventional magnetism and (magneto-)transport is expected.
AgCrSe2 is a promising primer among non oxy delafossites, which exhibit an unusual liquid-like thermal conduction originating from the complex interplay of magnetic and charge degrees of freedom [10,11,12]. In particular the spin polarization of the charge carriers (Rashba effect) originate strong correlations and unconventional thermoelectricity .
This project combines the expertise in the field of oxy-delafossite at the MPI CPfS  with the search for new correlated triangular lattice, delafossite-like, systems. The aim is (i) to synthesize new materials (chemical vapor transport & solid state reaction - M. Schmidt, S. Khim) accompanied by structural characterization, (ii) to determine the thermodynamic (heat conductivity, specific heat) properties and the electronic (and magneto-) transport (M. Baenitz) and (iii) to apply microscopic spectroscopy like electron spin resonance (ESR, J. Sichelschmidt) and nuclear magnetic resonance (NMR, M. Baenitz). In addition, in-house theory support on band structure (H. Rosner) and magnetic exchange models (B. Schmidt) is available.