Veranstaltungsdetails

22.5.2012, 17:00
Jungiusstr. 11, Hörsaal AP

SFB 668 - Kolloquium

Dr. Steffen Wirth (MPI Dresden):

Scanning Tunneling Microscopy on heavy fermion metals

Heavy fermion metals are often characterized by a variety of relevant energy scales and competing interactions which may result in such fascinating phenomena as quantum criticality and unconventional superconductivity. Therefore, these materials have advanced to suitable model systems by means of which electronic interactions can be studied in detail. Here, we focus on results obtained by Scanning Tunneling Microscopy and Spectroscopy (STM/S). Following a brief introduction to heavy fermion physics we will discuss the material YbRh2Si2 and its doped counterparts Yb(Rh1−xMx)2Si2 (M = Co, Ir). They are of specific topical interest due to a quantum critical point which appears to result not only from an antiferromagnetic instability but also from a Kondo break-down of the heavy quasiparticles [1]. We present very ecent STM and STS studies at low temperature [2]. The topography combined with chemical analysis allows for structural investigations of our high-quality single crystals. The hybridization of conduction and 4f electrons results in a gap-like feature of the tunneling conductance. Importantly, the crystal field excitations are unambiguously reflected by STS. A strongly temperature dependent peak in tunneling conductance is attributed to a resonance resulting from the Kondo lattice. In the CeMIn5 class of compounds the relation between superconductivity and antiferromagnetism will be discussed [3]. Magnetotransport measurements on CeIrIn5 indicated a precursor state to superconductivity. A gap detected by low-temperature STS in CeCoIn5 is compatible with dx2−y2 symmetry of the superconducting order parameter and is, again, consistent with a precursor state to superconductivity. [1] S. Friedemann et al., Proc. Natl. Acad. Sci. USA 107 (2010) 14547. [2] S. Ernst et al., Nature 474 (2011) 362. [3] S. Nair et al., Proc. Natl. Acad. Sci. USA 107 (2010) 9537.