•  Disorder phenomena
•  Magnetism
•  Electronic correlations in metallic, semiconducting and insulating compounds with transition metals, lanthanides and actinides
•  Quantum criticality
•  Unconventional superconductivity
•  Thermoelectricity

Further information you can find under the research field  "Solid State Physics".

Research

Our research deals with strongly correlated electron systems (SCES) which determine the physical (low-energy) properties of several classes of materials of current fundamental and applied interest. These include heavy-fermion metals, high-T_c cuprates, transition-metal pnictide  and chalcogenide superconductors, colossal magnetoresistance materials and correlated semiconductors. Our discovery of heavy-fermion superconductivity in CeCu₂Si₂ (F. Steglich et al., Phys. Rev. Lett. 43, 1892 (1979)) has pioneered the research on SCES and unconventional superconductivity. Convincing experimental evidence for non-phononic Cooper pairings, mediated by both antiferromagnetic magnons in UPd₂Al₃ (N.K. Sato et al., Nature 410, 340 (2001)) and, very recently, nearly quantum critical spin-density-wave fluctuations in CeCu₂Si₂ (O. Stockert et al., Nature Phys. 7, 119 (2011)) was demonstrated by our group via inelastic neutron-scattering and thermodynamic measurements at ambient pressure. Another unconventional Cooper-pairing mechanism, i.e., via critical valence fluctuations, was highlighted by transport measurements on Ge-doped CeCu₂Si₂ under high pressure (H.Q. Yuan et al., Science 302, 2104 (2003)). Together with our  Max-Planck Partner Group (H.Q. Yuan) at Zhejiang University, Hangzhou (PR China),  we are investigating non-centrosymmetric superconductors which contain mixtures of even- and odd-parity Cooper pairs, depending on the strength of the antisymmetric spin-orbit coupling.

Our recent investigations of incipient magnetism in clean heavy-fermion metals have largely contributed to the discovery that the heavy ("composite") charge carriers disintegrate at a "Kondo breakdown" quantum critical point (or: a zero-temperature 4f-selective Mott transition) coinciding with an antiferromagnetic one in YbRh₂Si₂ (J. Custers et al., Nature 424, 525 (2003); S. Paschen et al., Nature 432, 881 (2004); P. Gegenwart et al., Science 315, 969 (2007); S. Friedemann et al., Proc. Natl. Acad. Sci. USA 107, 14547 (2010); H. Pfau et al., Nature 484, 493 (2012)). This work has revolutionized the understanding of the Kondo lattice, which is considered to be a prototype of SCES (Scientific Report 2009).

Except for superconducting Fe-pnictide and -chalcogenide compounds, we are interested in semiconducting Fe-based intermetallics with small band width. In cooperation with Bo Iversen's group at the University of Aarhus (Denmark) we are studying the properties of FeSb₂ with "colossal Seebeck effect" (A. Bentien et al., Europhys. Lett. 80, 17008 (2007)). Further interesting thermoelectric materials are compounds with cage structure like clathrates (F.M. Grosche et al., Phys. Rev. Lett. 87, 247003 (2001) and skutterudites (J. Sichelschmidt et al., Phys. Rev. Lett. 96, 037406 (2006)). These materials are investigated in collaboration with the Research Area Chemical Metals Science (J. Grin).

In a joint cooperation with the Research Area Inorganic Chemistry (R. Kniep) and our Max-Planck Partner Group at the W. Trzebiatowski Institute, Polish Academy of Sciences, Wroclaw we hope to find out the microscopic nature of those structural ("quantum") defects which cause a "nonmagnetic Kondo effect" in certain intermetallic compounds with PbFCl structure.

In our studies, special emphasis is put on exploring new systems in form of polycrystalline material and high-quality single crystals, synthesized by the Competence Group Materials Development, the Research Fields Inorganic Chemistry and Chemical Metals Science as well as several foreign groups. Comprehensive studies of SCES require experiments in wide ranges of the parameters temperature T,  pressure p  and magnetic field B (Competence Group Extreme Conditions). The available parameter ranges are: T: 0.007 - 400 K (in house) and 0.0005 - 1 K (in collaboration with E. Schuberth, WMI, TUM), p: 0 - 10 GPa (hydrostatic) and 0 - 1 GPa (uniaxial) as well as B: 0 - 20 T (static, in house) and 0 - 80 T (pulsed, in collaboration with HLD, FZD).

Projects

o Quantum criticality in Kondo-lattice systems (Manuel
   Brando, Christoph Geibel, Cornelius Krellner, Michael
   Nicklas,  Jörg Sichelschmidt, Oliver
   Stockert,  Steffen Wirth,  Stefan Kirchner - MPI PKS,  Philipp
   Gegenwart - U. Göttingen):
   - Classification of quantum critical points (QCPs)
   - Unconventional QCPs
   - Orbital-selective Mott transitions
   - Disorder, frustration
   - Spin liquids
   - Lifshitz transitions
o Unconventional superconductivity in:
   - Heavy-fermion metals (Christoph Geibel, Michael 
      Nicklas,  Oliver Stockert, Steffen Wirth)
   - Transition-metal pnictides and chalcogenides (Michael Baenitz, 
      Christoph Geibel, Cornelius Krellner, Michael Nicklas, Steffen Wirth)   
- Intermetallics lacking a center of inversion (Manuel
      Brando, Christoph Geibel, Michael Nicklas, Oliver 
      Stockert,  Steffen Wirth,  Huiqiu Yuan - Zheijiang U.,
      Hangzhou)
o Thermoelectricity in correlated semiconductors
   (Michael Baenitz,  Peijie Sun, Juri Grin,  Bo
   Iversen - U. Aarhus)
o Quantum defects in metals (Rüdiger Kniep, Marcus Schmidt,
    Tomasz Cichorek - INTiBS, PAN, Wroclaw)

Methods

o Materials development, single-crystal growth (Christoph 
   Geibel, Cornelius Krellner, Juri Grin, Rüdiger Kniep)
o Thermodynamic, magnetic and transport measurements at 
  - low temperatures and high static magnetic fields (Manuel
    Brando, Thomas Lühmann)
  - high pressures (Michael Nicklas)
o STS and magnetotransport (Steffen Wirth)
o Thermal transport (Ulrike Stockert, Peijie Sun)
o Neutron scattering (Oliver Stockert)
o NMR (Michael Baenitz)
o ESR and FIR (Jörg Sichelschmidt)
o Magnetic, calorimetric, dilatometric and electrical
   conductivity measurements in pulsed high magnetic fields
   (Ramzy Daou, Michael Nicklas)

Third Party Funding, External Cooperations

o  DFG-Forschergruppe 960 "Quantum Phase Transitions"
o DFG-Schwerpunktprogramm 1458 
   "Hochtemperatursupraleitung in Eisenpniktiden"
o Multidisciplinary University Research Initiative (MURI)
   "Solid State Cooling"

 Recent publications

Contact
Prof. Dr. Frank Steglich
Tel:		+49 (0)351 4646-3900
Fax:		+49 (0)351 4646-3902
	E-Mail	steglich[at]cpfs.mpg.de