Univ. Prof.

Dr. Silke BÜHLER-PASCHEN

QUANTUM MATERIALS GROUP

Sketch of a temperature (T) – magnetic field (B) phase diagram around an unconventional quantum critical point
Dilution refrigerator for the investigation of low-temperature properties of quantum critical compounds

QUANTUM CRITICALITY AND HEAVY FERMION COMPOUNDS

 

A quantum critical point (QCP) develops in a material at the absolute zero in temperature when an order parameter is continuously suppressed to zero by variation of a non-thermal tuning parameter such as pressure, magnetic field or chemical composition. QCPs are of great current interest because of their singular ability to influence the finite temperature properties of materials. Recently, heavy-fermion metals have played a key role in the study of antiferromagnetic QCPs. Our current investigations focus on:

 

  • Ce3Pd20Si6: This is one of the few cubic systems showing clear signatures of a magnetic field induced quantum critical point. The presence of two different Ce sites and two low-temperature phase transitions that are presumably related to these two sites are particularly intriguing.
  • YbRh2Si2: The Néel temperature of only 70 mK of this heavy-fermion antiferromagnet is continuously suppressed by application of small magnetic fields. Measurements of the Hall effect indicate a collaps of the Fermi surface at the QCP, calling for entirely new theoretical descriptions.
  • Search for new quantum critical systems.