Dissecting the Heaviest Fermion

Scientific Achievement

YbPtBi has the largest known electronic specific heat yet also manifests long-range magnetic order below 0.4 K. 

Dissecting fermions
Elastocaloric data taken on YbPtBi (right) using single crystal shaped to be mounted in a strain cell (lower left) and temperature scales determined (upper left).

For nearly 30 years, the order of multiple temperature scales, including Neel, Kondo, crystal-electric field (CEF) splittings, has remained ambiguous.  The elastocaloric effect and symmetry arguments are used to identify TN = 0.4 K < TΔCEF = 1.5 K < TK = 10 K. 

Significance and Impact

This demonstrates the use of elastocaloric measurements in probing CEF splitting, and determines that the first excited CEF state is well below the Kondo temperature.

Research Details
  • Electrical resistance, x-ray diffraction, synchrotron Mossbauer spectroscopy and partial fluorescence–yield x-ray absorption spectroscopy measurements on EuPd3S4 were performed under pressure up to 30-60 GPa
  • Comprehensive temperature – pressure phase diagram was constructed. 
     

E. Gati, B. Schmidt, S. Bud’ko, A. Mackenzie, and P. Canfield, “Controlling crystal electric field levels through symmetry-breaking uniaxial pressure in a cubic super heavy fermion” npj Quantum Materials, DOI: 10.1038/s41535-023-00596-1