Fermi Surface Gapping in the Hidden Order State of PrFe4P12 by Point-Contact Spectroscopy

We have applied point-contact spectroscopy (PCS) to investigate the nonmagnetic hidden order (HO) state of the skutterudite compound PrFe4P12 with its transition temperature THO ∼ 6.5 K. Its point-contact conductance curves exhibit a reproducible gap structure in the HO state below THO and its temperature dependent gap magnitude follows a BCS-like mean-field behavior. A Fano-like conductance shape is observed to emerge below the coherence temperature of PrFe4P12. In a magnetic field, the gap feature is gradually suppressed and evolves into a pronounced Fano peak, signaling the heavy fermion state and vividly demonstrating the competition between HO and the formation of heavy fermion states. Our results strongly suggest the itinerant characteristic of f electrons in PrFe4P12, which constrains theoretical models to explain the HO mechanism.