Indications of a magnetic‐field‐driven anisotropy in the hybridization gap semiconductor CeOs₄As₁₂

Abstract

The filled skutterudite compound CeOs 4 As 12 displays phenomena that are associated with hybridization between the 4felectron and conduction-electron states. This holds especially true for a semiconducting ground state with a main energy gap as small as D/k B ¼ 45 K. When subjected to magnetic field, the hybridization gap semiconductor CeOs 4 As 12 becomes metallic below around 2.5 K. Preliminary electrical-resistivity experiments provide evidence for an anisotropy of magnetic-fieldinduced insulator-metal transition in this cubic material. Our findings suggest a contribution of the quartet 4f-G À 67 states to transport properties of CeOs 4 As 12 .

Angular Magnetoresistance of a Possible Kondo Insulator CeOs4Sb12Measured at Ultra-Low Temperatures

“…Whereas differences between transverse [3] and longitudinal (our work) arrangements have a minor significance only, anisotropy effects in the cubic compound CeOs 4 Sb 12 remain to be solved. We note that indications towards a field-induced anisotropy effect on a narrow hybridization gap have been observed in the closely related system CeOs 4 As 12 [7]. Figure 3 presents results of angular magnetoresistance measurements performed for the sample CeOs 4 Sb 12 whose ρ(T ) was discussed above.…”

“…As a result, the zerofield resistivity of CeOs 4 Sb 12 increases by nearly two orders of magnitude upon cooling below T = 60 K [3]. Surprisingly, the Sommerfeld coefficient of the electronic specific heat is enhanced γ ≈ 180 mJ K −2 mol −1 , as compared to other Ce-filled skuterrudite semiconductors [4][5][6][7]. Such an unusual duality of 4f -electron states in CeOs 4 Sb 12 is further suggested by photoemission spectroscopy experiments which demonstrated a symmetrydependent hybridization effect [8].…”

Electron transport and magnetic properties of the filled skutterudite compound ThFe4As12

“…It should be emphasized that in the valence fluctuation model or Kondo-effect scenario an opening of a narrow energy gap at the Fermi level is predicted. Most likely, such Kondo physics is realized in CeOs 4 As 12 where the residual resistivity is reduced by more than a factor of 10 with B = 5 T at T < 3 K [11,16].…”