Non‐magnetic Kondo effect in M –As–Se ( M = Zr, Hf, Th) phases

Thermodynamic and transport properties of the tetragonal M –As–Se ( M  = Zr, Hf, Th) phases demonstrate that these materials are disordered metals with the electronic‐specific‐heat coefficient as small as, e.g., 0.3 mJ K −2  mol −1 for Th–As–Se. Remarkably, all the M –As–Se systems display a magnetic‐field‐independent AT 1/2 term in the low‐temperature electrical resistivity. As observed for ZrAs 1.595 Se 0.393 , the magnitude of this extra term may vary by a factor of nearly 3 as well as the resistivity minimum is shifted from 10.8 to about 15.0 K, dispite virtually the same electron‐diffusion constant. On the other hand, a magnetic‐field ( B  ≤ 14 T) dependence of the electron transport in arsenide selenides is strongly material dependent: both the positive and negative sign of the magnetoresistivity being proportional to either B 2 or B 1/2 were found. These observations point to a non‐magnetic Kondo effect due to a random distribution of structural two‐level systems in the disordered As/Se sublattice.