Effects of magnetic field on the pseudogap in the Kondo semiconductor CeRhAs

The magnetization and magnetoresistance of single-crystalline CeRhAs, which is the so-called Kondo semiconductor with an energygap of ∼280 K, have been measured in pulsed magnetic field up to 55 T. At 1.3 K, the slopes of the magnetization M for H∥b and H∥c decrease slightly at around 16 and 13 T, respectively, while M(H∥a) shows monotonous dependence. Weak anisotropy is observed on the whole, M_b(H)>M_c(H)>M_a(H). M_b(H) reaches only to 0.07 μ_B/f.u. at 55 T, which indicates the non-magnetic state being stable even in the high magnetic field. Strongly anisotropic behaviors are observed in the magnetoresistance. The longitudinal magnetoresistance (LMR) along the b- and c-axis show characteristic structures partly associated with the anomalies of the magnetizations, while the LMR along the a-axis shows only a broad maximum. The transverse magnetoresistances (TMR) for I∥b and I∥c follow the relation Δρ(H)/ρ(0)∝H^α(α=1.5-1.7) below 5 T, whereas TMR for I∥a exhibits only the weak field dependence. These results suggest the existence of a narrow and anisotropic structure within the wide pseudogap structure in the density of states.