Heavy-fermion behaviours in URu2Si2

We analyse the magnetic susceptibility X and the specific heat C of the heavy-fermion material URu2Si2, assuming a variety of the crystal field level schemes. The heavy-fermion behaviours of X and C above TN = 17.5 K are shown to be reproduced fairly well in the singlet-singlet-singlet (Gamma(3)-Gamma(1)-Gamma(2)) level scheme proposed by Santini and Amoretti, and also in a novel level scheme of Gamma(1)-singlet ground state with Gamma(5)-doublet excited state. We discuss that the novel singlet-doublet level scheme is favourable for the close proximity of weak antiferromagnetism to the hidden order in URu2Si2, and the most probable candidate of the hidden order is a J(x)(J(y)(2) - J(z)(2-))-type octupolar ordering.