Novel antiferromagnetic ground state in non-centrosymmetric heavy-fermion superconductor CePtSi

Kaneko, Koji   ; Stockert, O.*; Skoulatos, M.*; Schneidewind, A.*; Takeuchi, Tetsuya*; Matsuda, Tatsuma; Haga, Yoshinori   ; Settai, Rikio*; Onuki, Yoshichika; Metoki, Naoto   

The discovery of heavy-fermion superconductivity in non-centrosymmetric compound CePtSi brings a new essence in the field of condensed matter physics, since a novel type of superconducting properties are expected to emerge. CePtSi shows an antiferromagnetic (AFM) order at =2.2 K and enters into a heavy-fermion superconducting state below 0.5 K. We identified anomalous external magnetic field response in CePtSi by neutron scattering experiments in the AFM state. An observed huge increase in AFM intensity corresponds to an increase of the staggered moment under uniform field, opposite of what is observed in ordinary antiferromagnets. These features suggest that the magnetic order in CePtSi is not a simple AFM one, and imply that large fraction of magnetic response could be still missing in this compound.