Effect of magnetic field 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   

CePtSi without inversion symmetry exhibits an antiferromagnetic (AFM) order at 2.2 K and enters into a heavy-fermion superconducting state below 0.5 K. Additional anomalies inside the AFM state were found under external magnetic fields in the vicinity of the upper critical field of the superconducting state. Our neutron scattering experiments under magnetic fields revealed that the application of the magnetic fields leads to an enormous enhancement in the AFM peak intensity in CePtSi, opposite to what is observed in usual antiferromagnets. We have clarified that the reported anomaly under the magnetic fields corresponds to inflection points in the field variation of the AFM intensity. The observed huge increase in AFM intensity corresponds to an increase of the ordered moment under the magnetic fields. These results imply an existence of a missing magnetic response in the ground state, which might be related to the formation of the superconducting state in CePtSi.