F Flavigny, P Doornenbal, A Obertelli, J-P Delaroche, M Girod, J Libert, T R Rodriguez, G Authelet, H Baba, D Calvet, F Château, S Chen, A Corsi, A Delbart, J-M Gheller, A Giganon, A Gillibert, V Lapoux, T Motobayashi, M Niikura, N Paul, J-Y Roussé, H Sakurai, C Santamaria, D Steppenbeck, R Taniuchi, T Uesaka, T Ando, T Arici, A Blazhev, F Browne, A Bruce, R Carroll, L X Chung, M L Cortés, M Dewald, B Ding, S Franchoo, M Górska, A Gottardo, A Jungclaus, J Lee, M Lettmann, B D Linh, J Liu, Z Liu, C Lizarazo, S Momiyama, K Moschner, S Nagamine, N Nakatsuka, C Nita, C R Nobs, L Olivier, R Orlandi, Z Patel, Zs Podolyák, M Rudigier, T Saito, C Shand, P A Söderström, I Stefan, V Vaquero, V Werner, K Wimmer, Z Xu

We report on the first γ-ray spectroscopy of low-lying states in neutron-rich ^{98,100}Kr isotopes obtained from ^{99,101}Rb(p,2p) reactions at ∼220  MeV/nucleon. A reduction of the 2_{1}^{+} state energies beyond N=60 demonstrates a significant increase of deformation, shifted in neutron number compared to the sharper transition observed in strontium and zirconium isotopes. State-of-the-art beyond-mean-field calculations using the Gogny D1S interaction predict level energies in good agreement with experimental results. The identification of a low-lying (0_{2}^{+}, 2_{2}^{+}) state in ^{98}Kr provides the first experimental evidence of a competing configuration at low energy in neutron-rich krypton isotopes consistent with the oblate-prolate shape coexistence picture suggested by theory.