Unusual oscillation in tunneling magnetoresistance near a quantum critical point in Sr3Ru2O7

We performed single-electron tunneling measurements on bilayer ruthenate Sr3Ru2O7. We observe an unusual oscillation in tunneling magnetoresistance near the metamagnetic quantum phase transition. The characteristic features of this oscillation suggest that it is unrelated to traditional quantum oscillations caused by orbit quantization. In addition, tunneling spectra are found to change sharply in the low bias voltage range of V<2 mV near the transition field. These observations reveal that the Fermi surface of Sr3Ru2O7 changes in a surprising way as the system undergoes strong critical fluctuations.