Figure 5: Quantum oscillations indicate a Fermi surface reconstruction.

Comparison between the Shubnikov–de Haas frequencies observed in the in-plane transport across the hysteretic transition (left), as well as de Haas–van Alphen oscillations measured by magnetic torque (right) for 20° away from H||c. On entering the high-resistance state (red), two new frequencies appear, and thus indicate a Fermi surface reconstruction at the transition. The large hysteresis allows to directly compare the frequency spectrum of the upper branch with the lower branch within the same field window (middle). The high-frequency oscillations appear over the whole hysteretic region on the upper branch and are completely absent in the lower branch. The appearance of the frequency can thus be clearly linked to the transition, and does not occur simply due to the enhancement of quantum oscillations in higher fields. The magnetic torque is a thermodynamic quantity, and can thus shed light on the thermodynamic character of the transition. We observe the appearance of high-frequency components also in the torque, in agreement with ref. 28, indicating the thermodynamic nature of the transition despite the absence of a clear anomaly.