Fermi Surface Reconstruction In Fese Under High Pressure

We report Shubnikov-de Haas (SdH) oscillation measurements on FeSe under high pressure up to P = 16.1 kbar. We find a sudden change in SdH oscillations at the onset of the pressure-induced antiferromagnetism at P similar to 8 kbar. We argue that this change can be attributed to a reconstruction of the Fermi surface by the antiferromagnetic order. The negative dT(c)/dP observed in a range between P similar to 8 and 12 kbar may be explained by the reduction in the density of states due to the reconstruction. The ratio of the transition temperature to the effective Fermi energy remains high under high pressure: k(B)T(c)/E-F similar to 0.1 even at P = 16.1 kbar.