We report resistance and magnetic torque experiments under a high magnetic field up to 45 T in a three dimensional quantum Hall (QH) system $(\mathrm{T}\mathrm{M}\mathrm{T}\mathrm{S}\mathrm{F}{)}_2{\mathrm{C}\mathrm{l}\mathrm{O}}_4$, where $\mathrm{T}\mathrm{M}\mathrm{T}\mathrm{S}\mathrm{F}=\mathrm{\text{tetramethyltetraselenafulvalene}}$. The Hall resistance shows huge oscillations accompanied with sign reversal after the final QH state, where the Landau level filling factor is unity, is removed above 26 T. The magnetic torque also oscillates with the field. The results suggest that a novel quantum state, where the character of the carriers periodically changes with the field, is stabilized in the extreme quantum limit.

• Received 10 August 2004

DOI:https://doi.org/10.1103/PhysRevLett.94.077206