We report anomalous structure in the magnetoresistance of SiO2/Si(100)/SiO2 quantum wells. When Landau levels of opposite valleys are driven through coincidence at the Fermi level, the longitudinal resistance displays elevations at filling factors that are integer multiples of 4 (ν=4i) accompanied by suppression on either side of ν=4i. This persists when either the magnetic field or the valley splitting is swept, leading to resistance ridges running along ν=4i. The range of field over which they are observed points to the role of spin degeneracy, which is directly confirmed by their disappearance with the addition of an in-plane magnetic field. The data suggest a new type of many-body effect arising from the combined degeneracy due to the valley and the spin degrees of freedom.
Takashina, K., Brun, M., Ota, T., Maude, D. K., Fujiwara, A., Ono, Y., Takahashi, Y., & Hirayama, Y. (2007). Anomalous resistance ridges along filling factor ν=4i. Physical Review Letters, 99(3), . https://doi.org/10.1103/PhysRevLett.99.036803