Shubnikov-de Haas oscillations in GaAs quantum wells in tilted magnetic   fields
  We report on quantum magneto-oscillations in an ultra-high mobility GaAs/AlGaAs quantum well at very high tilt angles. Unlike previous studies, we find that the spin and cyclotron splittings become equal over a continuous range of angles, but only near certain, angle-dependent filling factors. At high enough tilt angles, Shubnikov-de Haas oscillations reveal a prominent beating pattern, indicative of consecutive level crossings, all occurring at the same angle. We explain these unusual observations by an in-plane field-induced increase of the carrier mass, which leads to accelerated, filling factor-driven crossings of spin sublevels in tilted magnetic fields. 
A. T. Hatke, M. A. Zudov, L. N. Pfeiffer, and K. W. West
cond-mat.mes-hall