Direct observation of multiple spin zeroes in the underdoped high   temperature superconductor YBa2Cu3O6+x
  We report the direct observation of multiple `spin zeroes' in angle-dependent magnetic quantum oscillations measured up to 85T in YBa2Cu3O6+x, at which the amplitude falls to a deep minimum accompanied by a phase inversion of the measured quantum oscillations, enabling the product of the effective mass and effective g-factor m*g* to be tightly constrained. We find an evolution of the location of the spin zeros with applied magnetic field, and suggest that this effect and the absence of a spin zero at low angles can be produced by more than one Fermi surface component, and an effective g-factor with a subtle anisotropy between in-plane and out-of-plane crystalline directions. 
Suchitra E. Sebastian, N. Harrison, M. M. Altarawneh, F. F. Balakirev,   C. H. Mielke, Ruixing Liang, D. A. Bonn, W. N. Hard...
cond-mat.supr-con