Key points are not available for this paper at this time.
An even-denominator rational quantum number has been observed in the Hall resistance of a two-dimensional electron system. At partial filling of the second Landau level =2+ (1/2= 5) / 2 and at temperatures below 100 mK, a fractional Hall plateau develops at ₗₘ= (h/e^2) / (5/2 defined to better than 0. 5%. Equivalent even-denominator quantization is absent in the lowest Landau level under comparable conditions.
Willett et al. (Mon,) studied this question.