Spin-Dependent Weakly-Interacting-Massive-Particle--Nucleon Cross
  Section Limits from First Data of PandaX-II Experiment
  New constraints are presented on the spin-dependent WIMP-nucleon interaction
from the PandaX-II experiment, using a data set corresponding to a total
exposure of 3.3$\times10^4$ kg-days. Assuming a standard axial-vector
spin-dependent WIMP interaction with $^{129}$Xe and $^{131}$Xe nuclei, the most
stringent upper limits on WIMP-neutron cross sections for WIMPs with masses
above 10 GeV/c$^{2}$ are set in all dark matter direct detection experiments.
The minimum upper limit of $4.1\times 10^{-41}$ cm$^2$ at 90\% confidence level
is obtained for a WIMP mass of 40 GeV/c$^{2}$. This represents more than a
factor of two improvement on the best available limits at this and higher
masses. These improved cross-section limits provide more stringent constraints
on the effective WIMP-proton and WIMP-neutron couplings.
