  A search for $C\!P$ violation in $\Lambda^0_b \to p K^-$ and $\Lambda^0_b \to
p \pi^-$ decays is presented using a sample of $pp$ collisions collected with
the LHCb detector and corresponding to an integrated luminosity of 3.0
fb$^{-1}$. The $C\!P$-violating asymmetries are measured to be
$A_{\mathrm{CP}}^{pK^-} = -0.020 \pm 0.013\pm 0.019$ and
$A_{\mathrm{CP}}^{p\pi^-} = -0.035 \pm 0.017 \pm 0.020 $, and their difference
$A_{\mathrm{CP}}^{pK^-}-A_{\mathrm{CP}}^{p\pi^-} = 0.014 \pm 0.022 \pm 0.010$,
where the first uncertainties are statistical and the second systematic. These
are the most precise measurements of such asymmetries to date.
