  We show how an electrical measurement can detect the pairing of electrons on
the same side of the Fermi surface (Amperian pairing), recently proposed by
Patrick Lee for the pseudogap phase of high-$T_c$ cuprate superconductors.
Bragg scattering from the pair-density wave introduces odd multiples of
$2k_{\rm F}$ momentum shifts when an electron incident from a normal metal is
Andreev-reflected as a hole. These Andreev-Bragg reflections can be detected in
a three-terminal device, containing a ballistic Y-junction between normal leads
$(1,2)$ and the superconductor. The cross-conductance $dI_1/dV_2$ has the
opposite sign for Amperian pairing than it has either in the normal state or
for the usual BCS pairing.
