  Materials with a small superconducting energy gap are expected to favor a
high detection efficiency of low-energy photons in superconducting nanowire
single-photon detectors. We developed a TaN detector with smaller gap and lower
density of states at the Fermi energy than in comparable NbN devices, while
other relevant parameters remain essentially unchanged. The observed reduction
of the minimum photon energy required for direct detection is in line with
model predictions of $\approx1/3$ as compared to NbN.
