Two different types of Cooper pair transistors, with Al and Nb islands, have been investigated in a
tunable electromagnetic environment. The device with an Al island demonstrates gate charge
modulation with 2e periodicity in a wide range of environmental impedances at bath temperatures
below 340 mK. Contrary to the results of the Al sample, the authors were not able to detect 2e
periodicity under any conditions on similar samples with Nb island. The authors attribute this to the
material properties of Nb.