  We present experiments on single Cooper-pair transistors made of two
different superconducting materials. We chose Ti and Al to create an energy gap
profile such that the island has a higher gap than the leads, thereby acting as
a barrier to quasiparticle tunneling. Our transport measurements demonstrate
that quasiparticle poisoning is suppressed in all our TiAlTi structures (higher
gap for the island) with clear 2e periodicity observed, whereas full
quasiparticle poisoning is observed in all AlTiAl devices (higher gap for the
leads) with e periodicity.
