When a topological insulator is incorporated into a Josephson
junction,
the system is predicted to reveal the fractional Josephson effect
with a 4π-periodic current–phase relation. Here, we report
the measurement of a 4π-periodic switching current through an
asymmetric SQUID, formed by the higher-order topological insulator
WTe2. Contrary to the established opinion, we show that
a high asymmetry in critical current and negligible loop inductance
are not sufficient by themselves to reliably measure the current–phase
relation. Instead, we find that our measurement is heavily influenced
by additional inductances originating from the self-formed PdTexinside the junction. We therefore develop
a method to numerically recover the current–phase relation
of the system and find the 1.5 μm long junction to be best described
in the short ballistic limit. Our results highlight the complexity
of subtle inductance effects that can give rise to misleading topological
signatures in transport measurements.