  Fourier transform scanning tunneling spectroscopy (FT-STS), or quasiparticle
interference (QPI), has become an influential tool for the study of a wide
range of important materials in condensed matter physics. However, FT-STS in
complex materials is often challenging to interpret, requiring significant
theoretical input in many cases, making it crucial to understand potential
artifacts of the measurement. Here, we compare the most common modes of
acquiring FT-STS data and show through both experiment and simulations that
artifact features can arise that depend on how the tip height is stabilized
throughout the course of the measurement. The most dramatic effect occurs when
a series of dI/dV maps at different energies are acquired with simultaneous
constant current feedback; here a feature that disperses in energy appears that
is not observed in other measurement modes. Such artifact features are similar
to those arising from real physical processes in the sample and are susceptible
to misinterpretation.
