  The general intuition that heavier partons suffer weaker energy loss inside a
quark-gluon plasma (QGP) medium is critically re-examined. Within a linear
Boltzmann transport model that includes both Yukawa and string types of
interactions between heavy quarks and the QGP, we find that while the radiative
energy loss is suppressed by the parton mass, heavier partons can experience
stronger string potential scatterings with the medium. Their competition may
result in less energy loss of bottom quarks than charm quarks at low transverse
momentum ($p_\mathrm{T}$) but an inverse order at high $p_\mathrm{T}$. Our
model calculation shows a weaker nuclear modification on bottom particles than
charm particles at low $p_\mathrm{T}$, as observed by both RHIC and LHC
experiments, but predicts an opposite hierarchy at high $p_\mathrm{T}$. A
larger momentum space transport coefficient ($\hat{q}$) and a smaller spatial
diffusion coefficient ($D_\mathrm{s}$) are found for bottom quarks than for
charm quarks.
