  A gated Hall-bar device is made from an epitaxially grown, free-standing InSb
nanosheet on a hexagonal boron nitride (hBN) dielectric/graphite gate structure
and the electron transport properties in the InSb nanosheet are studied by
gate-transfer characteristic and magnetotransport measurements at low
temperatures. The measurements show that the carriers in the InSb nanosheet are
of electrons and the carrier density in the nanosheet can be highly efficiently
tuned by the graphite gate. The mobility of the electrons in the InSb nanosheet
is extracted from low-field magneotransport measurements and a value of the
mobility exceeding ~18000 cm$^2$V$^{-1}$s$^{-1}$ is found. High-field
magentotransport measurements show well-defined Shubnikov-de Haas (SdH)
oscillations in the longitudinal resistance of the InSb nanosheet.
Temperature-dependent measurements of the SdH oscillations are carried out and
key transport parameters, including the electron effective mass
m$^*$$\sim$0.028 m$_0$ and the quantum lifetime $\tau$$\sim$0.046 ps, in the
InSb nanosheet are extracted. It is for the first time that such experimental
measurements have been reported for a free-standing InSb nanosheet and the
results obtained indicate that InSb nanosheet/hBN/graphite gate structures can
be used to develop advanced quantum devices for novel physics studies and for
quantum technology applications.
