  We report the X-ray timing results of the black hole candidate MAXI J1820+070
during its 2018 outburst using the Hard X-ray Modulation Telescope
(Insight-HXMT) and Neutron Star Interior Composition Explorer Mission (NICER)
observations. Low frequency quasi-periodic oscillations (LFQPOs) are detected
in the low/hard state and the hard intermediate state, which lasted for about
90 days. Thanks to the large effective area of Insight-HXMT at high energies
and NICER at low energies, we are able to present the energy dependence of the
LFQPO characteristics and phase lags from 0.2 keV to 200 keV, which has never
been explored by previous missions. We find that the centroid frequency of the
LFQPOs do not change significantly with energy, while the full width at half
maximum (FWHM) and fractional rms show a complex evolution with energy. The
LFQPO phase lags at high energies and low energies show consistent
energy-dependence relations taking the ~2 keV as reference. Our results suggest
that the LFQPOs from high energy come from the LT precession of the
relativistic jet, while the low-energy radiation is mainly from the
perpendicular innermost regions of the accretion disk.
