  The recent discovery of barred spiral galaxies in the early universe ($z>2$)
poses questions of how these structures form and how they influence galaxy
evolution in the early universe. In this study, we investigate the morphology
and kinematics of the far infrared (FIR) continuum and [CII] emission in
BRI1335-0417 at $z\approx 4.4$ from ALMA observations. The variations in
position angle and ellipticity of the isophotes show the characteristic
signature of a barred galaxy. The bar, $3.3^{+0.2}_{-0.2}$ kpc long in radius
and bridging the previously identified two-armed spiral, is evident in both
[CII] and FIR images, driving the galaxy's rapid evolution by channelling gas
towards the nucleus. Fourier analysis of the [CII] velocity field reveals an
unambiguous kinematic $m=2$ mode with a line-of-sight velocity amplitude of up
to $\sim30-40$ km s$^{-1}$; a plausible explanation is the disk's vertical
bending mode triggered by external perturbation, which presumably induced the
high star formation rate and the bar/spiral structure. The bar identified in
[CII] and FIR images of the gas-rich disk galaxy ($\gtrsim 70$\% of the total
mass within radius $R\approx 2.2$ disk scale lengths) suggests a new
perspective of early bar formation in high redshift gas-rich galaxies -- a
gravitationally unstable gas-rich disk creating a star-forming gaseous bar,
rather than a stellar bar emerging from a pre-existing stellar disk. This may
explain the prevalent bar-like structures seen in FIR images of high-redshift
submillimeter galaxies.
