  We study the process $e^{+}e^{-}\to\Lambda_{c}^{+}\bar{\Lambda}_c^{-}$ at
twelve center-of-mass energies from $4.6119$ to $4.9509~\mathrm{GeV}$ using
data samples collected by the BESIII detector at the BEPCII collider. The Born
cross sections and effective form factors ($|G_{\mathrm{eff}}|$) are determined
with unprecedented precision after combining the single and double-tag methods
based on the decay process $\Lambda_{c}^{+}\to pK^{-}\pi^{+}$. Flat cross
sections around $4.63~\mathrm{GeV}$ are obtained and no indication of the
resonant structure $Y(4630)$, as reported by Belle, is found. In addition, no
oscillatory behavior is discerned in the $|G_{\mathrm{eff}}|$ energy-dependence
of $\Lambda_{c}^{+}$, in contrast to what is seen for the proton and neutron
cases. Analyzing the cross section together with the polar-angle distribution
of the $\Lambda_{c}^{+}$ baryon at each energy point, the moduli of electric
and magnetic form factors ($|G_{E}|$ and $|G_{M}|$) are extracted and
separated. For the first time, the energy-dependence of the form factor ratio
$|G_{E}/G_{M}|$ is observed, which can be well described by an oscillatory
function.

High Energy Physics - Experiment