  Unconventional superconductivity often emerges at the border of long-range
magnetic orders. Understanding the low-energy charge dynamics may provide
crucial information on the formation of superconductivity. Here we report the
unpolarized/polarized optical conductivity study of high quality MnP single
crystals at ambient pressure. Our data reveal two types of charge carriers with
very different lifetimes. In combination with the first-principles
calculations, we show that the short-lifetime carriers have flat Fermi sheets
which become gapped in the helimagnetic phase, causing a dramatic change in the
low-frequency optical spectra, while the long-lifetime carriers are anisotropic
three-dimensional like which are little affected by the magnetic transitions
and provide major contributions to the transport properties. This
orbital-dependent charge dynamics originates from the special crystal structure
of MnP and may have an influence on the unconventional superconductivity and
its interplay with helimagnetism at high pressures.
