  Understanding the normal state transport properties in hole-doped
high-temperature cuprate superconductors (HTCSs) is a challenging task which
has been widely believed to be one of the key steps toward revealing the
pairing mechanism of high-temperature superconductivity. Here, we present a
true intrinsic and universal doping dependence of in-plane dc conductivity for
all underdoped HTCSs. The doping dependence of in-plane dc conductivity
normalized to that at optimal doping can be represented by a simple exponential
formula. The doping behavior of the square of the nodal Fermi velocity derived
by the high-resolution laser-based angle-resolved photoemission spectroscopy in
the superconducting state follows reasonably well the universal intrinsic
doping behavior. Our findings suggest a commonality of the low-energy
quasiparticles both in the normal and superconducting states that place a true
universal and stringent constraint on the mechanism of high-temperature
superconductivity for HTCSs.
