  We analyze the quark spectral function above and below the critical
temperature for deconfinement and at finite momentum in quenched lattice QCD.
It is found that the temporal quark correlation function in the deconfined
phase near the critical temperature is well reproduced by a two-pole ansatz for
the spectral function. The bare quark mass and momentum dependences of the
spectral function are analyzed with this ansatz. In the chiral limit we find
that even near the critical temperature the quark spectral function has two
collective modes corresponding to the normal and plasmino excitations in the
high temperature (T) limit. The pole mass of these modes at zero momentum,
which should be identified to be the thermal mass of the quark, is
approximately proportional to T in a rather wide range of T in the deconfined
phase.
