The pair-potential and current density around a single vortex of the two-dimensional chiral p-wave superconductor with d = z (px ± ipy) are determined self-consistently within the quasiclassical theory of superconductivity. Shrinking of the vortex core at low temperatures are considered numerically and analytically. Temperature-dependences of the spatial variation of pair-potential and circular current around the core and density of states at zero energy are the same as those in the isotropic s-wave case. When the senses of vorticity and chirality are opposite, however, we find two novel results; 1) the scattering rate due to non-magnetic impurities is considerably suppressed, compared to that in the s-wave vortex. From this observation, we expect that the chiral p-wave superconductors provide the best chance to observe the shrinking of the vortex ("Kramer-Pesch effect") experimentally.2) The pair-potential of chiral p-wave superconductors inside vortex core recovers a combined time-reversal-Gauge symmetry, although this symmetry is broken in the region far from the vortex core. This local recovery of symmetry leads to the suppression of the impurity effect inside vortex core.KEYWORDS: Superconductivity, vortex, quasiclassical theory, Kramer-Pesch effect, chiral superconductors §1. IntroductionThe superconducting state in Sr 2 RuO 4 1) is expected to be unconventional; a Knight shift measurement in planar magnetic field suggests odd-parity pairing with d vector perpendicular to the RuO 2 plane.2) Muon spin relaxation experiment suggests spontaneous magnetization;3) this means that time-reversal symmetry is broken spontaneously in the superconducting state. The simplest pairing symmetry which is consistent with the above two experimental results and the tetragonal crystal symmetry is given by the odd-parity pairing with d =ẑ (p x ± ip y ).4) This is commonly called the "chiral p-wave superconducting state" because the Cooper pair has a definite angular momentum L z = ±1 in the internal motion. A singly quantized vortex is, on the other hand, a configuration of the pair-potential where the center-of-mass motion of Cooper pair has an angular momentum. The interplay between vorticity and chirality would bring about intriguing phenomena in vortex physics of Sr 2 RuO 4 . Indeed, several authors 5-8) have argued that the impurity effects in vortex core of chiral p-wave superconductor is considerably suppressed, compared to that in s-wave vortex core. The fact that the superclean regime is realized within the core of chiral pwave vortex has several implications. First, the flux flow conductivity is expected to be enhanced at low temperatures in the chiral p-wave vortex states.8) Second, a large Hall effect is also expected. Third, the shrinkage of vortex cores at low temperatures, which is referred to as "the Kramer-Pesch (KP) effect", 9) is free from the * E-mail: yusuke@phys.c.u-tokyo.ac.jp * * E-mail: hayashi@mp.okayama-u.ac.jp smearing due to impurities. The vortex shrinking effect in chiral p-wave superconductors i...