Scanning tunneling spectroscopy (STS) studies reveal long-range (~100 nm) spatial homogeneity in optimally and underdoped superconducting YBa 2 Cu 3 O 7−δ (YBCO) single crystals and thin films, and macroscopic spatial modulations in overdoped (Y 0.7 Recently, it has been proposed that the interaction of nodal quasiparticles with thermally induced vortex loops [7] may give rise to the MFL behavior in the normal state and below the pseudogap temperature (T*) [13]. Generally speaking, an important consequence of the d-wave pairing symmetry is the presence of nodal quasiparticles at low temperature, and that of strong phase fluctuations is the separation of the pair formation temperature (T MF ~ T*) from the superconducting transition temperature (T c ) [7], with T c << T*. Given the fact that the low-energy excitations are important manifestations of the pairing state, we expect nodal quasiparticles to play a major role in determining the physical properties of the cuprates. On the other hand, if the Fermi surface were fully gapped due to broken time-reversal (T) symmetry in the pairing state, as suggested by certain theories [14,15], the lowenergy excitation spectra at T << T* would have been modified significantly. It is therefore important to establish the purity and possible doping dependence of the pairing symmetry in the cuprate superconductors. In particular, whether a small broken T-symmetry component may exist in the form of (d x 2 -y 2+id xy ) or (d x 2 -y 2+is) pairing should be carefully examined. In this work, we report studies of the quasiparticle tunneling spectra on the YBa 2 Cu 3 O 7-δ (YBCO) system over a wide range of doping levels. Several key results are noteworthy. First, we observed long-range (~ 100 nm)