Properties of quarkonia at T_c

We discuss how the spectral changes of quarkonia at T_c can reflect the 'critical' behaviour of QCD phase transition. Starting from the temperature dependences of the energy density and pressure from the lattice QCD calculation, we extract the temperature dependences of the scalar and spin 2-gluon condensates near T_c. We also parameterize these changes into the electric and magnetic condensates near T_c. While the magnetic condensate hardly changes across T_c, we find that the electric condensate increases abruptly above T_c. A similar abrupt change is also seen in the scalar condensate. Using the QCD second-order Stark effect and QCD sum rules, we show that these sudden changes induce equally abrupt changes in the mass and width of J/ψ, both of which are larger than 100 MeV at slightly above T_c.