  We present angle-resolved photoemission experiments on 1T-TiSe2 at
temperatures ranging from 13K to 288K. The data evidence a dramatic
renormalization of the conduction band below 100K, whose origin can be
explained with the exciton condensate phase model. The renormalization
translates into a substantial effective mass reduction of the dominant charge
carriers and can be directly related to the low temperature downturn of the
resistivity of 1T-TiSe2. This observation is in opposition to the common belief
that strong interactions produce heavier quasiparticles through an increased
effective mass.
