Compactifying the rank two Hitchin system via spectral data on semistable curves

We study resolutions of the rational map to the moduli space of stable curves that associates with a point in the Hitchin base the spectral curve. In the rank two case the answer is given in terms of the space of quadratic multi-scale differentials introduced in [BCGGM3]. This space defines a compactification (of the projectivization) of the regular locus of the GL(2,ℂ)-Hitchin base and provides a compactification of the Hitchin system by compactified Jacobians of pointed stable curves. We show how the classical GL(2,ℂ)- and SL(2,ℂ)-spectral correspondence extend to the compactified Hitchin system by a correspondence along an admissible cover between torsion-free rank 1 sheaves and (multi-scale) Higgs pairs of rank 2.