  We present the Spitzer Infrared Spectrograph (IRS) spectrum of SR20, a 5--10
AU binary T Tauri system in the $\rho$ Ophiuchi star forming region. The
spectrum has features consistent with the presence of a disk; however, the
continuum slope is steeper than the $\lambda^{-4/3}$ slope of an infinite
geometrically thin, optically thick disk, indicating that the disk is outwardly
truncated. Comparison with photometry from the literature shows a large
increase in the mid-infrared flux from 1993 to 1996. We model the spectral
energy distribution and IRS spectrum with a wall + optically thick irradiated
disk, yielding an outer radius of 0.39$_{+0.03}^{-0.01}$ AU, much smaller than
predicted by models of binary orbits. Using a two temperature $\chi^2$
minimization model to fit the dust composition of the IRS spectrum, we find the
disk has experienced significant grain growth: its spectrum is well-fit using
opacities of grains larger than 1 $\mu$m. We conclude that the system
experienced a significant gravitational perturbation in the 1990s.
