Figure 1. (a) Hierarchy and interplay of underlying degrees of freedom in 2DEG SrTiO3. The angle-resolved photoemission spectroscopy (ARPES) measurements of 2DEG states in SrTiO3 (b) and InAs (c). The distributions in (b) and (c) clearly indicated that the electron mobility in SrTiO3 and InAs are high. A spectral weight in SrTiO3 extending below the band bottom suggested strong interaction electrons, which was not observed in a nearly free electron semiconductor InAs. The parabolic dispersion relations are plotted as solid lines in b and c to guide the eye. Note that Figure 1a was reproduced from reference [9], Figure 1b and Figure 1c were reproduced from reference [11].