Tunable Kondo Effect in SrTiO$_3$*

Correlated, low-dimensional systems offer the possibility of tuning complex physical phenomena. Using strong electric fields applied with an electrolytic gate, we continuously tune through three regimes of transport in SrTiO$_3$: an insulator, a metal and a Kondo metal. Two of these regimes -- the metallic and Kondo metal state -- are investigated as a function of temperature and magnetic field, where clear signatures of each regime are evident and discussed. This diverse system not only displays behavior distinct from conventional two-dimensional electron gases, but also show similarities to the LaAlO$_3$/SrTiO$_3$ interface, elucidating on some of the phenomena observed in this heterostructure of debated origin.