High mobility and suppression of superconductivity in SrTiO₃ 2D electron gases

We present a new technique to create two-dimensional electron gases (2DEGs) on SrTiO₃ (STO) surfaces that achieves both micron-scale patterning and high carrier mobilities. Combining electron beam lithography with hydrogen plasma exposure, we patterned Hall bar devices directly on insulating STO substrates. Cryogenic measurements revealed high electron mobilities up to 7400 cm²/(V∙s). This technique allows us to start with a high electron density of 3×10¹⁴ cm⁻² and, through aging, tune it into the range where a superconducting dome is typically observed. However, even at carrier densities as low as 5×10¹³ cm⁻², our devices did not show a superconducting transition. We will discuss how this behavior fits into a broader trend of competition between high mobility and robust superconductivity in STO 2DEGs. Our device geometry also enables us to conveniently define side gates with gate-channel separations ranging from 5 to 80 μm. These side gates showed reproducible gate capacitances with symmetric dual gate response. A sharp dependence of gate effect on electron density was observed, stemming from combined electron mobility and capacitive density modulation contributions.