Charge transport and distribution at the interfaces of SrTiO₃/LaAlO₃/SrTiO₃ (100) (STO/LAO/STO (100))

The existence of a quasi-2-dimensional hole gas (q2DHG) in STO/LAO/STO (100) has been revealed by several groups. In this report, the STO(6-uc)/LAO(t-uc)/STO (100) samples with t = 5 and 3 were grown using oxide MBE technique. From magneto-transport measurements at low temperatures and difference gate voltages (V_g), a clear signature for the existence of q2DHG was uncovered from rigorous two band model fittings to magneto-conductance data. At T = 2K and V_g = + 100V, the sheet density for q2DHG is as large as 1.47 x 10¹³ per cm². Intriguingly, both the sheet densities for q2DEG and q2DHG increase with increasing positive V_g, which supports for a spatially separated electron-hole bilayer at the interfaces [1]. On the other hand, STEM-EELS measurements with atomic scale resolution across the interfaces were performed. The suppressed q2DHG in STO/LAO/STO (100) in the ultra-thin LAO limit can be attributed to the depolarization field within the LAO layer, arising from the strain-field interference across the two closely-spaced interfaces [2]. In principle, q2DHG can emerge by compensating the depolarization field, which is achievable either by increasing the LAO thickness or by electrical gating. [1] Singh et al., PRM 2, 114009 (2018). [2] Su et al., PRM 3, 075003 (2019).