Abstract
Investigating Shubnikov-de Haas (SdH) oscillations in high magnetic fields, we experimentally infer the electronic band structure of the quasi-two-dimensional electron gas (2DEG) at the ionic-liquid gated amorphous (a)-LaAlO$_3$/KTaO$_3$ interface. The angular dependence of SdH oscillations indicates a 2D confinement of a majority of electrons at the interface. However, additional SdH oscillations with an angle-independent frequency observed at high tilt angles indicate the coexistence of 3D charge carriers extending deep into the KTaO$_3$. The SdH oscillations measured in magnetic fields perpendicular to the interface show four frequencies corresponding to four 2D subbands with different effective masses (0.20 $m_e$ - 0.55 $m_e$). The single-frequency oscillations originating from 3D electrons yields a larger effective mass of $\sim$ 0.70 $m_e$. Overall, the inferred subbands are in good agreement with the theoretical-calculations and angle-resolved photoemission spectroscopy studies on 2DEG at KTaO$_3$ surface.
Highlights
Due to its fundamental complexity and potential applications in new-generation semiconductor and spintronic devices, the two-dimensional electron gas (2DEG) formed at the interface between two insulating transition metal oxides has triggered significant attention in the past decade [1,2,3,4]
The transport measurements in high magnetic fields were carried out a few months after device fabrication and IL gating treatment
To evaluate the dimensionality of the electronic states at the interface, we have examined the angular dependence of the Shubnikov-de Haas (SdH) oscillations
Summary
Due to its fundamental complexity and potential applications in new-generation semiconductor and spintronic devices, the two-dimensional electron gas (2DEG) formed at the interface between two insulating transition metal oxides has triggered significant attention in the past decade [1,2,3,4]. The 2DEG at perovskite oxide interfaces with strong spin-orbit coupling was first discovered for LaAlO3/SrTiO3 (LAO/STO) heterointerface [5,6,7]. 2D-superconductivity with higher critical temperature has been reported at the KTO surface [14] and KTO-based interfaces [15,16] of high carrier densities (n 5 × 1013 cm−2). Tight-binding calculations for the 2DEG at the KTO surface predict a strong mixing of dxy, dxz, and dyz orbitals driven by spin-orbit coupling and a reconstruction of orbital symmetries of subbands [19]. These findings are experimentally supported by angle-resolved photoemission spectroscopy (ARPES) measurements on oxygen-deficient. A back-gate-dependent study on device-2 provides additional smaller amplitude and higher frequency oscillations, barely visible in the raw data, in the low-density regime
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