Quantized Ballistic Transport of Electrons and Electron Pairs in LaAlO₃/SrTiO₃ Nanowires

Abstract

SrTiO-based heterointerfaces support quasi-two-dimensional (2D) electron systems that are analogous to III-V semiconductor heterostructures, but also possess superconducting, magnetic, spintronic, ferroelectric, and ferroelastic degrees of freedom. Despite these rich properties, the relatively low mobilities of 2D complex-oxide interfaces appear to preclude ballistic transport in 1D. Here we show that the 2D LaAlO/SrTiO interface can support quantized ballistic transport of electrons and (nonsuperconducting) electron pairs within quasi-1D structures that are created using a well-established conductive atomic-force microscope (c-AFM) lithography technique. The nature of transport ranges from truly single-mode (1D) to three-dimensional (3D), depending on the applied magnetic field and gate voltage. Quantization of the lowest e/ h plateau indicate a ballistic mean-free path l ∼ 20 μm, more than 2 orders of magnitude larger than for 2D LaAlO/SrTiO heterostructures. Nonsuperconducting electron pairs are found to be stable in magnetic fields as high as B = 11 T and propagate ballistically with conductance quantized at 2 e/ h. Theories of one-dimensional (1D) transport of interacting electron systems depend crucially on the sign of the electron-electron interaction, which may help explain the highly ballistic transport behavior. The 1D geometry yields new insights into the electronic structure of the LaAlO/SrTiO system and offers a new platform for the study of strongly interacting 1D electronic systems.

Pascal conductance series in ballistic one-dimensional LaAlO 3 /SrTiO 3 channels

“…Quantized transport was first observed in III-V quantum point contacts (15,16) and subsequently in 1D systems (17)(18)(19). Quantized conduction within 1D electron waveguides was recently demonstrated within LaAlO3/SrTiO3 heterostructures (9). A unique aspect of this SrTiO3-based system is the existence of tunable electron-electron interactions (20) that lead to pairing (8) and superconductivity (21).…”

“…The conductance of these electron waveguides depends principally on the chemical potential and the applied external magnetic field ⃗ . The chemical potential is adjusted with a local side gate (9), and for most experiments described here the external magnetic field is oriented perpendicular to the LaAlO3/SrTiO3 interface: ⃗ = . Quantum-point contacts formed in semiconductor heterostructures (15,16) exhibit conductance steps which typically follow a linear sequence: 2 × (1, 2, 3, 4, … ) ⋅ 2 /ℎ, where the factor of 2 reflects the spin degeneracy.…”

Quantized conductance in a one-dimensional ballistic oxide nanodevice

“…spin coherence [38]. Note that because of the reduced electron mobility in this depleted regime (µ 100 cm 2 V −1 s −1 ), the magnetic field used in this study is too weak to generate Landau levels and form hybrid magneto-electric subbands [36].…”

Band Structure and Spin–Orbital Texture of the (111)‐KTaO3 2D Electron Gas

“…This is exemplified by the observation of superconductivity, [3] magnetism, [4] strong electron lattice interactions, [5] and quasi 1D conductivity [6] in the 2DEG stabilized in (001)-oriented SrTiO 3 (STO) which is, by far, the most studied system among ABO 3 transition metal oxides. It is this plethora of bulk properties that enrich the phase diagrams of transition metal oxides compared to those of conventional semiconductors, and which renders 2DEGs in correlated materials so promising for the discovery of new functionalities and emergent physical phenomena.…”