Electrostatic Modulation of LaAlO₃/SrTiO₃ Interface Transport in an Electric Double‐Layer Transistor

Abstract

The correlated charge, spin, orbital, and lattice degrees of freedom in transition metal oxides make them an attractive platform to explore rich physics and potential applications. [ 1,2 ] Oxide interfaces offer even more exciting opportunities due to the emerging effects such as broken inversion symmetry, interfacial exchange interaction, and spatial confi nement. [ 3,4 ] Heterostructures composed by non-magnetic band insulators LaAlO 3 (LAO) and SrTiO 3 (STO) have attracted much attention recently, and the unexpected conduction is often linked to the electronic reconstruction at the polar (LAO)-nonpolar (STO) heterointerface. [ 5,6 ] One defi ning feature of the interface conduction is the thickness dependence, i.e., it is insulating when the LAO thickness is below four unit cells (u.c.), whereas the conduction emerges above the critical thickness. [ 7 ] Furthermore, the carriers in the two-dimensional electron gas (2DEG) are confi ned within several nm near the interface as a result of broken symmetry, and the profi le of distribution has a sensitive dependence on the carrier density. [8][9][10][11][12][13] Based on the 2DEG at the LAO/ STO interface, nanoscale control of the insulator-to-metal transition using local probes has also been demonstrated. [ 14,15 ] The recent revelation of magnetism at the LAO/STO interface added another facet to the exciting physics. [16][17][18][19][20] Two notable sources were proposed for leading to the weak magnetism discovered in the LAO/STO heterostructures: One is the intrinsic electron reconstruction [ 16,21 ] and the other is the extrinsic oxygen vacancies. [ 22 ] In addition, the inhomogeneous distribution of magnetic dipoles as demonstrated in a recent scanning superconducting quantum interference device (SQUID) microscopy study clearly underscores the critical role of disorder in forging the magnetic landscape. [ 20 ] In spite of the efforts, [ 16,[18][19][20]23 ] the nature of magnetism discovered in samples prepared in a wide range of conditions remains as an issue of debate.To shed light on the physics of LAO/STO interface and to modulate its properties, electric fi eld effect was proven to be a powerful tool. [ 7,[24][25][26][27] In particular, an insulator-to-metal transition has been achieved by using electric fi eld gating at room temperature. [ 7 ] In these previous efforts, the STO substrates were used as the dielectric insulator in the back-gate confi guration, and high voltages of tens to hundreds of volts were required. Recently, ferroelectric Pb(Zr 0.2 Ti 0.8 )O 3 was used to bias the LAO/STO interface in a top-gate confi guration, and nonvolatile modulation of the 2DEG was demonstrated. [ 28 ] As a breakthrough in such electric fi eld effect studies, electric double-layer transistors (EDLTs) with the top-gate confi guration were employed to trigger the transformation of ground states in some key materials. [29][30][31] However, so far there has been no report on applying this powerful technique to exploring the transport properties of oxide interfaces.In...

Magnetic two-dimensional electron gas at the manganite-buffered LaAlO3/SrTiO3 interface

“…As shown by the solid line in Fig. 3(c), the resistance upturn can be well reproduced by the standard formula [28][29][30] …”

Magnetic Interactions at the Nanoscale in Trilayer Titanates

“…3(a), the other dominant feature in transport is the pronounced upturn of the sheet resistances at lower temperature. Previous work on titanate heterojunctions has attributed such an upturn to the Kondo effect [12,[63][64][65][66], after carefully ruling out the contributions from weak-localization [67] and electronelectron interactions [68]. One of the key features of the Kondo effect that immediately differentiates it from weak-localization and electron-electron interactions is the universal scaling behavior [see Fig.…”

Electrical Manipulation of Orbital Occupancy and Magnetic Anisotropy in Manganites

“…[25] XPS depth profiling in our previous work. [22] Compared with the electrostatic manipulation based on the capacitance of EDL, [26] the change of x in our system is rather large as the variation of oxygen vacancies is sensitive to the external electric field. We now address the question how the orbital occupancy varies under the electric field.…”