Universal conductance fluctuations in electrolyte-gated SrTiO3 nanostructures

Abstract

We report low-temperature magnetoconductance measurements of a patterned two-dimensional electron system (2DES) at the surface of strontium titanate, gated by an ionic liquid electrolyte. We observe universal conductance fluctuations, a signature of phase-coherent transport in mesoscopic devices. From the universal conductance fluctuations we extract an electron dephasing rate linear in temperature, characteristic of electron-electron interaction in a disordered conductor. Furthermore, the dephasing rate has a temperature-independent offset, suggestive of unscreened local magnetic moments in the sample.Strontium titanate (STO) has been the subject of a resurgence of experimental interest, mainly because of the recent ability to create STO-based materials with electrons confined in one and two spatial dimensions [1]. STO is also known to host a wide variety of electronic ground states determined by the density of electrons. These two aspects combine to create a promising system for studying nanoscale electronics where the interactions between electrons can be controlled simply by a gate voltage. Two-dimensional electron systems in STO have primarily been created in three different ways: growing a polar overlayer, usually lanthanum aluminate(LAO), to create a heterointerface[2], δ-doping with Nb or La [3,4], or with an electrolyte gate in an electric double-layer transistor (EDLT) configuration [5][6][7]. Low-temperature transport in these systems has revealed a wide variety of electronic ground states. Undoped STO is an insulator, but at ∼1x10 13 cm −2 the system becomes a metal. At higher densities (∼3x10 13 cm −2 ) -still much lower than typical BCS superconductors -the system becomes a two-dimensional superconductor. Early evidence suggests that the entrance into a superconducting state is a Berezinskii-KosterlitzThouless transition [8]. At even higher densities, a ferromagnetic phase appears to exist [9,10] and may even coexist with superconductivity [11][12][13].The handful of experiments on the quantum transport properties of two-dimensional electrons in STO have thus far focused on locally patterned LAO/STO, and have produced several interesting observations. The Rashba spin-orbit interaction -extracted from weak antilocalization measurements -is relatively large and tunable by application of a gate voltage. Further increases of the spinorbit strength have been linked to quantum critical points in the system [14,15]. Universal conductance fluctuations (UCF) corresponding to phase coherence lengths of several microns have recently been observed in LAO/STO microstructures [16]. Recently, conductive atomic force microscope tips have been used to create nanoscale conduction paths at the LAO/STO interface [17,18].In contrast, in electrolyte-gated STO some of the most basic properties of the quantum transport have yet to be investigated. In this work, we apply the EDLT technique to an undoped STO sample with nanopatterned metallic gates to study STO 2DESs with lateral confinement on the hundred-nanometer scale. ...

Physics of SrTiO3-based heterostructures and nanostructures: a review

“…The reported dephasing length are around ~100 300 nm at low temperature [512,513]. Note that the extrapolated dephasing rate does not vanish at 0 K for both reports [512,513]. Stanwyck et al [513]suggested that Kondo scattering may occur, though a Kondo resistance minimum is not reported.…”

“…Note that the extrapolated dephasing rate does not vanish at 0 K for both reports [512,513]. Stanwyck et al [513]suggested that Kondo scattering may occur, though a Kondo resistance minimum is not reported. UCF is also reported for the superconducting critical current of a Josephson junction created from LaAlO 3 /SrTiO 3 [514].…”

Unraveling the effect of electron-electron interaction on electronic transport in La-doped SrSnO3 films

“…It is also noteworthy that the phase coherence length in this sample is 260 nm at 1.8 K, which increases to 460 nm at 1.8 K with increasing carrier density (n 3D = 5.5 × 10 19 cm -3 ) (see figure S1). Significantly, this value is twice as large as the largest value reported for the doped SrTiO 3 at similar temperatures 32,33 indicating potential applications of doped SSO films in quantum coherent devices. We also calculated the electronelectron interaction characteristic length l ee , using ee 2 B D l k T π = h , where D is the diffusion constant of electrons 29 (see SI).…”

Potential Fluctuations at Low Temperatures in Mesoscopic-Scale SmTiO3/SrTiO3/SmTiO3 Quantum Well Structures

“…[40][41][42][43] As shown in the figures, the magnetofingerprint is fairly retraceable on the timescale of tens of minutes, but time-varying disorder (due to the presumed two-level fluctuators responsible for the voltage fluctuations) scrambles the MR on the time scale of hours.…”