Role of Percolation in the Conductance of Electrolyte-Gated<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>SrTiO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>

Li, Mingyang; Graf, Tanja; Schladt, Thomas D.; Jiang, Xin; Parkin, Stuart S. P.

doi:10.1103/physrevlett.109.196803

Cited by 59 publications

(86 citation statements)

References 30 publications

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“…An upturn and saturation in the low temperature resistivity as shown in Fig. 4(b) was previously reported in electrolyte-gated STO, associated to the Kondo effect from local Ti 3þ magnetic moments [20,51]. However, as shown in Fig.…”

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confidence: 68%

Electronic Degeneracy and Intrinsic Magnetic Properties of EpitaxialNb: SrTiO3Thin Films Controlled by Defects

et al. 2015

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We report thermoelectric power experiments in e-doped thin films of SrTiO 3 (STO) which demonstrate that the electronic band degeneracy can be lifted through defect management during growth. We show that even small amounts of cationic vacancies, combined with epitaxial stress, produce a homogeneous tetragonal distortion of the films, resulting in a Kondo-like resistance upturn at low temperature, large anisotropic magnetoresistance, and nonlinear Hall effect. Ab initio calculations confirm a different occupation of each band depending on the degree of tetragonal distortion. The phenomenology reported in this Letter for tetragonally distorted e-doped STO thin films, is similar to that observed in LaAlO 3 =STO interfaces and magnetic STO quantum wells. DOI: 10.1103/PhysRevLett.115.166801 PACS numbers: 73.50.-h, 75.47.Lx, 77.84.Bw The possibility of growing epitaxial interfaces with atomic precision leads to unexpected functionalities in polar interfaces between oxide insulators [1][2][3]. In particular, the two-dimensional electron gas (2DEG) emerging at the interface between SrTiO 3 (STO) and LaAlO 3 (LAO) [4,5], can be tuned to produce a very rich phase diagram, including magnetism and superconductivity [6,7]. These properties are common to the 2DEGs stabilized at the bare surface of bulk STO, and are derived to a large extent from the arrangement and filling of the Ti-t 2g -derived subbands close to the conduction band minimum [8][9][10][11]. This orbital reconstruction can be intrinsic, to cancel the electrostatic energy of the polar interface [12], but could also be caused by the structural distortions and atomic vacancies which relax the epitaxial strain in these thin-film heterostructures. However, the effect of cationic and anionic vacancies on the transport properties of both STO [13] and LAO/STO interfaces [14] is mostly considered from the point of view of their acceptor or donor nature over the total charge density, although vacancies distribute along the crystal structure expanding the unit cell due to an increased Coulomb repulsion [15]. In the case of epitaxial thin films below a certain critical thickness, this has to be necessarily accommodated purely as an increase of the c-axis parameter, due to the clamping of the in-plane lattice parameters to the substrate [16]. In this case, if the tetragonal distortion is homogeneous throughout the film instead of localized around defects, an important effect over the band structure can be anticipated.Here we show that the formation of cation or anion vacancies during epitaxial growth results in a homogeneous tetragonal distortion along the films, which determines their transport properties. Ab initio calculations and thermoelectric power experiments under different degrees of stress suggest that the band degeneracy characteristic of STO can be lifted for sufficiently distorted films. A resistance upturn at low temperature, large anisotropic magnetoresistance (AMR), and a nonlinear Hall effect are observed. This phenomenology was previously observed in...

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confidence: 68%

Electronic Degeneracy and Intrinsic Magnetic Properties of EpitaxialNb: SrTiO3Thin Films Controlled by Defects

et al. 2015

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“…19). Indeed, evidence for such scattering is found from the Kondo effect observed in 2DEGs formed at the surface of STO single crystals when electrolyte gated 20,21 and the observation of magnetism at the LAO/STO interface [22][23][24] , which have both been attributed to the formation of Ti 3 þ magnetic centres 20,21,25,26 .…”

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confidence: 99%

Spin injection and detection in lanthanum- and niobium-doped SrTiO3 using the Hanle technique

et al. 2013

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There has been much interest in the injection and detection of spin-polarized carriers in semiconductors for the purposes of developing novel spintronic devices. Here we report the electrical injection and detection of spin-polarized carriers into Nb-doped strontium titanate single crystals and La-doped strontium titanate epitaxial thin films using MgO tunnel barriers and the three-terminal Hanle technique. Spin lifetimes of up to B100 ps are measured at room temperature and vary little as the temperature is decreased to low temperatures. However, the mobility of the strontium titanate has a strong temperature dependence. This behaviour and the carrier doping dependence of the spin lifetime suggest that the spin lifetime is limited by spin-dependent scattering at the MgO/strontium titanate interfaces, perhaps related to the formation of doping induced Ti 3 þ . Our results reveal a severe limitation of the three-terminal Hanle technique for measuring spin lifetimes within the interior of the subject material.

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“…Interestingly, the dephasing rate clearly does not extrapolate to zero at zero temperature, suggesting a temperature-independent source of dephasing in our device, possibly local magnetic moments. Previous studies of EDLT-STO systems have shown Kondo effect at n > 6 * 10 13 with T K > 10 K [7,21]. At our lower carrier density, we might expect much lower T K , so our entire experimental temperature range could be T K , a regime in which magnetic impurities are predicted [22,23] and experimentally demonstrated [24,25] to yield constant-in-temperature dephasing.…”

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Universal conductance fluctuations in electrolyte-gated SrTiO3 nanostructures

Stanwyck¹,

Gallagher²,

Williams³

et al. 2013

Applied Physics Letters

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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. ...

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Role of Percolation in the Conductance of Electrolyte-GatedSrTiO3

Cited by 59 publications

References 30 publications

Electronic Degeneracy and Intrinsic Magnetic Properties of EpitaxialNb: SrTiO3Thin Films Controlled by Defects

Electronic Degeneracy and Intrinsic Magnetic Properties of EpitaxialNb: SrTiO3Thin Films Controlled by Defects

Spin injection and detection in lanthanum- and niobium-doped SrTiO3 using the Hanle technique

Universal conductance fluctuations in electrolyte-gated SrTiO3 nanostructures

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