Evidence for charge–vortex duality at the LaAlO3/SrTiO3 interface

Mehta, Manan; Dikin, Dmitriy A.; Bark, Chung Wung; Ryu, Sangwoo; Folkman, C. M.; Eom, C. B.; Chandrasekhar, Venkat

doi:10.1038/ncomms1959

Cited by 50 publications

(62 citation statements)

References 28 publications

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“…(14) In the far region we have different expressions for the top-and back-gating configurations. For the latter the far region coincides with the bulk of the STO substrate, where (21) …”

Section: Electrostatic Energymentioning

confidence: 99%

“…Here the electrostatic potential confining the electron gas at the interface is calculated self-consistently, finding that the electron confinement at the interface may induce phase separation, to avoid a thermodynamically unstable state with a negative compressibility. This provides a generic robust and intrinsic mechanism for the experimentally observed inhomogeneous character of these interfaces.PACS numbers: 73.43.Nq,73.21.Fg, The two-dimensional electron gas (2DEG) that forms at the interface of two insulating oxides, like LaAlO 3 /SrTiO 3 and LaTiO 3 /SrTiO 3 (hereafter generically referred to as LXO/STO) [1][2][3][4], exhibits a rich phenomenology, such as a gate-tunable metal-tosuperconductor transition [5][6][7][8], a magnetic-field-tuned quantum criticality [9], and inhomogeneous magnetic responses [10][11][12][13][14][15]. Tunneling [16,17] and SQUID magnetometry [18] provide clear evidence of an inhomogeneous interface on both micro-and nanoscopic scales.…”

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confidence: 99%

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Phase Separation from Electron Confinement at Oxide Interfaces

et al. 2016

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Oxide heterostructures are of great interest both for fundamental and applicative reasons. In particular the two-dimensional electron gas at the LaAlO3/SrTiO3 or LaTiO3/SrTiO3 interfaces displays many different physical properties and functionalities. However there are clear indications that the interface electronic state is strongly inhomogeneous and therefore it is crucially relevant to investigate possible intrinsic electronic mechanisms underlying this inhomogeneity. Here the electrostatic potential confining the electron gas at the interface is calculated self-consistently, finding that the electron confinement at the interface may induce phase separation, to avoid a thermodynamically unstable state with a negative compressibility. This provides a generic robust and intrinsic mechanism for the experimentally observed inhomogeneous character of these interfaces.PACS numbers: 73.43.Nq,73.21.Fg, The two-dimensional electron gas (2DEG) that forms at the interface of two insulating oxides, like LaAlO 3 /SrTiO 3 and LaTiO 3 /SrTiO 3 (hereafter generically referred to as LXO/STO) [1][2][3][4], exhibits a rich phenomenology, such as a gate-tunable metal-tosuperconductor transition [5][6][7][8], a magnetic-field-tuned quantum criticality [9], and inhomogeneous magnetic responses [10][11][12][13][14][15]. Tunneling [16,17] and SQUID magnetometry [18] provide clear evidence of an inhomogeneous interface on both micro-and nanoscopic scales. Transport measurements report further signs of inhomogeneity and a percolative metal-to-superconductor transition with a sizable fraction of the 2DEG never becoming superconducting down to the lowest accessible temperatures [19][20][21][22]. For both fundamental reasons and applicative purposes, like device design, it is crucial to identify possible intrinsic mechanisms that may render the 2DEG so strongly inhomogeneous via a phase separation (PS). This is precisely the focus of the present work.Here, we identify a very effective electron-driven mechanism leading to PS, based on the confinement of the 2DEG at the interface. From customary self-consistent calculations of the confining potential well in semiconductors, it is well known [23] that a finite lateral extension usually renders the 2DEG more compressible than its strictly 2D counterpart. This effect is much stronger in LXO/STO than in ordinary semiconductor interfaces, due to the huge dielectric constant of STO, allowing for much larger electron densities, with a strong amplification of the self-consistent adjustments of the confining potential. As a consequence, a non-rigid band structure arises, which varies with the local electron density: an increased electron density is accompanied by a corresponding increase of the positive countercharges (due to oxygen vacancies and/or polarity catastrophe [24][25][26][27][28][29]), from which the interfacial electrons are introduced and restoring the overall charge neutrality. For small-to-moderate increases of electron and countercharge densities the potential well deepens and the e...

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“…(14) In the far region we have different expressions for the top-and back-gating configurations. For the latter the far region coincides with the bulk of the STO substrate, where (21) …”

Section: Electrostatic Energymentioning

confidence: 99%

mentioning

confidence: 99%

Phase Separation from Electron Confinement at Oxide Interfaces

et al. 2016

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“…Duality is also applied to many other systems, for example, boson duality in two-dimensional electron gases 18 . Recently, evidence for the vortex-charge duality near a SIT was found in LaAlO 3 /SrTiO 3 interfaces 13 .Here, we experimentally investigate the duality symmetry across the B-SIT. We apply a duality transformation relating states within the superconductor to states in the B-driven insulator.…”

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confidence: 99%

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confidence: 99%

Duality symmetry and its breakdown in the vicinity of the superconductor–insulator transition

et al. 2013

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The superconductor-insulator transition (SIT) is an accessible quantum phase transition 1,2 that is observed in a number of systems and can be driven by various experimental means 3-9 . A central outstanding issue regards the physical nature of the insulating phase terminating superconductivity 10 . Theoretical advances led to the proposition that this insulator is a new state of matter, termed a superinsulator 11,12 , because its properties can be inferred from the superconductor by invoking duality symmetry 13 . Here we report on the observation of duality symmetry near the magnetic-field-driven SIT in amorphous indium oxide. However, we show that the symmetry is broken by the emergence of the strong insulating state at low temperature.For the magnetic-field-driven SIT (B-SIT) in disordered films, the concept of vortex-charge duality was investigated in ref. 14, using the dirty boson model. In the superconductor, Cooper pairs are condensed into a superfluid at low temperature (T ) values leading to a zero resistivity (ρ) state, with vortices as bosonic excitations introducing dissipation and causing finite ρ. According to the duality concept, in the insulating state, vortices are condensed in a collective mode with zero conductivity (σ ), and the Cooper pairs are the bosonic excitation contributing to a finite σ .The vortex-charge duality has also been applied to the analysis of Josephson junction arrays 15,16 , which are often used as a model system for the SIT in disordered films 11,12,17 . In these systems the insulating state is commonly ascribed to a Coulomb blockade of superconducting islands. Duality is also applied to many other systems, for example, boson duality in two-dimensional electron gases 18 . Recently, evidence for the vortex-charge duality near a SIT was found in LaAlO 3 /SrTiO 3 interfaces 13 .Here, we experimentally investigate the duality symmetry across the B-SIT. We apply a duality transformation relating states within the superconductor to states in the B-driven insulator. We observe vortex-charge duality symmetry that holds up to one order of magnitude in B, T and ρ. The new aspect of this work is that we find systematic deviations from duality symmetry that originate in the B-induced magnetoresistance (ρ(B)) peak 5 . These deviations are qualitatively different at low and high T , as will be shown in detail below.In Fig. 1 we present ρ(B) isotherms obtained from sample RAM005b, which is superconducting at B = 0 with T c = 1.3 K. For all T values where reliable Ohmic data could be collected ρ increases with B until it reaches a T -dependent peak at B peak between 8.5-9.7 T. We restrict ourselves to T > 0.15 K because in the insulating phase, at T < 0.15 K, severe bi-stability of the electron T develops 19 , resulting in strongly nonlinear I -V , that prevented reliable measurements of ρ.The isotherms exhibit a weakly T -dependent crossing point close to h/(2e) 2 , where h is Planck's constant and 2e is the charge

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“…The properties of this 2DEG are intriguing within several respects: it can be made superconducting when the carrier density is tuned by means of gate voltage (see Fig. 1), both in LaAlO 3 /SrTiO 3 (henceforth, LAO/STO) 1,2 and LaTiO 3 /SrTiO 3 (henceforth, LTO/STO) 3,4 interfaces, thus opening the way to voltage-driven superconducting devices; it exhibits magnetic properties; [5][6][7][8][9][10] it displays a strong and tunable 11,12 Rashba spin-orbit coupling; 13 it is extremely two-dimensional, having a lateral extension ≈ 5 nm, thereby enhancing the effects of disorder due to extrinsic and/or intrinsic 12 sources.…”

Section: Introductionmentioning

confidence: 99%

Inhomogeneous multi carrier superconductivity at LaXO₃/SrTiO₃(X = Al or Ti) oxide interfaces

Caprara

Bucheli

Scopigno

et al. 2014

Supercond. Sci. Technol.

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Several experiments reveal the inhomogeneous character of the superconducting state that occurs when the carrier density of the two-dimensional electron gas formed at the LaXO3/SrTiO3 (X=Al or Ti) interface is tuned above a threshold value by means of gating. Re-analyzing previous measurements, that highlight the presence of two kinds of carriers, with low and high mobility, we shall provide a description of multi-carrier magneto-transport in an inhomogeneous two-dimensional electron gas, gaining insight into the properties of the physics of the systems under investigation. We shall then show that the measured resistance, superfluid density, and tunneling spectra result from the percolative connection of superconducting "puddles" with randomly distributed critical temperatures, embedded in a weakly localizing metallic matrix. We shall also show that this scenario is consistent with the characteristics of the superconductor-to-metal transition driven by a magnetic field. A multi-carrier description of the superconducting state, within a weak-coupling BCS-like model, will be finally discussed.

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Evidence for charge–vortex duality at the LaAlO3/SrTiO3 interface

Cited by 50 publications

References 28 publications

Phase Separation from Electron Confinement at Oxide Interfaces

Phase Separation from Electron Confinement at Oxide Interfaces

Duality symmetry and its breakdown in the vicinity of the superconductor–insulator transition

Inhomogeneous multi carrier superconductivity at LaXO₃/SrTiO₃(X = Al or Ti) oxide interfaces

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Evidence for charge–vortex duality at the LaAlO3/SrTiO3 interface

Cited by 50 publications

References 28 publications

Phase Separation from Electron Confinement at Oxide Interfaces

Phase Separation from Electron Confinement at Oxide Interfaces

Duality symmetry and its breakdown in the vicinity of the superconductor–insulator transition

Inhomogeneous multi carrier superconductivity at LaXO3/SrTiO3(X = Al or Ti) oxide interfaces

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Product

Resources

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Inhomogeneous multi carrier superconductivity at LaXO₃/SrTiO₃(X = Al or Ti) oxide interfaces