Magnetic field dependence of dephasing rate due to diluted Kondo impurities

Micklitz, Tobias; Costi, T. A.; Rosch, Achim

doi:10.1103/physrevb.75.054406

Cited by 31 publications

(28 citation statements)

References 37 publications

(100 reference statements)

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“…Except for very low temperatures, where a small residual inelastic scattering is observed, 22,23 these calculations are in very good agreement with the experiments that clearly show that magnetic impurities in concentration as small as 1 ppm can induce substantial inelastic scattering. 13,24,25 The source of the small residual inelastic scattering is unclear: It may be due to some mispositioned magnetic impurities with anomalously small Kondo temperature or structural defects created by the ion implantation, but an intrinsic effect cannot be excluded either, although the residual dephasing seems to be proportional to the impurity concentration. Furthermore, we have to emphasize that other experiments on very dirty metals probably cannot be explained in terms of magnetic scattering, and possibly other mechanisms are needed to account for the dephasing observed at very low temperatures in these systems.…”

Section: Introductionmentioning

confidence: 95%

Theory of inelastic scattering from quantum impurities

et al. 2007

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We use the framework set up recently to compute non-perturbatively inelastic scattering from quantum impurities [G. Zar\'and {\it et al.}, Phys. Rev. Lett. {\bf 93}, 107204 (2004)] to study the the energy dependence of the single particle $S$-matrix and the inelastic scattering cross section for a number of quantum impurity models. We study the case of the spin $S=1/2$ two-channel Kondo model, the Anderson model, and the usual $S=1/2$ single-channel Kondo model. We discuss the difference between non-Fermi liquid and Fermi liquid models and study how a cross-over between the non-Fermi liquid and Fermi liquid regimes appears in case of channel anisotropy for the $S=1/2$ two-channel Kondo model. We show that for the most elementary non-Fermi liquid system, the two-channel Kondo model, half of the scattering remains inelastic even at the Fermi energy. Details of the derivation of the reduction formulas and a simple path integral approach to connect the $T$-matrix to local correlation functions are also presented.Comment: published versio

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Section: Introductionmentioning

confidence: 95%

Theory of inelastic scattering from quantum impurities

et al. 2007

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“…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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confidence: 99%

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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“…The Kondo problem is of central importance for understanding low-temperature anomalies in low-dimensional disordered metals [1,2,3,4,5,6,7,8,9,10,11,12], such as the saturation of the dephasing rate [13] and the non-Fermi-liquid behavior of certain magnetic alloys [1,14]. For a clean metal, the screening of a spin-1/2 magnetic impurity is governed by a single energy scale, the Kondo temperature T K .…”

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confidence: 99%

Nonperturbative Scaling Theory of Free Magnetic Moment Phases in Disordered Metals

et al. 2007

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The crossover between a free magnetic moment phase and a Kondo phase in low dimensional disordered metals with dilute magnetic impurities is studied. We perform a finite size scaling analysis of the distribution of the Kondo temperature as obtained from a numerical renormalization group calculation of the local magnetic susceptibility and from the solution of the self-consistent Nagaoka-Suhl equation. We find a sizable fraction of free (unscreened) magnetic moments when the exchange coupling falls below a disorder-dependent critical value Jc. Our numerical results show that between the free moment phase due to Anderson localization and the Kondo screened phase there is a phase where free moments occur due to the appearance of random local pseudogaps at the Fermi energy whose width and power scale with the elastic scattering rate 1/τ .The Kondo problem is of central importance for understanding low-temperature anomalies in low-dimensional disordered metals [1,2,3,4,5,6,7,8,9,10,11,12], such as the saturation of the dephasing rate [13] and the non-Fermi-liquid behavior of certain magnetic alloys [1,14]. For a clean metal, the screening of a spin-1/2 magnetic impurity is governed by a single energy scale, the Kondo temperature T K . Thermodynamic observables and transport properties obey universal functions which scale with T K . Thus, in a metal where nonmagnetic disorder is also present, two fundamental questions naturally arise: (i) Is the Kondo temperature modified by nonmagnetic disorder? (ii) Is the one-parameter scaling behavior still valid? It is well known [1,2,5,7,11] that magnetic moments remain unscreened when conduction electrons are localized due to disorder. However, in weakly disordered two-dimensional electron systems, the localization length is macroscopically large, and so is the number N c of eigenstates with a finite amplitude at the position of the magnetic impurity. In this case, one does not expect to find unscreened magnetic moments for experimentally relevant values of the exchange coupling J.Another situation where magnetic moments remain free in metals at low temperatures occurs when the density of states has a global pseudogap at the Fermi energy E F , namely,. In clean metals, the pseudogap quenches the Kondo screening when J falls below a critical value J c (α). So far, only a few values of α have been realized experimentally: α = 1 in graphene and in d-wave superconductors and α = 2 in p-wave superconductors. In this Letter we examine the quantum phase diagram of magnetic moments diluted in two-dimensional disordered metals using a modified version of the numerical renormalization group (NRG) method. We find a free moment phase which we attribute to the random occurrence of local pseudogaps. The existence of free moments is confirmed directly with NRG by the Curie-like behavior of the the local magnetic susceptibility at low temperatures. Finite-size scaling is performed to demonstrate the robustness of our finding. Furthermore, the distribution of Kondo temperatures obtained numeric...

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Magnetic field dependence of dephasing rate due to diluted Kondo impurities

Cited by 31 publications

References 37 publications

Theory of inelastic scattering from quantum impurities

Theory of inelastic scattering from quantum impurities

Universal conductance fluctuations in electrolyte-gated SrTiO3 nanostructures

Nonperturbative Scaling Theory of Free Magnetic Moment Phases in Disordered Metals

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