Slow Conductance Relaxation in Insulating Granular Al: Evidence for Screening Effects

Delahaye, Julien; Honoré, Jean; Grenet, T.

doi:10.1103/physrevlett.106.186602

Cited by 16 publications

(33 citation statements)

References 35 publications

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“…The similar trend is seen in granular Al films [43]. Indeed samples of thickness 10 and 20 nm having similar preexponential factors in (4) have activation energies different by approximately the factor of 2 [43], i.e. for G 0 ≈ 0.8 · 10 −5 one has * 10 /k B = 31 K and * 20 /k B = 14 K, while for C 0 ≈ 0.18 · 10 −5 one has * 10 /k B = 57 K and * 20 /k B = 23 K, respectively.…”

Section: Field Confinementsupporting

confidence: 79%

See 1 more Smart Citation

Fluctuator Model of Memory Dip in Hopping Insulators

Burin

Kurnosov

2012

J Low Temp Phys

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Section: Field Confinementsupporting

confidence: 79%

“…Also the activation energy should decrease when the sample thickness increases, see (3). The similar trend is seen in granular Al films [43]. Indeed samples of thickness 10 and 20 nm having similar preexponential factors in (4) have activation energies different by approximately the factor of 2 [43], i.e.…”

Section: Field Confinementsupporting

confidence: 68%

Fluctuator Model of Memory Dip in Hopping Insulators

Burin

Kurnosov

2012

J Low Temp Phys

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“…The relative amplitude of the relaxation increases with R s but no significant difference was observed between 12.5nm and 2.5nm thick films of similar R s (see the insert of Figure 1). This is qualitatively similar to what is seen in indium oxide [18][19][20] and granular Al thin films [10,17].…”

supporting

confidence: 86%

Observation of thermally activated glassiness and memory dip in a-NbSi insulating thin films

Delahaye¹,

Grenet²,

Marrache‐Kikuchi³

et al. 2014

EPL

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We present electrical conductance measurements on amorphous NbSi insulating thin films. These films display out-of equilibrium electronic features that are markedly different from what has been reported so far in disordered insulators. Like in the most studied systems (indium oxide and granular Al films), a slow relaxation of the conductance is observed after a quench to liquid helium temperature which gives rise to the growth of a memory dip in MOSFET devices. But unlike in these systems, this memory dip and the related conductance relaxations are still visible up to room temperature, with clear signatures of a temperature dependent dynamics. [5,6] and thallium oxide films [7]. Until very recently, the glassy features like the memory dip and its activationless logarithmic slow relaxation were believed to be of universal character. However a new behaviour was evidenced two years ago in discontinuous metal films [6]: the conductance relaxations were found to be strongly suppressed below a well-defined temperature T*, whereas nothing similar was seen in indium oxide [8,9] and granular Al films [10], the two most extensively studied systems so far.These glassy features remain for a large part unexplained but they might be the experimental signature of an electron glass [2,11,12]. This hypothesis is supported by the fact that all systems in which out-of-equilibrium effects are observed have a large charge carrier density compared to standard doped semiconductors close to the metal-insulator transition [7,13]. In indium oxide films, the charge carrier density was indeed found to influence the gate voltage width of the memory dip and the conductance dynamics itself [13], even if aspects of this last result were questioned recently [14].In order to make some progress towards the understanding of these phenomena, it is of crucial importance to identify among the observed properties what is universal and what is specific to each system. In this respect, the exploration of new systems is an incomparable source of information. We present here the first investigation of out of equilibrium phenomena in amorphous (a-) insulating NbSi thin films. We show that this system also displays slow conductance relaxations after a quench from room to liquid helium temperature, as well as gate voltage (V g ) history memory. However the characteristics of the memory dip as well as the effects of temperature are different from all known systems and strongly indicate a thermal activation of the dynamics [8][9][10].Our NbSi films were obtained by co-deposition of Nb and Si at room temperature and under ultrahigh vacuum (typically a few 10 −8 mbar) [15]. Samples for conductance relaxation measurements (see below) were deposited on sapphire substrates coated with a 25 nm thick SiO underlayer designed to smooth the substrate and were protected from oxidation by a 25 nm thick SiO overlayer. Samples for electrical field effect measurements were deposited on Si++ wafers (the gate) coated with 100 nm of thermally grown SiO 2 (the gate insulator). ...

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“…In 2.5 nm thick films, the relaxation slope at 30 V is at least 5 times smaller than at 0 V, which means that L sc is of the order or larger than 2.5 nm. In granular Al films, a screening length of about 10 nm was extracted from 20 and 100 nm thick films background relaxations, which was found to be roughly constant with R s in the samples investigated, probably due to the granular nature of the system [28].…”

Section: Background Relaxations and Screening Length Valuesmentioning

confidence: 85%

“…Assuming that the relaxation modes are homogeneously distributed throughout the thickness of the films (see Figure 4), the G vs. ln(t) relaxation slopes should be proportional to the thickness of the relaxing layer, i.e. T h when measured at V geq and (T h − L sc ) far enough from V geq when the slope is (almost) V g -independent [28]. By comparing the G vs. ln(t) relaxation slopes at V geq = 0V and at 30V in our 12.5 nm thick films, we get L sc estimates of 1.3 -1.9 nm for sample B3, 4 nm for B2 and 7 nm for B1 (the interatomic distance d N b−Si is around 0.26 nm [36]).…”

Section: Background Relaxations and Screening Length Valuesmentioning

confidence: 99%

Electron glass effects in amorphous NbSi films

et al. 2020

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We report on non equilibrium field effect in insulating amorphous NbSi thin films having different Nb contents and thicknesses. The hallmark of an electron glass, namely the logarithmic growth of a memory dip in conductance versus gate voltage curves, is observed in all the films after a cooling from room temperature to 4.2 K. A very rich phenomenology is demonstrated. While the memory dip width is found to strongly vary with the film parameters, as was also observed in amorphous indium oxide films, screening lengths and temperature dependence of the dynamics are closer to what is observed in granular Al films. Our results demonstrate that the differentiation between continuous and discontinuous systems is not relevant to understand the discrepancies reported between various systems in the electron glass features. We suggest instead that they are not of fundamental nature and stem from differences in the protocols used and in the electrical inhomogeneity length scales within each material.

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Slow Conductance Relaxation in Insulating Granular Al: Evidence for Screening Effects

Cited by 16 publications

References 35 publications

Fluctuator Model of Memory Dip in Hopping Insulators

Fluctuator Model of Memory Dip in Hopping Insulators

Observation of thermally activated glassiness and memory dip in a-NbSi insulating thin films

Electron glass effects in amorphous NbSi films

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