Localized states in glasses

Galperin, Y. M.; Карпов, В. Г.; Козуб, В. И.

doi:10.1080/00018738900101162

Cited by 200 publications

(107 citation statements)

References 100 publications

Supporting

Mentioning

104

Contrasting

Order By: Relevance

“…Of course, in such cases free energy formulations must be employed that allow one to count the number of configurational states unambiguously, while using "inherent" structures based on potential energy stationary points alone is of limited utility. The strongly quantum case can be loosely understood by transcribing the complex multiparticle rearrangements onto a single collective "reaction" coordinate (as in the soft potential model (Galperin et al, 1991)). In fact, this analogy to a single coordinate soft potential model is quite loose because of the much higher density of states of the ripplons (that give rise to the Boson Peak and correspond to the vibrations of the membrane) compared with the density of states of the soft potential model, which is one dimensional so that only one coordinate is vibrationally excited.…”

Section: Quantum Effects Beyond the Strict Semi-classical Picture mentioning

confidence: 99%

The Microscopic Quantum Theory of Low Temperature Amorphous Solids

Lubchenko¹,

Wolynes²

2007

Advances in Chemical Physics

View full text Add to dashboard Cite

The quantum excitations in glasses have long presented a set of puzzles for condensed matter physicists. A common view is that they are largely disordered analogs of elementary excitations in crystals, supplemented by two level systems which are chemically local entities coming from disorder. A radical revision of this picture argues that the excitations in low temperature glasses are deeply connected to the energy landscape of the glass when it vitrifies: the excitations are not low excited states built on a single ground state but locally defined resonances, high in the energy spectrum of a solid. According to a semiclassical analysis, the two level systems involve resonant collective tunneling motions of around two hundred molecular units which are relics of the mosaic of cooperative motions at the glass transition temperature Tg. The density of states of the TLS is determined by Tg and the mosaic's length scale, which is a weak function of the cooling rate. The universality of phonon scattering in insulating glasses is explained. The Boson Peak and the plateau in thermal conductivity, observed at higher temperatures, are also quantitatively understood within the picture as arising from the same cooperative motions, but now accompanied by thermal activation of the mosaic's vibrational modes. The dynamics of some of the local structural transitions have significant quantum corrections to the semiclassical picture. These corrections lead to a deviation of the heat capacity and conductivity from the standard tunneling model results and explain the anomalous time dependence of the heat capacity. Interaction between tunneling centers contributes to the large and negative value of the Grüneisen parameter often observed in glasses.

show abstract

Section: Quantum Effects Beyond the Strict Semi-classical Picture mentioning

confidence: 99%

The Microscopic Quantum Theory of Low Temperature Amorphous Solids

Lubchenko¹,

Wolynes²

2007

Advances in Chemical Physics

View full text Add to dashboard Cite

show abstract

“…The soft-potential model, an extension of the well-known two-level system model, is capable of explaining the thermal properties of amorphous solids up to 100 K. 22 It postulates the existence of ''soft potentials,'' which are local defects with small harmonic constants. In case the lowest energy levels have a separation smaller than a characteristic energy W, they reduce to two-level systems.…”

Section: Elastic-scattering Mechanismsmentioning

confidence: 99%

Transport of 29cm−1phonons in hydrogenated amorphous silicon

1996

View full text Add to dashboard Cite

The scattering of 29 cm Ϫ1 phonons in hydrogenated amorphous silicon ͑a-Si:H͒ at 2 K is investigated by means of optically generated heat pulses and the ruby phonon detector. The transport is shown to be governed by elastic spatial diffusion and a diffusion coefficient of ϳ1 cm 2 /s. Resonant scattering by soft oscillators, as well as Rayleigh scattering by microvoids or by the disordered network itself account for the experimental findings. In optically excited a-Si:H, the transmission of 29 cm Ϫ1 phonons is reduced by inelastic scattering, proportional to the optical excitation density in a-Si:H and recovers on a 40-ns time scale. These results are discussed in terms of interaction of 29 cm Ϫ1 phonons with optically generated long-lived very high-frequency phonons in a-Si:H. ͓S0163-1829͑96͒00541-3͔

show abstract

“…Since the tunneling probability depends exponentially on the distance between a trap and the channel there is an exponentially wide distribution of the characteristic times, . A wide distribution of  results in the 1/f overall noise spectral density is written as [27][28] [9][10][11][12][13][14][15]. The above scenario also leads not only to decrease of noise at some gate bias but also to increase of the noise at other gate bias, which was not observed experimentally.…”

mentioning

confidence: 99%

“…In the framework of the mobility-fluctuation model, the noise spectral density of the elemental fluctuation events contributing to 1/f noise in any material is given by [27][28] ). In graphene,  is limited by the long-range Coulomb scattering from charged defects even at room temperature (RT) [29][30], in contrast to semiconductors or metals,…”

mentioning

confidence: 99%

Reduction of 1/f noise in graphene after electron-beam irradiation

Hossain

Rumyantsev

Shur

et al. 2013

Applied Physics Letters

View full text Add to dashboard Cite

We investigated the effect of the electron-beam irradiation on the level of the low-frequency 1/f noise in graphene devices. It was found that 1/f noise in graphene reveals an anomalous characteristic -it reduces with increasing concentration of defects induced by irradiation. The increased amount of structural disorder in graphene under irradiation was verified with microRaman spectroscopy. The bombardment of graphene devices with 20-keV electrons reduced the noise spectral density, S I /I 2 (I is the source-drain current) by an order-of magnitude at the radiation dose of 10 4 C/cm 2 . Our theoretical considerations suggest that the observed noise reduction after irradiation can be more readily explained if the mechanism of 1/f noise in graphene is related to the electron-mobility fluctuations. The obtained results are important for the proposed graphene applications in analog, mixed-signal and radio-frequency systems, integrated circuit interconnects and sensors.Noise Suppression in Graphene, UCR -RPI -Ioffe (2012) 3The level of the flicker 1/f noise [1] is one of the key metrics that each new material has to pass before it can be used for practical devices (f is the frequency) [2]. Graphene [3] has shown a great potential for applications in high-frequency communications [4][5], analog circuits [6] and sensors [7][8]. The envisioned applications require a low level of 1/f noise, which contributes to the phase-noise of communication systems [2] and limits the sensor sensitivity [7]. Despite significant research efforts [9][10][11][12][13][14][15] there is still no conventionally accepted model for physical mechanisms behind 1/f noise in graphene. Correspondingly, no comprehensive methods for 1/f noise suppression in graphene devices have been developed.In this Letter we show that 1/f noise in graphene reveals an anomalous characteristic -it reduces with increasing concentration of defects induced by irradiation. We found that bombardment of graphene devices with 20-keV electrons can reduce the noise spectral density, S I /I 2 (I is the source-drain current) by an order-of magnitude at the radiation dose (RD) of 10 4 C/cm 2 . Our theoretical analysis suggests that the observed noise suppression after introduction of defects can be explained if the mechanism of 1/f noise in graphene is related to the electron-mobility fluctuations rather than to the carrier-density fluctuations. Apart from contributing to understanding the physics behind 1/f noise in graphene our results can possibly offer a practical method for noise reduction in various graphene devices. Graphene is relatively susceptible to the electron and ion bombardment owing to its single-atom thickness [21][22][23]. Electron irradiation can introduce different types of defects in graphene Noise Suppression in Graphene, UCR -RPI -Ioffe (2012) 5 depending on the beam energy and local environment, e.g. presence of organic contaminants. For this study we selected the electron energy of 20 keV in order to exclude the severe knock-on damage to ...

show abstract

Localized states in glasses

Cited by 200 publications

References 100 publications

The Microscopic Quantum Theory of Low Temperature Amorphous Solids

The Microscopic Quantum Theory of Low Temperature Amorphous Solids

Transport of 29cm−1phonons in hydrogenated amorphous silicon

Reduction of 1/f noise in graphene after electron-beam irradiation

Contact Info

Product

Resources

About