Amorphous Solid without Low Energy Excitations

Liu, Xiao; White, Bruce; Pohl, Robert Wichard; Iwanizcko, E.; Jones, K. M.; Mahan, A. H.; Nelson, B. P.; Crandall, Richard S.; Vepřek, S.

doi:10.1103/physrevlett.78.4418

Cited by 165 publications

(126 citation statements)

References 18 publications

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“…Nonetheless, previous reports (30)(31)(32)(33) claiming the absence of TLS in amorphous solids are scarce and somewhat controversial. Angell et al (34) proposed the designation of "superstrong liquids" for some "tetrahedral liquids" which could be potential "perfect glasses," with a residual entropy near zero, and where the defect-related boson peak and TLS excitations were weak or absent.…”

Section: Discussionmentioning

confidence: 99%

Suppression of tunneling two-level systems in ultrastable glasses of indomethacin

Pérez-Castañeda

Rodríguez-Tinoco

Rodríguez‐Viejo

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

129

116

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Glasses and other noncrystalline solids exhibit thermal and acoustic properties at low temperatures anomalously different from those found in crystalline solids, and with a remarkable degree of universality. Below a few kelvin, these universal properties have been successfully interpreted using the tunneling model, which has enjoyed (almost) unanimous recognition for decades. Here we present low-temperature specific-heat measurements of ultrastable glasses of indomethacin that clearly show the disappearance of the ubiquitous linear contribution traditionally ascribed to the existence of tunneling twolevel systems (TLS). When the ultrastable thin-film sample is thermally converted into a conventional glass, the material recovers a typical amount of TLS. This remarkable suppression of the TLS found in ultrastable glasses of indomethacin is argued to be due to their particular anisotropic and layered character, which strongly influences the dynamical network and may hinder isotropic interactions among low-energy defects, rather than to the thermodynamic stabilization itself. G lasses or amorphous solids are well known (1, 2) to exhibit thermal and acoustic properties very different from those of their crystalline counterparts. Even more strikingly, many of these properties are very similar for any glass, irrespective of the type of material, chemical bonding, etc. Hence the low-temperature properties of noncrystalline solids are said to exhibit a universal "glassy behavior." In particular, below 1−2 K the specific heat of glasses depends approximately linearly on temperature, C p ∝T, and the thermal conductivity almost quadratically, κ ∝ T 2 , in clear contrast with the cubic dependences successfully predicted by Debye theory for crystals. In addition, a broad maximum in C p /T 3 [originated from the so-called "boson peak" in the reduced vibrational density of states g(ω)/ω 2 ] is also typically observed in glasses around 3−10 K, as well as a universal plateau in the thermal conductivity κ(T) in the same temperature range (1, 2).Very soon after the seminal paper by Zeller and Pohl (1) in 1971, Phillips (3) and Anderson et al. (4) independently introduced the well-known standard tunneling model (TM). The fundamental idea of the TM is the ubiquitous existence of atoms or small groups of atoms in amorphous solids due to the intrinsic atomic disorder, which can perform quantum tunneling between two configurations of very similar energy, usually named twolevel systems (TLS). This simple model was able to account for the abovementioned thermal and acoustic anomalies of glasses below 1−2 K, and soon acquired unanimous recognition. Only very few authors (5) posed then criticisms against the standard TM, pointing out how improbable it was that a random ensemble of independent tunneling states would produce essentially the same universal constant for the thermal conductivity or the acoustic attenuation in any substance. Indeed, significant discrepancies with the TM below ∼100 mK have also been reported (6-9), in particular ...

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Section: Discussionmentioning

confidence: 99%

Suppression of tunneling two-level systems in ultrastable glasses of indomethacin

Pérez-Castañeda

Rodríguez-Tinoco

Rodríguez‐Viejo

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

129

116

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“…Some recent works in this direction are Ref. [19] on hydrogenated silicon altering the amorphous network and density-dependent voids in silicon [20].…”

Section: Quantum Friction Due To Tunneling Two-level Systemsmentioning

confidence: 99%

Tunable low-temperature dissipation scenarios in palladium nanomechanical resonators

et al. 2017

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We study dissipation in palladium (Pd) nanomechanical resonators at low temperatures in the linear response regime. Metallic resonators have shown characteristic features of dissipation due to tunneling two-level systems (TLS). The system described here offers a unique tunability of the dissipation scenario by adsorbing hydrogen (H 2 ), which induces a compressive stress. The intrinsic stress is expected to alter TLS behavior. We find a sublinear ∼T 0.4 dependence of dissipation in a limited temperature regime. As seen in TLS dissipation scenarios, we find a logarithmic increase of frequency from the lowest temperatures till a characteristic temperature T co is reached. In samples without H 2 , T co ∼ 1 K was seen, whereas with H 2 it is clearly reduced to ∼700 mK. Based on standard TLS phenomena, we attribute this to enhanced phonon-TLS coupling in samples with compressive strain. We also find that with H 2 there is a saturation in low-temperature dissipation, which may possibly be due to super-radiant interaction between TLS and phonons. We discuss the data in the scope of TLS phenomena and similar data for other systems.

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“…High temperature a-Si:H, deposited by the hot wire (HW) technique, has demonstrated very different structural and electronic properties, including a reduced Staebler-Wronski metastability, a different H NMR 'signature', improved structural ordering, and a dramatic reduction in film internal friction, which until now had been thought to be unachievable for an amorphous material [1][2][3][4]. The additional possibility of depositing such materials at high deposition rates [5] has only added to its attractiveness as a candidate for incorporation into a solar cell structure.…”

Section: Introductionmentioning

confidence: 99%

H Out-Diffusion and Device Performance in n-i-p Solar Cells Utilizing High Temperature Hot Wire a-Si:H i-Layers

Mahan¹,

Iwaniczko²,

Wang³

et al. 1998

MRS Proc.

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. Hydrogen out-diffusion from the n/i interface region plays a major role in controlling the fill factor (FF) and resultant efficiency of n-i-p a-Si:H devices, with the i-layer deposited at high substrate temperatures by the hot wire technique. Modeling calculations have shown that a thin, highly defective layer at this interface, perhaps caused by significant H out-diffusion and incomplete lattice reconstruction, results in sharply lower device FFs due to the large voltage dropped across this defective layer. We have therefore employed buffer layers designed to retard this out-diffusion. We find that an increased H content, either in the n-layer or a thin intrinsic low temperature buffer layer, does not significantly retard this out-diffusion, as observed by SIMS H profiles on devices. However, if this low temperature buffer layer is thick enough, the out-diffusion is minimized, yielding nearly flat H profiles and a much improved device performance. We discuss this behavior in the context of the H chemical potentials and H diffusion coefficients in the high temperature, buffer, n-, and stainless steel substrate layers. Finally, we report a 9.8% initial active area device, fabricated at 16.5Å/s, using the insights obtained in this study. Light soaking data are also reported.

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Amorphous Solid without Low Energy Excitations

Abstract: We have measured the low temperature internal friction ͑Q 21 ͒ of amorphous silicon ͑a-Si͒ films. e-beam evaporation or 28 Si 1 implantation leads to the temperature-independent Q 21

Cited by 165 publications

References 18 publications

Suppression of tunneling two-level systems in ultrastable glasses of indomethacin

Suppression of tunneling two-level systems in ultrastable glasses of indomethacin

Tunable low-temperature dissipation scenarios in palladium nanomechanical resonators

H Out-Diffusion and Device Performance in n-i-p Solar Cells Utilizing High Temperature Hot Wire a-Si:H i-Layers

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