Novel Dielectric Relaxation in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>Li</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>doped KCl

Enss, C.; Gaukler, M.; Nullmeier, Martina; Weis, Robert M.; Würger, Aloïs

doi:10.1103/physrevlett.78.370

Cited by 4 publications

(7 citation statements)

References 12 publications

(22 reference statements)

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“…Although a sophisticated theory has not been worked out until now, we are able to show that the resulting dynamics is in qualitative agreement with hitherto unexplained experimental facts. The viewpoint developed here is motivated by recent investigations of TSs in KCl [27][28][29]. Such crystals doped with lithium are considered to be a model system for defect tunneling.…”

Section: Enss and S Hunklingermentioning

confidence: 99%

Incoherent Tunneling in Glasses at Very Low Temperatures

Enss

Hunklinger

1997

Phys. Rev. Lett.

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It has been known for many years that the low temperature properties of amorphous solids are dominated by the presence of tunneling states which can be described phenomenologically by the tunneling model. However, new experimental results indicate that at very low temperatures the dynamics of these states differ significantly from that predicted by the model. Here we propose a new approach which overcomes these difficulties by taking into account the elastic interaction between the tunneling systems. It leads to a crossing from coherent to an incoherent tunneling motion for systems with a small tunnel splitting and allows one to resolve the discrepancies mentioned above.[S0031-9007(97)04261-0] PACS numbers: 61.43.Fs, 62.65. + k, 77.22.Gm The starting point of the systematic investigation of the low temperature properties of glasses was the pioneering work by Zeller and Pohl [1] in which they showed that low temperature thermal conductivity and specific heat of amorphous solids differ fundamentally from those of crystals and are universal for a wide variety of disordered solids. Shortly afterwards a phenomenological description of these observations was developed independently by Phillips [2] and Anderson et al. [3]. This so-called tunneling model (TM) is based on the assumption that atoms or small clusters of atoms exist in amorphous structures, which are able to tunnel between different potential minima. In the following, we call these systems "tunneling states" (TS). In the simplest case they can be considered as "particles" moving in a double-well potential consisting of two harmonic potentials separated by a barrier height V . In general, the depth of the wells differs by an asymmetry energy D. The tunneling splitting results from the overlap of the wave function of a particle in two wells and can be approximated by D 0 E 0 exp͑2l͒, with l ͑d͞2h͒ p 2mV . Here m denotes the effective mass of the tunneling entity, E 0 the ground state energy, and d the distance of the wells in configurational space.Because of the structural disorder of glasses, the local environment of different TSs will vary and their characteristic parameters will exhibit a broad distribution. In the TM, D and l are assumed to be independent quantities which are uniformly distributed. This is generally expressed by the relation P͑D, l͒dDdl PdDdl, where P is a constant. Although there is no theoretical justification for this simple assumption, it has essentially been confirmed by many experiments carried out at low temperatures (for review articles, see Refs. [4][5][6]).In the past few years, however, a growing number of discrepancies between predictions of the TM and observations at temperatures below 100 mK have been reported. Here we briefly recall four examples of these discrepancies and show how these discrepancies can be explained by taking into account incoherent tunneling.Let us first consider the temperature variation of the sound velocity. There exist two mechanisms contributing to this phenomenon, namely, the interaction of the T...

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Section: Enss and S Hunklingermentioning

confidence: 99%

Incoherent Tunneling in Glasses at Very Low Temperatures

Enss

Hunklinger

1997

Phys. Rev. Lett.

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“…The Gaussian distribution P is roughly constant for |J ij | smaller than J/ √ N and vanishes rapidly for higher values, whereas the more precise function P 0 shows a power law behavior. We repeat that, with (8), their second moments are identical.…”

Section: Introductionmentioning

confidence: 81%

“…Recent measurements of the dielectric constant of KCL:Li revealed relaxational motion of the lithium impurities over several decades in the kHz range. 8 Such a broad relaxation spectrum is characteristic for disordered system in general. Therefore we discuss in some detail the distribution of relaxation rates…”

Section: B Rate Distributionmentioning

confidence: 99%

“…More recently, sensitive echo measurements gave precise information on pairs of interacting impurities that occur at low doping 7 . At impurity concentrations of a few hundred ppm, the dipolar couplings destroy the coherent motion of the impurities 8 . Though a few questions would seem settled, 9 the role of interaction, especially the dynamical aspects, is still controversial.…”

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confidence: 99%

“…7, that shows a strong broadening with rising concentration. Indeed, the relaxation spectra observed at high concentrations become very broad and develop a significant low-frequency wing 8 . On the other hand, specific heat measurements give clear evidence for a broadened density of states, in qualitative agreement with Fig.…”

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Collective phenomena in defect crystals

Kühn

Würger²

2000

Phys. Rev. B

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We investigate effects of interactions between substitutional defects on the properties of defect crystals at low temperatures, where defect motion is governed by quantum effects. Both, thermal and dynamical properties are considered. The influence of interactions on defect motion is described via a collective effect. Our treatment is semiclassical in the sense that we analyze collective effects in a classical setting, and analyze the influence on quantized defect motion only thereafter. Our theory describes a crossover to glassy behavior at sufficiently high defect concentration. Our approach is meant to be general. For the sake of definiteness, we evaluate most of our results with parameters appropriate for Li-doped KCl crystals.

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Dynamics of glasses at very low temperatures

Hunklinger

1998

Physica A: Statistical Mechanics and its Applications

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Novel Dielectric Relaxation inLi+doped KCl

Cited by 4 publications

References 12 publications

Incoherent Tunneling in Glasses at Very Low Temperatures

Incoherent Tunneling in Glasses at Very Low Temperatures

Collective phenomena in defect crystals

Dynamics of glasses at very low temperatures

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