Intrinsic Electric Dipole Moment of Tunneling Systems in Silica Glasses

Golding, B.; Schickfus, M. von; Hunklinger, Siegfried; Dransfeld, Klaus

doi:10.1103/physrevlett.43.1817

Cited by 113 publications

(62 citation statements)

References 11 publications

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“…Furthermore, the TLS have an electric dipole moment which is also accessible experimentally. Using the partial charges of the BKS potential we obtain an average dipole moment of 0.65 D which is in excellent agreement with the experimental value of 0.5 D [28].…”

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confidence: 85%

What Is Moving in Silica at 1 K? A Computer Study of the Low-Temperature Anomalies

Reinisch

Heuer

2005

Phys. Rev. Lett.

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Though the existence of two-level systems (TLS) is widely accepted to explain low temperature anomalies in many physical observables, knowledge about their properties is very rare. For silica which is one of the prototype glass-forming systems we elucidate the properties of the TLS via computer simulations by applying a systematic search algorithm. We get specific information in the configuration space, i.e. about relevant energy scales, the absolute number of TLS and electric dipole moments. Furthermore important insight about the real-space realization of the TLS can be obtained. Comparison with experimental observations is included.PACS numbers: 61.43.Fs, 63.50.+x, Most kinds of disordered solids show anomalous behavior at very low temperatures (Kelvin regime and below) as compared to their crystalline counterparts. Many of the observed features can be explained by the Standard Tunneling Model (STM) [1,2] and its generalization, which is the Soft-Potential Model [3,4]. The basic idea of the STM is to postulate the possibility of localized transitions between different configurations, i.e. adjacent minima of the potential energy landscape. Such a transition can be described by a double-well potential (DWP), characterized by an asymmetry ∆, potential height V and distance d between both configurations. From a quantum-mechanically perspective at low temperatures the system is tunneling between both configurations and the DWP is characterized by the lowest two eigenstates. If their energy difference E is in the Kelvin regime, these DWP may contribute to the low-temperature anomalies. Then one may speak of Two Level Systems (TLS). The TLS can couple to strain and electric fields and therefore show up in observables like thermal conductivity, sound absorption and dielectric response [5]. Recently, even observations about the interaction of different TLS have been reported [6,7,8].So far it has not been possible to derive a theory of the low-temperature anomalies of real glass-forming systems from first principles, except for mean-field models [9] and random first order transition theory [10]. Thus for a prototype system like SiO 2 the STM has to be basically considered as phenomenological. Important questions emerge. Computer simulations may help to shed some light on the nature of the low-temperature anomalies. In previous work on SiO 2 the trajectories, generated either by molecular dynamics [11,12] or by the activationrelaxation technique [13], have been analyzed with respect to transition events between different structures. Both approaches yield some interesting insight into the nature of relaxation processes in SiO 2 . (Q1), however, requires a systematic search procedure, and (Q2) and (Q3) a sufficiently large number of characteristic DWP and thus an efficient search method. This has not been the scope of previous simulations on SiO 2 .In recent years we have developed a set of simulation techniques which allow us to approach these questions [14,15]. (Q1) Starting from representative low-energy structures we...

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supporting

confidence: 85%

What Is Moving in Silica at 1 K? A Computer Study of the Low-Temperature Anomalies

Reinisch

Heuer

2005

Phys. Rev. Lett.

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“…8,9 Subsequent acoustic and microwave measurements also have verified the model. 10,11 It is generally accepted that O-H bonds in the oxide are one of the microscopic origins for such TLS. 12 The TLS in amorphous oxides are found to be ubiquitous in solid-state quantum devices such as superconducting qubits, 13 optical, 14 and microwave resonators, 15 leading to qubit decoherence and excess phase noise.…”

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confidence: 99%

Optomechanical effects of two-level systems in a back-action evading measurement of micro-mechanical motion

Suh¹,

Weinstein²,

Schwab³

2013

Applied Physics Letters

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We show that the two-level systems (TLS) in lithographic superconducting circuits act as a power-dependent dielectric leading to non-linear responses in a parametrically coupled electromechanical system. Driven TLS shift the microwave resonance frequency and modulate the mechanical resonance through the optical spring effect. By pumping with two tones in a back-action evading measurement, these effects produce a mechanical parametric instability which limits single quadrature imprecision to 1.4 xzp. The microwave resonator noise is also consistent to a TLS-noise model. These observations suggest design strategies for minimizing TLS effects to improve ground-state cooling and quantum non-demolition measurements of motion.

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“…Not all TLS have large electric dipoles [8,9]. For example, it has been determined [11] that OH − impurities in SiO 2 have dipole moments of around 3.7 D and dominate ǫ ′ , while the intrinsic SiO 2 TLS have moments of 0.6 D. The TLS dielectric response is proportional to p 2 , so dielectric measurements are most sensitive to nearly degenerate TLS with substantial electric dipole moments. In contrast, the acoustic dispersion is influenced by all TLS with elastic couplings, not just those with large p.…”

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confidence: 99%

Evidence for Growth of Collective Excitations in Glasses at Low Temperatures

1998

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We present new data on the nonequilibrium acoustic response of glasses to an applied dc electric field below 1K. When compared with the analogous dielectric response of the same material, the acoustic data show, within experimental precision, identical dependence on the perturbing field, but stronger temperature dependence. These data are difficult to reconcile with simple generalizations of the dipole gap model of two-level system (TLS) dielectric response, unless we assume that as T is decreased, interaction-based TLS collective effects increase.The equilibrium thermodynamic, acoustic, and dielectric properties of amorphous materials at low temperatures are described well by the tunneling two-level system (TLS) model [1]. Given a large number of independent TLS with a broad distribution of energy asymmetries ∆ and tunneling parameters ∆ 0 (P (∆, ∆ 0 ) = P 0 /∆ 0 , where P 0 is a contant), the model predicts a specific heat C ∼ T and a thermal conductivity κ ∼ T 2 , in fair agreement with the universal behavior noted by Zeller and Pohl [2]. TLS reach thermal equilibrium with the phonon bath by coupling to local strain fields u, which shift asymmetries by γ · u, where γ ≈ 1 eV. Via this coupling, the TLS contribute to the equilibrium sound speed and internal friction [3]. If the TLS have intrinsic electric dipole moments of magnitude p, the TLS contribution to the equilibrium dielectric response [4] is strictly analogous.The equilibrium sound speed v has a maximum at a temperature T m ≈ 50 mK. For T > T m , the "relaxational regime", TLS behavior is dominated by single-phonon relaxational processes, while for T < T m , the "resonant regime", resonant quantum tunneling of the TLS dominates their response to an ac strain field. The real part of the dielectric response ǫ ′ behaves analogously, but with an overall sign difference. In both v and ǫ ′ the crossover temperature T m at measuring frequency ω is set by the TLS-phonon coupling, T m = ω A 1 3 , where A ∝ γ 2 . Recent measurements [5][6][7] of the nonequilibrium dielectric response of glasses are consistent with a model [14] in which weak dipolar TLS-TLS interactions produce a "dipole gap" in the TLS density of states near zero local electric and strain fields. The gap is necessary to ensure the stability of the ground state, and has been discussed elsewhere [16] in connection with spin glasses.We concentrate on "sweep" experiments, in which an applied electric field, E dc , is slowly varied in time as a triangle wave, and the nonequilibrium dielectric response is measured as a function of that field. This response shows a minimum at zero applied bias (a "zero bias hole"), which becomes sharper and deeper as the temperature is lowered. These sweep data are interpreted as an observation of the proposed gap in the TLS density of states. While the external field is swept, TLS with short relaxation times compared to the period of the sweep partly fill the zero bias hole, an effect which is most important when T < ∼ 15 mK. Slower TLS continue to exhibit a depresse...

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Intrinsic Electric Dipole Moment of Tunneling Systems in Silica Glasses

Cited by 113 publications

References 11 publications

What Is Moving in Silica at 1 K? A Computer Study of the Low-Temperature Anomalies

What Is Moving in Silica at 1 K? A Computer Study of the Low-Temperature Anomalies

Optomechanical effects of two-level systems in a back-action evading measurement of micro-mechanical motion

Evidence for Growth of Collective Excitations in Glasses at Low Temperatures

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