Effect of the Aharanov-Bohm phase on the magnetic-field dependence of two-pulse echoes in glasses at low temperatures

Akbari, Alireza; Langari, A.

doi:10.1103/physrevb.72.024203

Cited by 5 publications

(4 citation statements)

References 34 publications

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“…The absence of a magnetoacoustic response in such glasses with ATS can be understood in terms of the much higher resonance frequencies of the NM-pockets and channels, and experiments should be done in such conditions. As for the PE-experiments, the orbital-coupling approach with the inclusion of TS-TS interactions has been shown to provide a partial explanation for the B-dependence of the PE-amplitude at ultralow temperatures [18]. The present theory, interaction improved, is expected to also provide an explanation for such data, the so-called isotope effect [8] being, possibly, fabrication-rather than isotope-related.…”

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confidence: 66%

Multiple-well tunneling model for the magnetic-field effect in ultracold glasses

Jug

2009

Phys. Rev. B

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Puzzling observations of both thermal and dielectric responses in multi-silicate glasses at low temperatures T to static magnetic fields B have been reported in the last decade and call for an extension of the standard two-level systems tunneling model. An explanation is proposed, capable of capturing at the same time the T -and B-dependence of the specific heat Cp and of the dielectric constant ǫ in these glasses. This theory points to the existence of anomalous multi-welled tunneling systems in the glasses -alongside the standard two-level systems -and indications are given for glasses which should achieve larger electric magnetocapacitive enhancements.PACS numbers: 61.43. Fs, 77.22.Ch, 65.60.+a The last decade has seen much renewed interest in the physics of cold non-metallic glasses, materials displaying some universal physical properties attributed to the lowenergy excitations characterising most amorphous solids. The two-level systems (2LS) tunneling model (TM) [1] has been rather successful in explaining a variety of interesting phenomena dealing with the thermal, dielectric and acoustic properties of structural glasses at temperatures T < 1 K. Limitations and failures of the 2LS TM (treating cooperative motion in terms of single particles, mostly) on the other hand, have been also discussed [2].These materials do not present, normally, any remarkable magnetic-field response phenomena other than possibly a weak contribution from trace paramagnetic Feimpurities. It came thus as a great surprise when measurements showed [3] that in some multi-component silicate glasses (but not in pure a-SiO 2 ) one is able to observe changes in the dielectric constant ǫ(T, B) and already in magnetic fields B as weak as a few Oe. A typical glass showing a strong response has some 100 ppm Fe 3+ and the composition Al 2 O 3 -BaO-SiO 2 (in short AlBaSi-O, in this paper). Measurements made on a thick sol-gel fabricated AlBaSi-O film showed changes in δǫ/ǫ = [ǫ(B) − ǫ(0)]/ǫ(0) of order 10 −4 and characterised by an enhancement peaking around 0.03 T for 10 mK < T < 200 mK then followed by a reduction of ǫ for B > 0.1 T. A further enhancement was also observed at much higher fields (B > 10 T).Another, cleaner, multi-component silicate glass (borosilicate BK7, with 6 ppm Fe 3+ ) and a dirtier one (borosilicate Duran, with 120 ppm Fe 3+ ) have shown similar -but weaker -magnetic anomalies, |δǫ/ǫ| ∼ 10 −5 , seemingly excluding the paramagnetic impurities as their source [4]. Yet another multi-silicate glass, aSiO 2+x C y H z was investigated [5], confirming the unusual findings in AlBaSi-O. A convincing explanation for the unusual electric magnetocapacitance behavior of these cold glasses has not yet been found.Recently, some consensus has been gained by the idea of a coupling of the standard 2LS to the magnetic field via nuclei in the glasses carrying an electric quadrupole moment as well as a magnetic dipole one [6]. The nuclear mechanism is supported by some features of the observed magnetic-field dependence of the polarization...

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confidence: 66%

Multiple-well tunneling model for the magnetic-field effect in ultracold glasses

Jug

2009

Phys. Rev. B

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“…All theoretical models that have been proposed to explain the above-mentioned magnetic anomalies are based on modifications of the standard tunnelling model [3], leading to the Bdependence of the energy spectrum of a certain subsystem of TS ensemble. These models and their applications are described in [4,8,[10][11][12][13][14][15].…”

Section: Figurementioning

confidence: 99%

Hole-compensated Fe³⁺impurities in quartz glasses: a contribution to subkelvin thermodynamics

Borisenko

2007

J. Phys.: Condens. Matter

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This paper studies the contribution of [FeO] impurity substitution centres to subkelvin thermodynamic properties of quartz glasses. In the scenario considered an Fe ion substitutes for a Si ion in the metallic sublattice of quartz, and one of the neighbouring oxygen ions captures a hole, which compensates the local charge defect. The Fe cation and the O anion, on which the hole is localized, form a bound small polaron. In this configuration the Fe cation is subject to a crystal field with an approximate C symmetry axis along the Fe-O direction. This axis plays a quantization role for the Fe electronic spin. The hole is assumed to be tunnelling between two neighbouring oxygen ions, switching the quantization axis between two directions and therefore entangling the spin states. Due to this coupling between spin and spatial degrees of freedom an [FeO] centre may be considered as a paramagnetic tunnelling system (PTS). An explicit form derived for a single-PTS low-energy spectrum, together with the model parameter distribution function introduced, allows for a complete thermodynamic description of the [FeO]-based PTS ensemble. In particular, a contribution to the ac dielectric constant, derived as a function of magnetic field and temperature, allows a semiquantitative fit to recent experimental data for the iron-contaminated multicomponent glass BaO-AlO-SiO. Taking into account a spin interaction between Fe and O ions also allows us to account for the anomalous magnetothermal behaviour of the low-temperature specific heat, recently reported for the glasses BaO-AlO-SiO and Duran and earlier for Pyrex.

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“…Several generalizations of the standard TLS model have been reported after the anomalous behavior of glasses in a magnetic field. According to these solutions, the models can be divided into "orbital" 10,11,12,13 and "spin" models (nuclear quadrupole effect) 14,15,16,17 . The "orbital" models can provide an explanation for some of the magnetic field effects by considering the flux dependence of the tunneling splitting.…”

Section: Introductionmentioning

confidence: 99%

Quadrupole effect on the heat conductivity of cold glasses

Akbari

2008

Physica B: Condensed Matter

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At very low temperatures, the tunneling theory for amorphous solids predicts a thermal conductivity κ ∝ T p , with p = 2. We have studied the effect of the Nuclear Quadrupole moment on the thermal conductivity of glasses at very low temperatures. We developed a theory that couples the tunneling motion to the nuclear quadrupoles moment in order to evaluate the thermal conductivity. Our result suggests a cross over between two different regimes at the temperature close to the nuclear quadrupoles energy. Below this temperature we have shown that the thermal conductivity is larger than the standard tunneling result and therefore we have p < 2. However, for temperatures higher than the nuclear quadrupoles energy, the result of standard tunneling model has been found.

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Effect of the Aharanov-Bohm phase on the magnetic-field dependence of two-pulse echoes in glasses at low temperatures

Cited by 5 publications

References 34 publications

Multiple-well tunneling model for the magnetic-field effect in ultracold glasses

Multiple-well tunneling model for the magnetic-field effect in ultracold glasses

Hole-compensated Fe³⁺impurities in quartz glasses: a contribution to subkelvin thermodynamics

Quadrupole effect on the heat conductivity of cold glasses

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Effect of the Aharanov-Bohm phase on the magnetic-field dependence of two-pulse echoes in glasses at low temperatures

Cited by 5 publications

References 34 publications

Multiple-well tunneling model for the magnetic-field effect in ultracold glasses

Multiple-well tunneling model for the magnetic-field effect in ultracold glasses

Hole-compensated Fe3+impurities in quartz glasses: a contribution to subkelvin thermodynamics

Quadrupole effect on the heat conductivity of cold glasses

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Hole-compensated Fe³⁺impurities in quartz glasses: a contribution to subkelvin thermodynamics