Direct Coupling of Magnetic Fields to Tunneling Systems in Glasses

Ludwig, Stefan; Enss, C.; Strehlow, Peter; Hunklinger, Siegfried

doi:10.1103/physrevlett.88.075501

Cited by 49 publications

(64 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The general feature is in agreement with the experiments on multicomponent glasses (Fig.2 in Ref. [9]). …”

Section: B Dependence On the Electric Fieldsupporting

confidence: 81%

“…Moreover the amount of magnetic impurities present in the nonmagnetic glasses seems to be irrelevant and the observed magnetic field effect is strongly influenced by the applied electric field 8 . On the other hand, recent polarization echo experiments show a strong and nonmonotonic dependence of echo amplitude on the applied magnetic field 9,10 . These experiments give us an insight into the coupling of the tunneling centers to the magnetic field.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Akbari

Langari

2005

Phys. Rev. B

View full text Add to dashboard Cite

The anomalous response of glasses in the echo amplitude experiment is explained in the presence of a magnetic field. We have considered the low energy excitations in terms of an effective two level system. The effective model is constructed on the flip-flop configuration of two interacting two level systems. The magnetic field affects the tunneling amplitude through the Aharanov-Bohm effect. The effective model has a lower scale of energy in addition to the new distribution of tunneling parameters which depend on the interaction. We are able to explain some features of echo amplitude versus a magnetic field, namely, the dephasing effect at low magnetic fields, dependence on the strength of the electric field, pulse separation effect and the influence of temperature. However this model fails to explain the isotope effects which essentially can be explained by the nuclear quadrupole moment. We will finally discuss the features of our results.

show abstract

“…The general feature is in agreement with the experiments on multicomponent glasses (Fig.2 in Ref. [9]). …”

Section: B Dependence On the Electric Fieldsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

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

Akbari

Langari

2005

Phys. Rev. B

View full text Add to dashboard Cite

show abstract

“…The nuclear mechanism is supported by some features of the observed magnetic-field dependence of the polarization echo (PE) experiments in the mentioned multi-silicate glasses in the millikelvin range [7]. Moreover the amplitude of the PE in Glycerol glass was shown to become strongly B-dependent only upon deuteration and thus the introduction of quadrupole-moment carrying nuclei in the glass [8].…”

mentioning

confidence: 71%

“…AlBaSi-O [11], [3], [7] YES YES ? YES Duran [11], [4], [7] YES weak ? YES BK7 [11], [4], [13], [7] weak weak NO YES AF45 [13] ?…”

mentioning

confidence: 99%

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

Jug

2009

Phys. Rev. B

View full text Add to dashboard Cite

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...

show abstract

“…This phenomenological model has also explain the T 2 dependence of the thermal conductivity at very low temperature. However, several empirical facts are still challenging the theory [3,4]. Furthermore, after 30 years of research there is yet no accepted picture of what these two-levels systems are.…”

Section: Anomalous Properties Of Amorphous Solidsmentioning

confidence: 99%

On the rigidity of amorphous solids

2005

View full text Add to dashboard Cite

We poorly understand the properties of amorphous systems at small length scales, where a continuous elastic description breaks down. This is apparent when one considers their vibrational and transport properties, or the way forces propagate in these solids. Little is known about the microscopic cause of their rigidity. Recently it has been observed numerically that an assembly of elastic particles has a critical behavior near the jamming threshold where the pressure vanishes. At the transition such a system does not behave as a continuous medium at any length scales. When this system is compressed, scaling is observed for the elastic moduli, the coordination number, but also for the density of vibrational modes. In the present work we derive theoretically these results, and show that they apply to various systems such as granular matter and silica, but also to colloidal glasses. In particular we show that: (i) these systems present a large excess of vibrational modes at low frequency in comparison with normal solids, called the "boson peak" in the glass literature. The corresponding modes are very different from plane waves, and their frequency is related to the system coordination; (ii) rigidity is a non-local property of the packing geometry, characterized by a length scale which can be large. For elastic particles this length diverges near the jamming transition; (iii) for repulsive systems the shear modulus can be much smaller than the bulk modulus. We compute the corresponding scaling laws near the jamming threshold. Finally, we discuss the implications of these results for the glass transition, the transport, and the geometry of the random close packing.

show abstract

Direct Coupling of Magnetic Fields to Tunneling Systems in Glasses

Cited by 49 publications

References 14 publications

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

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

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

On the rigidity of amorphous solids

Contact Info

Product

Resources

About