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

Springer Proceedings in Physics

2017

Self Cite

The problems of the intermediate-range atomic structure of glasses and of the mechanism for the glass transition are approached from the low-temperature end in terms of a scenario for the atomic organization that justifies the use of an extended tunneling model. The latter is crucial for the explanation of the magnetic and compositional effects discovered in non-metallic glasses in the Kelvin and milli-Kelvin temperature range. The model relies on the existence of multi-welled local potentials for the effective tunneling particles that are a manifestation of a non-homogeneous atomic structure deriving from the established dynamical heterogeneities that characterize the supercooled liquid state. It is shown that the extended tunneling model can successfully explain a range of experiments at low temperatures, but the proposed non-homogeneous atomic structure scenario is then tested in the light of available high resolution electron microscopy imaging of the structure of some glasses and of the behaviour near the glass transition.

Section: The Cellular Model For the Atomic Structure Of Glasses And Tmentioning

confidence: 81%

Section: The Magnetic Field Dependent Dielectric Constantmentioning

confidence: 94%

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The Polycluster Theory for the Structure of Glasses: Evidence from Low Temperature Physics

Springer Proceedings in Physics

2017

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“…This figure shows the physical origin of the magnetic effects: the quantum states being conserved in number, they are very rapidly shifted towards high values of the energy when a magnetic field, even very weak, is switched on. Our ETM has been able to explain the magnetic effects in the heat capacity [1], in the real [45] and imaginary [47] parts of the dielectric constant and in the polarization echo amplitude [47] measurements reported to date for various glasses at low temperatures, as well as the composition-dependent anomalies [19,46]. The new physics is provided by the magnetic-field dependent TS Figure 6: (colour online) The magnetic-sensitive part of the density of states (DOS) as a function of the A-B phase ϕ (proportional to the magnetic field B) and different energies (n AT S P * has been set to 1).…”

Section: The Quantum Mechanics Of the Three Welled Potentialmentioning

confidence: 90%

Realistic tunnelling states for the magnetic effects in non-metallic real glasses

Bonfanti

Kob

2015

Philosophical Magazine

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The discovery of magnetic and compositional effects in the low temperature properties of multicomponent glasses has prompted the need to extend the standard two-level systems (2LSs) tunneling model. A possible extension [1] assumes that a subset of tunneling quasi-particles is moving in a threewelled potential (TWP) associated with the ubiquitous inhomogeneities of the disordered atomic structure of the glass. We show that within an alternative, cellular description of the intermediate-range atomic structure of glasses the tunneling TWP can be fully justified. We then review how the experimentally discovered magnetic effects can be explained within the approach where only localized atomistic tunneling 2LSs and quasi-particles tunneling in TWPs are allowed. We discuss the origin of the magnetic effects in the heat capacity, dielectric constant (real and imaginaryi parts), polarization echo and SQUID magnetization in several glassy systems. We conclude by commenting on a strategy to reveal the mentioned tunneling states (2LSs and TWPs) by means of atomistic computer simulations and discuss the microscopic nature of the tunneling states in the context of the potential energy landscape of glass-forming systems.arXiv:1508.02424v1 [cond-mat.dis-nn] 10 Aug 2015 1 IntroductionThe physics of glasses, especially at low temperatures, continues to attract considerable interest. At low temperatures glasses are believed to be characterized by low-energy excitations going under the name of tunneling systems, or states (TSs) which are normally described in terms of double-welled potentials (DWPs) and two-level systems (2LSs) with energy asymmetry and tunneling barrier uniformly distributed in the amorphous solid [2,3]. Little is still known about the nature of the TSs, but the general consensus is still that the intermediate-range atomic structure of glasses is well described by Zachariasen's 1932 continuous random network model [4,5] (thus, homogeneously disordered like for a liquid) and the 2LSs arise out of two slightly similar, localized atomic configurations. With this characterization the 2LSs have been employed in the 1970s and 80s to explain with some success the anomalies in the properties of glasses at low temperatures. Recently, the field has been witnessing a renaissance since the discovery that there are unexpected magnetic effects in insulating glasses [6,7,8,9] and that the TSs are responsible for the decoherence of phase qubits made of superconducting Josephson-junctions [10,11,12,13,14]. The 2LSs are thought to be ubiquitous in the junction's tunneling barrier which, though very thin, is considered to be amorphous and described by Zachariasen-Warren's model [4,5]. On the other hand, the low-temperature glasses have also been studied as a paradigm where to conduct research on the physics of aging so common to many disordered systems out of equilibrium [15,16]. In this context, the relevant degrees of freedom have also been described in terms of 2LSs, with some success [17]. Yet, deviations from the behaviour pred...

“…However, the magnetic effects discovered in the multisilicate glasses in recent times [1]- [3], and also some older data from mixed (SiO2)1−x(K2O)x and (SiO2)1−x(Na2O)x glasses [4], indicate the need for a suitable generalization of the 2LS TM. We show that, not only for the magnetic effects [3,5] but also for the mixed glasses in the absence of a field, the right extension of the 2LS TM is provided by the (anomalous) multilevel tunneling systems approach proposed by one of us. It appears that new 2LS develop via dilution near the hull of the SiO4-percolating clusters in the mixed glasses.…”

mentioning

confidence: 86%

Evidence for a two-component tunnelling mechanism in the multicomponent glasses at low temperatures

Paliienko

2010

EPL

The dielectric anomalies of window-type glasses at low temperatures (T < 1 K) are rather successfully explained by the two-level systems (2LS) tunneling model (TM). However, the magnetic effects discovered in the multisilicate glasses in recent times [1]- [3], and also some older data from mixed (SiO2)1−x(K2O)x and (SiO2)1−x(Na2O)x glasses [4], indicate the need for a suitable generalization of the 2LS TM. We show that, not only for the magnetic effects [3,5] but also for the mixed glasses in the absence of a field, the right extension of the 2LS TM is provided by the (anomalous) multilevel tunneling systems approach proposed by one of us. It appears that new 2LS develop via dilution near the hull of the SiO4-percolating clusters in the mixed glasses.