Realistic Tunneling States for the Magnetic Effects in Non-Metallic Real Glasses
Giancarlo Jug, Silvia Bonfanti, Walter Kob
备注：
48 pages, 27 figures; mini-review for the Proceedings of the XIV International Workshop on Complex Systems (Fai della Paganella, Trento, March 2015) (submitted to Phil.Mag.). arXiv admin note: text overlap with arXiv:cond-mat/0210221 by other authors
The discovery of magnetic and compositional effects in the low temperature properties of multi-component glasses has prompted the need to extend the standard two-level systems (2LSs) tunneling model. A possible extension \cite{Jug2004} assumes that a subset of tunneling quasi-particles is moving in a three-welled 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 imaginary 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.
The low temperature acoustic properties of bulk metallic glasses measured over a broad range of frequencies rigorously test the predictions of the standard tunneling model. The strength of these experiments and their analyses is mainly based on the interaction of the tunneling states with conduction electrons or quasiparticles in the superconducting state. A new series of experiments at kHz and GHz frequencies on the same sample material essentially confirms previous measurements and their discrepancies with theoretical predictions. These discrepancies can be lifted by considering more correct…
Glasses are featured with a disordered amorphous structure, being opposite to crystals that are constituted by periodic lattices. In this study we report that the exceptional thermodynamic and kinetic stability of an ultra-stable binary ZrCu metallic glass, fabricated by high-temperature physical vapor deposition, originates from ubiquitous crystal-like medium range order (MRO) constituted by Voronoi polyhedron ordering with well-defined local translational symmetry beyond nearest atomic neighbors. The crystal-like MRO significantly improves the thermodynamic and kinetic stability of the glass…
The attenuation rate of vibrational excitations in various metallic liquids and glasses has been reported to change from the quadratic dependence on wavevector at low wavevectors to the linear dependence at high wavevectors. However, the origin of this behavior is not clear. Here, the analysis of this phenomenon through molecular dynamics is presented for prototypical metallic liquids, Cu56Zr44 and Fe. It is shown that the crossover wavevector is strongly correlated with the structural coherence length characterizing coarse-grained density correlations. We suggest that the linear dependence is…
Low temperature properties of glasses are derived within a generalized tunneling model, considering the motion of charged particles on a closed path in a double-well potential. The presence of a magnetic induction field B violates the time reversal invariance due to the Aharonov-Bohm phase, and leads to flux periodic energy levels. At low temperature, this effect is shown to be strongly enhanced by dipole-dipole and elastic interactions between tunneling systems and becomes measurable. Thus, the recently observed strong sensitivity of the electric permittivity to weak magnetic fields can be ex…
Cycling of a metallic glass between ambient and cryogenic temperatures can induce higher-energy states characteristic of glass formation on faster cooling. This rejuvenation, unexpected because it occurs at small macroscopic strains and well below the temperatures of thermally induced structural change, is important, for example, in improving plasticity. Molecular-dynamics simulations elucidate the mechanisms by which thermal cycling can induce relaxation (reaching lower energy) as well as rejuvenation. Thermal cycling, over tens of cycles, drives local atomic rearrangements progressively eras…
Amorphous solids exhibit quasi-universal low-temperature anomalies whose origin has been ascribed to localized tunneling defects. Using an advanced Monte Carlo procedure, we create {\it in silico} glasses spanning from hyperquenched to ultrastable glasses. Using a multidimensional path-finding protocol, we locate tunneling defects with energy splittings smaller than $k_{B}T_Q$, with $T_Q$ the temperature below which quantum effects are relevant ($T_Q \approx 1 \,$K in most experiments). We find that as the stability of a glass increases, its energy landscape as well as the manner in which it i…
We theoretically investigate high-pressure effects on the atomic dynamics of metallic glasses. The theory predicts compression-induced rejuvenation and the resulting strain hardening that have been recently observed in metallic glasses. Structural relaxation under pressure is mainly governed by local cage dynamics. The external pressure restricts the dynamical constraints and slows down the atomic mobility. In addition, the compression induces a rejuvenated metastable state (local minimum) at a higher energy in the free energy landscape. Thus, compressed metallic glasses can rejuvenate and the…
An atomistic understanding of annealing embrittlement is a longstanding issue for metallic glasses, which is still lacking due to the insurmountable gap between the thermal history of atomic models and laboratory-made samples. Here, based on a thermal-cycling annealing method that can vary the effective quenching rate over ten orders of magnitude, we perform an atomistic study of the ductile-brittle transition in a ternary model metallic glass, which can be keyed to the annealing embrittlement in bulk metallic glasses. We reveal that thermal annealing can effectively obliterate thermally activ…
The role of minor alloying in the plasticity of bulk metallic glasses
金属玻璃的微合金化是一项技术研究。一个原来的韧性Pd基单片块状金属玻璃（Pd $_{40}$ Ni $_{40}$ P $_{20}$）选择性地操纵通过添加Fe或Co的合金化效果是极端的，表现出无论是特殊的延展性Co添加或Fe添加后，在单轴压缩或3点弯曲下测试时，立即灾难性的失败。非晶结构的特点是变形前相对于其中程秩序（MRO），使用可变分辨率波动电子显微镜（VR-FEM）。我们观察到的韧性和脆性金属玻璃之间的MRO显着差异，与韧性玻璃表现出丰富的结构多样性和MRO相关长度高达6 nm。MRO的不均匀性似乎使更容易剪切带，从而提高变形能力。
Crystallization of metallic glass as a grain-boundary nucleated process: experimental and theoretical evidence for the grain structure of metallic glasses
NOMATEN Centre of Excellence, National Center for Nuclear Research（国家核研究中心 NOMATEN 卓越中心）；Center for Complexity and Biosystems, Department of Physics "Aldo Pontremoli", University of Milan（米兰大学物理学院复杂性与生物系统中心）；Saarland University, Chair of Metallic Materials（萨尔兰大学金属材料讲席）；Glass and Time , IMFUFA, Department of Science and Environment, Roskilde University（罗斯基勒大学科学与环境学院 IMFUFA 玻璃与时间）；Department of Materials Science, Montanuniversität Leoben（莱奥本矿业大学材料科学系）；Erich Schmid Institute of Materials Science, Austrian Academy of Sciences（奥地利科学院埃里希·施密德材料科学研究所）；Department of Materials Science and Engineering, Johns Hopkins University（约翰斯·霍普金斯大学材料科学与工程系）；Department of Mechanical Engineering, Johns Hopkins University（约翰斯·霍普金斯大学机械工程系）；Department of Physics and Astronomy, Johns Hopkins University（约翰斯·霍普金斯大学物理与天文学系）；Hopkins Extreme Materials Institute, Johns Hopkins University（约翰斯·霍普金斯大学霍普金斯极端材料研究所）；Technical University of Berlin, Chair of Metallic Materials（柏林工业大学金属材料讲席）
Breakdown of material-time scaling in the microscopic dynamics of metallic glasses
Institute of Frontier Materials on Earth and in Space, German Aerospace Center（地球与太空前沿材料研究所，德国航空航天中心）；Institut Néel, Université Grenoble Alpes and Centre National de la Recherche Scientifique（内尔研究所，格勒诺布尔阿尔卑斯大学及法国国家科学研究中心）；European Synchrotron Radiation Facility（欧洲同步辐射装置）；Institute for Condensed Matter Physics, Technical University of Darmstadt（凝聚态物理研究所，达姆施塔特工业大学）；Department of Physics, Institute of Energy Technologies, Universitat Politècnica de Catalunya—BarcelonaTech（物理系，能源技术研究所，加泰罗尼亚理工大学）
Transmutation-accelerated sampling method for multi-component ZrCu(Al) metallic glasses
NOMATEN Centre of Excellence, National Center for Nuclear Research（NOMATEN卓越中心，国家核研究中心）；Univ. Lyon, INSA-Lyon, CNRS, LaMCoS, UMR 5259（里昂大学，里昂国立应用科学学院，法国国家科学研究中心，LaMCoS实验室）；Laboratoire de Mécanique des Solides, CNRS, Ecole Polytechnique（固体力学实验室，法国国家科学研究中心，巴黎综合理工学院）；Aalto University（阿尔托大学）
Compressed correlation functions and fast aging dynamics in metallic glasses
我们提出的X射线光子相关光谱测量的原子动力学在Zr 67 Ni 33金属玻璃，远低于其玻璃化转变温度。我们发现密度涨落的衰减可以用压缩的、比指数快的关联函数来描述，这种关联函数可以用著名的Kohlrausch-Williams-Watts函数来模拟，其形状指数β大于1。这个参数还被发现是独立的等待时间和波矢量，导致的可能性，重新调整所有的关联函数到一个单一的主曲线。在玻璃态的动力学的特征还在于不同的老化制度，坚持在深玻璃态。这些功能似乎是普遍的金属玻璃，并建议一个非扩散性质的动态。这种普遍性是支持的可能性，描述的结构弛豫时间与等待时间的快速增加，使用一个独特的模型函数，独立的系统的微观细节。
Using inelastic neutron scattering and molecular dynamics simulations on a model Zr-Cu-Al metallic glass, we show that transverse phonons persist well into the high-frequency regime, and can be detected at large momentum transfer. Furthermore, the apparent peak width of the transverse phonons was found to follow the static structure factor. The one-to-one correspondence, which was demonstrated for both Zr-Cu-Al metallic glass and a 3-dimensional Lennard-Jones model glass, suggests a universal correlation between the phonon dynamics and the underlying disordered structure. This remarkable corre…
