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Coupling of quasi-localized and phonon modes in glasses at low frequency

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Chinese Physics B 2024年第5期33卷 564-571页

作者：段军蔡松林丁淦戴兰宏蒋敏强 State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Engineering Science University of Chinese Academy of SciencesBeijing 101408China

boson peak of glasses,a THz vibrational excess compared to Debye squared-frequency law,remains mysterious in condensed-matter physics and material science.It appears in many different kinds of glassy matters and is also argued to exist in damped crystals.A consensus is that boson peak originates from the coupling of the(quasi)-localized non-phonon modes and the plane-wave-like phonon modes,but the coupling behavior is still not fully understood.In this paper,by modulating the content of localized modes and the frequencies of phonon modes,the coupling is clearly reflected in the localization and anharmonicity of low-frequency vibrational modes.The coupling enhances with increasing cooling rate and sample size.For finite sample size,phonon modes do not fully intrude into the low frequency to form a dense spectrum and they are not sufficiently coupled to the localized modes,thus there is no Debye level and boson peak is ill-defined.This suggestion remains valid in the presence of thermal motions induced by temperature,even though the anharmonicity comes into play.Our results point to the coupling of quasi-localized and phonon modes and its relation to the boson peak.

关键词： metallic glasses low-frequency vibrational modes plane wave boson peak

Resolving aging dynamics of a 3D colloidal glass

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Science China(Physics,Mechanics & Astronomy) 2024年第3期67卷 110-118页

作者： XiaoJuan Wang Jun Duan Gan Ding YunZhuo Lu Xing Lu LanHong Dai MinQiang Jiang State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Materials Science and Engineering Dalian Jiaotong UniversityDalian 116028China School of Engineering Science University of Chinese Academy of SciencesBeijing 100049China

Physical aging is an inherent property of glassy matter, but understanding its microscopic mechanism remains a challenge particularly at the particle level. In this work, we use a confocal microscope to in-situ trace the particle trajectories in a 3D colloidal glass for 73000 s, aiming at resolving the aging dynamics. By calculating the mean square displacement of particle motions, we find that the glass aging with time can be divided into three stages: β relaxation, α relaxation and free diffusion. The system's mean square displacement at each aging state is quantitatively resolved into three contributions of particle dynamics modes: vibration within the nearest-neighbor cages, hopping between cages and cooperative rearrangement. We further calculate the particle's free volume and find that the β-to-α transition is accompanied by the temporary increase of the system-averaged free volume due to pronounced hops of particles. Nevertheless, the temporal autocorrelation of the free volume spatial distribution still obeys a monotonically stretched exponential decay with an exponent of 0.76, which is related to the sub-diffusion dynamics of cooperative rearrangements and hops mixed in α relaxation. According to the resolved vibrational displacements,we calculate the vibrational density of states of this 3D glass, and the characteristic boson peak is reproduced at low frequencies.Our findings shed insight into the particle-level aging dynamics of a real glass under purely thermal activation.

关键词： colloidal glass physical aging particle dynamics free volume boson peak

boson peak in Sm-Al-Co ternary metallic glasses and its possible structural origin

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Chinese Physics B 2010年第1期19卷 441-445页

作者：刘慧美陆成亮王克锋刘俊明王清董闯 Laboratory of Solid State Microstructures Nanjing University International Centre for Materials Physics Chinese Academy of Sciences State Key Laboratory of Materials Modification Dalian University of Technology

The low temperature specific heat of Sm-AI-Co ternary metallic glasses is investigated and a clear anomaly associated with the boson peak is identified. While this anomaly depends slightly on the chemical composition, it has no dependence on external magnetic field. To figure out the mechanism of the boson peak, we interpret the data within various model frameworks. Unlike earlier work, our study shows that this boson peak is mainly ascribed to an additional T2 term of the specific heat, which may originate from the quasi-two-dimensional and short-range ordered structure units possibly existing in the metallic glasses.

关键词： metallic glasses boson peak specific heat

Abnormal specific heat at low temperatures and transport properties in Mg-Cu-Ag-Gd bulk metallic glass

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Journal of Rare Earths 2023年第2期41卷 277-282页

作者： Qiang Zheng Xiu Su Lingyun Li Juan Du Institute of Materials School of Materials Science and EngineeringShanghai UniversityShanghai 200072China

We report the pronounced low-temperature specific-heat Cpanomalies in the Mg_(59.5)Cu_(22.9)Ag_(6.6)Gd_(11)bulk metallic glass(BMG).The extrapolated electron’s temperature coefficientγ0Kis up to 681.8 mJ/(molGd·K^(2))at 0 K,which is a heavy-fermion-like behavior.The low temperature specific heat indicates an enhancement of the conduction-electron effective mass m*below 7.5 K,suggesting that the Mg_(59.5)Cu_(22.9)Ag_(6.6)Gd_(11)BMG is not free-electron-like solid.The excess specific heat in the Mg-based BMG is interpreted with tunneling states and spin glass state(magnetism)which are determined by subtracting electrons’and phonons’contribution to the specific heat below 12 K.The boson peak(BP)temperature is located at 27 K,which is much higher than the reported values of other BMGs.And,a BP height of 0.047 mJ/(mol·K^(4))is obtained due to reduced free volume during copper mold casting with a slow cooling rate.The electrical resistivity was also investigated between 2 and 300 K,which has a negative temperature coefficient of resistivity(TCR)below 35 K(Kondo temperature,TK)and a positive value of 3.9×10^(-4)/K above 35 K.There is a minimum at about 35 K for the electrical resistivity,which can be explained by the Kondo effect.For the resistivity above 35 K,it can be explained by the FaberZiman model due to the T-dependence change of structure factor.

关键词： Specific heat boson peak Electrical resistivity Bulk metallic glass(BMG) Spin glass behavior Rare earths

Role of disorder in determining the vibrational properties of mass-spring networks

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Frontiers of physics 2017年第3期12卷 175-185页

作者： Yunhuan Nie Hua Tong Jun Liu Mengjie Zu Ning Xu CAS Key Laboratory of Soft Matter Chemistry Hefei National Laboratory for Physical Sciences at the Micrascale and Department of Physics University of Science and Technology of China Hefei 230026 China Institute of Industrial Science University of Tokyo Meguro-ku Tokyo 153-8505 Japan

By introducing four fundamental types of disorders into a two-dimensional triangular lattice separately, we determine the role of each type of disorder in the vibration of the resulting mass-spring networks. We are concerned mainly with the origin of the boson peak and the connection between the boson peak and the transverse Ioffe-Regel limit. For all types of disorders, we observe the emergence of the boson peak and Ioffe-Regel limits. With increasing disorder, the boson peak frequency ωBP, transverse Ioffe-Regel frequency ω^TIR, and longitudinal Ioffe-Regel frequency wLn all decrease. We find that there are two ways for the boson peak to form： developing from and coexisting with （but remaining independent of） the transverse van Hove singularity without and with local coordination number fluctuation. In the presence of a single type of disorder, ωTR 〉 wBp, and ωTIR≈BP only when the disorder is sufficiently strong and causes spatial fluctuation of the local coordination number. Moreover, if there is no positional disorder, ωTIR ≈ωLIR. Therefore, the argument that the boson peak is equivalent to the transverse Ioffe-Regel limit is not general. Our results suggest that both local coordination number and positional disorder are necessary for the argument to hold, which is actually the case for most disordered solids such as marginally jammed solids and structural glasses. We further combine two types of disorders to cause disorder in both the local coordination number and lattice site position. The density of vibrational states of the resulting networks resembles that of marginally jammed solids well. However, the relation between the boson peak and the transverse Ioffe-Regel limit is still indefinite and condition-dependent. Therefore, the interplay between different types of disorders is complicated, and more in-depth studies are required to sort it out.

关键词： disorder boson peak Ioffe-Regel limit amorphous solid