arXiv subjects

D. M. Zhang

Publications and source records attributed to D. M. Zhang.

10 recordsLinked to original sources

arXiv2025

Temporal Renormalization and the Critical-like Behavior in Supercooled Liquids

Inspired by the Kadanoff transformation in the standard renormalization group theory, we propose a temporal renormalization scheme. A Boltzmann factor that explicitly depends on the renormalized timescale is constructed, permitting thermodynamic quantities to be evaluated self-consistently across different timescales. By applying the scheme to the long-time dynamics of supercooled liquids, we uncover critical-like behaviors of supercooled liquid with three characteristic renormalization timescales: At the first timescale s_α, the system appears to be "thermodynamically frozen", i.e., the energy fluctuation becomes temperature-independent throughout the supercooled regime. At the second timescale s_β, the third-order moment of energy distribution reaches a maximum, and s_β is nearly temperature-independent. At the third timescale s_γ, the third-order moment of energy distribution passes through a minimum, and s_γ diverges as a power law s_γ=(T-T_{c})^(-γ). The scaling relations may reveal an intrinsic behavior in supercooled liquids, highlighting their unique feature. The current findings also demonstrate that temporal renormalization provides a powerful lens for investigating the timescale-specific dynamics.

cond-mat.stat-mech↗

arXiv2025

Crossover between Solid-like and Liquid-like Behavior in Supercooled Liquids

In supercooled liquids, at a temperature between the glass transition temperature Tg and the melting point Tm, thermodynamic properties remain continuous, while dynamic behavior exhibits anomalies. The origin of such thermodynamics-dynamic decoupling has long been a puzzle in the field of glass researches. In this study, we show that the ratio of the alpha-relaxation time associated with the relative and center-of-mass coordinate of nearest-neighbor atomic pairs can effectively characterize the dynamic features of supercooled liquids. With this approach, supercooled liquids can be categorized into two distinct 'states' based on their dynamics: solid-like and liquid-like behaviors. We further propose four possible paths from the liquid to the final glass state, each exhibiting unique thermodynamic and dynamic behaviors. Two of these paths predict a characteristic temperature Tx between Tm and Tg, where a crossover between solid-like and liquid-like behaviors occurs in supercooled liquids. The molecular dynamics simulations of several supercooled liquids reveal that the actual path followed by all these systems undergo the crossover between solid-like and liquid-like behaviors. Tx is found to reside in a similar temperature range as the critical temperature Tc in the mode-coupling theory and the breakdown temperature Tb of the Stokes-Einstein relation. This crossover provides a new microscopic perspective for explaining macroscopic dynamic anomalies, and the absence of a typical thermodynamic phase transition at Tg.

cond-mat.soft↗

arXiv2025

Scaling in Kinetics of Supercooled Liquids

The present study introduces a renormalization based approach to investigate the relaxation dynamics within supercooled liquids. By applying a numerical scale transformation to potential energies along the temporal axis, we have established a novel framework that elucidates the underlying kinetics of supercooled liquids. Our findings indicate that the skewness of the potential energy distribution attains its maximum at a characteristic time scale, D, which exhibits a Curie like scaling relationship with temperature. This scaling relationship is characterized by an exponent, g, that experiences a discontinuous transition at a critical cooling rate, signifying a kinetic like phase transition.We further demonstrate that g maintains an approximate scaling relationship with the cooling rate, where the product of g and the logarithm of the cooling rate is approximately constant.This constant, however, varies depending on whether the cooling rate is above or below the critical value, effectively classifying supercooled liquids into two distinct categories: the glass transition as the destiny of supercooled liquid, GDL, and the crystallization as the destiny of supercooled liquid, CDL. Furthermore, we identify that Ts corresponds to the glass transition temperature for GDL and the crystallization temperature for CDL, respectively. We have successfully developed a theoretical model,which not only derives the Curie like power law but also provides profound insights into the physical implications of D, g and Ts. This research delineates the differences between GDL and CDL, and offers a fresh perspective for exploring the nature of glasses. The findings contribute to the broader understanding of the dynamics of supercooled liquids and the mechanisms of glass formation.

cond-mat.soft↗

arXiv2022

The Angell Plot from the Potential Energy Landscape Perspective

Within the scenario of the potential energy landscape (PEL), a thermodynamic model has been developed to uncover the physics behind the Angell plot. In our model, by separating the barrier distribution in PELs into a Gaussian-like and a power-law form, we obtain a general relationship between the relaxation time and the temperature. The wide range of the experimental data in the Angell plot, as well as the molecular-dynamics data, can be excellently fitted by two characteristic parameters, the effective barrier (ω) and the effective width (σ) of a Gaussian-like distribution. More importantly, the fitted ω and σ^2 for all glasses are found to have a simple linear relationship within a very narrow band, and fragile and strong glasses are well separated in the ω-σ^2 plot, which indicates that glassy states only appear in a specific region of the PEL.

cond-mat.mtrl-sci↗

arXiv2022

Discovery of a paired Gaussian and long-tailed distribution of potential energies in nanoglasses

It is generally believed that the intrinsic properties of glasses are intimately related to potential-energy landscapes (PELs). However, little is known about the PELs of glasses below the glass transition temperature (Tg). Taking advantage of lower potential-energy barriers in nanosystems, we have systematically investigated the dynamics behavior of two nanoglasses, Al43 and Al46. Structure transformation is identified in our pure molecular-dynamics simulation far below Tg, which manifests the existence of metabasins in PELs, at least for nanoglasses. Surprisingly, we find that the distribution of potential energies shows a paired Gaussian and long-tailed distribution at temperatures below and approaching Tg; correspondingly, the distribution of the α-relaxation time exhibits an exponential-like decay. In contrast to the Gaussian distribution of energy in typical liquids and solids, the unexpected distribution may reflect the intrinsic feature of nanoglasses. Associated with the exponential-like distribution of the α-relaxation time, the stretched-exponential structural relaxation is found, and the maximum stretched behavior appears around Tg. Despite our studies focused on nanoglasses, the current finding may shed light on future studies of bulk glasses.

cond-mat.soft↗

arXiv2013

Growth and Characterization of Hybrid Insulating Ferromagnet-Topological Insulator Heterostructure Devices

We report the integration of the insulating ferromagnet GdN with epitaxial films of the topological insulator Bi2Se3 and present detailed structural, magnetic and transport characterization of the heterostructures. Fabrication of multi-channel Hall bars with bare and GdN-capped sections enables direct comparison of magnetotransport properties. We show that the presence of the magnetic overlayer results in suppression of weak anti-localization at the top surface.

cond-mat.mes-hall↗

arXiv2013

Tunneling Tuned Spin Modulations in Ultrathin Topological Insulator Films

Quantitative understanding of the relationship between quantum tunneling and Fermi surface spin polarization is key to device design using topological insulator surface states. By using spin-resolved photoemission spectroscopy with p-polarized light in topological insulator Bi2Se3 thin films across the metal-to-insulator transition, we observe that for a given film thickness, the spin polarization is large for momenta far from the center of the surface Brillouin zone. In addition, the polarization decreases significantly with enhanced tunneling realized systematically in thin insulating films, whereas magnitude of the polarization saturates to the bulk limit faster at larger wavevectors in thicker metallic films. Our theoretical model calculations capture this delicate relationship between quantum tunneling and Fermi surface spin polarization. Our results suggest that the polarization current can be tuned to zero in thin insulating films forming the basis for a future spin-switch nano-device.

cond-mat.mes-hall↗

arXiv2011

Electronic properties of edge-functionalized zigzag graphene nanoribbons on SiO2 substrate-v2

Based on first-principles calculations, electronic properties of edge-functionalized zigzag graphene nanoribbons (ZGNRs) on SiO2 substrate are presented. Metallic or semiconducting properties of ZGNRs are revealed due to various interactions between edge-hydrogenated ZGNRs and different SiO2 (0001) surfaces. Bivalent functional groups decorating ZGNRs serve as the bridge between active edges of ZGNRs and SiO2. These functional groups stabilize ZGNRs on substrate, as well as modify the edge states of ZGNRs and further affect their electronic properties. Band gaps are opened owing to edge states destruction and distorted lattice in ZGNRs.

cond-mat.mtrl-sci↗

arXiv2011

Electronic properties of edge-functionalized zigzag graphene nanoribbons on SiO2 substrate

cond-mat.mtrl-sci↗

arXiv2010

Coherent Heteroepitaxy of Bi2Se3 on GaAs (111)B

We report the heteroepitaxy of single crystal thin films of Bi2Se3 on the (111)B surface of GaAs by molecular beam epitaxy. We find that Bi2Se3 grows highly c-axis oriented, with an atomically sharp interface with the GaAs substrate. By optimizing the growth of a very thin GaAs buffer layer before growing the Bi2Se3, we demonstrate the growth of thin films with atomically flat terraces over hundreds of nanometers. Initial time-resolved Kerr rotation measurements herald opportunities for probing coherent spin dynamics at the interface between a candidate topological insulator and a large class of GaAs-based heterostructures.

cond-mat.mtrl-sci↗