Interaction between Surface Acoustic Wave and Quantum Hall Effects

Surface acoustic wave(SAW)is a powerful technique for investigating quantum phases appearing in twodimensional electron systems.The electrons respond to the piezoelectric field of SAW through screening,attenuating its amplitude,and shifting its velocity,which is described by the relaxation model.In this work,we systematically study this interaction using orders of magnitude lower SAW amplitude than those in previous studies.At high magnetic fields,when electrons form highly correlated states such as the quantum Hall effect,we observe an anomalously large attenuation of SAW,while the acoustic speed remains considerably high,inconsistent with the conventional relaxation model.This anomaly exists only when the SAW power is sufficiently low.

Regulating Anderson localization with structural defect disorder

Localization due to disorder has been one of the most intriguing theoretical concepts that evolved in condensed matter physics.Here,we expand the theory of localization by considering two types of disorders at the same time,namely,the original Anderson’s disorder and the structural defect disorder,which has been suggested to be a key component in recently discovered two-dimensional amorphous materials.While increasing the degree of both disorders could induce localization of wavefunction in real space,we find that a small degree of structural defect disorder can significantly enhance the localization.As the degree of structural defect disorder increases,localized states quickly appear within the extended phase to enter a broad crossover region with mixed phases.We establish two-dimensional diagrams for the wavefunction localization and conductivity to highlight the interplay between the two types of disorders.Our theoretical model provides a comprehensive understanding of localization in two-dimensional amorphous materials and highlights the promising tunability of their transport properties.

Enhanced anomalous Hall effect in kagome magnet YbMn_(6)Sn_(6)with intermediate-valence ytterbium

We report on the magnetization and anomalous Hall effect(AHE)in the high-quality single crystals of the kagome magnet YbMn_(6)Sn_(6),where the spins of the Mn atoms in the kagome lattice order ferromagnetically and the intermediate-valence Yb atoms are nonmagnetic.The intrinsic mechanism plays a crucial role in the AHE,leading to an enhanced anomalous Hall conductivity(AHC)compared with the other rare-earth RMn_(6)Sn_(6)compounds.Our band structure calculation reveals a strong hybridization between the 4f electrons of Yb and conduction electrons.

Layered kagome compound Na_(2)Ni_(3)S_(4)with topological flat band

We report structural and electronic properties of Na_(2)Ni_(3)S_(4),a quasi-two-dimensional compound composed of alternating layers of[Ni_(3)S_(4)]^(2-)and Na^(+).The compound features a remarkable Ni-based kagome lattice with a square planar configuration of four surrounding S atoms for each Ni atom.Magnetization and electrical measurements reveal a weak paramagnetic insulator with a gap of about 0.5 eV.Our band structure calculation highlights a set of topological flat bands of the kagome lattice derived from the rotated dxz-orbital with C_(3)+T symmetry in the presence of crystal-field splitting.

Effects of Adsorption of Albumin and Gamma-Globulin on the Tribological Performance of a Diamond-Like Carbon Film

The effects of surface adsorption of bovine serum albumin(BSA) and human gamma-globulin(HGG) on the tribological performance of a DLC film were investigated using a quartz crystal microbalance with dissipation(QCM-D), a ball-on-disk reciprocating tribometer, and a three-electrode electrochemical cell. The results showed that the wear depth in the BSA solution was higher than that in the HGG solution. In the HGG solution, the HGG-adsorbed layer could act as a lubricating layer and protect the DLC film from wear. The wear volume of DLC film in BSA and HGG mixture solution was higher than that in single HGG solution. This may be because the BSA molecules inhibit the formation of HGG adsorbed layer during sliding.

Effects of Localized Interface Phonons on Heat Conductivity in Ingredient Heterogeneous Solids

Phonons are the primary heat carriers in non-metallic solids.In compositionally heterogeneous materials,the thermal properties are believed to be mainly governed by the disrupted phonon transport due to mass disorder and strain fluctuations,while the effects of compositional fluctuation induced local phonon states are usually ignored.Here,by scanning transmission electron microscopy electron energy loss spectroscopy and sophisticated calculations,we identify the vibrational properties of ingredient-dependent interface phonon modes in Alx Ga1-x N and quantify their various contributions to the local interface thermal conductance.We demonstrate that atomic-scale compositional fluctuation has significant influence on the vibrational thermodynamic properties,highly affecting the mode ratio and vibrational amplitude of interface phonon modes and subsequently redistributing their modal contribution to the interface thermal conductance.Our work provides fundamental insights into understanding of local phonon-boundary interactions in nanoscale inhomogeneities,which reveal new opportunities for optimization of thermal properties via engineering ingredient distribution.

Gate-controlled magnetic transitions in Fe_(3)GeTe_(2)with lithium ion conducting glass substrate

Since the discovery of magnetism in two dimensions,effective manipulation of magnetism in van der Waals magnets has always been a crucial goal.Ionic gating is a promising method for such manipulation,yet devices gated with conventional ionic liquid may have some restrictions in applications due to the liquid nature of the gate dielectric.Lithium-ion conducting glass-ceramics(LICGC),a solid Li^(+)electrolyte,could be used as a substrate while simultaneously acts as a promising substitute for ionic liquid.Here we demonstrate that the ferromagnetism of Fe_(3)GeTe_(2)2(FGT)could be modulated via LICGC.By applying a voltage between FGT and the back side of LICGC substrate,Li^(+)doping occurs and causes the decrease of the coercive field(Hc)and ferromagnetic transition temperature(Tc)in FGT nanoflakes.A modulation efficiency for H_(c)of up to~24.6%under V_(g)=3.5 V at T=100 K is achieved.Our results provide another method to construct electrically-controlled magnetoelectronics,with potential applications in future information technology.

Accurate GW_(0) band gaps and their phonon-induced renormalization in solids

Recent years,huge progress of first-principles methods has been witnessed in calculating the quasiparticle band gaps,with many-body perturbation theory in the GW approximation being the standard choice,where G refers to Green’s function and W denotes the dynamically screened Coulomb interaction.Numerically,the completeness of the basis set has been extensively discussed,but in practice far from carefully addressed.Beyond the static description of the nuclei,the electron–phonon interactions(EPIs)are ubiquitous,which cause zero-point renormalization(ZPR)of the band gaps.Therefore,to obtain high quality band gaps,one needs both accurate quasiparticle energies and accurate treatments of EPIs.In this article,we review methods on this.The completeness of the basis set is analyzed in the framework of linearized augmented plane waves,by adding high-energy local orbitals(HLOs).The electron–phonon matrix elements and self-energy are discussed,followed by the temperature dependence of the band gaps in both perturbative and non-perturbative methods.Applications of such an analysis on bulk wurtzite BeO and monolayer honeycomb BeO are given.Adding HLOs widens their GW_(0) band gaps by∼0.4 eV while ZPR narrows them by similar amount.These influences cancel each other,which explains the fortuitous agreement between experiment and theory when the basis set is incomplete and the EPIs are absent.The phonon-induced renormalization,a term often neglected in calculations of the band gaps,is also emphasized by its large magnitude.

Erratum to“Accurate GW_(0) band gaps and their phonon-induced renormalization in solids”

After having Eq.(25),since∑1e-iq.rδvKS(r)/δR1ka|R=R^(0)=∑1e-iq·(r-R1δVKS(r-R1)/δRoka)|R=R^0hasthe lattice periodicity,the matrix inEq.

Concerted versus stepwise mechanisms of cyclic proton transfer:Experiments, simulations, and current challenges

Proton transfer(PT) is a process of fundamental importance in hydrogen(H)-bonded systems. At cryogenic or moderate temperatures, pronounced quantum tunneling may happen due to the light mass of H. Single PT processes have been extensively studied. However, for PT involving multiple protons, our understanding remains in its infancy stage due to the complicated interplay between the high-dimensional nature of the process and the quantum nature of tunneling. Cyclic H-bonded systems are typical examples of this, where PT can happen separately via a “stepwise” mechanism or collectively via a “concerted” mechanism. In the first scenario, some protons hop first, typically resulting in metastable intermediate states(ISs) and the reaction pathway passes through multiple transition states. Whilst in the concerted mechanism, all protons move simultaneously, resulting in only one barrier along the path. Here, we review previous experimental and theoretical studies probing quantum tunneling in several representative systems for cyclic PT, with more focus on recent theoretical findings with path-integral based methods. For gas-phase porphyrin and porphycene, as well as porphycene on a metal surface, theoretical predictions are consistent with experimental observations, and enhance our understanding of the processes. Yet, discrepancies in the PT kinetic isotope effects between experiment and theory appear in two systems,most noticeably in water tetramer adsorbed on NaCl(001) surface, and also hinted in porphycene adsorbed on Ag(110)surface. In ice Ih, controversy surrounding concerted PT remains even between experiments. Despite of the recent progress in both theoretical methods and experimental techniques, multiple PT processes in cyclic H-bonded systems remain to be mysterious.

Growth and applications of graphene on copper

Since the first isolation of graphene by Geim and Novoselov in 2004,this two-dimensional(2D)material has attracted significant attention from the scientific and engineering communities.^(1)Due to its structure with a single layer of covalently bonded sp^(2)-hybridized carbon atoms,graphene has superior mechanical,electrical,optical,and thermal properties.^(2-4)Although mechanical exfoliation remains an ideal method for obtaining highquality graphene,its scalability is severely limited;thus,it is impractical for industrial applications.In pursuit of a method suitable for large-scale production,research has been performed using chemical vapor deposition(CVD)methods for synthesizing graphene on metal substrates.

Recent progress on surface chemistryⅠ:Assembly and reaction

Surface chemistry focuses on the investigation of the adsorption,migration,assembly,activation,reaction,and desorption of atoms and molecules at surfaces.Surface chemistry plays the pivotal roles in both fundamental science and applied technology.This review will summarize the recent progresses on surface assembly,synthesis and catalysis investigated mainly by scanning tunneling microscopy and atomic force microscopy.Surface assemblies of water and small biomolecules,construction of Sierpin′ski triangles and surface chirality are summarized.On-surface synthesis of conjugated carbo-and heterocycles and other kinds of carbon nanostructures are surveyed.Surface model catalysis,including single-atom catalysis and electrochemical catalysis,are discussed at the single-atom level.

Ferromagnetic half levitation of LK-99-like synthetic samples

We successfully synthesized polycrystalline LK-99-like ceramic samples with a solid-state-sintering method.Powder X-ray diffraction shows that the main contents are Pb_(10-x)Cu_(x)(PO_(4))_(6)O and Cu_(2)S,consistent with recent reports (arXiv:2307.12037;arXiv:2308.01192).In some small flaky fragments,we successfully observed“half levitation”atop a Nd_(2)Fe_(14)B magnet.Using magnetization measurements on such small pieces,as well as on a large piece which does not exhibit the half levitation,we show that the samples ubiquitously contain weak yet definitive soft ferromagnetic components.We argue that,together with the pronounced shape anisotropy of the small fragments,the soft ferromagnetism is sufficient to explain the observed half levitation in strong vertical magnetic fields.Our measurements do not indicate the presence of the Meissner effect,nor zero resistance,in our samples,leading us to believe that our samples do not exhibit superconductivity.The precise chemical composition and the physics behind the ferromagnetic component remain outstanding questions to be addressed in future research.

Exfoliation of 2D van der Waals crystals in ultrahigh vacuum for interface engineering

Two-dimensional(2D)materials and their heterostructures have been intensively studied in recent years due to their potential applications in electronic,optoelectronic,and spintronic devices.Nonetheless,the realization of 2D heterostructures with atomically flat and clean interfaces remains challenging,especially for air-sensitive materials,which hinders the in-depth investigation of interface-induced phenomena and the fabrication of high-quality devices.Here,we circumvented this challenge by exfoliating 2D materials in an ultrahigh vacuum.Remarkably,ultraflat and clean substrate surfaces can assist the exfoliation of 2D materials,regardless of the substrate and 2D material,thus providing a universal method for the preparation of heterostructures with ideal interfaces.In addition,we studied the properties of two prototypical systems that cannot be achieved previously,including the electronic structure of monolayer phospherene and optical responses of transition metal dichalcogenides on different metal substrates.Our work paves the way to engineer rich interface-induced phenomena,such as proximity effects and moirésuperlattices.

Dynamic phase transition theory

Thermodynamic conventions suffer from describing dynamical distinctions,especially when the structural and energetic changes induced by rare events are insignificant.By using the ensemble theory in the trajectory space,we present a statistical approach to address this problem.Rather than spatial particle-particle interaction which dominates thermodynamics,the temporal correlation of events dominates the dynamics.The zeros of dynamic partition function mark phase transitions in the space-time,i.e.,dynamic phase transition(DPT),as Yang and Lee formulate traditional phase transitions,and hence determine dynamic phases on both sides of the zeros.Analogous to the role of temperature(pressure) as thermal(mechanical) potential,we interpret the controlling variable of DPT,i.e., dynamic field,as the dynamical potential.These findings offer possibility towards a unified picture of phase and phase transition.

模块化局域元素供应技术批量制备12英寸过渡金属硫族化合物

二维过渡金属二硫族化合物(TMDs)因其原子级厚度、高载流子迁移率和超快电荷转移等优点而被认为是下一代半导体器件的核心材料.与传统半导体工业类似,晶圆级TMDs材料的批量生产是其集成电路发展的先决条件.然而,由于生长过程中需要严格满足多种前驱体的有效传输,TMDs晶圆的制备能力通常局限在每批次单片和小片(主要尺寸为2~4英寸).本研究开发了一种用于批量生产晶圆级TMDs的模块化生长策略,可以制造从2英寸(每批15片)到突破性的12英寸(每批3片)的TMDs晶圆.其中,每个模块包括供应TMDs晶圆生长的自充足的局域前驱体供应单元,通过将多个模块堆叠组装形成阵列可实现批量化制备.利用包括光谱学、电子显微镜和电学测量在内的多种表征技术,可以证明制得的单层薄膜具有高结晶度和大面积均匀性.此外,该模块化单元可以将制备的晶圆级MoS_(2)取代转换为多种结构,例如,Janus型MoSSe结构,MoS_(2(1-x))Se_(2x)合金以及MoS_(2)-MoSe_(2)平面异质结等,充分体现了本制备策略的可扩展性.本研究展现了高质量和高产量的晶圆批量生产能力,有望推动二维半导体从实验室规模到工业化规模的无缝过渡,实现与传统硅基技术的互补.

Graphene-driving strain engineering to enable strain-free epitaxy of AlN film for deep ultraviolet light-emitting diode

The energy-efficient deep ultraviolet(DUV)optoelectronic devices suffer from critical issues associated with the poor quality and large strain of nitride material system caused by the inherent mismatch of heteroepitaxy.In this work,we have prepared the strain-free AlN film with low dislocation density(DD)by graphene(Gr)-driving strain-pre-store engineering and a unique mechanism of strain-relaxation in quasi-van der Waals(QvdW)epitaxy is presented.The DD in AlN epilayer with Gr exhibits an anomalous sawtooth-like evolution during the whole epitaxy process.Gr can help to enable the annihilation of the dislocations originated from the interface between AlN and Gr/sapphire by impelling a lateral two-dimensional growth mode.Remarkably,it can induce AlN epilayer to pre-store sufficient tensile strain during the early growth stage and thus compensate the compressive strain caused by hetero-mismatch.Therefore,the low-strain state of the DUV light-emitting diode(DUV-LED)epitaxial structure is realized on the strain-free AlN template with Gr.Furthermore,the DUV-LED with Gr demonstrate 2.1 times enhancement of light output power and a better stability of luminous wavelength compared to that on bare sapphire.An in-depth understanding of this work reveals diverse beneficial impacts of Gr on nitride growth and provides a novel strategy of relaxing the vital requirements of hetero-mismatch in conventional heteroepitaxy.

ZrTe_(5)中的面内垂直电流方向的负磁阻现象

拓扑材料独特的能带结构有时会导致一些不同寻常的磁输运现象,其中包括当外磁场施加在平行电流方向上时产生的面内纵向负磁阻效应.这种负磁阻效应被普遍认为是拓扑材料中存在手征反常的一个标志.本文报道了一种当面内磁场分别平行和垂直电流方向时,在拓扑材料ZrTe_(5)中观察到的面内负磁阻现象.该现象揭示了一种超出手征反常范畴的不同寻常的量子输运行为.研究人员构建了一种同时考虑贝里曲率和轨道磁矩的普适模型,用以定量解释他们观察到的实验现象.本文的研究结果为探索拓扑材料中的面内负磁阻现象提供了一种新的见解和思路.

Recent progress on surface chemistryⅡ:Property and characterization

Surface with well-defined components and structures possesses unique electronic,magnetic,optical and chemical properties.As a result,surface chemistry research plays a crucial role in various fields such as catalysis,energy,materials,quantum,and microelectronics.Surface science mainly investigates the correspondence between surface property and functionality.Scanning probe microscopy(SPM)techniques are important tools to characterize surface properties because of the capability of atomic-scale imaging,spectroscopy and manipulation at the single-atom level.In this review,we summarize recent advances in surface electronic,magnetic and optical properties characterized mainly by SPM-based methods.We focus on elucidating theπ-magnetism in graphene-based nanostructures,construction of spin qubits on surfaces,topology properties of surface organic structures,STM-based light emission,tip-enhanced Raman spectroscopy and integration of machine learning in SPM studies.