In the last decade, motivated by advances in cell biology, theoretical studies of the cell tissue as active matter have emerged as a new area in soft matter physics. This article reviews recent theoretical progresses based on the active network (AN) model of cell tissue. In the mesoscopic scale, the non-equilibrium dynamics of cell tissue is mainly driven by the self-propulsion of cells and non-propulsion activities, like active contractility or cellular tension/volume oscillation. AN models of self-propelled cells can reproduce complex dynamics of cell tissue in vivio, such as activity/adhesion driven solid-liquid transition, flocking and active turbulence. The AN model incorporating cellular tension fluctuation can also simulate the cell volume oscillation waves in embryo of Drosophila, and predict the fluctuation-driven solid-liquid transition of cell tissue. The structural phase transition and density fluctuation of cell tissue were also studied by using AN models, which deepens our understanding of this unique non-equilibrium soft matter system.
The discovery of nematic triplet superconductivity in doped topological insulators CuxBi2Se3 triggers interest in the identification of the d-vector of the triplet,which is related to the antinodal direction of the gap function and determines whether the superconductor is topological.We perform self-consistent analysis of the vortex state properties in a nematic spin-triplet px-wave superconductor.We first derive a Ginzburg-Landau theory to determine the shape of the vortex and vortex lattice.We find the spatial profile of the isolated vortex is elongated along the antinodal direction,and the vortex lattice is a distorted triangular lattice elongated along x,becoming square in the specific case of a small circular Fermi surface.Finally,we calculate the local density of states self-consistently for an isolated vortex and the vortex lattice using the microscopic Bogoliubov-de Gennes equation.We find that the profile of the local density of states at low in-gap energies is always elongated along the antinodal direction.Our findings are valuable for the experimental detection of the antinodal direction of the gap function in nematic triplet superconductors,and subsequently the identification of the topological character of the superconducting state as in CuxBi2Se3.
Flat band has attracted more and more interest in recent years,motivated by its discovery in twisted bilayer graphene(TBG).In this work,we report our study of the impurity effect on this flat band system,which is an important issue for real materials.Employing the Lanczos recursive method,we solve the local density of states(LDOS)around a potential impurity.We find for large impurity size,a series of bound states are formed inside the impurity,and the flat band peak in LDOS is suppressed near the impurity boundary and shifted by the impurity potential deep inside the impurity.As the impurity size becomes smaller,the effect on the flat band becomes weaker,as anticipated from the large scale of the underlying Wannier function.This property distinguishes with the usual flat band systems with small localized Wannier orbitals,and indicates the flat band in TBG is more stable against small-size impurities.
The antiferromagnetic(AFM)spin waves are promising for being utilized in high-speed and energy-efficient information processing.However,the excitation and detection of terahertz spin waves in AFM systems is challenging.Here,we demonstrate low-frequency Raman spectroscopy as a powerful tool for spin-wave detection in AFM systems.We present a systematic study of AFM magnons in Cr2O3,a prototypical uniaxial antiferromagnet,via Raman measurements down to 2.3 cm-1(69 GHz).We resolved the magnon Zeeman splitting and the spin-flop transition.We further determined the sign of angular momentum of the magnon branches via polarization-resolved Raman processes.We also obtained the anisotropy energy,the g-factor,and the spin-flop field of Cr2O3 as a function of temperatures and magnetic fields.A spin-wave renormalization theory accounts for all experimental observations.
Two-dimensional(2D)transition metal dichalcogenides(TMDCs)with a unique unity of favorable electronic and mechanical properties have been developed for fundamen-tal studies and applications in electronics,spintronics,optoelectronics,energy harvesting and catalysis.However,as they are unstable under harsh conditions,and prone to degradation in the ambient environment,most TMDCs applications are limited.In this review,we analyze the recent advances in the research of environmental stability in TMDCs,covering the latest growth methods,the fundamental mechanisms for stability and kinds of routes to protect 2D TMDCs materials from aging and deterioration.By analyzing key factors that affect TMDCs stability from the growth process,we present a short review of optimizing growth methods for improving the stability of TMDCs.Finally,by providing insights into existing factors,this review is expected to guide the growth of stable TMDCs,which could lead to a new potential approach to growing advanced materials and designing more unexplored heterostructures.
回音壁模式微腔因模式体积小、超高 Q 值和低阈值的优点得到了广泛的关注,但是在旋转对称的回音壁微腔中会产生多纵模激光辐射,并且辐射的方向性较差,在实际应用中受到限制,寻求有效方法实现回音壁激光的单模辐射是微腔激光器走向实际应用的关键问题.本综述重点阐述了近年来回音壁激光单模调控的几种方法,包括减小腔体尺寸、外加选模结构、基于游标效应、基于宇称时间对称性破缺、变形微腔等,并对单模回音壁激光的发展前景进行了展望.通过本综述以期为相关领域研究人员提供参考,深入理解回音壁激光单模调控的物理机理.
近来,以共轭聚合物为沟道材料的有机电化学晶体管(OECT)因其易于制备、具有离子–电子转换能力和生物界面相容性而成为研究热点.然而,已报道的用于OECT沟道材料的大多是p型共轭聚合物,而基于n型共轭聚合物开发的OECT则很少,而不平衡的发展阻碍了复杂互补电路的实现.最近被报道的新兴n型共轭聚合物半导体Poly(benzimidazobenzophenanthroline)(BBL)OECT为解决上述问题提供了一个有效的方案.但BBL薄膜本身具有脆性无法拉伸,无法满足柔性器件的使用需求,大大阻碍了其应用及发展.本工作中,我们提出了一种器件可拉伸的n型BBL OECT器件的制备方法,并验证了其在汗液传感方面的可行性.
从本质上讲,规范场是物理学中(量子场论,基本粒子理论)重要的研究领域(1979年、1999年和2004年共有六位物理学家获得诺贝尔奖,他们的研究工作直接或间接与规范场有关),而纤维丛则是数学中(微分几何、群论、李代数)的热门课题(1986年唐纳森因研究纤维丛获得菲尔茨奖).近年来,对杨–米尔斯方程、纤维丛和规范场的研究正在深入开展,因此,本文着重从物理概念出发,分别论述规范场在量子场论中,纤维丛在微分几何中相关概念的形成、发展,以及与杨–米尔斯方程之间的关系,特别是从电磁场、弱力和强力的统一方面,显示了规范场的重要性和深远意义,为了使更多的相关专业读者能在这一重要的领域中迅速获得必要的专业知识,产生探索和创新的热情,在综述中对阿贝尔规范场到非阿贝尔规范场,以及对称性自发破缺的基本概念和处理方法,进行了详细的论述,特别是初步探讨了杨–米尔斯方程的空间属性,目的是希望能更好地将规范场、纤维丛这二者与杨–米尔斯方程联系起来,加深对纤维丛的联络在更深层次的了解,由于这类问题是一个有意义的研究方向,值得有志者去深入探索.
In this paper, the historical origins of quantum entanglement in particle physics are systematically and thoroughly investigated. 1957, Bohm and Aharonov noted that the Einstein-Podolsky-Rosen correlation had been experimentally realised in the 1949 experiment of Chien-Shiung Wu and Shaknov. This was the first time in history that spatially separated quantum entanglement was explicitly realised in a controlled experiment. Wheeler first proposed such an experiment as a test of quantum electrodynamics, but his calculation was in error; the correct theoretical calculations came from Ward and Price, as well as from Snyder, Pasternack and Hornbostel, and the result was in accordance with Yang's 1949 selection rule. After the publication of Bell's inequality in 1964, it was considered whether it could be tested by using the Wu-Shaknov experiment. This gave an impetus to the field, and a new experiment was done by Wu's group, though it was not successful as a test of Bell inequality violation. In 1957, Tsung-Dao Lee, Reinhard Oehme and Chen Ning Yang established the quantum mechanical description of the kaons and found that the neutral kaon is a two-state system. In 1958, based on an approach similar to Yang's 1949 selection rule, Goldhaber, Lee and Yang were the first to write down the entangled states of kaon pairs, in which a single kaon can be charged or neutral. This gave, for the first time, quantum entanglement of internal degrees of freedom of high-energy particles other than photons. In 1960, as unpublished work, Lee and Yang discussed the consequences of quantum entanglement of neutral kaon pairs. We also describe several physicists in the past, especially Ward. A Chinese version of this paper was published in early 2023.
氧化物超导体是非常规超导体最重要的表现形式之一,其中铊系、汞系和铜碳系列超导体的超导临界转变温度(Tc)都可达到 110 K及以上,高的超导转变温度和液氮温区较高的不可逆磁场,以及广泛应用潜能备受人们关注.显然,高的超导临界温度使超导应用的冷却介质选择增多,经济实用的冷却剂可望扩大这些高超导转变温度超导体的应用领域和增加长期运行可行性.本文对 110 K超导临界温度超导材料包括铊系、汞系和铜碳系超导体的发展历程和超导性能进行介绍和总结,并从理论上去分析超导转变温度的影响因素,定性解释高温超导体高Tc 的原因.特别关注分析了它们不可逆场的差异,展望这些高临界温度超导体的可能新型应用.
二阶非线性光学效应源于电子势函数的非谐性,可实现激光的频率转换,被广泛应用于基础科学研究和现代激光技术.单层过渡金属硫族化合物具有极大的二阶非线性系数,作为基础单元实现高效的非线性光学响应潜力巨大.如何保持单层材料的极大非线性系数,扩展材料厚度及响应频段,提升非线性响应,是重要挑战.本文主要介绍了基于单层过渡金属硫族化合物的二阶非线性光学效应的调控,包括单层过渡金属硫族化合物的频率依赖及不同对称性相的多层堆叠等,并总结了过渡金属硫族化合物非线性光学效应的应用前景.
基于密度泛函理论的第一性原理方法已经成为人们研究材料结构、性质以及进行新功能材料设计的重要手段.对于掺杂和界面体系,人们常常需要使用超胞来描述.超胞的使用导致能带折叠,从而掩盖能带结构的重要特征,为人们分析掺杂和界面效应对材料能带结构的影响带来困难.本文概述了超胞导致的能带折叠现象,重点介绍了基于平面波和原子轨道的能带反折叠方法、声子能带反折叠方法及相关计算工具,给出了该方法在掺杂和界面体系电子、声子能带结构方面应用的例子,并对该方法进行了展望.
Thermal Hall effect (THE) is to describe the phenomenon where heat carriers are deflected by an external magnetic field applied perpendicular to the heat flow, and thus the carriers gain transverse velocity, leading to a finite temperature gradient on the two sides orthogonal to the heat flow and field. THE is predicted to occur in systems with nontrivial Berry curvatures and thus can reveal topological properties, similar to the electrical Hall effect. However, THE is not limited to charge excitations as in the electrical Hall effect, but rather, to all kinds of excitations that are able to conduct heat, making it possible to explore the exotic properties in strongly correlated electronic systems, which are typically insulators. Therefore, THE is more universal than the electrical form and has become a powerful probe in detecting charge-neutral excitations, such as phonons and magnons. Moreover, there are some sources such as chiral phonons, which are beyond a simple nontrivial-Berry-curvature scenario, that can also give rise to THE;examining THE wherein will shed light on the complex microscopic mechanism hidden in materials. Despite these, heat signals are much weaker than electrical ones. Especially for measurements of the thermal Hall conductivity, it is often needed to collect weak signals on top of a large background. This makes measuring the THE challenging—but thanks to the sustained efforts of the community, this field is developing rapidly in recent years, with many interesting results on the measurements of the thermal Hall conductivity. In this review article, we try to summarize some of these exciting accomplishments, point out remaining outstanding issues, and suggest possible future directions.
实现室温超导一直是人们长期追寻的梦想，寻找和合成出具有室温超导性的新材料已成为凝聚态物理学家和材料物理学家的“圣杯”。近年来，随着理论和实验相继发现超导临界温度高于200 K的H 3 S和LaH 10 ，氢基超导体已逐渐成为实现室温超导的最佳候选，成为物理学、材料科学等多学科研究的热点领域之一。在本文中，我们将概述超导材料的发展历史和几种典型超导材料，重点介绍当前高压下氢基超导体的研究进展及面临的挑战，详细讨论中低压力范围氢基高温超导体的设计思路，展望氢基超导体在低压甚至常压下实现高温乃至室温的可能性。
When taking into account the electronic correlations such as the onsite Coulomb repulsion and coupling between electrons, spins and orbitals, many fascinating novel quantum states beyond the free-electron framework can emerge, e.g., unconventional superconductiv- ity and quantum spin liquids. The understanding of these new states not only will expand the existing territory of our knowledge, but also likely lead to revolution in quantum science and technology. Therefore, studying the strongly correlated physics is a cutting-edge theme in condensed matter physics. The parent state of cuprate high-temperature superconductors is a Mott insulator, an insulating state due to the strong electronic correlation, whereas the band theory predicts it to be metallic. Due to the Coulomb gap in Mott insulators, the charge degree of freedom is often frozen, which makes electrical transport measurements inapplicable. As a probe sensitive to the elementary excitations of quasiparticles not limited to electrons, but also including magnons, spinons, as well as phonons, thermal transport measurements play an important role in the study of strongly correlated electronic systems. In this paper, we review some of the recent interesting results on unconventional superconductors, heavy fermions and quantum spin liquids utilizing the longitudinal thermal transport measurements, complimentary to our recent review article on the progress of the transverse thermal conduc- tivity measurements on the thermal Hall effect.
RuSb2, as a sister material of thermoelectric material FeSb2, has been extensively studied focusing on the comparisons with FeSb2, however, the properties of RuSb2 under pressure have not been surveyed thoroughly yet. In this work, we studied the properties of RuSb2 under pressure and explored the similarities and differences of crystal and electronic structures between the Ru-pnictides partners RuP2 and RuAs2. Using the crystal structures search method together with first-principles calculations, we found that this family undergoes a serial of structural phase transitions: (I) For RuSb2: P nnm → I4/mcm → I4/mmm; (II) for RuP2: P nnm → I41/amd → Cmcm; (III) for RuAs2: P nnm → P-62m. The newly found five phases are all energetically and dynamically stable at high-pressure and exhibit metallic properties. The four high pressure phases of RuSb2 and RuP2 can be quenched to zero pressure. The superconducting transition temperatures of I4/mcm and I4/mmm phases of RuSb2 and I41/amd and Cmcm phase of RuP2 are predicted to be approximately 7.3 K, 10.9 K, 13.0 K, and 10.1 K at 0 GPa, respectively. In addition, the I4/mcm and I4/mmm phases of RuSb2 and the I41/amd phase of RuP2 exhibit non-trivial topological properties. Our studies illustrate that pressure is an effective way to tune the structural, electronic, and superconducting behavior of the Ru-pnictides compounds.
阻挫量子磁体中的新奇物态与效应是凝聚态物理研究的重要前沿方向,因其与高温超导、拓扑量子计算等的密切联系,近年来吸引了人们浓厚的研究兴趣.实验上,阻挫自旋液体候选材料的新进展层出不穷,人们系统地研究了若干三角晶格、笼目晶格和六角Kitaev阻挫磁体等材料,发现其在一定条件下展现出自旋液体态的特征,但澄清其中的量子物态是充满挑战的量子多体问题.作者最近的工作指出,可以从有限温度张量重正化群多体计算入手,开展热力学性质的精确计算与分析,确定阻挫磁体的微观自旋模型,做出进一步理论预言并开展实验验证,从而建立量子磁性系统的多体计算精确研究方案.有限温度张量重正化群方法是计算大尺寸二维阻挫量子自旋模型有限温度性质的有力工具,在本文中作者首先介绍新近发展的系列张量重正化群方法,包括线性和指数张量重正化群等.随后,作者讨论有限温度张量方法在三角晶格量子伊辛磁体TmMgGaO4和六角晶格Kitaev磁体α-RuCl3的微观自旋模型中的具体应用:通过高精度和全面的多体计算,揭示出其中存在演生U(1)对称性与拓扑相变,以及高场量子自旋液体态等新颖的结论,这些理论预言也陆续被实验所证实.通过上述实例,作者展示了有限温度张量重正化群计算方法在自旋液体候选材料研究中的应用价值,并期待这些方法能在强关联量子物质研究中发挥重要作用.
二维磁性材料是当前凝聚态物理的研究热点.近来的实验发现双层CrI3存在与三维块体不同的层间反铁磁序,表现出独特的量子限域效应和潜在的器件应用,受到了人们的广泛关注.大量的研究表明层间磁序跟堆垛密切相关,但仍存在争议.本文主要综述双层磁性材料层间磁序及其应用的研究进展,重点介绍了磁性与堆垛方式之间的关联,指出了密度泛函理论在层间磁性机理研究中存在的挑战,阐述了层间磁序相关的器件应用,并对未来可能的研究方向进行了展望.
拓扑超流态是一种奇异物质态,它的内部受能隙保护,而在其系统边缘却可以容纳无能隙的Majorana费米子.由于该粒子满足非阿贝尔统计,并且受拓扑保护具有良好的稳定性,用它们携带量子化的信息,可以用于拓扑量子计算的研究.近年来,理论工作预测了各类系统中可能存在的拓扑超流态.我们首先介绍了在各类光晶格模型中的拓扑超流,光晶格的超冷原子具有良好的可控性与普适性,是实现拓扑超流的理想模型系统.接下来我们介绍了自旋轨道耦合调控下的拓扑超流,自旋轨道耦合效应是诱导拓扑相的重要条件,并且人们已经在实验上合成了人工自旋轨道耦合,这为实验上观测拓扑超流取得了突破性的进展.随着近年来实验技术的提高,曾经难以在实验中观测的,被人们所忽略的拓扑Fulde-Ferrell-Larkin-Ovchinnikov(FFLO)超流相也成为了人们研究的热点,因此我们接下来介绍了拓扑的FFLO超流.此外,我们还介绍了拓扑超流其他方面的进展,包括孤子引诱的拓扑超流、三组分的拓扑超流、大陈数的拓扑超流以及拓扑超流临界温度的提高.在实验中,如何检测与实现拓扑超流,是其研究目的及意义所在,因此我们在文章的最后介绍了拓扑超流的识别与实现.
重费米子材料作为一类典型的强关联电子体系,蕴含着非常规超导、奇异金属、量子临界、磁有序、重电子态、关联拓扑态等新奇的量子态,而4f电子在其中扮演着重要的作用.随着高分辨角分辨光电子能谱和薄膜生长技术的发展,精确探测重费米子材料中4f电子在能量/动量空间的色散和谱权重成为了可能,这为从微观上理解这类材料中的电子关联效应和新奇量子现象提供了重要的基础.本论文总结了几个典型的重费米子单晶和薄膜体系的电子态研究,包括Ce-115体系、CeCu2Si2、CeRh6Ge4以及单晶Ce膜等.这些结果为理解重费米子体系中重电子态的形成和温度演化、近藤杂化的能带/动量依赖、重电子能带与超导的关系、近藤效应与磁性和其它量子态的竞争、4f电子的维度调控等重要物理问题提供了谱学证据.
