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.
