Journal of Physics: Condensed Matter最新文献

We revisit the electronic structure of Nickel (Ni) using the density functional theory (DFT) and dynamical mean-field theory (DMFT) for the theoretical description of its electronic structure properties along with finite-temperature magnetism. Our study provides a comprehensive account of electronic and magnetic properties with the same set of Coulomb interaction parameters, U=5.78 eV and J=1.1 eV calculated using first-principles approach. The nature of theoretical magnetization curves obtained from DFT and DFT+DMFT as well as the experimental curve show deviation from the standard models of magnetism, viz Stoner and spin fluctuation model. In comparison to DFT+DMFT method, temperature dependent DFT approach is found to well describe the finite-temperature magnentization curve of Ni below critical temperature (T 631 K). The study finds significant Pauli-spin susceptibility contribution to paramagnetic spin susceptibility. Excluding the Pauli-spin response yields a linear Curie-Weiss dependence of the inverse paramagnetic susceptibility at higher temperatures. Also, the presence of mixed valence electronic configuration (3d8, 3d9 and 3d7) is noted. The competing degrees of both the itinerant and localized moment picture of 3d states are found to dictate the finite-temperature magnetization of the system. Furthermore, the quasiparticle scattering rate is found to exhibit strong deviation from T 2 behaviour in temperature leading to the breakdown of conventional Fermi-liquid theory. In addition to the 6 eV satellite, our calculated electronic excitation spectrum shows the possible presence of satellite feature extending $sim$10 eV binding energy, which has also been reported experimentally. Interestingly, our G0W0 results find the presence of plasmonic excitation contribution to the intensity of famous 6 eV satellite along with the electronic correlation effects, paving way for its reinterpretation. .

Active agents, which convert energy into directed motion, are inherently non-equilibrium systems. Inspired by living organisms and polymer physics, connected active agents with various topologies have recently garnered significant attention. These agents have positional degrees of freedom with well-defined topologies, while activity introduces extra degrees of freedom. The intricate interplay of activity, elasticity, noise, and conformational degrees of freedom gives rise to novel non-equilibrium behaviors in chain-like structures. This review categorizes active agents into three types based on their alignment mechanisms: Active Brownian agents, Vicsek-type agents, and self-aligning agents. It further provides the results when these agents are connected through different topological structures in two-dimensional spaces, at interfaces, in three-dimensional environments, and under confinement. The goal is to shed light on the fundamental physics that govern their non-equilibrium behavior at the level of individual chains and to highlight potential research directions. These findings hold significant potential for advancing the design of metamaterials and swarm robotics.

An electron in solid can be dressed by the lattice distortions of surroundings, forming a localized composite quasiparticle called small polaron, whose formation has been customarily attributed to the electron-phonon couplings that the ion polarization traps the excess electron. Here we present a theory of electron-polarization induced small polaron, in which the carrier localization happens spontaneously and drives subsequent ion relaxation. This mechanism of polaron formation is qualitatively different than the Mott-Stoneham picture in that there is no need to overcome a kinetic barrier for the carrier to self-trap to form a polaron.Through a combination of first-principles theory and model Hamiltonian, we show that this is the mechanism for polaron formation in the monolayer two-dimensional transition metal halides, CrI₂, CoCl₂and CoBr₂. These findings may explain the exceptional stability and manipulability of polarons in this class of materials by scanning tunneling microscopy.

Cationic redistribution in spinel ferrite systems greatly influences the magnetic ordering and the associated phenomena. Here, the effect of the synthesis condition on the cationic redistribution and its correlation with the magnetic properties were explored in the Cu2+substituted ZnFe₂O₄spinel ferrite. X-ray photoelectron spectroscopy and X-ray diffraction studies reveal that the variation of sintering temperature redistributes the cations between tetrahedral and octahedral sublattices. Results from low field dc-magnetic susceptibility measurements show that the susceptibility increases with decreasing sintering temperature of the sample. Furthermore, the ac-susceptibility results suggest that the sample sintered at 1048 K (1148 K) exhibits spin-glass behavior with a glass transition temperature of ~ 49.2 K (47.1 K) and a cluster-glass behavior at a higher temperature of ~ 317 K (330 K), characteristics that are absent in the sample sintered at 1248 K. The sample annealed at 1048 K exhibits a magnetocaloric effect with a maximum isothermal entropy change of ~ 1.21 J-kg^-1-K^-1at μ₀H=5 T. .

The transition from planar to three-dimensional (3D) magnetic nanostructures represents a significant advancement in both fundamental research and practical applications, offering vast potential for next-generation technologies like ultrahigh-density storage, memory, logic, and neuromorphic computing. Despite being a relatively new field, the emergence of 3D nanomagnetism presents numerous opportunities for innovation, prompting the creation of a comprehensive roadmap by leading international researchers. This roadmap aims to facilitate collaboration and interdisciplinary dialogue to address challenges in materials science, physics, engineering, and computing. The roadmap comprises eighteen sections, roughly divided into three blocks. The first block explores the fundamentals of 3D nanomagnetism, focusing on recent trends in fabrication techniques and imaging methods crucial for understanding complex spin textures, curved surfaces, and small-scale interactions. Techniques such as two-photon lithography and focused electron beam-induced deposition enable the creation of intricate 3D architectures, while advanced imaging methods like electron holography and synchrotron x-ray tomography provide nanoscale spatial resolution for studying magnetization dynamics in three dimensions. Various 3D magnetic systems, including coupled multilayer systems, artificial spin-ice, magneto-plasmonic systems, topological spin textures, and molecular magnets are discussed. The second block introduces analytical and numerical methods for investigating 3D nanomagnetic structures and curvilinear systems, highlighting geometrically curved architectures, interconnected nanowire systems, and other complex geometries. Finite element methods are emphasized for capturing complex geometries, along with direct frequency domain solutions for addressing magnonic problems. The final block focuses on 3D magnonic crystals and networks, exploring their fundamental properties and potential applications in magnonic circuits, memory, and spintronics. Computational approaches using 3D nanomagnetic systems and complex topological textures in 3D spintronics are highlighted for their potential to enable faster and more energy-efficient computing.

Tin (Sn) perovskites have emerged as promising alternatives to address the toxicity concerns associated with lead-based (Pb) perovskite light-emitting diodes (PeLEDs). However, the inherent oxidation of Sn perovskite films leads to a serious efficiency roll-off in PeLEDs at increased current densities. Although three-dimensional (3D) CsSnBr₃perovskites exhibit decent carrier mobilities and thermal stability, their rapid crystallization during solution processing results in inadequate surface coverage. This inadequate coverage increases non-radiative recombination and leakage current, thereby hindering Sn PeLED performance. Herein, we present a multi-cation synergistic strategy by introducing the organic cations formamidinium (FA⁺) and thiophene ethylamine (TEA⁺) into CsSnBr₃perovskites. The addition of organic cations delays crystallization by forming hydrogen bonds interacting with the CsSnBr₃. The smaller FA⁺enters the perovskite lattice and improves crystallinity, while the larger TEA⁺ cation enhances surface coverage and passivates defect states. By further optimizing the interface between PEDOT:PSS and perovskite layers through the use of ethanolamine (ETA) and a thin layer of LiF, we achieved a red Sn-based PeLED with an emission wavelength of 670 nm, a maximum luminance of 151 cd m^-2, and an external quantum efficiency (EQE) of 0.21%. .

Activity and autonomous motion are fundamental aspects of many living and engineering systems. Here, the scale of biological agents covers a wide range, from nanomotors, cytoskeleton, and cells, to insects, fish, birds, and people. Inspired by biological active systems, various types of autonomous synthetic nano- and micromachines have been designed, which provide the basis for multifunctional, highly responsive, intelligent active materials. A major challenge for understanding and designing active matter is their inherent non-equilibrium nature due to persistent energy consumption, which invalidates equilibrium concepts such as free energy, detailed balance, and time-reversal symmetry. Furthermore, interactions in ensembles of active agents are often non-additive and non-reciprocal. An important aspect of biological agents is their ability to sense the environment, process this information, and adjust their motion accordingly. It is an important goal for the engineering of micro-robotic systems to achieve similar functionality. Many fundamental properties of motile active matter are by now reasonably well understood and under control. Thus, the ground is now prepared for the study of physical aspects and mechanisms of motion in complex environments, the behavior of systems with new physical features like chirality, the development of novel micromachines and microbots, the emergent collective behavior and swarming of intelligent self-propelled particles, and particular features of microbial systems. The vast complexity of phenomena and mechanisms involved in the self-organization and dynamics of motile active matter poses major challenges, which can only be addressed by a truly interdisciplinary effort involving scientists from biology, chemistry, ecology, engineering, mathematics, and physics. The 2025 motile active matter roadmap of Journal of Physics: Condensed Matter reviews the current state of the art of the field and provides guidance for further progress in this fascinating research area.

Short-range spin correlations, memory and rejuvenation effects have been reported in the trication oxispinel ZnMnCoO₄whose low-temperature spin dynamics, triggered by magnetic frustration (fr∼6), could be better explained by the 'phenomenological' hierarchical free-energy model than the short-range droplet theory. Accordingly, the aging mechanism of the system had an asymmetric memory response to the positive and negative thermal cycles within the cluster-glass state (T<32.6 K) and demonstrated a hierarchical organization of the phase space where its metastable energy states undergo continuous splitting with decreasing temperature. An attempt to reproduce the time evolution of the isothermal remanent magnetization in the system led to an investigation of various relaxation models featuring semi-logarithmic, algebraic, fractional or stretched-exponential tails. Nevertheless, Weron's probabilistic relaxation model (here, the fractal characterβ∼0.4, the hierarchical constraintk>0, and the order parameterq(T∼0.12TSG) = 1.88) based on a purely stochastic approach, was best suited for understanding the slow spin dynamics of the cluster-glass phase in the entire temporal range. A comprehensive picture of the magnetic phase map was developed for the system, aided by magnetometry techniques and heat-capacity studies.

Here, we investigate the thermoelectric properties of the marcasite-type compounds MSb₂(M = Ta, Nb) in the temperature range of 310-730 K. These compounds were synthesized by a solid-state reaction followed by the spark plasma sintering process. The Rietveld refinement method confirms the monoclinic phase with space groupC2/mfor both compounds. The observed values of Seebeck coefficients exhibit non-monotonic behaviour in the studied temperature range, with the maximum magnitude of -14.4 and -22.7 µV K^-1for TaSb₂and NbSb₂, respectively at ∼444 K. The negative sign ofSin the full temperature window signifies then-type behaviour of these compounds. Both electrical and thermal conductivities show decreasing trends with increasing temperature. The experimentally observed thermoelectric properties are understood through the first-principles DFT and Boltzmann transport equation. A pseudogap in the density of states around the Fermi level characterizes the semimetallic behaviour of these compounds. The multi-band electron and hole pockets were found to be mainly responsible for the temperature dependence of transport properties. The experimental power factors are found to be ∼0.09 and ∼0.42 mW m^-1K^-2at 300 K for TaSb₂and NbSb₂, respectively. We found that there is much room for improvement of power factor by tuning carrier concentration. The DFT-based calculations predict the maximum possible power factors at fairly high doping concentrations. The present study suggests that the combined DFT and Boltzmann transport theory are found to be reasonably good at explaining the experimental transport properties, and moderate power factors are predicted.

We have studied the origin of zero volume expansion below the Curie temperature (Tc), variable range hopping (VRH) behavior using structural, magnetic, transport and thermal studies on the oxygen deficient double perovskite NdBaCo₂O5+δ(δ∼0.65). The valence state of Co ions and the possible properties exhibited by such compound were studied using electronic structure calculations forδ= 0.75. Careful investigation of structure shows that the compound stabilizes in tetragonal structure (P4/mmm) having2ap×2ap×2ap(222) superstructure, where a_pis the cubic perovskite lattice parameter. The compound exhibits a minimum in resistivity, ferromagnetic (FM) and ferrimagnetic (FeM) transitions around 375 K, 120 K (Tc) and 60 K, respectively with signature of Griffiths phase aboveTc. Our detailed structural analysis suggests signature of the onset of the above magnetic transitions at temperatures well above its stabilization at long range level thereby leading to VRH behavior. The observed zero thermal expansion in volume belowTcappears to be due to competing magnetic interactions within and between the magnetic sublattices. Our electronic structure calculations in FM and FeM configurations show (a) Co ions stabilize in intermediate spin (IS) state, having oxidation state less than +3, (b) half metallicity, (c) the behavior of the density of states is in line with the resistivity results, and (d) unusually high orbital angular moment in Co ions with inclusion of spin orbit coupling (soc). Our results show the possibility of coupling between magnetism and ferroelectricity. We believe that our results especially on the valence state of the Co ion, zero thermal expansion in volume, short range magnetic orderings and the connection between different degrees of freedom will be helpful in clearing the ambiguities existing in literature on the nature of magnetism and thereby aiding in designing new functionalities by maneuvering the strength of soc.