Condensed Matter Research Articles

Optical skyrmions: from fundamental to applications

Abstract Skyrmions are topologically protected quasi-particles that have aroused substantial interest in nuclear physics and condensed matter physics. For instance, magnetic skyrmions are regarded as having potential applications in high-density information storage due to their ultracompact size, topologically protected stability, and low driven current. Recently, optical analogs have been discovered in light field, known as optical skyrmions. With similar intriguing properties, research on optical skyrmions has grown dramatically. Several types of optical skyrmions defined by various optical parameters have been uncovered. Along with the fundamental physics studies, methods for generating, modifying, and detecting optical skyrmions have also been developed, which in turn enriches the toolkit for light field modulation and detection. It has shown promising applications in high-precision positioning, information storage, and optical communication. In this paper, we begin with the fundamental theory and then introduce generalized classes of optical skyrmions, with a particular emphasis on optical spin skyrmions. We discuss their generation, modulation, and detection methods. Additionally, we highlight the emerging applications of optical skyrmions, showcasing the potential of these unique properties for future advancements.

Septuple XBi2Te4 (X=Ge, Sn, Pb) intercalated MnBi2Te4 for realizing interlayer ferromagnetism and quantum anomalous hall effect

Realizing the quantum anomalous Hall effect (QAHE) at high temperatures remains a significant challenge in condensed matter physics. MnBi2Te4, an intrinsic magnetic topological insulator, presents a promising platform for QAHE. However, its inherent interlayer antiferromagnetic coupling hinders practical realization at high temperatures. In this study, we propose a novel approach to achieve interlayer ferromagnetic (FM) coupling in MBT bilayer by intercalating the septuple-layer of topological insulators XBi2Te4 (X=Ge, Sn, Pb). Using first-principles calculations, we demonstrate that the pz orbital of the X atom mediates interactions between interlayer Mn atoms, enabling FM coupling. Monte Carlo simulations predict a magnetic transition temperature of 38 K for the MnBi2Te4/PbBi2Te4/MnBi2Te4 heterostructure. Our band structure and topological analyses confirm the preservation of QAHE in all MnBi2Te4/XBi2Te4/MnBi2Te4 heterostructures, while the MnBi2Te4/PbBi2Te4/MnBi2Te4 heterostructure exhibits a topological band gap of 72 meV, significantly exceeding that of the pure MnBi2Te4 bilayer. Furthermore, a continuum model is developed to elucidate the underlying mechanism of the nontrivial topological states. Our work provides a practical pathway to achieving interlayer FM coupling in MnBi2Te4 bilayers, paving the way for high-temperature QAHE and advancing the development of magnetic topological insulators for quantum and spintronic applications.

Many-body perturbation theory for strongly correlated effective Hamiltonians using effective field theory methods

Introducing low-energy effective Hamiltonians is usual to grasp most correlations in quantum many-body problems. For instance, such effective Hamiltonians can be treated at the mean-field level to reproduce some physical properties of interest. Employing effective Hamiltonians that contain many-body correlations renders the use of perturbative many-body techniques difficult because of the overcounting of correlations. In this work, we develop a strategy to apply an extension of the many-body perturbation theory starting from an effective interaction that contains correlations beyond the mean-field level. The goal is to re-organize the many-body calculation to avoid the overcounting of correlations originating from the introduction of correlated effective Hamiltonians in the description. For this purpose, we generalize the formulation of the Rayleigh-Schrödinger perturbation theory by including free parameters adjusted to reproduce the appropriate limits. In particular, the expansion in the bare weak-coupling regime and the strong-coupling limit serves as a valuable input to fix the value of the free parameters appearing in the resulting expression. This method avoids double counting of correlations using beyond-mean-field strategies for the description of many-body systems. The ground state energy of various systems relevant for ultracold atomic, nuclear, and condensed matter physics is reproduced qualitatively beyond the domain of validity of the standard many-body perturbation theory. Finally, our method suggests interpreting the formal results obtained as an effective field theory using the proposed reorganization of the many-body calculation. The results, like ground state energies, are improved systematically by considering higher orders in the extended many-body perturbation theory while maintaining a straightforward polynomial expansion.

Local Wisdom and Interfaith Harmony: Ancestral Guidance in Promoting Religious Moderation in East Nusa Tenggara, Indonesia

The Lamaholot local wisdom encapsulated in the phrase /koda kirin nulun walen melan senaren/ transcends mere kinship expressions. This phrase serves as a guiding principle for the Lamaholot community in East Flores Regency, particularly in fostering the values of religious moderation. This research aims to investigate how this Lamaholot expression aids in internalizing religious moderation values in Pepakgeka Village. The study employs a descriptive field research methodology with an ethnographic approach. Data were collected through observations, interviews, and documentation. Analysis was conducted using Huberman and Miles' framework, which includes phases of data collection, data condensation, and conclusion drawing. The research was carried out from August to October 2024. The results indicate that the local wisdom /koda kirin nulun walen melan senaren/ is effective in promoting the values of religious moderation. The essence of local wisdom is communicated through advice shared in speech (koda kirin) and through actions (nulun walen), enabling the Lamaholot people to aspire to be virtuous individuals (melan senaren). The foundation of religious moderation within the Lamaholot community is deeply embedded in local wisdom, including the expression /koda kirin nulun walen melan senaren/, which has been upheld since ancient times and is reflected in their everyday speech and behavior.

Emergent physics

In this essay we present a brief critical scrutiny of some popular theoretical models developed by the scientific community within the framework of Fundamental Physics. These models develop the hypothesis that it is possible that current physical laws can be derived or emerge from much more fundamental physical entities than those studied to date, which constitutes another way to achieve the Unification of said laws within a single common conceptual structure. We expose String-nets of Condensed Matter Physics, Loop Quantum Gravity, Superstrings and Branes, Entropic Gravity, the BCJ model, Stochastic Quantum Mechanics, Matrix Statistical Quantum Mechanics, and AdS/CFT Duality. These models are a small sample of an important trend that is gaining strong momentum within the scientific community.

Information Theoretical Analysis of Quantum Mixedness in a Finite Model of Interacting Fermions.

In this study, we utilize information theory tools to investigate notable features of the quantum degree of mixedness (Cf) in a finite model of N interacting fermions. This model serves as a simplified proxy for an atomic nucleus, capturing its essential features in a more manageable form compared to a realistic nuclear model, which would require the diagonalization of matrices with millions of elements, making the extraction of qualitative features a significant challenge. Specifically, we aim to correlate Cf with particle number fluctuations and temperature, using the paradigmatic Lipkin model. Our analysis reveals intriguing dependencies of Cf on the total fermion number, showcasing distinct behaviors at different temperatures. Notably, we find that the degree of quantum mixedness exhibits a strong dependence on the total fermion number, with varying trends across different temperature regimes. Remarkably, this dependence remains unaffected by the strength of the fermion-fermion interaction (as long as it is non-zero), underscoring the robustness of the observed phenomena. Through comprehensive numerical simulations, we provide illustrative graphs depicting these dependencies, offering valuable insights into the fundamental characteristics of quantum many-body fermion systems. Our findings illuminate the intricate dynamics of the degree of mixedness, a crucial quantum property, with potential implications for diverse fields ranging from condensed matter physics to quantum information science.

Yang-Lee zeros for real-space condensation

Using the electrostatic analogy, we derive an for the limiting Yang-Lee zero distribution in the random allocation model of general weights. This exhibits a real-space condensation phase transition, which is induced by a pressure change. The exact solution allows one to read off the scaling of the density of zeros at the critical point and the angle at which the locus of zeros hits the critical point. Since the order of the phase transition and critical exponents can be tuned with a single parameter for several families of weights, the model provides a useful testing ground for verifying various relations between the distribution of zeros and the critical behavior, as well as for exploring the behavior of physical quantities in the mesoscopic regime, i.e., systems of large but finite size. The main result is that asymptotically the Yang-Lee zeros are images of a conformal mapping, given by the generating function for the weights, of uniformly distributed complex phases. Published by the American Physical Society 2025

Gigantic Tellegen responses in metamaterials

Tellegen medium has long been a topic of debate, with its existence being contested over several decades. It was first proposed by Tellegen in 1948 and is characterized by a real-valued cross coupling between electric and magnetic responses, distinguishing it from the well-known chiral medium that has imaginary coupling coefficients. Significantly, Tellegen responses are closely linked to axion dynamics, an extensively studied subject in condensed matter physics. Here, we report the realization of Tellegen metamaterials in the microwave region through a judicious combination of subwavelength metallic resonators, gyromagnetic materials, and permanent magnets. We observe the key signature of the Tellegen response – a Kerr rotation for reflected wave, while the polarization remains the same in the transmission direction. The retrieved effective Tellegen parameter is several orders of magnitude greater than that of natural materials. Our work opens door to a variety of nonreciprocal photonic devices and may provide a platform for studying axion physics.

The Nordic-walking mechanism and its explanation of deconfined pseudocriticality from Wess-Zumino-Witten theory

The understanding of phenomena falling outside the Ginzburg-Landau paradigm of phase transitions represents a key challenge in condensed matter physics. A famous class of examples is constituted by the putative deconfined quantum critical points between two symmetry-broken phases in layered quantum magnets, such as pressurised SrCu2(BO3)2. Experiments find a weak first-order transition, which simulations of relevant microscopic models can reproduce. The origin of this behaviour has been a matter of considerable debate for several years. In this work, we demonstrate that the nature of the deconfined quantum critical point can be best understood in terms of a novel dynamical mechanism, termed Nordic walking. Nordic walking denotes a renormalisation group flow arising from a beta function that is flat over a range of couplings. This gives rise to a logarithmic flow that is faster than the well-known walking behaviour, associated with the annihilation and complexification of fixed points, but still significantly slower than the generic running of couplings. The Nordic-walking mechanism can thus explain weak first-order transitions, but may also play a role in high-energy physics, where it could solve hierarchy problems. We analyse the Wess-Zumino-Witten field theory pertinent to deconfined quantum critical points with a topological term in 2+1 dimensions. To this end, we construct an advanced functional renormalisation group approach based on higher-order regulators. We thereby calculate the beta function directly in 2+1 dimensions and provide evidence for Nordic walking.

Acoustic shock wave-induced superheating-assisted dynamic recrystallization - a case study of D-tartaric acid.

Superheating-assisted melting and crystallization are prominent subjects in condensed matter physics. However, understanding the superheating concepts under acoustic shocked conditions remains a mystery. Herein, we demonstrate superheating on the basis of dynamic recrystallization in a D-tartaric acid powder sample, which nearly attains an ideal crystal structure and morphology under the 100-shocked conditions compared to the control sample and the obtained results are evaluated by conventional diffraction, spectroscopic and microscopic techniques. From the XRD results, the intensities of the planes (100) and (110) are found to have increased under the 100-shocked conditions, whereas the intensity ratio (011)/(110) has been significantly reduced. Moreover, the intensity ratio of major internal Raman modes such as vC-O (1694 and 1700 cm-1), vC-H (2933 and 2967 cm-1) and vO-H (3331 and 3403 cm-1) has been considerably modified with respect to the number of shock pulses such that the sample produces an ideal Raman spectrum of D-tartaric acid, and thereby the intensities of the lattice Raman modes also support this claim. Most importantly, the SEM results demonstrate the formation of an ideal morphology of D-tartaric acid from the irregular morphological pattern upon exposure to 100 shocks due to the superheating and dynamic recrystallization process. The proposed technique is strongly suggested for materials processing to enhance technological significance for all classes and scales of materials.

Recent research progress of ultracold-atom quantum simulation of Fermi-Hubbard model

<sec>Fermi-Hubbard model is a fundamental lattice model describing correlated electron systems in condensed matter physics and is closely related to high-temperature superconductivity. In recent years, cold-atom quantum simulations have become an important paradigm for studying the Fermi-Hubbard model, and advances in quantum many-body computations have contributed to our understanding of its fundamental properties. Notably, a recent ultracold-atom experiment achieving the well-known antiferromagnetic (AFM) phase transition in the three-dimensional (3D) Hubbard model represents a key step in quantum simulation, laying a foundation for exploring the link between the quantum magnetism and high-temperature superconductivity. In this paper, the experimental and theoretical research progress of Fermi-Hubbard model in 3D systems is reviewed, the development history and present status in this field are discussed, and the future development direction is also prospected.</sec><sec>The paper is organized as follows. To begin with, recent progress of observing AFM phase transitions in the 3D Hubbard model is reviewed, focusing on an ultracold-atom experiment conducted by the research group at the University of Science and Technology of China (USTC). Next, a theoretical introduction to the fundamental properties of the 3D Hubbard model is provided, in which prior theoretical studies is summarized, the current research status is outlined, and some unresolved or under-explored problems are discussed. In Section 3, the quantum simulation of the Hubbard model using ultracold atoms in optical lattices is discussed, and the basic principle, historical developments and key challenges are outlined. The USTC team overcame these challenges through innovative techniques such as atom cooling, large-scale uniform box traps, and precise measurements of the AFM structure factor. Their work successfully confirms the AFM phase transition via the critical scaling analysis. Finally, the significance of this achievement is emphasized, and the future research prospects of the 3D Hubbard model are discussed, including experimental studies on the doped regions and related theoretical benchmarks.</sec>

Modulational Instability and Dynamical Growth Blockade in the Nonlinear Hatano–Nelson Model

AbstractThe Hatano–Nelson model is a cornerstone of non‐Hermitian physics, describing asymmetric hopping dynamics on a 1D lattice, which gives rise to fascinating phenomena such as directional transport, non‐Hermitian topology, and the non‐Hermitian skin effect. It has been widely studied in both classical and quantum systems, with applications in condensed matter physics, photonics, and cold atomic gases. Recently, nonlinear extensions of the Hatano–Nelson model have opened a new avenue for exploring the interplay between nonlinearity and non‐Hermitian effects. Particularly, in lattices with open boundary conditions, nonlinear skin modes and solitons, localized at the edge or within the bulk of the lattice, have been predicted. In this work, the nonlinear extension of the Hatano–Nelson model with periodic boundary conditions is examined and a novel dynamical phenomenon arising from the modulational instability of nonlinear plane waves: growth blockade is revealed. This phenomenon is characterized by the abrupt halt of norm growth, as observed in the linear Hatano–Nelson model, and can be interpreted as a stopping of convective motion arising from self‐induced disorder in the lattice.

Percolative phase transition in few-layered MoSe2 field-effect transistors using Co and Cr contacts.

The metal-to-insulator phase transition (MIT) in two-dimensional (2D) materials under the influence of a gating electric field has revealed interesting electronic behavior and the need for a deeper fundamental understanding of electron transport processes, while attracting much interest in the development of next-generation electronic and optoelectronic devices. Although the mechanism of the MIT in 2D semiconductors is a topic under debate in condensed matter physics, our work demonstrates the tunable percolative phase transition in few-layered MoSe2 field-effect transistors (FETs) using different metallic contact materials. Here, we attempted to understand the MIT through temperature-dependent electronic transport measurements by tuning the carrier density in a MoSe2 channel under the influence of an applied gate voltage. In particular, we have examined this phenomenon using the conventional chromium (Cr) and ferromagnetic cobalt (Co) as two metal contacts. For both Cr and Co, our devices demonstrated n-type behavior with a room-temperature field-effect mobility of 16 cm2 V-1 s-1 for the device with Cr-contacts and 92 cm2 V-1 s-1 for the device with Co-contacts, respectively. With low temperature measurements at 50 K, the mobilities increased significantly to 65 cm2 V-1 s-1 for the device with Cr and 394 cm2 V-1 s-1 for the device with Co-contacts. By fitting our experimental data to the percolative phase transition theory, the temperature-dependent conductivity data show a transition from an insulating-to-metallic behavior at a bias of ∼28 V for Cr-contacts and ∼20 V for Co-contacts. This cross-over of the conductivity can be attributed to an increase in carrier density as a function of the gate bias in temperature-dependent transfer characteristics. By extracting the critical exponents, we find that the transport behavior in the device with Co-contacts aligns closely with the 2D percolation theory. In contrast, the devices with Cr-contacts deviate significantly from the 2D limit at low temperatures.

Aubry-André-Harper momentum-state chain in curved spacetime

Anderson localization is a profound phenomenon in condensed matter physics, representing a fundamental transition of eigenstates induced by disorder. The one-dimensional Aubry-André-Harper (AAH) model, an iconic quasiperiodic lattice model, is one of the simplest models that demonstrate the Anderson localization transition. Recently, with the growing interest in quantum lattice models in curved spacetime (CST), the AAH model in CST has been proposed as a way to explore the interplay between Anderson localization and CST physics. While a few CST lattice models have been realized in optical waveguide systems to date, significant challenges remain in the experimental preparation and measurement of states, primarily due to the difficulty of dynamically modulating lattices in such systems. In this study, we propose an experimental scheme using a momentum-state lattice (MSL) in an ultracold atom system to realize the AAH model in CST and study the Anderson localization in this context. Thanks to the individual controllability of the coupling between each pair of adjacent momentum states, the coupling amplitude in the MSL can be encoded as a power-law position-dependent form $J_n \propto n^{\sigma}$, facilitating effective simulation of CST. Numerical calculation results of the MSL Hamiltonian show an emergence of the phase separation in a 34-site AAH chain in CST, where wave packet dynamics exhibit localized behavior on one side of the critical site and extended behavior on the other. The phase separation critical site is observed by extracting turning points of the evolving fractal dimension and the wave packet width derived from evolution dynamic simulations. Furthermore, by modulating the spacetime curvature parameter $\sigma$, we propose a method for eigenstates preparation of the AAH chain in CST, and perform numerical simulations in the MSL. Through calculating the fractal dimension of eigenstates prepared following the aforementioned method, we analyze the localization properties of eigenstates under various quasiperiodic modulation phases, confirming the coexistence of localized phase, swing phase, and extended phase in the energy spectrum. Unlike traditional localized and extended phases, eigenstates in the swing phase of the AAH model in CST exhibit different localization properties under different modulation phases, indicating the prescence of a swing mobility edge. Our results provide a feasible experimental approach to study Anderson localization in CST and introduce a new platform for realizing quantum lattice models in curved spacetime.

Evolution from the Kondo phase to the RKKY phase in the small impurity spacing regime of the two-impurity Anderson model

Abstract Understanding the quantum critical phenomena is one of the most important and challenging tasks in condensed matter physics and the two-impurity Anderson model (TIAM) is a good starting point for this exploration. To this end, we employ the algebraic equation of motion approach to calculate the TIAM and analytically obtain the explicit single-particle impurity Green function under the soft cut-off approximation (SCA). This approach effectively incorporates the impurity spacing as an intrinsic parameter. By solving the pole equations of the Green function, we have, for the first time, qualitatively calculated the spectral weight functions of the corresponding low-energy excitations. We find that when the impurity spacing is less than one lattice distance, the dynamic Rudermann–Kittel–Kasuya–Yosida (RKKY) interaction effectively enters, resulting in a rapid increase in the spectral weights of the RKKY phase, which ultimately surpass those of the Kondo phase; while the spectral weights of the Kondo phase are strongly suppressed. From the perspective of spectral weights, we further confirm the existence of a crossover from the Kondo phase to the RKKY phase in the TIAM. Based on these results, the reasons for the phenomenon of the Kondo resonance splitting are also discussed.

Study on the characteristics of sulfate ion in condensable particulate matter from sewage sludge co-combustion in coal-fired power plants

Study on the characteristics of sulfate ion in condensable particulate matter from sewage sludge co-combustion in coal-fired power plants

Rethinking primary particulate matter: Integrating filterable and condensable particulate matter in measurement and analysis.

The current definition of primary particulate matter (PM) encompasses filterable PM (FPM) and condensable PM (CPM), which are evaluated using two distinct conventional measurement methods: cooling and dilution. While the cooling method exclusively considers the homogenous formation of CPM, the dilution method, closer to real-world conditions, neglects FPM characterization. To overcome this limitation, we propose a doubled-dilution system that enables the parallel characterization of both FPM and primary PM without diverting FPM from the CPM formation pathway. The doubled-dilution system has been investigated from a laboratory scale to a full-scale coal-fired power plant to facilitate simultaneous, real-time measurements of primary PM and FPM size distributions. Moreover, the formation rates of homogeneous and heterogeneous nucleation were compared. The evolution of the primary PM size revealed a bimodal distribution, and the filter-based mass concentration results demonstrated a pronounced preference for heterogeneous reactions (17.6 times higher than homogeneous nucleation). In particular, primary PM emissions were underestimated by up to 65.3% when only homogeneous CPM formation was considered, underscoring the importance of including FPM during primary PM measurements. Considering these results, we advocate adopting the term "primary PM" over "CPM."

Phase-separated condensates in autophagosome formation and autophagy regulation.

Biomacromolecules partition into numerous types of biological condensates or membrane-less organelles via liquid-liquid phase separation (LLPS). Newly formed liquid-like condensates may further undergo phase transition to convert into other material states, such as gel or solid states. Different biological condensates possess distinct material properties to fulfil their physiological functions in diverse cellular pathways and processes. Phase separation and condensates are extensively involved in the autophagy pathway. The autophagosome formation sites in both yeast and multicellular organisms are assembled as phase-separated condensates. TORC1, one of the core regulators of the autophagy-lysosome pathway, is subject to nonconventional regulation by multiple biological condensates. TFEB, the master transcription factor of the autophagy-lysosome pathway, phase separates to assemble liquid-like condensates involved in transcription of autophagic and lysosomal genes. The behaviors and transcriptional activity of TFEB condensates are governed by their material properties, thus suggesting novel autophagy intervention strategies. The phase separation process and the resulting condensates are emerging therapeutic targets for autophagy-related diseases.

Origin of the formation of isostructural bcc-Fe+bcc-Cu nanocomposites in Fe–Cu alloy via vacuum co-deposition

This study examined the influence of substrate temperature and the ratio of iron and copper vapor flow on the structural state of Fe–Cu vacuum condensates. XRD patterns of the condensates deposited under specific electron beam physical vapor deposition process parameters revealed peaks corresponding to either bcc or bcc+fcc phases. Analysis of the lattice parameter of the single bcc structure indicates that only a portion of the copper atoms dissolve in the bcc-Fe lattice, while undissolved copper atoms form bcc-Cu inclusions that are coherent with the bcc-Fe lattice. A model for the formation of the bcc-Cu structure as an adaptive phase is proposed. The formation of the adaptive phase in vacuum condensates is driven by the bcc-Cu epitaxy on the surface of bcc-Fe crystallites and excess vacancies in the condensate structure. As the copper concentration in the isostructural Fe–Cu composite increases, the level of microstrain in its bcc crystal lattice also increases. The transformation of bcc-Cu particles into fcc-Cu via a shear mechanism occurs when heated above 400 °C. It was found that increasing the deposition temperature reduces the concentration range for the formation of the isostructural composite. It is suggested that higher deposition temperatures and increased copper concentration lead to larger copper particle sizes and reduced excess vacancy concentration, which disrupts their coherence with the bcc-Fe matrix. As a result, a composite with a eutectic-like microstructure consisting of bcc-Fe and fcc-Cu phases forms directly during vapor phase condensation.

Constant high-level visual acuity during total laparoscopic hysterectomy using the OpClear® system

Background Operative vision can frequently be critically reduced during laparoscopic surgery by condensation and other matter accumulating on the distal laparoscope lens. By delivering saline and carbon dioxide across the lens, the OpClear system is designed to maintain operative vision without needing scope removal for lens cleaning. This study evaluates the system’s efficacy in providing high-level visual acuity during laparoscopic hysterectomy while examining its utility through its impact on operative duration. Methods A retrospective audit compared efficacy and utility for the three years before and after the implementation of OpClear in a single unit. Thirty-three cases were reviewed pre-OpClear, while 82 cases were analysed in the post-OpClear group. All cases involved routine total laparoscopic hysterectomies (TLH) performed by the same surgeon (AT) with similar complexity levels. Results The OpClear system provided a consistently high level of visual acuity throughout the laparoscopic procedures. Scope removals, which typically result in non-productive operating time, were virtually eliminated. Consequently, in highly comparable cases, OpClear usage resulted in a 17-minute reduction in operating time over cases performed without the device. Additionally, in the OpClear group, there were trends towards reduced blood loss and shorter hospital stays, with patients in the OpClear group being discharged on first rather than second postoperatively. Conclusions The findings of this audit suggest that the OpClear system provides continuous high-level vision during laparoscopic hysterectomy. Further, reducing periods of non-productive time associated with scope removal for cleaning resulted in shorter operating times. Thus, the system has the potential to enhance safety, improve theatre utilisation and alleviate some of the surgical stresses associated with laparoscopic surgery.