Anomalous State Research Articles

Electric circuit simulation of Floquet topological insulators in Fourier space

We present a method for simulating any non-interacting and time-periodic tight-binding Hamiltonian in Fourier space using electric circuits made of inductors and capacitors. We first map the time-periodic Hamiltonian to a Floquet Hamiltonian, which converts the time dimension into a Floquet dimension. In electric circuits, this Floquet dimension is simulated as an extraspatial dimension without any time dependency in the electrical elements. The number of replicas needed in the Floquet Hamiltonian depends on the frequency and strength of the drive. We also demonstrate that we can detect the topological edge states (including the anomalous edge states in the dynamical gap) in an electric circuit by measuring the two-point impedance between the nodes. Our method paves a simple and promising way to explore and control Floquet topological phases in electric circuits.

Real-Space Observation of Ligand Hole State in Cubic Perovskite SrFeO3.

An anomalously high valence state sometimes shows up in transition-metal oxide compounds. In such systems, holes tend to occupy mainly the ligand p orbitals, giving rise to interesting physical properties such as superconductivity in cuprates and rich magnetic phases in ferrates. However, no one has ever observed the distribution of ligand holes in real space. Here, a successful observation of the spatial distribution of valence electrons in cubic perovskite SrFeO3 by high-energy X-ray diffraction experiments and precise electron density analysis using a core differential Fourier synthesis method is reported. A real-space picture of ligand holes formed by the orbital hybridization of Fe 3d and O 2p is revealed. The anomalous valence state in Fe is attributed to the considerable contribution of the ligand hole, which is related to the metallic nature and the absence of Jahn-Teller distortions in this system.

Conditions and thermophysical properties for transport of hydrocarbons and natural gas at high pressures: Dense phase and anomalous supercritical state

Hydrocarbons and natural gas, like other fluids exhibit anomalous behavior in the vicinity of their critical points (Pc, Tc), where flow oscillations, thermal instabilities, and decreased heat transfer can occur. This work, based on Peng-Robinson equations of state, demonstrates that in the case of mixtures, the cricondenbar, cricondentherm, and a part of the dense phase belong to this anomalous region. Consequently, the most desirable conditions for the transport of supercritical natural gas (SNG) are: above the critical pressure and critical temperature, above the cricondenbar and cricondentherm, and beyond the anomalous state. For methane, such conditions exist at pressure, P > 5 MPa and temperature, T > - 30 °C whereas for average composition of natural gases from US/Canada, West Asia, and North Sea, P ≥ 6 MPa and T > −30 °C may be appropriate/safe for SNG transport. Corresponding gray zones which will require special design considerations are also identified. Reduced pressure, (P/Pc) of 1.15 and reduced temperature, (T/Tc) of 1.25 and 1.4 may be appropriate to delimit the Unsafe Zone/Gray Zone and Gray Zone/Safe zone. In addition, the specific volume and kinematic viscosity show asymptotic behavior at high SC pressures that can have important implications in the transport of hydrocarbons and natural gas. Moreover, the critical temperature, cricondentherm, and anomalous region of natural gas can be moved to lower temperatures by adding one or more modifier gases with low Tc, e.g., methane, nitrogen, and argon; or, higher using gases with high Tc such as ethane, propane, and carbon dioxide. The pipelines carrying SNG, with Tc-modifications if needed, can therefore pass through polar, tropical, arid, and desert-like conditions.

Extreme events in the multi-proxy South Pacific drought atlas

Droughts are a natural occurrence in many small Pacific Islands and can have severe impacts on local populations and environments. The El Niño-Southern Oscillation (ENSO) is a well-known driver of drought in the South Pacific, but our understanding of extreme ENSO events and their influence on island hydroclimate is limited by the short instrumental record and the infrequency of ENSO extremes. To address this gap, we developed the South Pacific Drought Atlas (SPaDA), a multi-proxy, spatially resolved reconstruction of the November–April Standardised Precipitation Evapotranspiration Index for the southwest Pacific islands. The reconstruction covers the period from 1640 to 1998 CE and is based on nested principal components regression. It replicates historical droughts linked to ENSO events with global influence, compares well to previously published ENSO reconstructions, and is independently verified against fossil coral records from the Pacific. To identify anomalous hydroclimatic states in the SPaDA that may indicate the occurrence of an extreme event, we used an Isolation Forest, an unsupervised machine learning algorithm. Extreme El Niño events characterised by very strong southwest Pacific drought anomalies and a zonal SPCZ orientation are shown to have occurred throughout the reconstruction interval, providing a valuable baseline to compare to climate model projections. By identifying the spatial patterns of drought resulting from extreme events, we can better understand the impacts these events may have on individual Pacific Islands in the future.

Ultra-long-distance transport of supercritical natural gas (SNG) at very-high mass flow rates via pipelines through land, underground, water bodies, and ocean

A detailed study of SNG transport using a computational model that accounts for compressibility and Joule-Thomson effects is presented, for the first time. It shows that the transport distance and mass flow rate of supercritical natural gas (SNG) - above the cricondenbar and cricondentherm, and beyond the anomalous state - can exceed far beyond that achieved or proposed under high pressure, dense phase conditions, thus far. As an example, SNG (average composition of USA/Canada gas), at 800 kg/s can travel, without recompression, to 4801 km. It is revealed that the pressure-drop and pumping power per unit length decrease asymptotically as the inlet pressure increases beyond 20 MPa; orders-of-magnitude lower than that at low pressures. The increase in inlet pressure, pipe diameter, and/or heat conductance of the pipe wall increases the distance travelled by SNG whereas the increase in mass flow rate and surrounding temperature has a negative effect, including the strengthening of Joule-Thomson cooling near the exit. SNG pipelines at ocean bottom offer many advantages, including shorter distances, isothermal flows (∼4 °C), and balance between the outer and inner pressures. Also, SNG delivery at 6 MPa can allow regional distribution without immediate recompression. SNG pipelines therefore offer enormous possibilities of energy-efficient transport of natural gas to far-distant intra- and inter-continental destinations, not feasible thus far, which is urgently needed for uninterrupted supply of natural gas and worldwide energy security.

Anomalous Transport of Energetic Particles Interacting with Dynamic Small-Scale Magnetic Flux Rope Structures

le Roux and Zank [25] showed previously how one can derive from first principles a pitch-angle dependent fractional diffusion-advection kinetic equation to model the anomalous diffusion of energetic particles interacting with small-scale magnetic flux ropes (SMFRs) in the inner heliosphere on the basis of the standard focused transport equation. This equation has the following limitations: (1) The asymptotic power law of a Lévy distribution was specified to model the non-Gaussian statistics of the disturbed energetic particle trajectories generated during energetic particle interaction with numerous SMFRs. The second moment (variance) and higher moments of the Lévy distribution are infinite, indicating over-efficient non-local transport that is scale-free. (2) The theory does not naturally allow for a transition of anomalous transport to normal diffusion, or to a different anomalous diffusion state. An outline of a derivation is presented in which an exponentially truncated Lévy distribution was specified instead, resulting in a tempered fractional diffusion-advection kinetic equation that addresses these two concerns.

Anomalous flux state in higher-order topological superconductors

Anomalous flux state in higher-order topological superconductors

Leveraging and Refining Image Recognition Technology for Intelligent Logistics Sorting Systems

Obstacles in the realm of target detection, tracking accuracy, real-time performance, and robustness have been identified within the context of intelligent logistics sorting systems, which incorporate image recognition technology. Furthermore, the critical role of detecting anomalous states in augmenting sorting efficiency and curtailing errors is underscored. Image recognition technologies of a conventional nature tend to suffer from limitations in their applicability and robustness. In practical working environments, a paucity of abnormal data from logistics sorting targets is observed, which inhibits the application of supervised learning methods of deep learning. Addressing these challenges, an unsupervised deep learning method is introduced for the detection of anomalous states in logistics sorting targets. This approach reinterprets the detection of logistics sorting targets as an anomaly detection problem and utilizes Variational AutoEncoders (VAE) for modeling the distribution of normal data. This method's dependency rests exclusively on normal data for training, thereby circumventing the need for a substantial quantity of abnormal samples. In practical deployments, the anomalous state of logistics sorting targets is discerned by the method through the computation of similarity and implementation of labeling algorithms, evidencing robustness, generalizability, and adaptability. Overall, this method is presented as an effective solution for the detection of anomalous states within intelligent logistics sorting scenarios, serving to decrease labeling costs, enhance detection accuracy and efficiency, and satisfying the practical requisites of logistics sorting systems for abnormal state detection.

Lattice model for the quantum anomalous Hall effect in moiré graphene

Inspired by experiments on magic angle-twisted bilayer graphene, we present a lattice mean-field model for the quantum anomalous Hall effect in a moir\'e setting. Our hopping Hamiltonian provides a simple route to a moir\'e Chern insulator in commensurately twisted systems. We study our model in the ribbon geometry and demonstrate the presence of thick chiral edge states that have a transverse localization that scales with the moir\'e lattice spacing. We also study the electronic structure of a domain wall between opposite Chern insulators. Our model and results are relevant to experiments that will image or manipulate the moir\'e quantum anomalous Hall edge states.

Solid State Neuroscience: Spiking Neural Networks as Time Matter

We aim at building a bridge between to a priori disconnected fields: Neuroscience and Material Science. We construct an analogy based on identifying spikes events in time with the positions of particles of matter. We show that one may think of the dynamical states of spiking neurons and spiking neural networks as time-matter. Namely, a structure of spike-events in time having analogue properties to that of ordinary matter. We can define for neural systems notions equivalent to the equations of state, phase diagrams and their phase transitions. For instance, the familiar Ideal Gas Law relation (Pυ = constant) emerges as analogue of the Ideal Integrate and Fire neuron model relation (Iin ISI = constant). We define the neural analogue of the spatial structure correlation function, that can characterize spiking states with temporal long-range order, such as regular tonic spiking. We also define the “neuro-compressibility” response function in analogy to the lattice compressibility. We show that similarly to the case of ordinary matter, the anomalous behavior of the neuro-compressibility is a precursor effect that signals the onset of changes in spiking states. We propose that the notion of neuro-compressibility may open the way to develop novel medical tools for the early diagnose of diseases. It may allow to predict impending anomalous neural states, such as Parkinson’s tremors, epileptic seizures, electric cardiopathies, and perhaps may even serve as a predictor of the likelihood of regaining consciousness.

A two-dimensional kagome magnet with tunable topological phases

Kagome magnets have garnered a lot of investigation due to their plentiful topological states and promising, strong correlated phenomena. However, there have been few reports of two-dimensional (2D) van der Waals kagome magnets. Here, we suggest a stable 2D van der Waals kagome material, V3Br8, which exhibits a ferromagnetic ground state with a Curie temperature of 89 K. Near the Fermi level, there is only a set of three kagome bands from one spin species, which possesses Van Hove singularities at the M point and a Weyl point at the K point. It is interesting that its ground state is gapless at the K point and maintains a 2D Weyl half semimetal state even in the presence of spin-orbit coupling, while when the magnetization rotates from the in-plane direction of the ground state to the out-of-plane direction, the spin-orbit coupling will open an energy gap at the K point, resulting in a topological phase transition to a quantum anomalous Hall effect state. We further demonstrate that the tensile strain can optimize the band structure and raise the Curie temperature to above 100 K. In addition, a Li atom intercalated V3Br8 (V3Br8Li) is revealed to be a stable structure that can successfully tune the Fermi level to the Weyl point while maintaining the ferromagnetic ground state. Moreover, V3Br8Li displays an out-of-plane magnetism, producing the quantum anomalous Hall effect . Our findings provide a solid foundation for future research into topological states and singular effects in 2D kagome magnets.

Theoretical investigations on elastic properties, phase stability, and magnetism in Ni2Mn-based all- d−metal Heusler compounds

The elastic properties, phase stability, and magnetism and correlations among them in all-$d\text{\ensuremath{-}}\mathrm{metal}$ Heusler compounds, i.e., ${\mathrm{Ni}}_{2}\mathrm{Mn}T$ ($T=\mathrm{Sc}$, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, and W) were systematically investigated by first-principles calculations. The results indicated that ${\mathrm{Ni}}_{2}\mathrm{Mn}T$ compounds were not fully consistent with the conventional atomic preferential occupation rule in the Heusler family. Within the scope of Heusler structures, ${\mathrm{Ni}}_{2}\mathrm{Mn}T$ compounds containing early transition metal atoms preferred $L{2}_{1}\text{-type}$ structure, while those with late transition metal atoms were relatively stable in ${\mathrm{Hg}}_{2}\mathrm{CuTi}\text{\ensuremath{-}}\mathrm{type}$ structure. In $d\text{\ensuremath{-}}d$ interatomic hybridization-controlled all-$d\text{\ensuremath{-}}\mathrm{metal} {\mathrm{Ni}}_{2}\mathrm{Mn}T$ Heusler compounds, the atomic radius determined the lattice sizes. Owing to the strong couplings among elastic parameters, phonon modes, and electronic structure, the most likely martensitic phase transition could be expected in weakly magnetic ${\mathrm{Ni}}_{2}\mathrm{Mn}T$ compounds with late transition metal atoms. By applying hydrostatic pressure or imposing chemical pressure via adjusting the composition of Ti in an off-stoichiometric Ni-Mn-Ti system, magnetism was weakened, and the suppressed martensitic phase transition could be re-evoked. In this paper, we also revealed that experimentally observed antiferromagnetism in ${\mathrm{Ni}}_{2}\mathrm{MnTi}$ originated from the arrest of the atomic diffusion process during the transition from the high-temperature chemically disordered paramagnetic state to the low-temperature chemically and magnetically ordered ferromagnetic state, which resulted in the formation of an intermediate metastable and partially disordered antiferromagnetic phase. Comparatively, ${\mathrm{Ni}}_{2}\mathrm{Mn}T$ compounds with early transition metals showed better ductility. In representative ${\mathrm{Ni}}_{2}\mathrm{MnY}$ and ${\mathrm{Ni}}_{2}\mathrm{MnTa}$, it was found that nondirectional $d\text{\ensuremath{-}}d$ interatomic hybridization became prevailing and helped establish the metal bonding character, which consequently enhanced the ductility. This paper can provide more insight into understanding the mechanism of martensitic phase transition and the origin of experimental anomalous magnetic states as well as the scheme to design multiple functional magnetic materials with outstanding ductility in the all-$d\text{\ensuremath{-}}\mathrm{metal}$ Heusler family. Experimentally observed exceptional multicaloric effects in Ni-Mn-based compounds with outstanding mechanical properties make all-$d\text{\ensuremath{-}}\mathrm{metal}$ Heusler compounds attractive for potential solid-state refrigeration application.

Anomalous oxidation state of europium in the Sr3(PO4)2-type phosphors doped with alkaline cations

A series of new phosphors Sr2.98Eu0.01M0.01(PO4)2 (SEMP), M = Li+, Na+, K+ have been synthesized by high temperature solid state reaction. Powder X-ray diffraction study reveals that SEMP samples are isostructural to palmierite-type Sr3(PO4)2 phosphate. The anomalous reduction Eu3+ → Eu2+ in nonreduction media in Sr3(PO4)2 host has been reported for the first time. The blue emission from Eu2+ (∼425 nm) corresponding to the 4f65d1→4f7(8S7/2) transitions and red emission from Eu3+ (550–750 nm), corresponding to the 4f–4f transitions 5D0 → 7FJ (J = 0−4) were observed. The highest Eu3+ luminescence intensity was observed for Li+-doped host both at 296 K and at 10 K. The results show that the synthesized samples with tunable blue/red-orange emission can be considered for thermal sensing application.

Magnetic wallpaper Dirac fermions and topological magnetic Dirac insulators

Topological crystalline insulators (TCIs) can host anomalous surface states which inherits the characteristics of crystalline symmetry that protects the bulk topology. Especially, the diversity of magnetic crystalline symmetries indicates the potential for novel magnetic TCIs with distinct surface characteristics. Here, we propose a topological magnetic Dirac insulator (TMDI), whose two-dimensional surface hosts fourfold-degenerate Dirac fermions protected by either the {p}_{c}^{{prime} }4mm or p{4}^{{prime} }{g}^{{prime} }m magnetic wallpaper group. The bulk topology of TMDIs is protected by diagonal mirror symmetries, which give chiral dispersion of surface Dirac fermions and mirror-protected hinge modes. We propose candidate materials for TMDIs including Nd4Te8Cl4O20 and DyB4 based on first-principles calculations, and construct a general scheme for searching TMDIs using the space group of paramagnetic parent states. Our theoretical discovery of TMDIs will facilitate future research on magnetic TCIs and illustrate a distinct way to achieve anomalous surface states in magnetic crystals.

Evidence for an emergent anomalous metallic state in compressed titanium

The anomalous metallic state (AMS) emerging from a quantum superconductor-to-metal transition is a subject of great current interest since this exotic quantum state exhibits unconventional transport properties that challenge the core physics principles of Fermi liquid theory. As the AMS concept is historically derived from disordered two-dimensional (2D) systems, related studies have predominately concentrated on 2D materials. The AMS behaviors in three-dimensional (3D) systems have been rarely reported to date, which raises intriguing questions on the fundamental nature of pertinent physics. Here, we report experimental evidence for a 3D AMS in highly compressed titanium metal that exhibits superconductivity with a critical temperature (Tc) reaching near-record 25.1K among elemental superconductors, offering a favorable material template for exploring 3D AMS. At sufficiently strong magnetic fields, unusual transport behaviors set in over a wide pressure range, showcasing AMS hallmarks of a low-temperature saturation resistance below the Drude value and giant positive magnetoresistance. These findings reveal a 3D AMS in simple elemental systems and, more importantly, provide a fresh platform for probing the decades-long enigmatic underlying physics.

Anomalous topological waves in strongly amorphous scattering networks.

Topological insulators are crystalline materials that have revolutionized our ability to control wave transport. They provide us with unidirectional channels that are immune to obstacles, defects, or local disorder and can even survive some random deformations of their crystalline structures. However, they always break down when the level of disorder or amorphism gets too large, transitioning to a topologically trivial Anderson insulating phase. We demonstrate a two-dimensional amorphous topological regime that survives arbitrarily strong levels of amorphism. We implement it for electromagnetic waves in a nonreciprocal scattering network and experimentally demonstrate the existence of unidirectional edge transport in the strong amorphous limit. This edge transport is shown to be mediated by an anomalous edge state whose topological origin is evidenced by direct topological invariant measurements. Our findings extend the reach of topological physics to a class of systems in which strong amorphism can induce, enhance, and guarantee the topological edge transport instead of impeding it.

Field-induced reentrant insulator state of a gap-closed topological insulator ( Bi1−xSbx ) in quantum-limit states

In the extreme quantum limit states under high magnetic fields, enhanced electronic correlation effects can stabilize anomalous quantum states. Using band-tuning with a magnetic field, we realized a spin-polarized quantum limit state in the field-induced semimetallic phase of a topological insulator Bi_{1-x}Sb_x. Further increase in the field injects more electrons and holes to this state and results in an unexpected reentrant insulator state in this topological semimetallic state. A single-particle picture cannot explain this reentrant insulator state, reminiscent of phase transitions due to many-body effects. Estimates of the binding energy and spacing of electron-hole pairs and the thermal de Broglie wavelength indicate that Bi_{1-x}Sb_x may host the excitonic insulator phase in this extreme environment.

Anomalous Crustal Stress in the Eastern Tennessee Seismic Zone

AbstractThe eastern Tennessee seismic zone (ETSZ) experiences the second highest rates of natural seismicity in the central and eastern United States (CEUS), following the New Madrid area, yet the cause of elevated earthquake rates is unknown. We probe the origin of ETSZ seismicity using geomechanically constrained stress inversions of earthquake focal mechanisms from 57 earthquakes, including 24 newly derived here and five from the recent events not used in the previous stress studies. Highly oblique northwest–southeast (NW–SE) extension that is unique in the CEUS dominates the ETSZ—central Alabama to southeastern Kentucky—and preferentially reactivates normal to strike-slip faults in the northeast (NE) and southwest (SW) quadrants (strikes 018°–086° or 196°–272° and dips 55°–90°). This extension cannot be explained by the compressive tectonic plate-boundary tractions that cause oblique NE–SW contraction elsewhere in the CEUS. Although our analyses do not uniquely determine the origin of the anomalous stress, we favor isostatic disequilibrium, due to anything from surface processes to crust–mantle interactions, as the possible cause. Increased long-term seismic hazard in the ETSZ may be controlled by and confined to the spatial extent of this anomalous seismotectonic state.

Anomaly-based Network Intrusion Detection System using Deep Intelligent Technique

Background and objectives: Computer systems and network infrastructures are still exposed to many security risks and cyber-attack vulnerabilities despite advancements of information security. Traditional signature-based intrusion detection systems and security solutions by matching rule-based mechanism and prior knowledge are insufficient of fully protecting computer networks against novel attacks. For this purpose, Anomaly-based Network Intrusion Detection System (A-NIDS) as cyber security tool is considered for identifying and detecting anomalous behavior in the flow-based network traffic alongside with firewalls and other security measures. The main objective of the research is to improve the detection rate and reduce false-positive rates of the classifier using anomaly-based technique. Methods: an intelligent technique using deep learning algorithm and mutual information feature selection (MIFS) method to select optimal features on the benchmark datasets. Proposed method accurately capable of classifying normal and anomalous states of the data packets in a comprehensive way by combination of Long-Short term memory (LSTM) algorithm and MIFS method. Results: The model achieved encouraging results in terms of accuracy 99.79%, 0.002 false-positive rate with minimum time compared to other models recorded only 81.75s on CSE-CIC-IDS2018 dataset. At the end of the study, comparative studies are conducted to verify the effectiveness of proposed method on three realistic and latest intrusion detection datasets, named CSE_CIC-IDS2018, CIC-IDS2017, and NF-CSE-CIC-IDS2018 dataset. Conclusions: Proposed model in a combination of LSTM NN and Feature selection method (MIFS) increased detection rate and reduced false-positive alarms, also the model able to detect low frequent attacks while other existing models are suffering from.

Boundary discrete time crystals induced by topological superconductors in solvable spin chains

The Floquet time crystal, which breaks discrete time-translation symmetry, is an intriguing phenomenon in nonequilibrium systems. It is crucial to understand the rigidity and robustness of discrete time crystal (DTC) phases in a many-body system, and finding a precisely solvable model can pave a way for understanding of the DTC phase. Here, we propose and study a solvable spin chain model by mapping it to a Floquet superconductor through the Jordan-Wigner transformation. The phase diagrams of Floquet topological systems are characterized by topological invariants and tell the existence of anomalous edge states. The subharmonic oscillation, which is the typical signal of the DTC, can be generated from such edge states and protected by topology and solvability. We also examine the robustness of the DTC by adding symmetry-preserving and symmetry-breaking perturbations. Our results on the topologically protected DTC can provide a deep understanding of the DTC when generalized to other interacting or dissipative systems.