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822 result(s) for "Balakrishnan, G."
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Signatures of the Kondo effect in VSe2
VSe 2 is a transition metal dichaclogenide which has a charge- density wave transition that has been well studied. We report on a low-temperature upturn in the resistivity and, at temperatures below this resistivity minimum, an unusual magnetoresistance which is negative at low fields and positive at higher fields, in single crystals of VSe 2 . The negative magnetoresistance has a parabolic dependence on the magnetic field and shows little angular dependence. The magnetoresistance at temperatures above the resistivity minimum is always positive. We interpret these results as signatures of the Kondo effect in VSe 2 . An upturn in the susceptibility indicates the presence of interlayer V ions which can provide the localized magnetic moments required for scattering the conduction electrons in the Kondo effect. The low-temperature behaviour of the heat capacity, including a high value of γ, along with a deviation from a Curie-Weiss law observed in the low-temperature magnetic susceptibility, are consistent with the presence of magnetic interactions between the paramagnetic interlayer V ions and a Kondo screening of these V moments.
Real-space imaging of confined magnetic skyrmion tubes
Magnetic skyrmions are topologically nontrivial particles with a potential application as information elements in future spintronic device architectures. While they are commonly portrayed as two dimensional objects, in reality magnetic skyrmions are thought to exist as elongated, tube-like objects extending through the thickness of the host material. The study of this skyrmion tube state (SkT) is vital for furthering the understanding of skyrmion formation and dynamics for future applications. However, direct experimental imaging of skyrmion tubes has yet to be reported. Here, we demonstrate the real-space observation of skyrmion tubes in a lamella of FeGe using resonant magnetic x-ray imaging and comparative micromagnetic simulations, confirming their extended structure. The formation of these structures at the edge of the sample highlights the importance of confinement and edge effects in the stabilisation of the SkT state, opening the door to further investigation into this unexplored dimension of the skyrmion spin texture. Magnetic skyrmions are thought to possess a tube-like structure in three dimensions, but this has not been directly observed in experiment. Here, Birch et al. report real-space imaging of skyrmion tubes in a lamella of FeGe.
Unconventional Fermi surface in an insulating state
Insulators occur in more than one guise; a recent finding was a class of topological insulators, which host a conducting surface juxtaposed with an insulating bulk. Here, we report the observation of an unusual insulating state with an electrically insulating bulk that simultaneously yields bulk quantum oscillations with characteristics of an unconventional Fermi liquid. We present quantum oscillation measurements of magnetic torque in high-purity single crystals of the Kondo insulator SmB6, which reveal quantum oscillation frequencies characteristic of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and LaB6. The quantum oscillation amplitude strongly increases at low temperatures, appearing strikingly at variance with conventional metallic behavior.
Deriving the skyrmion Hall angle from skyrmion lattice dynamics
Magnetic skyrmions are topologically non-trivial, swirling magnetization textures that form lattices in helimagnetic materials. These magnetic nanoparticles show promise as high efficiency next-generation information carriers, with dynamics that are governed by their topology. Among the many unusual properties of skyrmions is the tendency of their direction of motion to deviate from that of a driving force; the angle by which they diverge is a materials constant, known as the skyrmion Hall angle. In magnetic multilayer systems, where skyrmions often appear individually, not arranging themselves in a lattice, this deflection angle can be easily measured by tracing the real space motion of individual skyrmions. Here we describe a reciprocal space technique which can be used to determine the skyrmion Hall angle in the skyrmion lattice state, leveraging the properties of the skyrmion lattice under a shear drive. We demonstrate this procedure to yield a quantitative measurement of the skyrmion Hall angle in the room-temperature skyrmion system FeGe, shearing the skyrmion lattice with the magnetic field gradient generated by a single turn Oersted wire. Skyrmions, when driven by any applied force, experience an addition sideways motion known as the skyrmion hall effect. Here, Brearton et al. present a reciprocal space method for determining the strength of the skyrmion hall effect, making measurement possible for skyrmion lattices.
Chiral singlet superconductivity in the weakly correlated metal LaPt3P
Chiral superconductors are novel topological materials with finite angular momentum Cooper pairs circulating around a unique chiral axis, thereby spontaneously breaking time-reversal symmetry. They are rather scarce and usually feature triplet pairing: a canonical example is the chiral p -wave state realized in the A -phase of superfluid He 3 . Chiral triplet superconductors are, however, topologically fragile with the corresponding gapless boundary modes only weakly protected against symmetry-preserving perturbations in contrast to their singlet counterparts. Using muon spin relaxation measurements, here we report that the weakly correlated pnictide compound LaPt 3 P has the two key features of a chiral superconductor: spontaneous magnetic fields inside the superconducting state indicating broken time-reversal symmetry and low temperature linear behaviour in the superfluid density indicating line nodes in the order parameter. Using symmetry analysis, first principles band structure calculation and mean-field theory, we unambiguously establish that the superconducting ground state of LaPt 3 P is a chiral d -wave singlet. Chiral superconductors are very rare topological materials. Here, the authors report spontaneous magnetic fields inside the superconducting state and low temperature linear behavior in the superfluid density in LaPt 3 P, suggesting a chiral d -wave singlet superconducting state.
Giant valley-Zeeman coupling in the surface layer of an intercalated transition metal dichalcogenide
Spin–valley locking is ubiquitous among transition metal dichalcogenides with local or global inversion asymmetry, in turn stabilizing properties such as Ising superconductivity, and opening routes towards ‘valleytronics’. The underlying valley–spin splitting is set by spin–orbit coupling but can be tuned via the application of external magnetic fields or through proximity coupling. However, only modest changes have been realized to date. Here, we investigate the electronic structure of the V-intercalated transition metal dichalcogenide V1/3NbS2 using microscopic-area spatially resolved and angle-resolved photoemission spectroscopy. Our measurements and corresponding density functional theory calculations reveal that the bulk magnetic order induces a giant valley-selective Ising coupling exceeding 50 meV in the surface NbS2 layer, equivalent to application of a ~250 T magnetic field. This energy scale is of comparable magnitude to the intrinsic spin–orbit splittings, and indicates how coupling of local magnetic moments to itinerant states of a transition metal dichalcogenide monolayer provides a powerful route to controlling their valley–spin splittings.The authors study the electronic structure of the intercalated transition metal dichalcogenide V1/3NbS2, showing that its bulk magnetism can lead to a strong tunability of spin–valley locked states at its surface.
Spin–valley locking in the normal state of a transition-metal dichalcogenide superconductor
Metallic transition-metal dichalcogenides (TMDCs) are benchmark systems for studying and controlling intertwined electronic orders in solids, with superconductivity developing from a charge-density wave state. The interplay between such phases is thought to play a critical role in the unconventional superconductivity of cuprates, Fe-based and heavy-fermion systems, yet even for the more moderately-correlated TMDCs, their nature and origins have proved controversial. Here, we study a prototypical example, 2H-NbSe 2 , by spin- and angle-resolved photoemission and first-principles theory. We find that the normal state, from which its hallmark collective phases emerge, is characterized by quasiparticles whose spin is locked to their valley pseudospin. This results from a combination of strong spin–orbit interactions and local inversion symmetry breaking, while interlayer coupling further drives a rich three-dimensional momentum dependence of the underlying Fermi-surface spin texture. These findings necessitate a re-investigation of the nature of charge order and superconducting pairing in NbSe 2 and related TMDCs. The origin of intertwined electronic orders in transition-metal dichalcogenides has long been debated. Here, Bawden et al . report that the normal state, from which these phases emerge, is unexpectedly spin-polarized, with spins locked to both valley and layer pseudospins.
YOLO glass: video-based smart object detection using squeeze and attention YOLO network
Visually impairments or blindness people need guidance in order to avoid collision risks with outdoor obstacles. Recently, technology has been proving its presence in all aspects of human life, and new devices provide assistance to humans on a daily basis. However, due to real-time dynamics or a lack of specialized knowledge, object detection confronts a reliability difficulty. To overcome the challenge, YOLO Glass a Video-based Smart object detection model has been proposed for visually impaired person to navigate effectively in indoor and outdoor environments. Initially the captured video is converted into key frames and pre-processed using Correlation Fusion-based disparity approach. The pre-processed images were augmented to prevent overfitting of the trained model. The proposed method uses an obstacle detection system based on a Squeeze and Attendant Block YOLO Network model (SAB-YOLO). A proposed system assists visually impaired users in detecting multiple objects and their locations relative to their line of sight, and alerts them by providing audio messages via headphones. The system assists blind and visually impaired people in managing their daily tasks and navigating their surroundings. The experimental results show that the proposed system improves accuracy by 98.99%, proving that it can accurately identify objects. The detection accuracy of the proposed method is 5.15%, 7.15% and 9.7% better that existing YOLO v6, YOLO v5 and YOLO v3, respectively.
Toggle-like current-induced Bloch point dynamics of 3D skyrmion strings in a room temperature nanowire
Research into practical applications of magnetic skyrmions, nanoscale solitons with interesting topological and transport properties, has traditionally focused on two dimensional (2D) thin-film systems. However, the recent observation of novel three dimensional (3D) skyrmion-like structures, such as hopfions, skyrmion strings (SkS), skyrmion bundles, and skyrmion braids, motivates the investigation of new designs, aiming to exploit the third spatial dimension for more compact and higher performance spintronic devices in 3D or curvilinear geometries. A crucial requirement of such device schemes is the control of the 3D magnetic structures via charge or spin currents, which has yet to be experimentally observed. In this work, we utilise real-space imaging to investigate the dynamics of a 3D SkS within a nanowire of Co 8 Zn 9 Mn 3 at room temperature. Utilising single current pulses, we demonstrate current-induced nucleation of a single SkS, and a toggle-like positional switching of an individual Bloch point at the end of a SkS. The observations highlight the possibility to locally manipulate 3D topological spin textures, opening up a range of design concepts for future 3D spintronic devices. In three dimensional systems with broken bulk inversion symmetry, skyrmions can form extended string-like structures. Here, Birch et al use scanning transmission x-ray microscopy to demonstrate the current induced generation and motion of these three dimensional skyrmion strings.
Visually impaired object segmentation and detection using hybrid Canny edge detector, Hough transform, and improved momentum search in YOLOv7
People with disabilities are now standardizing their lives with the advancement of Portable Assistive Technology (PAT). Among the physically challenged people, Visually Impaired People (VIP) undergo struggles to understand the perception of the surroundings, people, etc. In the outdoor, the challenge is perplex with the moving objects and barriers. The only solution for these is using object detection techniques to avert the barriers and to face the challenges in their routine life. In our work, we propose a novel, robust, economically efficient, simple, and handy solution with the assistance of smartphone. The objects can be captured with the aid of camera and segmented using the hybrid Canny Edge Detector and Hough Transform-based technique (HCED–HT) and detected with the robust Improved Momentum Search (IMS)-based YOLOv7. After detecting, the next step is to estimate the distance between the object and the VIPs and communicate to them using the audio devices or headphones. Simulations are demonstrated, and the outcomes are compared with existing approaches. Our proposed solution is the best to help the VIPs with accurate detection of objects, to provide information every now and then, and to do their daily routine without any fail.