Superconducting quadrupole magnet R&D in the interaction region of CEPC

To obtain high luminosity, compact high gradient quadrupole magnets QD0 and QF1 are required on both sides of the interaction points of the proposed Circular Electron Positron Collider (CEPC). QD0 is a double aperture superconducting quadrupole closest to the interaction point with a crossing angle between two aperture centerlines of 33 mrad. Magnetic field crosstalk between two apertures of QD0 is negligible using iron yoke, and the 3D coil end is optimized by ROXIE. In the design study, both NbTi conductor and HTS conductor are taken into account. The first step of the R&D is to design and manufacture a QD0 short model magnet with a magnetic length of 0.5 m. In this paper, the R&D status of QD0 short model magnet is described, and the design study of quadrupole magnet including NbTi technology and HTS Bi-2212 technology is presented.

Crystallization of Bosonic Quantum Hall States

The dominance of interactions over kinetic energy lies at the heart of strongly correlated quantum matter, from fractional quantum Hall liquids, to atoms in optical lattices and twisted bilayer graphene. Crystalline phases often compete with correlated quantum liquids, and transitions between them occur when the energy cost of forming a density wave approaches zero. A prime example occurs for electrons in high magnetic fields, where the instability of quantum Hall liquids towards a Wigner crystal is heralded by a roton-like softening of density modulations at the magnetic length. Remarkably, interacting bosons in a gauge field are also expected to form analogous liquid and crystalline states. However, combining interactions with strong synthetic magnetic fields has been a challenge for experiments on bosonic quantum gases. Here, we study the purely interaction-driven dynamics of a Landau gauge Bose-Einstein condensate in and near the lowest Landau level. We observe a spontaneous crystallization driven by condensation of magneto-rotons, excitations visible as density modulations at the magnetic length. Increasing the cloud density smoothly connects this behaviour to a quantum version of the Kelvin-Helmholtz hydrodynamic instability, driven by the sheared internal flow profile of the rapidly rotating condensate. At long times the condensate self-organizes into a persistent array of droplets, separated by vortex streets, which are stabilized by a balance of interactions and effective magnetic forces.

Vertical conductivity of superlattice in longitudinal strong magnetic field with intraband and interband transitions

The influence of interband and intraband transitions on oscillations of the vertical conductivity of superlattices in a strong magnetic field is considered. It was found that for the charged impurity scattering intraband transitions dominate in magnetic fields up to 2 T, and with a further increase in the magnetic field, interband transitions control. The conductivity oscillations are determined by a ratio of the magnetic length to the superlattice period and the effective mass anisotropy.

Writing 3D Nanomagnets Using Focused Electron Beams

Focused electron beam induced deposition (FEBID) is a direct-write nanofabrication technique able to pattern three-dimensional magnetic nanostructures at resolutions comparable to the characteristic magnetic length scales. FEBID is thus a powerful tool for 3D nanomagnetism which enables unique fundamental studies involving complex 3D geometries, as well as nano-prototyping and specialized applications compatible with low throughputs. In this focused review, we discuss recent developments of this technique for applications in 3D nanomagnetism, namely the substantial progress on FEBID computational methods, and new routes followed to tune the magnetic properties of ferromagnetic FEBID materials. We also review a selection of recent works involving FEBID 3D nanostructures in areas such as scanning probe microscopy sensing, magnetic frustration phenomena, curvilinear magnetism, magnonics and fluxonics, offering a wide perspective of the important role FEBID is likely to have in the coming years in the study of new phenomena involving 3D magnetic nanostructures.

Real-Time Magnetic Length-Based Vehicle Classification: Case Study for Inductive Loops and Wireless Magnetometer Sensors in Oklahoma State

Providing reliable, real-time vehicle volume and classification information is vital for 21st century intelligent transportation systems (ITS). Large vehicles have a major impact on traffic flow, as well as road maintenance. Information about passenger car versus truck volume is crucial for all transportation agencies. The work presented here provides a comprehensive method to develop length-based vehicle classification (LBVC) techniques that could be implemented using inductive loops (IDL) or magnetometer sensors (MAG). Distinctive LBVC schemes were developed to bin vehicles into groups based on structural similarity and statistical characteristics. Data collection, including vehicle magnetic length (VML) estimates using IDL and MAG, was performed at different sites located on Oklahoma highways and rural roadways to capture various traffic characteristics. Video images were utilized as ground-truth for accurate data labeling. Extensive data analyses, including machine learning methods and probabilistic modeling, were conducted to define decision boundaries for developed LBVC schemes. Three scenarios were developed for determining optimal thresholding methods: total classification accuracy maximization, per-group classification error minimization, and equal classification error optimization. Evaluation revealed consistent and accurate performance for all developed schemes. Classification accuracies of 97.70% and 99.00% were reported using MAG and IDL, respectively. The developed classification models are computationally efficient and can provide real-time LBVC data. The models are intended to supplement or replace axle-based data collection methods used throughout Oklahoma. The methodology developed in this work will also benefit other states and territories interested in developing LBVC schemes.

Absence of effects of an in-plane magnetic field in a quasi-two-dimensional electron system

The dynamics of a quasi-two-dimensional electron system (q2DES) in the presence of a tilted magnetic field is reconsidered employing the thin-layer method. We derive the effective equations for relativistic and nonrelativistic q2DESs. Through a perturbative expansion, we show that while the magnetic length is much greater than the confinement width, the in-plane magnetic field only affects the particle dynamics through the spin. Therefore, effects due to an in-plane magnetic vector potential reported previously in the literature for 2D quantum rings, 2D quantum dots and graphene are fictitious. In particular, the so-called pseudo chiral magnetic effect recently proposed in graphene is not realistic.

Landau-level quantization of the yellow excitons in cuprous oxide

Lately, the yellow series of P -excitons in cuprous oxide could be resolved up to the principal quantum number n = 25. Adding a magnetic field, leads to additional confinement normal to the field. Thereby, the transition associated with the exciton n is transformed into the transition between the electron and hole Landau levels with quantum number n , once the associated magnetic length becomes smaller than the related exciton Bohr radius. The magnetic field of this transition scales roughly as n ^–3. As a consequence of the extended exciton series, we are able to observe Landau level transitions with unprecedented high quantum numbers of more than 75.

Stability of Anomalous States of a Local Potential in Graphene

Graphene Landau levels have discrete energies consisting zero energy chiral states and non-zero energy states with mixed chirality. Each Landau level splits into discrete energies when a localized potential is present. A simple scaling analysis suggests that a localized potential can act as a strong perturbation, and that it can be even more singular in graphene than in ordinary two-dimensional systems of massful electrons. Parabolic, Coulomb, and Gaussian potentials in graphene may have anomalous boundstates whose probability density has a sharp peak inside the potential and a broad peak of size magnetic length l outside the potential. The n = 0 Landau level with zero energy has only one anomalous state while the n = ±1 Landau levels with non-zero energy have two (integer quantum number n is related to the quantized Landau level energies). These anomalous states can provide a new magnetospectroscopic feature in impurity cyclotron resonances of graphene. In the present work we investigate quantitatively the conditions under which the anomalous states can exist. These results may provide a guide in searching for anomalous states experimentally.