We conduct a comprehensive study of three different magnetic semiconductors, CrI3, CrBr3, and CrCl3, by incorporating both few-and bi-layer samples in van der Waals tunnel junctions. We find that the interlayer magnetic ordering, exchange gap, magnetic anisotropy, as well as magnon excitations evolve systematically with changing halogen atom. By fitting to a spin wave theory that accounts for nearest neighbor exchange interactions, we are able to further determine a simple spin Hamiltonian describing all three systems. These results extend the 2D magnetism platform to Ising, Heisenberg, and XY spin classes in a single material family. Using magneto-optical measurements, we additionally demonstrate that ferromagnetism can be stabilized down to monolayer in more isotropic CrBr3, with transition temperature still close to that of the bulk.

We describe an experimental protocol to characterize magnetic field dependent microwave losses in superconducting niobium microstrip resonators. Our approach provides a unified view that covers two well-known magnetic field dependent loss mechanisms: quasiparticle generation and vortex motion. We find that quasiparticle generation is the dominant loss mechanism for parallel magnetic fields. For perpendicular fields, the dominant loss mechanism is vortex motion or switches from quasiparticle generation to vortex motion, depending on cooling procedures. In particular, we introduce a plot of the quality factor versus the resonance frequency as a general method for identifying the dominant loss mechanism. We calculate the expected resonance frequency and the quality factor as a function of the magnetic field by modeling the complex resistivity. Key parameters characterizing microwave loss are estimated from comparisons of the observed and expected resonator properties. Based on these key parameters, we find a niobium resonator whose thickness is similar to its penetration depth is the best choice for X-band electron spin resonance applications. Finally, we detect partial release of the Meissner current at the vortex penetration field, suggesting that the interaction between vortices and the Meissner current near the edges is essential to understand the magnetic field dependence of the resonator properties.

The giant planar Hall effect arising from a chiral anomaly, and that is related to the Berry curvature, has been predicted but never observed in nonmagnetic type-II Dirac/Weyl semimetals. Here, we report an observation of the anisotropic planar Hall effect in type-II Weyl semimetal WTe 2. Interestingly, we observe a chiral-anomaly-induced sinusoidal angular-dependent planar Hall effect when the electric field is parallel to the tilting direction of Weyl cone, i.e., the b axis of WTe 2. The planar Hall effect amplitude is linearly dependent on the magnetic fields and decreases gradually as the temperature increases across the topological phase transition temperature. Our observations clearly reveal the footprints on transport from the chiral anomaly feature in type-II Weyl semimetals.

We use both classical magnetotransport and quantum oscillation measurements to study the thickness evolution of the extremely large magnetoresistance (XMR) material and type-II Weyl semimetal candidate, -MoTe2, protected from oxidation. We find that the magnetoresistance is systematically suppressed with reduced thickness. This occurs concomitantly with both a decrease in carrier mobility and increase in electron-hole imbalance. We model the two effects separately and conclude that the XMR effect is more sensitive to the former. Main text:Among the layered transition metal dichalcogenides (TMDCs), MoTe2 is a unique member that crystallizes in both semiconducting 2H and semimetallic 1T-type structures, making it an appealing candidate for novel phase-changing electronics [1]. It has already been demonstrated, for example, that transitions between the two can be controlled by strain, alloying, and electrostatic gating [2][3][4][5][6]. The semimetal polytype itself is interesting and exhibits different phases. First, true 1T coordination is unstable as in-plane bond distortions dimerize the Mo atoms along the b-axis. Two stacking configurations of these distorted layers along the c-axis give rise to distinct three-dimensional (3D) structures: the centrosymmetric (or 1T') phase at high temperature (above ~250K) and the noncentrosymmetric (or Td) phase at low temperature, with the difference being only a ~4 ∘ tilt in the unit cell. The latter structure notably hosts type-II Weyl nodes [7-13] and exhibits extremely large magnetoresistance (XMR) below ~20K [14]. XMR materials may be useful for spintronics and sensing applications. While both -MoTe2 and -WTe2, a structurally similar compound, have been shown to demonstrate XMR [14,15], its origin in the former is under debate. Transport studies have attributed the cause to a close compensation of electron and hole concentrations at low temperature for both materials [16-19]; however, angle-resolved photoemission experiments report that MoTe2 remains uncompensated at all temperatures [20], in contrast to WTe2 [21]. One can directly test the effect of charge (un)compensation on XMR in MoTe2 by changing the relative carrier concentrations, but this is generally difficult to do in bulk systems without introducing unwanted disorder.Recently, several of the authors have shown that the phase is realized in thin MoTe2

Rec_ntprogress inan ongoing development programleading tothedesign ofsuperconducting continuouswave (ew) linear accelerators for. high-brightness ion beams is reviewed. A new spoke-resonator geometry haeorporating a half-wavelength resonant line was fabricated and tested. This geometry serves as the basis for the constituent cavities of a superconducting section being designed for high-current testing with a deuterium beam. Considerable progress has been made in the design of this section. A multi-phased program leading to the development of a superconducting radio-frequency quadrupole (SCRFQ) has been initiated. Design considerations and test results from the various activities are presented.