Vortex pinning in Au-irradiated FeSe0.4Te0.6 crystals from the static limit to gigahertz frequencies

Fe(Se,Te) is one of the simplest compounds of iron-based superconductors, but it shows a variety of vortex pinning phenomena both in thin-film and single-crystal forms. These properties are particularly important in light of its potential for applications ranging from the development of coated conductors for high-field magnets to topological quantum computation exploiting the Majorana particles found in the superconducting vortex cores. In this paper, we characterize the pinning properties of FeSe 0.4 Te 0.6 single crystals, both pristine and Au-irradiated, with a set of characterization techniques ranging from the static limit to the GHz frequency range by using dc magnetometry, ac susceptibility measurements of both the fundamental and the third harmonic signals, and by microwave coplanar waveguide resonator measurements of London and Campbell penetration depths. We observed signatures of single vortex pinning that can be modeled by a parabolic pinning potential, dissipation caused by flux creep, and a general enhancement of the critical current density after 320 MeV Au ion irradiation

Modification of intergrain connectivity, upper critical field anisotropy, and critical current density in ion irradiated MgB2 films

We study the effect of 100 MeV Silicon and 200 MeV Gold ion irradiation on the inter and intra grain properties of superconducting thin films of Magnesium Diboride. Substantial decrease in inter-grain connectivity is observed, depending on irradiation dose and type of ions used. We establish that modification of sigma band scattering mechanism, and consequently the upper critical field and anisotropy, depends on the size and directional properties of the extrinsic defects. Post heavy ion irradiation, the upper critical field shows enhancement at a defect density that is five orders of magnitude less compared to neutron irradiation. The critical current density however is best improved through light ion irradiation.Comment: 18 pages, 4 figures, submitte

Josephson Plasma Resonance in Bi2Sr2CaCu2O8+yBi_2 Sr_2 Ca Cu_2 O_{8+y} with Spatially Dependent Interlayer-Phase Coherence

We study the Josephson plasma resonance (JPR) in Bi$_2$Sr$_2$CaCu$_2$O$_{8+y}$ (BSCCO) with spatially dependent interlayer-phase coherence (IPC). The half-irradiated BSCCO (HI-BSCCO), in which columnar defects are introduced only in a half of the sample, shows several resonance peaks, which are not simple superposition of the peaks in irradiated- and pristine-parts. JPR in HI-BSCCO changes its character from irradiated- to pristine-type at a crossover frequency ($\omega_{cr}$). We demonstrate that the one-dimensional \LSGE, which takes into account the spatial dependence of IPC, can reproduce most of the experimental findings including the presence of $\omega_{cr}$.Comment: 4 figure

Sub-Arcsecond Imaging of 3C123:108-GHz Continuum Observations of the Radio Hotspots

We present the results of sub-arcsecond 108 GHz continuum interferometric observations toward the radio luminous galaxy 3C123. Using multi-array observations, we utilize the high u,v dynamic range of the BIMA millimeter array to sample fully spatial scales ranging from 0.5" to 50". This allows us to make one-to-one comparisons of millimeter-wavelength emission in the radio lobes and hotspots to VLA centimeter observations at 1.4, 4.9, 8.4, and 15 GHz. At 108 GHz, the bright, eastern double hotspot in the southern lobe is resolved. This is only the second time that a multiple hotspot region has been resolved in the millimeter regime. We model the synchrotron spectra of the hotspots and radio lobes using simple broken power-law models with high energy cutoffs, and discuss the hotspot spectra and their implications for models of multiple hotspot formation.Comment: 16 pages, 3 Figures, ApJ Accepte

Gamma-Ray Spectroscopy of Λ16^{16}_\LambdaO and Λ15^{15}_\LambdaN Hypernuclei via the 16^{16}O(K−,π−)(K^-, \pi^-) reaction

he bound-state level structures of the $^{16}_{\Lambda}$O and $^{15}_{\Lambda}$N hypernuclei were studied by $\gamma$-ray spectroscopy using a germanium detector array (Hyperball) via the $^{16}$O ($K^-, \pi^- \gamma$) reaction. A level scheme for $^{16}_{\Lambda}$O was determined from the observation of three $\gamma$-ray transitions from the doublet of states ($2^-$,$1^-$) at $\sim 6.7$ MeV to the ground-state doublet ($1^-$,$0^-$). The $^{15}_{\Lambda}$N hypernuclei were produced via proton emission from unbound states in $^{16}_{\Lambda}$O . Three $\gamma$ -rays were observed and the lifetime of the $1/2^+;1$ state in $^{15}_{\Lambda}$N was measured by the Doppler shift attenuation method. By comparing the experimental results with shell-model calculations, the spin-dependence of the $\Lambda N$ interaction is discussed. In particular, the measured $^{16}_{\Lambda}$O ground-state doublet spacing of 26.4 $\pm$ 1.6 $\pm$ 0.5 keV determines a small but nonzero strength of the $\Lambda N$ tensor interaction.Comment: 22 pages, 17 figure