Superconductivity, pairing symmetry, and disorder in the doped topological insulator Sn_(1−x)In_xTe for x ≥ 0.10
Physical Review B
Jan 19, 2018
The temperature dependence of the London penetration depth Δλ(T) in the superconducting doped topological crystalline insulator Sn_(1−x)In_xTe was measured down to 450 mK for two different doping levels, x ≈ 0.45 (optimally doped) and x ≈ 0.10 (underdoped), bookending the range of cubic phase in the compound. The results indicate no deviation from fully gapped BCS-like behavior, eliminating several candidate unconventional gap structures. Critical field values below 1 K and other superconducting parameters are also presented. The introduction of disorder by repeated particle irradiation with 5 MeV protons does not enhance Tc, indicating that ferroelectric interactions do not compete with superconductivity.
Anisotropy and multiband superconductivity in Sr2RuO4 determined by small-angle neutron scattering studies of the vortex lattice
Physical Review B
Nov 14, 2017
Despite numerous studies the exact nature of the order parameter in superconducting Sr2RuO4 remains unresolved. We have extended previous small-angle neutron scattering studies of the vortex lattice in this material to a wider field range, higher temperatures, and with the field applied close to both the ⟨100⟩ and ⟨110⟩basal plane directions. Measurements at high field were made possible by the use of both spin polarization and analysis to improve the signal-to-noise ratio. Rotating the field towards the basal plane causes a distortion of the square vortex lattice observed for H∥⟨001⟩ and also a symmetry change to a distorted triangular symmetry for fields close to ⟨100⟩. The vortex lattice distortion allows us to determine the intrinsic superconducting anisotropy between the c axis and the Ru-O basal plane, yielding a value of ∼60 at low temperature and low to intermediate fields. This greatly exceeds the upper critical field anisotropy of ∼20 at low temperature, reminiscent of Pauli limiting. Indirect evidence for Pauli paramagnetic effects on the unpaired quasiparticles in the vortex cores are observed, but a direct detection lies below the measurement sensitivity. The superconducting anisotropy is found to be independent of temperature but increases for fields ≳1 T, indicating multiband superconductivity in Sr2RuO4. Finally, the temperature dependence of the scattered intensity provides further support for gap nodes or deep minima in the superconducting gap.
Metastability and hysteretic vortex pinning near the order-disorder transition in NbSe2 : Interplay between plastic and elastic energy barriers
Physical Review B
Mar 6, 2017
We studied thermal and dynamic history effects in the vortex lattice (VL) near the order-disorder transition in clean NbSe2 single crystals. Comparing the evolution of the effective vortex pinning and the bulk VL structure, we observed metastable superheated and supercooled VL configurations that coexist with a hysteretic effective pinning response due to thermal cycling of the system. A novel scenario, governed by the interplay between (lower) elastic and (higher) plastic energy barriers, is proposed as an explanation for our observations: Plastic barriers, which prevent the annihilation or creation of topological defects, require dynamic assistance to be overcome and to achieve a stable VL at each temperature. Conversely, thermal hysteresis in the pining response is ascribed to low energy barriers, which inhibit rearrangement within a single VL correlation volume and are easily overcome as the relative strength of competing interactions changes with temperature.
Measuring Intensity of Laser Light Penetrating Flight Decks in Laser Illuminations
Journal of Aviation Technology and Engineering
Oct 8, 2013
Since 2005, reported laser attacks from people on the ground directed towards arriving and departing aircraft have increased over 300%. A laser aimed at the windshield of an aircraft startles a pilot and may cause injury. This study determined empirical evidence of laser intensity in the flight deck and the potential for harm to the human eye at various distances. Results of this study revealed that relatively low-powered lasers had measured intensity levels through cockpit windshields at the 200 and 500 feet distances that may cause damage to crew members’ eyes according to standards established by the federal government. At longer distances of 1000, 1500, and 2000 feet, these same lasers did not reveal measured intensities at levels to cause damage to crew members’ eyes; however, they were considered as having potentially distracting visual effects in flight that were further categorized as temporary flash blindness, glare or disruption, and distraction or startle.