compounds were synthesized by solid-state reaction. The samples were characterized by x-ray diffraction measurements and found to have the ZrCuSiAs crystal structure. Electrical resistivity and magnetic susceptibility measurements were performed on all of the samples and specific heat measurements were made on those with Ln = La, Ce, and Yb. All of these compounds exhibit superconductivity in the range 1.9 K -5.4 K, which has not previously been reported for the compounds based on Ce, Pr, and Yb. The YbO 0.5 F 0.5 BiS 2 compounds was also found to exhibit magnetic order at ~2.7 K that apparently coexists with superconductivity below 5.4 K.
nanometallic optical antennas are rapidly gaining popularity in applications that require exquisite control over light concentration and emission processes. The search is on for highperformance antennas that offer facile integration on chips. Here we demonstrate a new, easily fabricated optical antenna design that achieves an unprecedented level of control over fluorescent emission by combining concepts from plasmonics, radiative decay engineering and optical beaming. The antenna consists of a nanoscale plasmonic cavity filled with quantum dots coupled to a miniature grating structure that can be engineered to produce one or more highly collimated beams. Electromagnetic simulations and confocal microscopy were used to visualize the beaming process. The metals defining the plasmonic cavity can be utilized to electrically control the emission intensity and wavelength. These findings facilitate the realization of a new class of active optical antennas for use in new optical sources and a wide range of nanoscale optical spectroscopy applications.
Electrical resistivity measurements as a function of temperature between 1 K and 300 K were performed at various pressures up to 3 GPa on the superconducting layered compounds LnO0.5F0.5BiS2 (Ln = La, Ce). At atmospheric pressure, LaO0.5F0.5BiS2 and CeO0.5F0.5BiS2 have superconducting critical temperatures, Tc, of 3.3 K and 2.3 K, respectively. For both compounds, the superconducting critical temperature Tc initially increases, reaches a maximum value of 10.1 K for LaO0.5F0.5BiS2 and 6.7 K for CeO0.5F0.5BiS2, and then gradually decreases with increasing pressure. Both samples also exhibit transient behavior in the region between the lower Tc phase near atmospheric pressure and the higher Tc phase. This region is characterized by a broadening of the superconducting transition, in which Tc and the transition width ∆Tc are reversible with increasing and decreasing pressure. There is also an appreciable pressure-induced and hysteretic suppression of semiconducting behavior up to the pressure at which the maximum value of Tc is found. At pressures above the value at which the maximum in Tc occurs, there is a gradual decrease of Tc and further suppression of the semiconducting behavior with pressure, both of which are reversible.
We report a strategy to induce superconductivity in the BiS2-based compound LaOBiS2. Instead of substituting F for O, we increase the charge-carrier density (electron dope) via substitution of tetravalent Th +4 , Hf +4 , Zr +4 , and Ti +4 for trivalent La +3 . It is found that both the LaOBiS2 and ThOBiS2 parent compounds are bad metals and that superconductivity is induced by electron doping with Tc values of up to 2.85 K. The superconducting and normal states were characterized by electrical resistivity, magnetic susceptibility, and heat capacity measurements. We also demonstrate that reducing the charge-carrier density (hole doping) via substitution of divalent Sr +2 for La +3 does not induce superconductivity.
Abstract. Measurements of electrical resistivity were performed between 3 and 300 K at various pressures up to 2.8 GPa on the BiS 2 -based superconductors LnO 0.5 F 0.5 BiS 2 (Ln = Pr, Nd).At lower pressures, PrO 0.5 F 0.5 BiS 2 and NdO 0.5 F 0.5 BiS 2 exhibit superconductivity with critical temperatures T c of 3.5 and 3.9 K, respectively. As pressure is increased, both compounds undergo a transition at a pressure P t from a low T c superconducting phase to a high T c superconducting phase in which T c reaches maximum values of 7.6 and 6.4 K for PrO 0.5 F 0.5 BiS 2 and NdO 0.5 F 0.5 BiS 2 , respectively. The pressure-induced transition is characterized by a rapid increase in T c within a small range in pressure of ∼0.3 GPa for both compounds. In the normal state of PrO 0.5 F 0.5 BiS 2 , the transition pressure P t correlates with the pressure where the suppression of semiconducting behaviour saturates. In the normal state of NdO 0.5 F 0.5 BiS 2 , P t is coincident with a semiconductor-metal transition. This behaviour is similar to the results recently reported for the LnO 0.5 F 0.5 BiS 2 (Ln = La, Ce) compounds. We observe that P t and the size of the jump in T c between the two superconducting phases both scale with the lanthanide element in LnO 0.5 F 0.5 BiS 2 (Ln = La, Ce, Pr, Nd).
We report on violet-emitting III-nitride light-emitting diodes (LEDs) grown on bulk GaN substrates employing a flip-chip architecture. Device performance is optimized for operation at high current density and high temperature, by specific design consideration for the epitaxial layers, extraction efficiency, and electrical injection. The power conversion efficiency reaches a peak value of 84% at 85 °C and remains high at high current density, owing to low current-induced droop and low series resistance.
This work presents a novel method to introduce a sustainable biaxial tensile strain larger than 1% in a thin Ge membrane using a stressor layer integrated on a Si substrate. Raman spectroscopy confirms 1.13% strain and photoluminescence shows a direct band gap reduction of 100meV with enhanced light emission efficiency. Simulation results predict that a combination of 1.1% strain and heavy n(+) doping reduces the required injected carrier density for population inversion by over a factor of 60. We also present the first highly strained Ge photodetector, showing an excellent responsivity well beyond 1.6um.
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