Positron charge sensing using a double-gated graphene field effect transistor.

We utilize a high-mobility double-gated graphene field-effect transistor to measure the accumulated charge created by positron annihilation in its back-gate. The device consists of an exfoliated graphene flake stacked between two hexagonal boron nitride flakes placed on a 1 cm substrate of 500 μm thick conducting p-doped Si capped by 285 nm-thick SiO. The device is placed in close proximity to a 780 kBq Na positron source emitting a constant flux of positrons.

Spectroscopy of NbSe Using Energy-Tunable Defect-Embedded Quantum Dots.

Quantum dots have sharply defined energy levels, which can be used for high resolution energy spectroscopy when integrated in tunneling circuitry. Here we report dot-assisted spectroscopy measurements of the superconductor NbSe, using a van der Waals device consisting of a vertical stack of graphene-MoS-NbSe. The MoS tunnel barriers host naturally occurring defects which function as quantum dots, allowing transport via resonant tunneling.

Quantum coherence phenomenon in disordered BiSeTe topological single crystal: effect of annealing.

We report a comparative magnetotransport study on pristine and annealed BiSeTe single crystals. The pristine sample shows a metallic trend from 300 to 180 K, and an insulating behavior for T  <  180 K, whereas the annealed sample exhibits an insulating nature in the entire 4.2-300 K temperature range.

Magneto-transport behaviour of Bi2Se3-xTex : role of disorder.

Magneto-resistance and Hall resistance measurements have been carried out in fast-cooled single crystals of Bi2Se3-xTex (x  =  0 to 2) in 4-300 K temperature range, under magnetic fields up to 15 T. The variation of resistivity with temperature that points to a metallic behaviour in Bi2Se3, shows an up-turn at low temperatures in the Te doped samples. Magneto-resistance measurements in Bi2Se3 show clear signatures of Shubnikov-de Hass (SdH) oscillations that gets suppressed in the Te doped samples.

Pressure-induced structural changes and insulator-metal transition in layered bismuth triiodide, BiI3: a combined experimental and theoretical study.

Noting that BiI3 and the well-known topological insulator (TI) Bi2Se3 have the same high symmetry parent structures, and that it is desirable to find a wide-band gap TI, we determine here the effects of pressure on the structure, phonons and electronic properties of rhombohedral BiI3. We report a pressure-induced insulator-metal transition near 1.5 GPa, using high pressure electrical resistivity and Raman measurements.