Classifying induced superconductivity in atomically thin Dirac-cone materials

Recently, Kayyalha et al. (2019 Phys. Rev. Lett. 122 047003) reported on anomalous enhancement of the self-field critical currents, Ic(sf,T), at low temperatures in Nb/BiSbTeSe2-nanoribbon/Nb Josephson junctions. The enhancement was attributed to the low-energy Andreev bound states arising from winding of the electronic wave function around the circumference of the topological insulator BiSbTeSe2 nanoribbon. In this paper, we show that identical enhancement in Ic(sf,T) and in the upper critical field, Bc2(T), at approximately same reduced temperatures, were reported by several research groups in atomically thin junctions based on a variety of Dirac-cone materials (DCM) earlier. Our analysis shows that in all these S/DCM/S systems the enhancement is due to a new superconducting band opening. Taking in account that several intrinsic superconductors also exhibit the effect of new superconducting band(s) opening when sample thickness becomes thinner than the ground state out-of-plane coherence length, we strength our previous proposal that there is a new phenomenon of additional superconducting band(s) opening in atomically thin films.Comment: 13 pages, 5 figure

Electric Discharge Caused by Expanding Armatures in Flux Compression Generators

In this letter, we experimentally demonstrate that explosively driven expansion of metallic armature of the magnetic flux compression generator (FCG) plays a dominant role in the formation of plasma and electric discharge initiation inside the FCG

Note: Autonomous Pulsed Power Generator Based on Transverse Shock Wave Depolarization of Ferroelectric Ceramics

Autonomous pulsed generators utilizing transverse shock wave depolarization (shock front propagates across the polarization vector P0) of Pb(Zr0.52Ti0.48)O3 poled piezoelectric ceramics were designed, constructed, and experimentally tested. It was demonstrated that generators having total volume of 50 cm3 were capable of producing the output voltage pulses with amplitude up to 43 kV with pulse duration 4 µs. A comparison of high-voltage operation of transverse and longitudinal shock wave ferroelectric generators is given

Pulse Charging of Capacitor Bank by Explosive-Driven Shock Wave Ferroelectric Generator

Ultracompact explosive-driven shock wave ferroelectric generators (FEGs) were used as autonomous primary power sources for charging capacitor banks of different capacitance. The FEGs utilized longitudinal (when the shock wave propagates along the polarization vector P) shock wave depolarization of Pb(Zr52Ti48)O3 (PZT) polycrystalline ferroelectric ceramic. PZT disks having diameters ranging from 25 to 27 mm and three different thicknesses: 0.65, 2.1, and 5.1 mm. It was experimentally shown that during the charging process the FEGs were capable of producing pulsed power with peak amplitudes up to 0.3 MW. Results for charging voltage, electric charge transfer and energy transfer from the FEGs to the capacitor banks of capacitances CL = 2.25, 4.5, 9.0, 18.0, and 36.0 nF are presented. Analysis of the experimental data shows that the maximum energy transfer from the FEG to the capacitor bank differs for each type of ferroelectric energy-carrying element, and is dependent upon the capacitance of the capacitor banks

Transverse Explosive Shock-Wave Compression of Nd₂Fe₁₄B High-Energy Hard Ferromagnets: Induced Magnetic Phase Transition

Investigations of the magnetic phase state of Nd2Fe14B high-energy hard ferromagnets under the action of an explosive shock wave traveling across the magnetization vector, M, have been performed. We demonstrate that the transverse shock-wave compression of an Nd2Fe14B hard ferromagnet with pressure at the shock wave front of P = 22.3 GPa causes a hard ferromagnet — to — weak magnet phase transition. Due to this phase transition, the magnetostatic energy stored for an indefinite period of time in the Nd2Fe14B ferromagnet is released within a short time interval and can be transformed into pulsed primary power. Based on this effect we have developed a new type of ultracompact (volumes from 9 to 50 cm3) autonomous explosive-driven source of primary power that is capable of powering a magnetic flux compression generator with current up to 4 kA, and of charging high-voltage Arkadiev-Marx type generator capacitor banks

High Voltage Charging of a Capacitor Bank

We have demonstrated the feasibility of charging a capacitor bank to a high voltage using an autonomous ultra-compact explosively driven source of prime power. The prime power source is a longitudinally driven shock wave depolarization of a ferroelectric ceramic. The energy-carrying elements of the shock wave ferroelectric generators (FEGs) were poled Pb(Zr52Ti48)O3 polycrystalline ceramic disks with 0.35 cm3 volume. FEGs charged 9 nF, 18 nF, and 36 nF capacitor banks and provided pulsed-power with peak amplitudes up to 0.29 MW. The maximum efficiency of electric charge transfer from shocked Pb(Zr52Ti48)O3 elements to a capacitor bank was 46%. We demonstrated experimentally that the FEG-capacitor bank system can perform as an oscillatory circuit. A methodology was developed for numerical simulation of the operation of the FEG-capacitor bank system; the simulation results were in a good agreement with the experimental results

Transformer-Type Seeding System of a Helical FCG Based on a Transverse Shock Wave Ferromagnetic Generator

A new application of the effect of transverse-shock-wave demagnetization of Nd2Fe14B high-energy hard ferromagnets for powering an explosive-driven helical flux compression generator (FCG) is proposed. The novel FCG seeding system based on a compact transverse shock-wave ferromagnetic generator (FMG) containing a 200-cm3 Nd2Fe14B energy-carrying element and a 12 g high explosive charge was designed, constructed, and tested. The proposed design is based on the idea that the wide coaxial single-turn pulse-generating coil of the FMG can simultaneously serve as a seed coil for the FCG. The coaxial single-turn pulse-generating coil of the FMG was wound on the initial part of the FCG helix; therefore, only transformer coupling existed between the pulse-generating system of the FMG and the helix of the FCG. This seeding system provides up to 180 A current amplitude and 55 mus current pulse duration to a helical FCG

Explosive-Driven Mini-System Based on Shock Wave Ferromagnetic Seed Source and Loop Magnetic Flux Compression Generator

Completely explosive pulsed power mini-systems based on the transverse shock wave ferromagnetic generator (FMG) served as a seed source and loop magnetic flux compression generator (LFCG) as a pulsed power amplifier were proposed, designed, built and tested. The physical principles and design of the developed FMG-LFCG system are described in detail. Experimental data are presented for the explosive operation and electrical performance of the system

New Concept for Constructing an Autonomous Completely Explosive Pulsed Power System: Transverse Shock Wave Ferromagnetic Primary Power Source and Loop Flux Compression Amplifier

A new design idea for a compact, autonomous, completely explosive pulsed power system is proposed. The system is based on the shock wave ferromagnetic generator (FMG) as a primary power source and a loop magnetic flux compression generator (LFCG) as a pulsed power amplifier. The FMG primary power source utilizes the effect of transverse shock wave demagnetization of Nd2Fe14B high-energy hard ferromagnets to produce the seed current. Results are presented of an experimental study and digital simulation of operation of the FMG-LFCG syste