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ISSN: 2772-8307
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cited:3
Optimisation of pulsed laser deposited Ba1-xKxBiO3 thin films with tunable superconducting properties by control of K doping level, x
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Article Number:Article 100115
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Abstract
Corresponding email:jld35@cam.ac.uk
The mid-TC superconductor Ba1-XKXBiO3 (BKBO) exhibits different superconducting mechanisms depending on x, in the range ∼ 0.35–0.65. The optimal doping for the highest TC is reported to be around x = 0.4. To understand more about the dependence of the superconducting mechanism on x, high quality and reproducible epitaxial films with controlled x are needed. This has been challenging owing to the volatility of K and (to a lesser extent) Bi. In this work, we use pulsed laser deposition (PLD) with several novel process steps to achieve high-quality films in a reproducible way. These include a modified method for target preparation, a low NO2 growth pressure, and precise positioning of substrates in the PLD plume. Optimum TC films (32 K onset) were grown from an x = 0.4 target, i.e. with no excess K, as is normally used. Stable, higher K content films (made from an x = 0.45 target), were also grown. These x = 0.45 films had a lower TC (22.5 K onset), as expected for (K) overdoped films, with very high upper critical field, HC2 (0 K), and irreversibility field, Hirr (0 K), values, from linear extrapolation, of ∼ 31.7 T and ∼ 28.8 T, respectively. The growth methodology demonstrated in this work is highly beneficial for fundamental mechanistic studies of this complex superconductor on which there is renewed interest, and where controlled compositions and crystalline quality are currently limited.
cited:3
High performance rapid single-flux-quantum bit-slice arithmetic logic unit
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Article Number:Article 100116
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Abstract
Corresponding email:tangguangming@ict.ac.cn
Two optimization technologies, namely, bypass and carry-control optimization, were demonstrated for enhancing the performance of a bit-slice Arithmetic Logic Unit (ALU) in 2n-bit Rapid Single-Flux-Quantum (RSFQ) microprocessors. These technologies can not only shorten the calculation time but also solve data hazards. Among them, the proposed bypass technology is applicable to any 2n-bit ALU, whether it is bit-serial, bit-slice or bit-parallel. The high performance bit-slice ALU was implemented using the 6 kA/cm2 Nb/AlOx/Nb junction fabrication process from Superconducting Electronics Facility of Shanghai Institute of Microsystem and Information Technology. It consists of 1693 Josephson junctions with an area of 2.46 0.81 mm2. All ALU operations of the MIPS32 instruction set are implemented, including two extended instructions, i.e., addition with carry (ADDC) and subtraction with borrow (SUBB). All the ALU operations were successfully obtained in SFQ testing based on OCTOPUX and the measured DC bias current margin can reach 86 - 104. The ALU achieves a 100 utilization rate, regardless of carry/borrow read-after-write correlations between instructions.
cited:29
Numerical simulation of dynamic loss and total loss in the REBCO tapes under perpendicular AC magnetic fields up to 8 T at 20 K and 50 K
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Article Number:Article 100117
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Abstract
Corresponding email:tangguangming@ict.ac.cn
REBCO tapes carry DC current under AC magnetic fields in proposed HTS fusion applications. AC loss will be generated in the process and it is important to understand the AC loss behaviour for safe operation of the fusion magnets. In this work, magnetisation loss (Qm), dynamic resistance (Rdyn), and total loss (Qtotal) in four different REBCO tapes are numerically studied, using the measured and , for the magnetic field amplitude applied perpendicularly up to 8 T at 20 K and 50 K, where represents the magnetic field and field angle () dependent critical current density. The peak of Theva data is different from that of other tapes. We artificially shifted the ab-plane peak of Theva to the left by 25° to match the peak value. The newly shifted data is named as Theva-shift, which was also investigated to study the influence of the Theva peak shift on AC loss. The normalised DC transport current level (i = It/Ic0) ranges from 0.05 to 0.9, where the DC current amplitude and the self-critical current of the tape are represented by It and Ic0, respectively. The simulation results show that the AC losses deviate significantly from the Brandt-Indenbom (BI) equation at high magnetic fields. Jc and instantaneous loss curves for different tapes show correlation at high magnetic fields. The simulation results also show how different characteristics for different tapes influence AC losses. When AC loss values are scaled by the self-field critical current, Qm without current and Qtotal with current in the different tapes show a good agreement. It implies that the temperature dependence of the two types of loss can be calculated from a known loss at one temperature and the self-field critical current.
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