Search

Graphene quantum Hall effect (QHE) resistance standards have the potential to provide superior realizations of three key units in the new International System of Units (SI): the ohm, the ampere, and the kilogram (Kibble Balance). However, these prospects require different resistance values than practically achievable in single graphene devices (~12.9 kΩ), and they need bias currents two orders of magnitude higher than typical breakdown currents I C  ~ 100 μA. Here we present experiments on quantization accuracy of a 236-element quantum Hall array (QHA), demonstrating R K /236 ≈ 109 Ω with 0.2 part-per-billion (nΩ/Ω) accuracy with I C  ≥ 5 mA (~1 nΩ/Ω accuracy for I C  = 8.5 mA), using epitaxial graphene on silicon carbide (epigraphene). The array accuracy, comparable to the most precise universality tests of QHE, together with the scalability and reliability of this approach, pave the road for wider use of graphene in the new SI and beyond., (© 2022. The Author(s).)

Documenting effectiveness of ADHD medication is essential throughout the course of treatment. A rating scale and a continuous performance test (CPT) with motion tracking were used to study the effect of ADHD medication including compliance during one year. Children (N = 78, age 6-18 years) with ADHD were tested with the QbTest at baseline, visit 1 (1 month after baseline) and visit 5 (12 months after baseline). The ADHD-Rating scale was rated by investigator interview at the same visits. QbTest results and ADHD-RS ratings showed reductions in symptoms on all cardinal parameters of the QbTest and on all ADHD-RS subscales between baseline and 1 month and between baseline and 12 months. There was a weak but significant correlation between the total change scores on the two measures from baseline to 1 month. Eighteen participants dropped out of the study before visit 5; at baseline, these children showed significantly lower results on the inattention parameter of the QbTest, with faster reaction time and lower variation in reaction time, suggesting they suffered less problems with inattention. Both the QbTest and the ADHD-RS showed robust ADHD symptom improvements indicative of medication effect, and the QbTest results might also predict non-compliance of medication. Further research is warranted to increase knowledge about reliable monitoring of long-term medication and compliance., (© 2021. The Author(s).)

Objective: Long-term effects of ADHD medication on cognitive functions are not well known. This study investigates development of cognitive functions and ADHD symptoms on well-controlled medication for 1 year in children and adolescents., Study Design: This study is part of an ongoing open uncontrolled trial of long-term medication for ADHD in children and adolescents aged 6-18 years with any form of ADHD, and frequently comorbid autism spectrum disorder (ASD, 29%) or autistic traits (24%). Other comorbidities were oppositional defiant disorder, dyslexia/language disorder, borderline intellectual functioning, developmental coordination disorder. This analysis includes 87 participants (61 boys, 26 girls) who completed Wechsler tests at baseline and after 12 months. ADHD symptoms were investigator-rated on the ADHD Rating Scale-IV at the same time points., Results: The whole group of children and adolescents showed significant improvements in Wechsler Full Scale IQ (FSIQ, mean at baseline 92.6, at 12 months 97.95), and on the Index Scales Verbal Comprehension, Working Memory and Processing Speed, after one year of well-controlled ADHD medication. Comorbid dyslexia/language impairment predicted a larger rise in FSIQ, but not gender, ADHD presentation or comorbid ASD. Robust improvements in ADHD symptoms were observed (mean ADHD-Rating Scale score at baseline 34.6, and at 12 months 18.3)., Conclusions: Cognitive test scores and ADHD symptoms were improved on well-controlled medication for 1 year in children and adolescents with ADHD, autism and other comorbidities. The main study limitation is the open uncontrolled trial design., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Quantum physics in one spatial dimension is remarkably rich, yet even with strong interactions and disorder, surprisingly tractable. This is due to the fact that the low-energy physics of nearly all one-dimensional systems can be cast in terms of the Luttinger liquid, a key concept that parallels that of the Fermi liquid in higher dimensions. Although there have been many theoretical proposals to use linear chains and ladders of Josephson junctions to create novel quantum phases and devices, only modest progress has been made experimentally. One major roadblock has been understanding the role of disorder in such systems. We present experimental results that establish the insulating state of linear chains of submicron Josephson junctions as Luttinger liquids pinned by random offset charges, providing a one-dimensional implementation of the Bose glass, strongly validating the quantum many-body theory of one-dimensional disordered systems. The ubiquity of such an electronic glass in Josephson-junction chains has important implications for their proposed use as a fundamental current standard, which is based on synchronization of coherent tunneling of flux quanta (quantum phase slips).

We have performed magnetotransport measurements on monolayer epitaxial graphene and analyzed them in the framework of the disordered Fermi liquid theory. We have separated the electron-electron and weak-localization contributions to resistivity and demonstrated the phase coherence over a micrometer length scale, setting the limit of at least 50 ps on the spin relaxation time in this material.

We have investigated the static and dynamic properties of long YBa2Cu3O(7-delta) 0-pi Josephson junctions and compared them with those of conventional 0 junctions. Scanning SQUID microscope imaging has revealed the presence of a semifluxon at the phase discontinuity point in 0-pi Josephson junctions. Zero field steps have been detected in the current-voltage characteristics of all junctions. Comparison with simulation allows us to attribute these steps to fluxons traveling in the junction for conventional 0 junctions and to fluxon-semifluxon interactions in the case of 0-pi Josephson junctions.