| 1. |
- Bauch, Thilo, 1972, et al.
(författare)
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High critical temperature superconductor Josephson junctions for quantum circuit applications
- 2009
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Ingår i: Physica Scripta. ; T137, s. 014006-
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Konferensbidrag (refereegranskat)abstract
- Recent findings of macroscopic quantum properties in high critical temperature superconductor (HTS) Josephson junctions (JJs) point toward the need to revise the role of zero energy quasi-particles in this novel superconductor. We will discuss the possibility of designing superconducting artificial atoms in a transmon configuration to study the low energy excitation spectra of HTS. We have engineered high quality grain boundary JJs on low dielectric constant substrates. By fabricating submicron junctions, we extract values of capacitance and Josephson critical current densities that satisfy the main transmon design requirements. Moreover, the measured critical current noise power extrapolated at 1 Hz gives a dephasing time of 25 ns, which indicates that the observation of macroscopic quantum coherent effects in HTS JJ is a feasible task.
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| 2. |
- Cedergren, Karin, 1975, et al.
(författare)
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Biepitaxial YBa2Cu3O7-x 0-pi Josephson junctions
- 2010
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 23:3, s. Article Number: 034027-
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Tidskriftsartikel (refereegranskat)abstract
- We present measurements performed on YBa2Cu3O7-x '0' and '0-pi' Josephson junctions fabricated using the biepitaxial technique with SrTiO3 as substrate and CeO2 as seed layer. Measurements of the critical current as a function of external magnetic field clearly show complementary behavior of the two kinds of junctions. Our results unambiguously show that the d-wave nature of the order parameter dominates the current transport across the junctions despite the faceting on the microscale along the grain boundary line.
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| 3. |
- Bauch, Thilo, 1972, et al.
(författare)
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Dynamics of d-wave YBa2Cu3O7-x
- 2007
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Ingår i: Superconductor Science and Technology. - 0953-2048 .- 1361-6668. ; 20:2, s. S98-S104
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Konferensbidrag (refereegranskat)abstract
- The predominant d-wave pairing symmetry in high temperature superconductors leads to an unconventional current phase relation in Josephson junctions. This circumstance may induce new effects in the dynamics of dc SQUIDs. In this contribution we report on the measurements of the dependence of the SQUID Josephson current on the external magnetic field taken at very low temperatures, down to 20 mK. Different grain boundaries have been fabricated by using the biepitaxial and the bicrystal technique. Some of the effects which are induced by a nonsinusoidal current phase relation can be clearly identified in the dynamics of the SQUIDs. The experimental data are also compared with theoretical simulations taking into account the inductance of the loop. The data show that, in specific conditions, a non-negligible inductance of the loop can induce effects similar to an unconventional current phase relation, with a pronounced second harmonic sin(2) term. This fact has to be taken into account when designing d-wave SQUIDs for quantum circuitry.
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| 4. |
- Bauch, Thilo, 1972, et al.
(författare)
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YBCOSQUIDs with unconventional current phase relation
- 2007
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 463-465:1 October 2007, s. 979-984
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the dynamics of YBa2Cu3O7-delta,5 (YBCO) dc sperconducting quantum interference devices (SQUIDs) characterized by an unconventional Josephson current phase relation (CPR). We have focused on SQUID configurations with Josephson junctions where the lobe of the order parameter in one electrode is facing a node in the other electrode. This order parameter arrangement should enhance the appearance of a sin(2(p) term in the CPR. The response of the critical current of the dc SQUID, under the effect of an external magnetic field, has been measured in temperature, down to 20 mK. Our experimental data have been compared with numerical simulations of the SQUIDs dynamics by considering a CPR of a single junction of the form I(phi) = I-I sin(phi) - I-II sin(2 phi) where I-I, and I-II are, respectively, the first and second harmonic component. In our devices the values of the sin(2 phi) term are such that the fundamental state of the SQUID is naturally double degenerate. This is of great relevance for applications of d-wave SQUIDs in quantum information processing. (C) 2007 Elsevier B.V. All rights reserved.
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| 5. |
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| 6. |
- Cedergren, Karin, 1975, et al.
(författare)
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Interplay between Static and Dynamic Properties of Semifluxons in YBa2Cu3O7−δ 0−π Josephson Junctions
- 2010
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 104:17, s. 177003 -
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the static and dynamic properties of long YBa2Cu3O7-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.
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| 7. |
- He, Hans, et al.
(författare)
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Accurate graphene quantum Hall arrays for the new International System of Units
- 2022
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Ingår i: Nature Communications. - : Nature Research. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- 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 IC ~ 100 μA. Here we present experiments on quantization accuracy of a 236-element quantum Hall array (QHA), demonstrating RK/236 ≈ 109 Ω with 0.2 part-per-billion (nΩ/Ω) accuracy with IC ≥ 5 mA (~1 nΩ/Ω accuracy for IC = 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).
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| 8. |
- He, Hans, et al.
(författare)
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Polymer-encapsulated molecular doped epigraphene for quantum resistance metrology
- 2019
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Ingår i: Metrologia. - : Institute of Physics Publishing. - 0026-1394 .- 1681-7575. ; 56:4
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Tidskriftsartikel (refereegranskat)abstract
- One of the aspirations of quantum metrology is to deliver primary standards directly to end-users thereby significantly shortening the traceability chains and enabling more accurate products. Epitaxial graphene grown on silicon carbide (epigraphene) is known to be a viable candidate for a primary realisation of a quantum Hall resistance standard, surpassing conventional semiconductor two-dimensional electron gases, such as those based on GaAs, in terms of performance at higher temperatures and lower magnetic fields. The bottleneck in the realisation of a turn-key quantum resistance standard requiring minimum user intervention has so far been the need to fine-tune the carrier density in this material to fit the constraints imposed by a simple cryo-magnetic system. Previously demonstrated methods, such as via photo-chemistry or corona discharge, require application prior to every cool-down as well as specialist knowledge and equipment. To this end we perform metrological evaluation of epigraphene with carrier density tuned by a recently reported permanent molecular doping technique. Measurements at two National Metrology Institutes confirm accurate resistance quantisation below 5n-1. Furthermore, samples show no significant drift in carrier concentration and performance on multiple thermal cycles over three years. This development paves the way for dissemination of primary resistance standards based on epigraphene
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| 9. |
- Johansson, Jesper, 1979, et al.
(författare)
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Properties of inductance and magnetic penetration depth in (103)-oriented YBa2Cu3O7-delta thin films
- 2009
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 79:21, s. 214513-
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Tidskriftsartikel (refereegranskat)abstract
- We present a study of the anisotropy of the inductance in (103) YBa2Cu3O7-delta (YBCO) films. YBCO superconducting quantum interference devices (SQUIDs) were fabricated by the biepitaxial technique. SQUIDs with (001)- and (103)-oriented YBCO electrodes characterized by different grain-boundary angles were realized on the same chip. Two extrainjection lines were attached to the (103) YBCO electrode. These devices, when operated in current injection mode, allow us to measure the inductance of the (103) YBCO electrode. We have found that the inductance L of the (103) YBCO can differ by a factor of 20 in the two extreme cases: L determined by current transport parallel to the ab planes and L dominated by the transport in the c-axis direction. The full in-plane angular dependence of the inductance has been obtained by considering geometrically identical SQUIDs oriented with different angles with respect to the [100] direction of the (103) film. From these measurements, we have determined the London penetration depths in the ab direction lambda(ab) and the c direction lambda(c) and their temperature dependence.
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| 10. |
- Lara Avila, Samuel, 1983, et al.
(författare)
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Disordered Fermi Liquid in Epitaxial Graphene from Quantum Transport Measurements
- 2011
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 107:16, s. 166602-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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