| 51. |
- Greibe, Tine, 1974, et al.
(författare)
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Improvement of chip design to reduce resonances in subgap regime of Josephson junctions
- 2009
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 150, s. 052063-
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Konferensbidrag (refereegranskat)abstract
- Excess current peaks in the IV curves of SIS Josephson junctions have been observed by some groups [1–3]. These peaks have the shape of a resonance as a function of voltage. The resonances appear in the subgap regime of the junctions and the subgap current (leakage current) is concealed. The positions of the resonances do not change as a magnetic field is applied to the junctions, but their amplitude decreases when the supercurrent is suppressed. We have measured the subgap current of Al/AlOx/Al junctions and we show that these resonances are due to resonant modes in the chip design which are excited by the ac-Josephson effect. We present a chip design that decreases the amplitude of the resonances to a such degree that the subgap current is quantifiable.
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| 52. |
- Gustafsson, David, 1982, et al.
(författare)
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Fully gapped superconductivity in a nanometresize YBa2Cu3O7-delta island enhanced by a magnetic field
- 2013
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Ingår i: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3387 .- 1748-3395. ; 8:1, s. 25-30
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Tidskriftsartikel (refereegranskat)abstract
- The symmetry of Cooper pairs is central to constructing a superconducting state. The demonstration of a d(x2-y2)-wave order parameter with nodes represented a breakthrough for high critical temperature superconductors (HTSs)(1,2). However, despite this fundamental discovery, the origin of superconductivity remains elusive, raising the question of whether something is missing from the global picture. Deviations from d(x2-y2)-wave symmetry(3,4), such as an imaginary admixture d(x2-y2) + is (or id(xy)), predict a ground state with unconventional properties exhibiting a full superconducting gap and time reversal symmetry breaking(5). The existence of such a state, until now highly controversial(6-10), can be proved by highly sensitive measurements of the excitation spectrum. Here, we present a spectroscopic technique based on an HTS nanoscale device that allows an unprecedented energy resolution thanks to Coulomb blockade effects, a regime practically inaccessible in these materials previously. We find that the energy required to add an extra electron depends on the parity (odd/even) of the excess electrons on the island and increases with magnetic field. This is inconsistent with a pure d(x2-y2)-wave symmetry and demonstrates a complex order parameter component that needs to be incorporated into any theoretical model of HTS.
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| 53. |
- Gustafsson, David, 1982, et al.
(författare)
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Low capacitance HTS junctions for single electron transistors
- 2009
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 470:SUPPL.1, s. S188-S190
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Konferensbidrag (refereegranskat)abstract
- We have fabricated and characterized YBa2Cu3O7-δ grain boundary junctions to determine their feasibility as tunnel barriers in single electron transistors. Superconducting quantum interference devices with injection lines have been used to measure the junctions capacitance. We have extracted capacitance values which allow us to achieve a Coulomb blockade regime for sufficiently small junction dimensions.
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| 54. |
- Gustafsson, David, 1982, et al.
(författare)
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Noise properties of nanoscale YBa2Cu3O7- δ Josephson junctions
- 2011
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 84:18
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Tidskriftsartikel (refereegranskat)abstract
- We present electric noise measurements of nanoscale biepitaxial YBa(2)Cu(3)O(7-delta) (YBCO) Josephson junctions fabricated by two different lithographic methods. The first (conventional) technique defines the junctions directly by ion milling etching through an amorphous carbon mask. The second (soft patterning) method makes use of the phase competition between the superconducting YBCO (Y123) and the insulating Y(2)BaCuO(5) (Y211) phase at the grain boundary interface on MgO (110) substrates. The voltage noise properties of the two methods are compared in this study. For all junctions (having a thickness of 100 nm and widths of 250-500 nm), we see a significant amount of individual charge traps. We have extracted an approximate value for the effective area of the charge traps from the noise data. From the noise measurements, we infer that the soft-patterned junctions with a grain-boundary (GB) interface manifesting a large c-axis tunneling component have a uniform barrier and a superconductor-insulator-superconductor (SIS) -like behavior. The noise properties of soft-patterned junctions having a GB interface dominated by transport parallel to the ab planes are in accordance with a resonant tunneling barrier model. The conventionally patterned junctions, instead, have suppressed superconducting transport channels with an area much less than the nominal junction area. These findings are important for the implementation of nanosized Josephson junctions in quantum circuits.
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| 55. |
- Gustafsson, David, 1982, et al.
(författare)
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Soft Nanostructuring of YBCO Josephson Junctions by Phase Separation
- 2010
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:12, s. 4824-4829
-
Tidskriftsartikel (refereegranskat)abstract
- We have developed a new method to fabricate biepitaxial YBa2Cu3O7-delta (YBCO) Josephson junctions at the nanoscale allowing junctions widths down to 100 nm and simultaneously avoiding the typical damage in grain boundary interfaces due to conventional patterning procedures By using the competition between the superconducting YBCO and the insulating Y-2 BaCuO5 phases during film growth we formed nanometer sized grain boundary junctions in the insulating Y2BaCuO5 matrix as confirmed by high resolution transmission electron microscopy Electrical transport measurements give clear indications that we are close to probing the intrinsic properties of the grain boundaries.
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| 56. |
- Gutierrez Latorre, Martí, 1993, et al.
(författare)
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Superconducting Microsphere Magnetically Levitated in an Anharmonic Potential with Integrated Magnetic Readout
- 2023
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Ingår i: Physical Review Applied. - 2331-7019. ; 19:5
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Tidskriftsartikel (refereegranskat)abstract
- Magnetically levitated superconducting microparticles offer a promising path to quantum experiments with picogram to microgram objects. In this work, we levitate a 700 ng∼1017amu superconducting microsphere in a magnetic chip trap in which detection is integrated. We measure the center-of-mass motion of the particle using a dc superconducting quantum interference device magnetometer. The trap frequencies are continuously tunable between 30 and 160 Hz and the particle remains stably trapped over days in a dilution-refrigerator environment. We characterize the motional-amplitude-dependent frequency shifts, which arise from trap anharmonicities, namely, Duffing nonlinearities and mode couplings. We explain this nonlinear behavior using finite-element modeling of the chip-based trap potential. This work may constitute a first step toward quantum experiments and ultrasensitive inertial sensors with magnetically levitated superconducting microparticles.
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| 57. |
- Harrysson Rodrigues, Isabel, 1993, et al.
(författare)
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Angular Dependence of InP High Electron Mobility Transistors for Cryogenic Low Noise Amplifiers under a magnetic field
- 2019
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Ingår i: IIS UTokyo SYMPOSIUM No.100.
-
Konferensbidrag (refereegranskat)abstract
- This work addresses the angular dependence of DC properties in 100nm InP HEMT devices under the influence of applied static magnetic field at 2 K. When kept at an angle 90o towards a magnetic field of 14 T, the maximum output drain current Ids was reduced more than 99 %. A rotation sweep of the transistor revealed a strong angular and B-field dependence on Ids. This was correlated with a reduction in dc transconductance and increase in on-resistance of the transistor. The RF properties of the transistor were tested by measuring an 0.3-14 GHz InP HEMT MMIC low-noise amplifier (LNA) at 2 K kept at an angle 90o towards a magnetic field up to 10 T. The gain and noise temperature were strongly decreased and increased, respectively, already below 1 T. The results show that precise alignment of the cryogenic InP HEMT LNA is crucial in a magnetic field. Even a slight mis-orientation of a few degrees leads to a strong degradation of the gain and noise temperature.
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| 58. |
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| 59. |
- Harrysson Rodrigues, Isabel, 1993, et al.
(författare)
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On the angular dependence of InP high electron mobility transistors for cryogenic low noise amplifiers in a magnetic field
- 2019
-
Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 9:8
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Tidskriftsartikel (refereegranskat)abstract
- The InGaAs-InAlAs-InP high electron mobility transistor (InP HEMT) is the preferred active device used in a cryogenic low noise amplifier (LNA) for sensitive detection of microwave signals. We have investigated the angular dependence of the InP HEMT when oriented in a magnetic field at 2 K ambient temperature up to 14 T. A sharp angular dependence as a function of the magnetic field was measured for the output current of the InP HEMT. This was accurately described by a geometrical magnetoresistance expression for all angles and magnetic field strengths. Key device parameters such as transconductance and on-resistance were significantly affected at small angles and magnetic fields. The strong angular dependence of the InP HEMT output current in a magnetic field has important implications for the alignment of cryogenic LNAs in microwave detection experiments involving magnetic fields. This work was performed in GigaHertz Centre in a joint research project between Chalmers University of Technology, Low Noise Factory AB, Wasa Millimeter Wave AB, Omnisys Instruments AB and RISE Research Institutes of Sweden. We are grateful to Serguei Cherednichenko for valuable assistance in the noise measurements and Niklas Wadefalk for the LNA design.
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| 60. |
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