The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Willem J. Perold - One of the best experts on this subject based on the ideXlab platform.
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A novel buffered high-Tc superconducting Step-edge Josephson junction
Superconductor Science and Technology, 2007Co-Authors: W F Van Staden, Ulrich Buttner, V V Srinivasu, Willem J. PeroldAbstract:A novel high-Tc superconducting (HTS) buffered Step-edge Josephson junction is fabricated. A 250 nm PrBa2Cu3O7 (PBCO) layer was epitaxially grown on a (001) MgO substrate by PLD, which acts as a buffered template for a Step-edge. Argon-ion milling was used to obtain a Step-edge with a Step Angle of 25°. The Step-edge is analysed in terms of an extended Wu and Chen model (Wu and Chen 2006 Rev. Sci. Instrum. 77 1). The model validity is confirmed by the correspondence between the theoretically proposed and experimentally observed Step Angles. A 150 nm YBa2Cu3O7−δ (YBCO) thin film was accordingly grown over the PBCO Step-edge and patterned by standard photolithography. I–V characteristics were obtained by DC and AC excitation of the patterned junctions. The IcRn product values are of the order of 1.6 mV and 0.36 mV at 53 K and 77 K, respectively. These values are higher than typical values found in the literature. The observation of Shapiro Steps confirms the presence of the Josephson effect in this novel junction topology.
W F Van Staden - One of the best experts on this subject based on the ideXlab platform.
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A novel buffered high-Tc superconducting Step-edge Josephson junction
Superconductor Science and Technology, 2007Co-Authors: W F Van Staden, Ulrich Buttner, V V Srinivasu, Willem J. PeroldAbstract:A novel high-Tc superconducting (HTS) buffered Step-edge Josephson junction is fabricated. A 250 nm PrBa2Cu3O7 (PBCO) layer was epitaxially grown on a (001) MgO substrate by PLD, which acts as a buffered template for a Step-edge. Argon-ion milling was used to obtain a Step-edge with a Step Angle of 25°. The Step-edge is analysed in terms of an extended Wu and Chen model (Wu and Chen 2006 Rev. Sci. Instrum. 77 1). The model validity is confirmed by the correspondence between the theoretically proposed and experimentally observed Step Angles. A 150 nm YBa2Cu3O7−δ (YBCO) thin film was accordingly grown over the PBCO Step-edge and patterned by standard photolithography. I–V characteristics were obtained by DC and AC excitation of the patterned junctions. The IcRn product values are of the order of 1.6 mV and 0.36 mV at 53 K and 77 K, respectively. These values are higher than typical values found in the literature. The observation of Shapiro Steps confirms the presence of the Josephson effect in this novel junction topology.
Thomas Kurner - One of the best experts on this subject based on the ideXlab platform.
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Power-Angular Spectra Correlation Based Two Step Angle of Arrival Estimation for Future Indoor Terahertz Communications
IEEE Transactions on Antennas and Propagation, 2019Co-Authors: Bile Peng, Ke Guan, Sebastian Rey, Thomas KurnerAbstract:The future terahertz (THz) communication is a promising solution to the high data rate and short-range communication due to its broad available bandwidth. However, the high propagation path loss and the limited output power of the amplifier require highly directive antennas with high antenna gain in order to realize a reasonable signal-to-noise ratio (SNR). An Angle-of-arrival (AoA) estimation is necessary to adjust the main lobe direction of the antenna. A major challenge of the AoA estimation is the compromise between accuracy and time consumption due to the big number of main lobe directions. This paper proposes a novel efficient AoA algorithm, which utilizes the fact that the power-angular spectrums (PASs) of different frequencies are highly correlated and the THz communication devices are equipped with radio frequency (RF) frontends of lower frequency. By means of a rough and quick estimation at the lower frequency, the range of the true AoA can be significantly confined and the precise estimation can be efficiently carried out. To begin with, an antenna model with discrete main lobe directions is proposed and the relationship between antenna gain, half power beamwidth (HPBW), and number of main lobe directions is analyzed. The PAS correlation is then validated with channel sounding measurement. The two-Step AoA estimation algorithm is derived, formulated, and finally validated with hardware demonstration.
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Two-Step Angle-of-arrival estimation for terahertz communications based on correlation of power-angular spectra in frequency
12th European Conference on Antennas and Propagation (EuCAP 2018), 2018Co-Authors: Bile Peng, Ke Guan, Sebastian Rey, Thomas KurnerAbstract:The future terahertz (THz) communications utilize the frequency range above 300 GHz and can realize a very high data rate. However, one major challenge is the Angle of arrival (AoA) estimation because the extremely high path loss requires adaptive high gain directive antennas (e.g. via beamforming). Although, this topic has been comprehensively studied, there is so far no adequate method subject to simple hardware design and computational effort as well as THz channel characteristics. This paper presents an AoA estimation algorithm in two Steps based on the correlation of power angular spectra (PAS) in different frequencies. A low frequency radio frequency (RF) frontend is applied for a rough and fast AoA estimation in the first Step and the THz RF frontend estimates the precise AoA within the angular range confined in the first Step to reduce the time consumption of AoA estimation. The correlation of PAS in different frequencies is the premise of the algorithm and is validated with a broadband channel sounder in a typical application scenario of indoor THz communication. Finally, the algorithm efficiency is analyzed with two exemplar scanning resolutions.
H.c. Yang - One of the best experts on this subject based on the ideXlab platform.
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High quality Step-edge substrates for high-Tc superconducting devices
Review of Scientific Instruments, 2006Co-Authors: C.h. Wu, Y. S. Tsai, K. L. Chen, Herng-er Horng, H.c. Yang, J C Chen, M. J. Chen, J. H. ChenAbstract:Despite the significant progress in fabrication methods of Step edge, the lack of reproducibility still hinders their use in more complicated systems. To pursue the high reproducibility and quality of Step edge for high-Tc superconducting devices, we have developed the technique to fabricate high quality Step-edge substrates with arbitrary Step Angles. We used two Steps to improve the Step ramp quality substantially. The surface microscopy of Step substrates shows high uniformity with respect to any Step Angle. There are no needles, waves, trenches, cascades, or other flaws on these surfaces. Serial Josephson junctions and superconducting quantum interference device arrays were fabricated onto Step-edge substrates. The Step-edge devices exhibit excellent results.
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Optimization of Step-edge substrates for high-TC superconducting devices
Physica C-superconductivity and Its Applications, 2005Co-Authors: M. J. Chen, K. L. Chen, Herng-er Horng, J C Chen, J. H. Chen, M. H. Hsu, Jen-tzong Jeng, T. S. Lai, H.c. YangAbstract:Abstract To pursue Step-edge for high- T C superconducting grain boundary junctions or SQUIDs with high reproducibility and quality, we have developed two-Step procedures of fabricating very good Step-edge substrates. A protocol of precisely controlling Step Angles for Josephson junctions has been established, with which we can predict the Step Angles as well as get a better control of the fabrication process. The procedures can improve the Step ramp quality substantially. There are no needles, waves, trenches, cascade, or other flaws on these surfaces. The Step substrates present good uniformity with respect to any Step Angle. We have characterized high- T C Step-edge dc SQUIDs connected in series. The I – V curves of SQUID arrays show the RSJ behavior. The enhanced modulation amplitude of 110 μV is achieved at 77 K with the Step-edge dc SQUID in series. The results clearly show the high uniformity and quality of the fabricated Step-edge Josephson junctions.
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Effects of Step-edge conditions on the magnetoresistance of La0.7Sr0.3MnO3 tunneling junctions
Thin Solid Films, 2004Co-Authors: Limin Wang, H.c. Yang, Chen-chung Liu, H.e. HorngAbstract:Abstract La0.7Sr0.3MnO3 (LSMO) tunneling magnetoresistance (TMR) junctions have been successfully fabricated on Step-edge (001) SrTiO3 substrates with various Step-edge conditions. We report the fabrication techniques of LSMO Step-edge TMR junctions in which the standard photolithography and ion-beam etching techniques are used to control the Step Angle and Step height. We study the influence of Step-edge conditions on the resistance and MR behavior of LSMO TMR junctions. It is found that the magnitude of junction resistance increases with an increase of Step Angle or with a decrease of d/H ratio, where d is the film thickness and H the Step height. Based on our results, we conclude that a suitable d/H ratio of ∼0.5–0.9 with a high Step Angle of φ≥70° can be regarded as the optimum conditions for the fabrication of Step-edge TMR junctions.
V V Srinivasu - One of the best experts on this subject based on the ideXlab platform.
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A novel buffered high-Tc superconducting Step-edge Josephson junction
Superconductor Science and Technology, 2007Co-Authors: W F Van Staden, Ulrich Buttner, V V Srinivasu, Willem J. PeroldAbstract:A novel high-Tc superconducting (HTS) buffered Step-edge Josephson junction is fabricated. A 250 nm PrBa2Cu3O7 (PBCO) layer was epitaxially grown on a (001) MgO substrate by PLD, which acts as a buffered template for a Step-edge. Argon-ion milling was used to obtain a Step-edge with a Step Angle of 25°. The Step-edge is analysed in terms of an extended Wu and Chen model (Wu and Chen 2006 Rev. Sci. Instrum. 77 1). The model validity is confirmed by the correspondence between the theoretically proposed and experimentally observed Step Angles. A 150 nm YBa2Cu3O7−δ (YBCO) thin film was accordingly grown over the PBCO Step-edge and patterned by standard photolithography. I–V characteristics were obtained by DC and AC excitation of the patterned junctions. The IcRn product values are of the order of 1.6 mV and 0.36 mV at 53 K and 77 K, respectively. These values are higher than typical values found in the literature. The observation of Shapiro Steps confirms the presence of the Josephson effect in this novel junction topology.