Constrictions Fabricated on YBCO Thin Film using the Femtosecond Laser: Limiting Factors.

Journal Article written by Patrice Umenne in the department of Electrical and Mining EngineeringIn this paper we report on the development of a new application of the femtosecond laser, namely, the fabrication of micron, sub-micron and nano sized constrictions on YBCO superconductive thin films. The fabricated micron, sub-micron and nano constrictions have widths of 1.09 um, 705 nm and 394.8 nm, respectively. The thickness of these constrictions ranged from about 160 nm to 190 nm, as defined by the depth profile on the 3D AFM images. The length of these constrictions ranged from 7.2 um to 7.5 um. The length of these constrictions depends on the size of the laser ablation spot used for cutting and on the separation distance between the laser ablation spots along the width of the sample.The University of South AfricaCollege of Engineering, Science and Technolog

Constrictions Fabricated on YBCO Thin Film using the Femtosecond Laser: Limiting Factors.

Journal Article written by Patrice Umenne in the department of Electrical and Mining EngineeringIn this paper we report on the development of a new application of the femtosecond laser, namely, the fabrication of micron, sub-micron and nano sized constrictions on YBCO superconductive thin films. The fabricated micron, sub-micron and nano constrictions have widths of 1.09 um, 705 nm and 394.8 nm, respectively. The thickness of these constrictions ranged from about 160 nm to 190 nm, as defined by the depth profile on the 3D AFM images. The length of these constrictions ranged from 7.2 um to 7.5 um. The length of these constrictions depends on the size of the laser ablation spot used for cutting and on the separation distance between the laser ablation spots along the width of the sample.The University of South AfricaCollege of Engineering, Science and Technolog

Microwave Power dependence of the I-V Characteristics of Submicron and Micron YBCO Constrictions.

Conference paper published by Patrice Umenne Electrical Engineering DepartmentIn this paper, the femtosecond laser technique was used to fabricate micron and submicron sized Josephson Junctions. The influence of an RF signal of frequency 19.5 GHz on the critical current of the micron sized Josephson junction of width 2.1 μm and the sub-micron sized Josephson junction of width 816 nm was analyzed. Both junctions showed the presence of Shapiro-like steps and critical current suppression due an increase in the RF Power. Critical current suppression occurs due to the varying magnetic field produced by the RF signal power.The University of South AfricaCollege of Engineering, Science and Technolog

Low-field microwave absorption in pulse laser deposited FeSi thin film

Low field microwave absorption (LFMA) measurements at 9.4 GHz (X-band), were carried out on pulse laser deposited (PLD) polycrystalline B20 cubic structure FeSi thin film grown on Si (111) substrate. The LFMA properties of the films were investigated as a function of DC field, temperature, microwave power and the orientation of DC field with respect to the film surface. The LFMA signal is very strong when the DC field is parallel to the film surface and vanishes at higher angles. The LFMA signal strength increases as the microwave power is increased. The LFMA signal disappears around 340 K, which can be attributed to the disappearance of ferromagnetic state well above room temperature in these films. We believe that domain structure evolution in low fields, which in turn modifies the low field permeability as well as the anisotropy, could be the origin of the LFMA observed in these films. The observation of LFMA opens the possibility of the FeSi films to be used as low magnetic field sensors in the microwave and rf frequency regions.University of Pretoria research development program and NRF/Ithemba LABS.http://www.elsevier.com/locate/jmmmnf201

Observation of shapiro-steps in AFM-plough micron-size YBCO planar constrictions

Using an Atomic Force Microscope (AFM), we successfully ploughed micron size planar constriction type junctions on YBa3Cu30 7-x thin films. The 100 nanometer (nm) thin films are deposited on MgO substrates by an Inverted Cylindrical Magnetron (ICM) sputtering technique. The films are then patterned into 8-10 micron size strips, using photolithography and dry etching. A diamond coated tip was used with the AFM in this process. We were able to observe well defined current-voltage (I-V) characteristics and Shapiro-steps, successfully demonstrating a possible Josephson effect in these constrictions. © 2009 IEEE.Using an Atomic Force Microscope (AFM), we successfully ploughed micron size planar constriction type junctions on YBa3Cu30 7-x thin films. The 100 nanometer (nm) thin films are deposited on MgO substrates by an Inverted Cylindrical Magnetron (ICM) sputtering technique. The films are then patterned into 8-10 micron size strips, using photolithography and dry etching. A diamond coated tip was used with the AFM in this process. We were able to observe well defined current-voltage (I-V) characteristics and Shapiro-steps, successfully demonstrating a possible Josephson effect in these constrictions. © 2009 IEEE.Conference PaperConference Pape

AFM nano-plough planar YBCO micro-bridges: Critical currents and magnetic field effects

The critical current (Ic) of YBa2Cu3O 7-x (YBCO) AFM plough micro-constrictions is measured as a function of temperature, width and the magnetic flux density (B), which was applied perpendicular to the YBCO ab-plane and surface of the bridges. C-axis oriented thin films of YBa2Cu3O7-x were deposited on MgO substrates using an inverted cylindrical magnetron (ICM) sputtering technique. The films were then patterned into 8-10 micron size strips, using standard photolithography and dry etching processes. Micro-bridges with widths between 1.9 μm to 4.1 μm were fabricated by using atomic force microscope (AFM) nanolithography techniques. Critical current versus temperature data shows a straight-line behavior, which is typical of constriction type Josephson junctions. The Ic versus B characteristics exhibited a modulation, and a suppression of the critical current of up to 84%. It was also found that the critical current increases with increasing constriction width. Copyright © 2010 American Scientific Publishers.Articl

Critical-current variation with Pr content in Y<SUB>1-x</SUB>Pr<SUB>x</SUB>Ba<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7</SUB> epitaxial films

c-axis-oriented epitaxial Y1-xPrxBa2Cu3O7 (x=0, 0.05, 0.1, 0.2, 0.3, and 0.35) thin films have been grown with the pulsed-laser-deposition method. Superconducting transition temperatures of the films are within &#177;2 K of the corresponding polycrystalline bulk samples. The critical current density Jc of Pr-doped films for x=0.1-0.3 is about two orders of magnitude lower than of the pure 1:2:3 films. This exponential fall in Jc with doping (x) can be understood semiquantitatively in terms of depairing due to a random-impurity (Pr-ion) potential causing localized suppression of the superconducting order parameter around the impurity to about the in-plane coherence length

Anisotropy In Bi2212 Single Crystals Studied By Non-resonant Microwave Absorption: Hysteresis And Line Shapes

Microwave absorption in a high quality Bi2212 single crystal is studied at 77 K, using non-resonant microwave absorption (NMA) technique. NMA line shape and low field hysteresis are highly anisotropic. Two peaks, a narrow P1-peak followed by a broad P2-peak are observed for applied field perpendicular to the ab-plane. For the applied field parallel to the ab-plane, the broad P2-peak disappears. For an intermediate orientation of the field, say ∼55°, to the ab-plane, the P1-like peak broadens considerably with a possible mixing of both P1-peak and P2-peak. While there is a pronounced hysteresis in the P1-peak just near zero field for applied field parallel to the ab-plane (Cu-O plane), this hysteresis in P1-peak is nearly absent when the field is applied perpendicular to the ab-plane. In both these orientations, hysteresis is absent in NMA signals beyond the P1-peak till very high fields. At the inte rmediate orientation angle of ∼55° to the ab-plane, the reverse sweep NMA signal collapses into the zero-base line. This is a remarkable hysteresis effect. This may be due to the interaction between Josephson vortices and Abrikosov vortices which can happen in tilted magnetic fields. © 2001 Elsevier Science B.V. All rights reserved.3621-4282285Bhat, S.V., Ganguly, P., Ramakrishnan, T.V., Rao, C.N.R., (1987) J. Phys. C, 20, pp. L559Masiakowski, J.T., Puri, M., Kevan, L., (1991) J. Phys. Chem., 95, p. 1393Rastogi, A., Sudershan, Y.S., Bhat, S.V., Grover, A.K., Yamaguchi, Y., Oka, K., Nishihara, Y., (1996) Phys. Rev. B, 53, p. 9366Srinivasu, V.V., Itoh, K.I., Hashizume, A., Sreedevi, V., Kohmoto, H., Endo, T., Ricardo da Silva, R., Hayashi, K., (2001) J. Supercond., 14, p. 43Srinivasu, V.V., Sreedevi, V., Itoh, K.I., Hashizume, A., Tada, M., Yamada, J., Moehlecke, S., Endo, T., (2000) Proc. Int. School on Crystal Growth Methods, p. 228. , ChennaiYamada, J., Srinivasu, V.V., Tada, M., Itoh, K.I., Hashizume, A., Kometani, I., Anwar, K., Endo, T., (1999) Advances in Superconductivity XII, p. 353. , T. Yamashita, K. Tanabe (Eds.), Springer, TokyoSrinivasu, V.V., Hashizume, A., Itoh, K.I., Mukaida, M., Endo, T., (2000) Proc. Int. School on Crystal Growth Methods, p. 233. , ChennaiSrinivasu, V.V., Hashizume, A., Itoh, K.I., Mukaida, M., Endo, T., (1999) Singapore J. Phys., 15, p. 9Endo, T., Yan, H., (1995) Studies of High Temp. Supercond., 14, pp. 65-106. , Ed. Anant Narlikar, Nova Science Publishers, New YorkEndo, T., Yan, H., Nagase, S., Shibata, H., (1995) J. Supercond., 8, p. 259Srinivasu, V.V., Thomas, B., Hegde, M.S., Bhat, S.V., (1994) J. Appl. Phys., 75, p. 4131Wu, W., Li, F., Jia, Y., Zhou, G., Qian, Y., Qin, Q., Zhang, Y., (1993) Physica C, 213, p. 133Koshelev, A.E., (1999) Phys. Rev. Lett., 83, p. 187Enriquez, H., Botemps, N., Fournier, P., Kapitulnik, A., Maignan, A., Ruyter, A., (1996) Phys. Rev. B, 53, pp. R1475