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Magnetic flux distribution around BSCCO single crystal d-dot
Physica C 470 (2010) S840–S841
Contents lists available at ScienceDirect
Physica C journal homepage: www.elsevier.com/locate/physc
Magnetic flux distribution around BSCCO single crystal d-dot Shuichi Kawamata a,d,*, Masanori Yamamoto a, Mayumi Uno b, Kazuo Satoh b, Taeko Yuki c, Tsutomu Yotsuya c,d, Takekazu Ishida a,d a
Department of Physics and Electronics, Osaka Prefecture University, Sakai 599-8531, Japan Technology Research Institute of Osaka Prefecture, Izumi 594-1157, Japan c Nanoscience and Nanotechnology Research Center, Osaka Prefecture University, Sakai 599-8531, Japan d Institute for Nanofabrication Research, Osaka Prefecture University, Sakai 599-8531, Japan b
a r t i c l e
i n f o
Article history: Accepted 7 January 2010 Available online 13 January 2010 Keywords: Bi-based cuprates Mesoscopic system Josephson effects Ar ion-milling Scanning SQUID microscope
a b s t r a c t We have proposed a composite structure named as d-dot where a d-wave superconducting square dot is embedded in s-wave superconductor matrix. Spontaneous vortices with a half flux quantum should appear in the four corners of the d-dot because p phase shift of d-wave order parameter occurs at around corner junctions. The d-wave cuprate superconductor BSCCO dot surrounded by a conventional s-wave superconductor Pb is prepared by using a photolithography process, an Ar ion-milling method, a vacuum evaporation and a lift-off technique. Local magnetic flux distribution around the BSCCO single crystal ddot is investigated by using a scanning SQUID microscope. The spontaneous half flux quantum is observed at one corner of the d-dot. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction It is well confirmed that high temperature cuprate superconductors have d-wave symmetry, dx2 y2 in which the phase of superconducting order parameter along the kx -direction is different from that along the ky -direction by p. We have proposed a composite structure named as d-dot where a d-wave superconducting square dot is embedded in s-wave superconductor matrix. Spontaneous vortices with a half flux quantum should appear in the four corners of the d-dot without applying external magnetic field because of p phase shift of d-wave order parameter at around corner junctions [1–3]. By using the Ginzburg–Landau equation with two-component superconducting order parameters, Kato et al. calculated the spatial distribution of local magnetic field distribution for the d-dot [1,3]. Because of breakdown of time reversal symmetry, the d-dot has twofold degenerated states. Koyama et al. formulated a canonical quantum theory which describes the quantum two-level system [4]. We have been preparing the d-dot experimentally by using epitaxial YBa2 Cu3 O7 thin films. Local magnetic field distribution around the d-dot has been measured by using a SQUID microscope.
* Corresponding author. Address: Department of Physics and Electronics, Osaka Prefecture University, Sakai 599-8531, Japan. E-mail address: [email protected] (S. Kawamata). 0921-4534/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2010.01.014
The possible candidates of the half flux quantum at the corners of the d-dot was suggested by the measurements [2,3]. In this report, the fabrication of a Bi2 Sr2 CaCu2 O8d (BSCCO) single crystal to prepare the d-dot is described. Local magnetic field profile around the BSCCO d-dot is investigated by using the SQUID microscope.
2. Fabrication of BSCCO d-dot The d-wave cuprate superconductor BSCCO dot surrounded by a conventional s-wave superconductor Pb is obtained as following procedure. The BSCCO single crystal grown by a traveling solvent floating zone method is attached on a Si substrate with polyimide adhesive. The BSCCO crystal is cleaved by Scotch tape to have thickness less than 2 lm. Photoresists are coated on the crystal and patterned to a square of 40 40 lm islands by a photolithography technique. By using an Ar ion-milling method, the crystal is etched down to the surface of the Si substrate. The three dimensional profile taken by a laser microscope is shown in Fig. 1. The height of the crystal from the surface of the Si substrate is 1:2 lm including the thickness of the polyimide adhesive. Au layer with the thickness of 6 nm is sputtered. Then, the Pb with the thickness of 0:35 lm is deposited by a vacuum evaporation method after the photoresist is coated on the BSCCO square dot. Finally, the extra Pb and photoresist are removed by a lift-off technique.
S. Kawamata et al. / Physica C 470 (2010) S840–S841
Fig. 1. Three dimensional profile of BSCCO crystal fabricated by using Ar ionmilling.
S841
Fig. 2. Magnetic field profile by SQUID microscope at 4.0 K under real zero field.
3. Measurements of local field profile 4. Summary The local magnetic field distribution around the d-dot is measured by using the scanning SQUID microscope. It is very important to carry out measurements in real zero field. Measurements are performed as following procedure. First we adjust the compensation field in order to minimize a residual magnetic field at 12 K well above transition temperature for Pb, T c ¼ 7:2 K. Then the sample is cooled down to 4 K at which both of the BSCCO and Pb are superconductive. Finally the measurements are carried out for the area of 64 64 lm with 1 lm step. Fig. 2 shows the local magnetic field distribution around the d-dot under real zero field. In the figure, the square indicates the position of the BSCCO d-dot which is determined by the measurement at 12 K under 0.1 Gauss. On the upper left corner, the spontaneous vortex with the magnitude of 0:53 0:07/0 appears. The half flux quantum is observed at one corner instead of the four corners of the d-dot. The condition in the fabrication process should be adjusted more precisely to observe the half flux quantum at four corners of the d-dot.
We have fabricated the d-dot of the BSCCO single crystal embedded in the conventional superconductor Pb. The local magnetic field distribution around the d-dot has been measured by using the scanning SQUID microscope. The spontaneous half flux quantum is observed at one corner of the d-dot.
References [1] M. Kato, M. Ako, M. Machida, T. Koyama, T. Ishida, Physica C 412–414 (2004) 352. [2] M. Fujii, T. Abe, H. Yoshikawa, S. Miki, S. Kawamata, K. Satoh, T. Yotsuya, M. Kato, M. Machida, T. Koyama, T. Terashima, S. Tsukui, M. Adachi, T. Ishida, Physica C 426–431 (2005) 104. [3] T. Ishida, M. Fujii, T. Abe, M. Yamamoto, S. Miki, S. Kawamata, K. Satoh, T. Yotsuya, M. Kato, M. Machida, T. Koyama, T. Terashima, S. Tsukui, M. Adachi, Physica C 437–438 (2006) 104. [4] T. Koyama, M. Machida, M. Kato, T. Ishida, Physica C 426–431 (2005) 1561.
Contents lists available at ScienceDirect
Physica C journal homepage: www.elsevier.com/locate/physc
Magnetic flux distribution around BSCCO single crystal d-dot Shuichi Kawamata a,d,*, Masanori Yamamoto a, Mayumi Uno b, Kazuo Satoh b, Taeko Yuki c, Tsutomu Yotsuya c,d, Takekazu Ishida a,d a
Department of Physics and Electronics, Osaka Prefecture University, Sakai 599-8531, Japan Technology Research Institute of Osaka Prefecture, Izumi 594-1157, Japan c Nanoscience and Nanotechnology Research Center, Osaka Prefecture University, Sakai 599-8531, Japan d Institute for Nanofabrication Research, Osaka Prefecture University, Sakai 599-8531, Japan b
a r t i c l e
i n f o
Article history: Accepted 7 January 2010 Available online 13 January 2010 Keywords: Bi-based cuprates Mesoscopic system Josephson effects Ar ion-milling Scanning SQUID microscope
a b s t r a c t We have proposed a composite structure named as d-dot where a d-wave superconducting square dot is embedded in s-wave superconductor matrix. Spontaneous vortices with a half flux quantum should appear in the four corners of the d-dot because p phase shift of d-wave order parameter occurs at around corner junctions. The d-wave cuprate superconductor BSCCO dot surrounded by a conventional s-wave superconductor Pb is prepared by using a photolithography process, an Ar ion-milling method, a vacuum evaporation and a lift-off technique. Local magnetic flux distribution around the BSCCO single crystal ddot is investigated by using a scanning SQUID microscope. The spontaneous half flux quantum is observed at one corner of the d-dot. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction It is well confirmed that high temperature cuprate superconductors have d-wave symmetry, dx2 y2 in which the phase of superconducting order parameter along the kx -direction is different from that along the ky -direction by p. We have proposed a composite structure named as d-dot where a d-wave superconducting square dot is embedded in s-wave superconductor matrix. Spontaneous vortices with a half flux quantum should appear in the four corners of the d-dot without applying external magnetic field because of p phase shift of d-wave order parameter at around corner junctions [1–3]. By using the Ginzburg–Landau equation with two-component superconducting order parameters, Kato et al. calculated the spatial distribution of local magnetic field distribution for the d-dot [1,3]. Because of breakdown of time reversal symmetry, the d-dot has twofold degenerated states. Koyama et al. formulated a canonical quantum theory which describes the quantum two-level system [4]. We have been preparing the d-dot experimentally by using epitaxial YBa2 Cu3 O7 thin films. Local magnetic field distribution around the d-dot has been measured by using a SQUID microscope.
* Corresponding author. Address: Department of Physics and Electronics, Osaka Prefecture University, Sakai 599-8531, Japan. E-mail address: [email protected] (S. Kawamata). 0921-4534/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2010.01.014
The possible candidates of the half flux quantum at the corners of the d-dot was suggested by the measurements [2,3]. In this report, the fabrication of a Bi2 Sr2 CaCu2 O8d (BSCCO) single crystal to prepare the d-dot is described. Local magnetic field profile around the BSCCO d-dot is investigated by using the SQUID microscope.
2. Fabrication of BSCCO d-dot The d-wave cuprate superconductor BSCCO dot surrounded by a conventional s-wave superconductor Pb is obtained as following procedure. The BSCCO single crystal grown by a traveling solvent floating zone method is attached on a Si substrate with polyimide adhesive. The BSCCO crystal is cleaved by Scotch tape to have thickness less than 2 lm. Photoresists are coated on the crystal and patterned to a square of 40 40 lm islands by a photolithography technique. By using an Ar ion-milling method, the crystal is etched down to the surface of the Si substrate. The three dimensional profile taken by a laser microscope is shown in Fig. 1. The height of the crystal from the surface of the Si substrate is 1:2 lm including the thickness of the polyimide adhesive. Au layer with the thickness of 6 nm is sputtered. Then, the Pb with the thickness of 0:35 lm is deposited by a vacuum evaporation method after the photoresist is coated on the BSCCO square dot. Finally, the extra Pb and photoresist are removed by a lift-off technique.
S. Kawamata et al. / Physica C 470 (2010) S840–S841
Fig. 1. Three dimensional profile of BSCCO crystal fabricated by using Ar ionmilling.
S841
Fig. 2. Magnetic field profile by SQUID microscope at 4.0 K under real zero field.
3. Measurements of local field profile 4. Summary The local magnetic field distribution around the d-dot is measured by using the scanning SQUID microscope. It is very important to carry out measurements in real zero field. Measurements are performed as following procedure. First we adjust the compensation field in order to minimize a residual magnetic field at 12 K well above transition temperature for Pb, T c ¼ 7:2 K. Then the sample is cooled down to 4 K at which both of the BSCCO and Pb are superconductive. Finally the measurements are carried out for the area of 64 64 lm with 1 lm step. Fig. 2 shows the local magnetic field distribution around the d-dot under real zero field. In the figure, the square indicates the position of the BSCCO d-dot which is determined by the measurement at 12 K under 0.1 Gauss. On the upper left corner, the spontaneous vortex with the magnitude of 0:53 0:07/0 appears. The half flux quantum is observed at one corner instead of the four corners of the d-dot. The condition in the fabrication process should be adjusted more precisely to observe the half flux quantum at four corners of the d-dot.
We have fabricated the d-dot of the BSCCO single crystal embedded in the conventional superconductor Pb. The local magnetic field distribution around the d-dot has been measured by using the scanning SQUID microscope. The spontaneous half flux quantum is observed at one corner of the d-dot.
References [1] M. Kato, M. Ako, M. Machida, T. Koyama, T. Ishida, Physica C 412–414 (2004) 352. [2] M. Fujii, T. Abe, H. Yoshikawa, S. Miki, S. Kawamata, K. Satoh, T. Yotsuya, M. Kato, M. Machida, T. Koyama, T. Terashima, S. Tsukui, M. Adachi, T. Ishida, Physica C 426–431 (2005) 104. [3] T. Ishida, M. Fujii, T. Abe, M. Yamamoto, S. Miki, S. Kawamata, K. Satoh, T. Yotsuya, M. Kato, M. Machida, T. Koyama, T. Terashima, S. Tsukui, M. Adachi, Physica C 437–438 (2006) 104. [4] T. Koyama, M. Machida, M. Kato, T. Ishida, Physica C 426–431 (2005) 1561.