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Switching current distribution in large Bi2Sr2CaCu2Oy intrinsic Josephson junctions
Physica C 460–462 (2007) 1483–1484 www.elsevier.com/locate/physc
Switching current distribution in large Bi2Sr2CaCu2Oy intrinsic Josephson junctions H. Kitano a
a,b,* ,
K. Ota a, A. Maeda
a,c
Department of Basic Science, University of Tokyo, 3-8-1, Komaba, Meguro-ku, Tokyo 153-8902, Japan PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan c CREST, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan
b
Available online 11 April 2007
Abstract We investigated the switching current distribution, P(I), from the zero-voltage state to a nonzero-voltage state in the intrinsic Josephson junctions of Bi2Sr2CaCu2Oy. Because of a reduction of the Josephson penetration depth attributed to an atomic-scale thickness of the superconducting layers, a depinning process of Josephson vortices was found to dominate the behavior of P(I) for the mesas with a lateral size larger than 10 lm. 2007 Elsevier B.V. All rights reserved. PACS: 74.50.+r; 74.72.Hs; 82.25.Cp Keywords: Intrinsic Josephson effect; Switching current distribution
1. Introduction The intrinsic Josephson junction (IJJ), which is naturally formed in high-Tc cuprate superconductors, is one of the most fascinating candidates for the future quantum information processing. In particular, the recent experiments for IJJs of Bi2Sr2CaCu2Oy (BSCCO) has been much attracted [1], because the macroscopic quantum tunneling (MQT) could be observed up to nearly 1 K, which was almost one order of magnitude higher than a typical value of the classical-to-quantum crossover temperature, T0, in other Josephson junctions (JJs) [2,3]. Toward a future realization of Josephson qubits utilizing IJJs, the stochastic switching events from the zero-voltage state to a finite voltage state in a current-biased IJJs should be investigated
*
Corresponding author. Present address: Department of Physics and Mathematics, Aoyama Gakuin University, 5-10-1, Fuchinobe, Sagamihara City, Kanagawa 229-8558, Japan. Tel.: +81 42 759 6286; fax: +81 42 759 6444. E-mail address: [email protected] (H. Kitano). 0921-4534/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.04.044
more extensively, since it provides a basis to the MQT process occurred below T0. In this paper, we investigated the switching current distribution, P(I), in IJJs of BSCCO above T0, where the thermal activated (TA) process is expected to dominate the switching events. We found that the measured P(I) for BSCCO mesas with a lateral size of 15–40 lm could not be always explained by the TA process of a classical particle moving in a tilted-washboard potential, which has often been used for the phase dynamics of a small JJ (SJJ) (L kJ, where L and kJ are a lateral size of junction and the Josephson penetration depth, respectively) [4]. We argue that this unusual behavior in P(I) is rather explained by regarding the fabricated IJJ as a large JJ (LJJ) (L > kJ), since an atomic-scale thickness of the superconducting layers in IJJs largely reduces kJ to 1 lm. 2. Experimental The small mesa structure was fabricated on the top of nearly optimally doped BSCCO single crystals by Arion etching (EIS-200ER, ELIONIX). Total numbers of
1484
H. Kitano et al. / Physica C 460–462 (2007) 1483–1484 60
SJJ LJJ
40×40 μ m2
T = 6.6 K
100
SJJ LJJ
15×15 μm2 40
T = 10 K
P(I)
Current (μA )
20
150
15×15 μm2
T = 10 K
P(I)
40
0
V
50
I
20
SiO Ag
-20
Au
0 4.2
BSCCO mesa
-40 -40
-20
0 20 Voltage ( mV )
40
Fig. 1. A typical I–V characteristics for the 15 · 15 lm2 mesa. The inset is a schematic viewgraph of the mesa structure.
4.3
4.4
4.5
4.6
Current (mA)
4.7
0
14
15
16
17
Current (μA)
Fig. 2. The switching current distribution for the 40 · 40 lm2 mesa (a) and the 15 · 15 lm2 mesa (b) at 10 K. Open circles show the experimental data. Dotted-broken (solid) lines are the calculated distribution of TA escape model for SJJ (LJJ).
junctions were estimated to be 20–30 typically, using an atomic-force microscope. The I–V characteristics of the mesa was measured by three-terminal method, as shown in Fig. 1. In this method, the contribution of a finite contact resistance is added to the zero-voltage state. All the measurements of P(I) were performed for the first branch in the I–V curve, by measuring the switching current for more than 1000 times repeatedly. Details of the device fabrication and of the measurement technique were described elsewhere [5].
previous results obtained from the magnetic field dependence of the critical current for small mesas [9]. Furthermore, it seems to be consistent with a recent measurement of P(I) for the IJJs with 1 · 1 lm2 by using a focused ion-beam technique, which suggested that the temperature dependence of P(I) was simply explained by the TA escape model for SJJ [1,10]. These results strongly suggest that the behavior of P(I) for IJJs with L > 10 lm is basically described by the escape model for LJJ.
3. Results and discussion
4. Conclusion
Fig. 2a and b show P(I) for the 40 · 40 lm2 and the 15 · 15 lm2 mesas, respectively, which were measured at T = 10 K. We tried to fit the measured P(I) to the TA escape models for both SJJ and LJJ. As well known, the escae process in SJJ is translated to a motion of a classical particle in a tilted-washboard potential [6], while that in LJJ is described by a depinning of Josephson vortex (or fluxon), which can be induced by a self-field effect, from a similar potential well [7,8]. Thus, the potential barrier height required for escape event is roughly reduced by a factor of (kJ/L)2 in LJJ, compared to SJJ. This suggests a broader distribution of P(I) for LJJ than that for SJJ at the same temperature. As shown in Fig. 2, we found that P(I) measured for the larger mesa was more successfully described by the TA model for LJJ rather than that for SJJ. We also estimated kJ as the fitting parameter in the TA model for LJJ for both mesas, which was found to be about 2–5 lm. Interestingly, this estimate is very similar to the
We investigated the switching current distribution, P(I), in IJJs of BSCCO above T0. We found that the phase dynamics of IJJs with L > 10 lm was basically in a LJJ regime. Thus, the behavior of P(I) was more quantitatively explained by the depinning of the Josephson vortices from a metastable state. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
K. Inomata et al., Phys. Rev. Lett. 95 (2005) 107005. T. Bauch et al., Phys. Rev. Lett. 94 (2005) 087003. R.F. Voss, R.A. Webb, Phys. Rev. Lett. 47 (1981) 265. M. Tinkham, Introduction to Superconductivity, second ed., McGraw-Hill, New York, 1996. K. Ota, H. Kitano, A. Maeda, Physica C 445–448 (2006) 955. T.A. Fulton, L.N. Dunkleberger, Phys. Rev. B 9 (1974) 4760. T. Kato, M. Imada, J. Phys. Soc. Jpn. 69 (2000) 2963. A. Wallraff et al., J. Low Temp. Phys. 118 (2000) 543. A. Irie et al., Phys. Rev. B 62 (2000) 6681. V.M. Krasnov, T. Bauch, P. Delsing, Phys. Rev. B 72 (2005) 012512.
Switching current distribution in large Bi2Sr2CaCu2Oy intrinsic Josephson junctions H. Kitano a
a,b,* ,
K. Ota a, A. Maeda
a,c
Department of Basic Science, University of Tokyo, 3-8-1, Komaba, Meguro-ku, Tokyo 153-8902, Japan PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan c CREST, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan
b
Available online 11 April 2007
Abstract We investigated the switching current distribution, P(I), from the zero-voltage state to a nonzero-voltage state in the intrinsic Josephson junctions of Bi2Sr2CaCu2Oy. Because of a reduction of the Josephson penetration depth attributed to an atomic-scale thickness of the superconducting layers, a depinning process of Josephson vortices was found to dominate the behavior of P(I) for the mesas with a lateral size larger than 10 lm. 2007 Elsevier B.V. All rights reserved. PACS: 74.50.+r; 74.72.Hs; 82.25.Cp Keywords: Intrinsic Josephson effect; Switching current distribution
1. Introduction The intrinsic Josephson junction (IJJ), which is naturally formed in high-Tc cuprate superconductors, is one of the most fascinating candidates for the future quantum information processing. In particular, the recent experiments for IJJs of Bi2Sr2CaCu2Oy (BSCCO) has been much attracted [1], because the macroscopic quantum tunneling (MQT) could be observed up to nearly 1 K, which was almost one order of magnitude higher than a typical value of the classical-to-quantum crossover temperature, T0, in other Josephson junctions (JJs) [2,3]. Toward a future realization of Josephson qubits utilizing IJJs, the stochastic switching events from the zero-voltage state to a finite voltage state in a current-biased IJJs should be investigated
*
Corresponding author. Present address: Department of Physics and Mathematics, Aoyama Gakuin University, 5-10-1, Fuchinobe, Sagamihara City, Kanagawa 229-8558, Japan. Tel.: +81 42 759 6286; fax: +81 42 759 6444. E-mail address: [email protected] (H. Kitano). 0921-4534/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.04.044
more extensively, since it provides a basis to the MQT process occurred below T0. In this paper, we investigated the switching current distribution, P(I), in IJJs of BSCCO above T0, where the thermal activated (TA) process is expected to dominate the switching events. We found that the measured P(I) for BSCCO mesas with a lateral size of 15–40 lm could not be always explained by the TA process of a classical particle moving in a tilted-washboard potential, which has often been used for the phase dynamics of a small JJ (SJJ) (L kJ, where L and kJ are a lateral size of junction and the Josephson penetration depth, respectively) [4]. We argue that this unusual behavior in P(I) is rather explained by regarding the fabricated IJJ as a large JJ (LJJ) (L > kJ), since an atomic-scale thickness of the superconducting layers in IJJs largely reduces kJ to 1 lm. 2. Experimental The small mesa structure was fabricated on the top of nearly optimally doped BSCCO single crystals by Arion etching (EIS-200ER, ELIONIX). Total numbers of
1484
H. Kitano et al. / Physica C 460–462 (2007) 1483–1484 60
SJJ LJJ
40×40 μ m2
T = 6.6 K
100
SJJ LJJ
15×15 μm2 40
T = 10 K
P(I)
Current (μA )
20
150
15×15 μm2
T = 10 K
P(I)
40
0
V
50
I
20
SiO Ag
-20
Au
0 4.2
BSCCO mesa
-40 -40
-20
0 20 Voltage ( mV )
40
Fig. 1. A typical I–V characteristics for the 15 · 15 lm2 mesa. The inset is a schematic viewgraph of the mesa structure.
4.3
4.4
4.5
4.6
Current (mA)
4.7
0
14
15
16
17
Current (μA)
Fig. 2. The switching current distribution for the 40 · 40 lm2 mesa (a) and the 15 · 15 lm2 mesa (b) at 10 K. Open circles show the experimental data. Dotted-broken (solid) lines are the calculated distribution of TA escape model for SJJ (LJJ).
junctions were estimated to be 20–30 typically, using an atomic-force microscope. The I–V characteristics of the mesa was measured by three-terminal method, as shown in Fig. 1. In this method, the contribution of a finite contact resistance is added to the zero-voltage state. All the measurements of P(I) were performed for the first branch in the I–V curve, by measuring the switching current for more than 1000 times repeatedly. Details of the device fabrication and of the measurement technique were described elsewhere [5].
previous results obtained from the magnetic field dependence of the critical current for small mesas [9]. Furthermore, it seems to be consistent with a recent measurement of P(I) for the IJJs with 1 · 1 lm2 by using a focused ion-beam technique, which suggested that the temperature dependence of P(I) was simply explained by the TA escape model for SJJ [1,10]. These results strongly suggest that the behavior of P(I) for IJJs with L > 10 lm is basically described by the escape model for LJJ.
3. Results and discussion
4. Conclusion
Fig. 2a and b show P(I) for the 40 · 40 lm2 and the 15 · 15 lm2 mesas, respectively, which were measured at T = 10 K. We tried to fit the measured P(I) to the TA escape models for both SJJ and LJJ. As well known, the escae process in SJJ is translated to a motion of a classical particle in a tilted-washboard potential [6], while that in LJJ is described by a depinning of Josephson vortex (or fluxon), which can be induced by a self-field effect, from a similar potential well [7,8]. Thus, the potential barrier height required for escape event is roughly reduced by a factor of (kJ/L)2 in LJJ, compared to SJJ. This suggests a broader distribution of P(I) for LJJ than that for SJJ at the same temperature. As shown in Fig. 2, we found that P(I) measured for the larger mesa was more successfully described by the TA model for LJJ rather than that for SJJ. We also estimated kJ as the fitting parameter in the TA model for LJJ for both mesas, which was found to be about 2–5 lm. Interestingly, this estimate is very similar to the
We investigated the switching current distribution, P(I), in IJJs of BSCCO above T0. We found that the phase dynamics of IJJs with L > 10 lm was basically in a LJJ regime. Thus, the behavior of P(I) was more quantitatively explained by the depinning of the Josephson vortices from a metastable state. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
K. Inomata et al., Phys. Rev. Lett. 95 (2005) 107005. T. Bauch et al., Phys. Rev. Lett. 94 (2005) 087003. R.F. Voss, R.A. Webb, Phys. Rev. Lett. 47 (1981) 265. M. Tinkham, Introduction to Superconductivity, second ed., McGraw-Hill, New York, 1996. K. Ota, H. Kitano, A. Maeda, Physica C 445–448 (2006) 955. T.A. Fulton, L.N. Dunkleberger, Phys. Rev. B 9 (1974) 4760. T. Kato, M. Imada, J. Phys. Soc. Jpn. 69 (2000) 2963. A. Wallraff et al., J. Low Temp. Phys. 118 (2000) 543. A. Irie et al., Phys. Rev. B 62 (2000) 6681. V.M. Krasnov, T. Bauch, P. Delsing, Phys. Rev. B 72 (2005) 012512.