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Vortex dynamics in low magnetic fields in single crystals Bi2Sr2CaCu2O8+δ
PHYSICA® ELSEVIER
Physica C 341-348 (2000) 1273-1274
www.elsevier.nl/Iocate/physc
Vortex Dynamics in Low Magnetic Fields in Single Crystals Bi2Sr2CaCu2Os+~ Jovan Mirkovi~ a and Kazuo Kadowaki b alnstitute of Materials Science, University of Tsukuba, Tsukuba 305-8573, Japan, and Faculty of Sciences, University of Montenegro, 81000 Podgorica, Montenegro, Yugoslavia bCREST, Japan Science and Technology Corporation (JST), and Institute of Materials Science, University of Tsukuba, Tsukuba 305-8573, Japan In-plane resistivity measurements were performed for two single crystals Bi2Sr2CaCu2Os+~ with electric contacts in the Corbino geometry in order to avoid the influence of the surface barriers and to probe the pure bulk properties of superconductors. The first-order vortex lattice melting transition was identified by the sharp resistance drop even as low as 1 Oe. It was found that the resistance level RT,~ where the melting transition occurs, does not depend on magnetic fields in the high temperature region. However, below appx. 55 K the resistance level RT,, sharply drops while the resistance anomaly itself loses sharpness and gradually disappears indicating that the melting transition may change its character from first-order to second-order phase transition.
1. I N T R O D U C T I O N Interplay of surface barriers and bulk pinning in high temperature superconductors could conceal and modify the true transport properties of Bi2Sr2CaCu2Os+~ if the platelet sample with conventional four probe electrocal leads configuration was measured in the vortex liquid state in the low magnetic fields [1,2]. In order to examine the pure bulk properties of Bi2Sr2CaCu2Os+~, we performed the in-plane resistivity measurements using electric contacts with the Corbino geometry (see Fig. 1) which excludes the surface barrier effect. Two Corbino discs of single crystals Bi2Sr2CaCu2Os+~ were prepared, for the inplane resistivity measurements: #S1 had the diameter D = 1.9 mm and thickness t = 20 #m with the transition temperature Tc = 90.4 K, while #$2 had D = 2.7 mm and t = 20 p m with T¢ = 90 K. The resistance was measured by the standard lock-in technique at 34 Hz as a function of temperature by different current levels in the various magnetic fields applied along the c-axis.
10 "~
' " ' " I' "V .....
/'/
1 02 •~ 0
cc
-3
10' 10 s
1 0 `6
80
82
84
86
88
90
92
T(K)
Figure 1. Temperature dependence of the inplane resistance in low magnetic fields parallel to c-axis measured by the current level of 10 mA on the Corbino disc #S1. H=40, 37.5, 35 .... , 7.5, 5, 2.5 and 1 Oe (from left to right). Inset: the electric contact geometry.
0921-4534/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII S0921-4534(00)00879-0
J Mirkovi~. K. Kadowaki/Physica C 341-348 (2000) 1273-1274
1274
10 z #$2
20 Oe
10 3
A
~//~
I
10'
I
10 s
10'
10 7 40
45
50
55
60
65
70
75
80
85
90
T(K)
Figure 2. A set of the resistance curves (#$2) as a function of temperature measured in various magnetic fields with the current of 15 mA.
2. R E S U L T S
Figure 1 shows the temperature dependence of the in-plane resistance in various low magnetic fields. The first-order vortex lattice melting transition[3] is identified by the sharp resistance drop[4] and the vortex liquid and vortex solid or Bragg-glass phase are clearly distinguished in the H - T phase diagram. Surprisingly, the signature of the first-order transition was detected even as small as 1 Oe without having any dramatic change. This noticeable observation suggests that the first-order phase transition may involve something more complicated processes than just the simple melting process, such as sublimation or decoupling of vortex lines into vortex pancakes. We note that the so called "nose" or "re-entrant" behavior of the melting line as predicted [5] was not confirmed even in such a dilute limit of vortices. The next experimental finding is the fact that the resistance level RTm where the sharp drop of the resistance occurs does not depend on magnetic fields below approximately 120 Oe. This is in contrast with the field dependence previously
reported from the measurements performed on the platelet samples but is in good accordance with the theoretical model proposed by Rojo et al.[6] based on the universalities of the structure factor at the freezing transition and Verlet criterion [7]. However, as the magnetic field is further increased and accordingly the melting transition temperature shifts down below appx. 55 K, the resistance level RTm begins to decrease. The resistance anomaly itself loses its sharpness and gradually disappears. This strongly indicates that the melting transition in this temperature region change its character from first-order to second-order phase transition, or some other dramatic processes would accompany. It is interesting to note that in magnetization measurements a weak anomaly characterized by a weak irreversibility magnetization behavior in the vortex liquid state was observed in the series of samples[8] in the same noted temperature region. Appearance of the novel vortex liquid phase suggested by [9] may explain this observation. One of the authors (J.M) thanks T. Mishonov and S. Savel'ev for useful discussions. REFERENCES
1. D.T. Fuchs et al. Nature 391,373 (1998). 2. J. Mirkovi~ et al. Adv. in Supercond. XI (ISS'98), p575, Springer-Verlag Tokyo, 1999. 3. P. Gammel et al. Phys. Rev. Lett. 61, 1666 (1988); E. Zeldov et al. Nature 375, 373 (1995); K. Kadowaki, Physica (Amsterdam) C236, 164 (1996). 4. J. Mirkovi6 and K. Kadowaki, Physica B (Proc. of 22nd Int. Conf. on Low Temp. Physics, 4-11 August,1999, Espoo, Finland). 5. G. Blatter et al. Phys. Rev. B54, 72 (1996). 6. A.G. Rojo et al., cond-mat, 9712017. 7. J.P. Hansen and L. Verlet, Phys. Rev. 184, 159 (1969). 8. K. Kimura et al. Physica B (Proc. of 22ud Int. Conf. on Low Temp. Physics, 4-11 August, 1999, Espoo, Finland). 9. Z. Te~anovid, Phys. Rev. B59, 6449 (1999); A. K. Nguyen and A. Sudb¢, Europhys. Lett. 46, 780 (1999).
Physica C 341-348 (2000) 1273-1274
www.elsevier.nl/Iocate/physc
Vortex Dynamics in Low Magnetic Fields in Single Crystals Bi2Sr2CaCu2Os+~ Jovan Mirkovi~ a and Kazuo Kadowaki b alnstitute of Materials Science, University of Tsukuba, Tsukuba 305-8573, Japan, and Faculty of Sciences, University of Montenegro, 81000 Podgorica, Montenegro, Yugoslavia bCREST, Japan Science and Technology Corporation (JST), and Institute of Materials Science, University of Tsukuba, Tsukuba 305-8573, Japan In-plane resistivity measurements were performed for two single crystals Bi2Sr2CaCu2Os+~ with electric contacts in the Corbino geometry in order to avoid the influence of the surface barriers and to probe the pure bulk properties of superconductors. The first-order vortex lattice melting transition was identified by the sharp resistance drop even as low as 1 Oe. It was found that the resistance level RT,~ where the melting transition occurs, does not depend on magnetic fields in the high temperature region. However, below appx. 55 K the resistance level RT,, sharply drops while the resistance anomaly itself loses sharpness and gradually disappears indicating that the melting transition may change its character from first-order to second-order phase transition.
1. I N T R O D U C T I O N Interplay of surface barriers and bulk pinning in high temperature superconductors could conceal and modify the true transport properties of Bi2Sr2CaCu2Os+~ if the platelet sample with conventional four probe electrocal leads configuration was measured in the vortex liquid state in the low magnetic fields [1,2]. In order to examine the pure bulk properties of Bi2Sr2CaCu2Os+~, we performed the in-plane resistivity measurements using electric contacts with the Corbino geometry (see Fig. 1) which excludes the surface barrier effect. Two Corbino discs of single crystals Bi2Sr2CaCu2Os+~ were prepared, for the inplane resistivity measurements: #S1 had the diameter D = 1.9 mm and thickness t = 20 #m with the transition temperature Tc = 90.4 K, while #$2 had D = 2.7 mm and t = 20 p m with T¢ = 90 K. The resistance was measured by the standard lock-in technique at 34 Hz as a function of temperature by different current levels in the various magnetic fields applied along the c-axis.
10 "~
' " ' " I' "V .....
/'/
1 02 •~ 0
cc
-3
10' 10 s
1 0 `6
80
82
84
86
88
90
92
T(K)
Figure 1. Temperature dependence of the inplane resistance in low magnetic fields parallel to c-axis measured by the current level of 10 mA on the Corbino disc #S1. H=40, 37.5, 35 .... , 7.5, 5, 2.5 and 1 Oe (from left to right). Inset: the electric contact geometry.
0921-4534/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII S0921-4534(00)00879-0
J Mirkovi~. K. Kadowaki/Physica C 341-348 (2000) 1273-1274
1274
10 z #$2
20 Oe
10 3
A
~//~
I
10'
I
10 s
10'
10 7 40
45
50
55
60
65
70
75
80
85
90
T(K)
Figure 2. A set of the resistance curves (#$2) as a function of temperature measured in various magnetic fields with the current of 15 mA.
2. R E S U L T S
Figure 1 shows the temperature dependence of the in-plane resistance in various low magnetic fields. The first-order vortex lattice melting transition[3] is identified by the sharp resistance drop[4] and the vortex liquid and vortex solid or Bragg-glass phase are clearly distinguished in the H - T phase diagram. Surprisingly, the signature of the first-order transition was detected even as small as 1 Oe without having any dramatic change. This noticeable observation suggests that the first-order phase transition may involve something more complicated processes than just the simple melting process, such as sublimation or decoupling of vortex lines into vortex pancakes. We note that the so called "nose" or "re-entrant" behavior of the melting line as predicted [5] was not confirmed even in such a dilute limit of vortices. The next experimental finding is the fact that the resistance level RTm where the sharp drop of the resistance occurs does not depend on magnetic fields below approximately 120 Oe. This is in contrast with the field dependence previously
reported from the measurements performed on the platelet samples but is in good accordance with the theoretical model proposed by Rojo et al.[6] based on the universalities of the structure factor at the freezing transition and Verlet criterion [7]. However, as the magnetic field is further increased and accordingly the melting transition temperature shifts down below appx. 55 K, the resistance level RTm begins to decrease. The resistance anomaly itself loses its sharpness and gradually disappears. This strongly indicates that the melting transition in this temperature region change its character from first-order to second-order phase transition, or some other dramatic processes would accompany. It is interesting to note that in magnetization measurements a weak anomaly characterized by a weak irreversibility magnetization behavior in the vortex liquid state was observed in the series of samples[8] in the same noted temperature region. Appearance of the novel vortex liquid phase suggested by [9] may explain this observation. One of the authors (J.M) thanks T. Mishonov and S. Savel'ev for useful discussions. REFERENCES
1. D.T. Fuchs et al. Nature 391,373 (1998). 2. J. Mirkovi~ et al. Adv. in Supercond. XI (ISS'98), p575, Springer-Verlag Tokyo, 1999. 3. P. Gammel et al. Phys. Rev. Lett. 61, 1666 (1988); E. Zeldov et al. Nature 375, 373 (1995); K. Kadowaki, Physica (Amsterdam) C236, 164 (1996). 4. J. Mirkovi6 and K. Kadowaki, Physica B (Proc. of 22nd Int. Conf. on Low Temp. Physics, 4-11 August,1999, Espoo, Finland). 5. G. Blatter et al. Phys. Rev. B54, 72 (1996). 6. A.G. Rojo et al., cond-mat, 9712017. 7. J.P. Hansen and L. Verlet, Phys. Rev. 184, 159 (1969). 8. K. Kimura et al. Physica B (Proc. of 22ud Int. Conf. on Low Temp. Physics, 4-11 August, 1999, Espoo, Finland). 9. Z. Te~anovid, Phys. Rev. B59, 6449 (1999); A. K. Nguyen and A. Sudb¢, Europhys. Lett. 46, 780 (1999).