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Electronic structure of impurity-substituted Bi2Sr2CaCu2O8+δ studied by angle-resolved photoemission spectroscopy
Journal of Physics and Chemistry of Solids 67 (2006) 271–273 www.elsevier.com/locate/jpcs
Electronic structure of impurity-substituted Bi2Sr2CaCu2O8Cd studied by angle-resolved photoemission spectroscopy K. Terashima a,*, D. Hashimoto a, H. Matsui a, T. Sato a, T. Takahashi a, T. Yamamoto b, K. Kadowaki b b
a Department of Physics, Tohoku University, Sendai 980-8578, Japan Institute of Materials Science, University of Tsukuba 1-1-1, Ten-nodai, Tsukuba, Ibaraki 305-8573, Japan
Abstract We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) on Co-, Ni-, and Zn-substituted Bi2Sr2CaCu2O8Cd (Bi2212) to study the impurity effect on the electronic structure. The shape of Fermi surface and the symmetry of superconducting gap are unchanged by impurities, while the superconducting coherent peak around (p, 0) is remarkably suppressed. The temperature dependence of the coherent-peak intensity shows a good correspondence to the reported superfluid density. The intensity of coherent peak scales well with the Tc in pristine, Co–, and Ni–Bi2212, but not in Zn–Bi2212, suggesting that non-magnetic Zn atoms destroy the superconductivity more strongly than the magnetic impurities. q 2005 Elsevier Ltd. All rights reserved. Keywords: D. Superconductivity
1. Introduction It is well known that even a small amount of impurities strongly suppresses the superconducting transition temperature (Tc) in high-temperature (high-Tc) superconductors. In contrast to the case of conventional BCS superconductors, non-magnetic impurities such as Zn [1] effectively destroy the superconductivity, showing the importance of the magnetic interaction in high-Tc superconductors. Impurity effects have been observed in many physical properties: (1) the residual resisitivity is increased by impurities [2,3]; (2) the suppression of superfluid density indicative of pair-breaking due to the impurity has been observed by mSR [4,5] and optical [6] experiments; (3) scanning tunneling spectroscopy (STS) experiment has revealed the existence of in-gap state as well as the suppression of the superconducting coherent peak [7,8]; (4) NMR experiment [9] suggests that non-magnetic impurity Zn induces an additional magnetic moment on the Cu site. In spite of these extensive experimental studies, there are few ARPES reports to study impurity effect on the electronic states near the Fermi level (EF) [10]. In this paper, we report ARPES results of Co-, Ni-, Znsubstituted Bi 2Sr 2CaCu2O 8Cd (Bi2212). We studied * Corresponding author. E-mail address: [email protected] (K. Terashima).
0022-3697/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2005.10.054
the impurity effect on the Fermi surface (FS), the superconducting gap anisotropy, and the spectral lineshape at the superconducting state. We found that while a small amount of impurities does not change the topology of FS or the d-wave gap symmetry, the coherent-peak intensity around (p, 0) is significantly suppressed and the effect is more pronounced in non-magnetic Zn substitution than in the cases of magnetic impurities Co and Ni. 2. Experiments High quality single crystals of Co-, Ni-, and Zn-substituted BI2212 were grown by the traveling-solvent floating-zone method. The actual content of impurity is estimated to be about 1%. The onset Tcs’ of Co– and Ni–Bi2212 crystals are 78 and 85 K, respectively, while we used two different Zn–Bi2212 crystals with different Tcs’ (81 and 85 K). ARPES measurements were performed using a GAMMADATA-SCIENTA SES-200 spectrometer with a high-flux discharge lamp and a toroidal grating monochrometor as well as at PGM beamline in Synchrotron Radiation Center, Wisconsin. We used the He Ia resonance line (21.218 eV) and 22-eV synchrotron radiation to excite photoelectrons. The energy and angular resolutions were set at 9–20 meV and 0.28, respectively. Clean surface for ARPES measurements was obtained by in situ cleaving of crystal in an ultrahigh vacuum better than 7!10K11 Torr. The Fermi level (EF) of the sample
272
K. Terashima et al. / Journal of Physics and Chemistry of Solids 67 (2006) 271–273
(b)
(a) (π,π)
(0,π)
(π,π)
(0,π)
Bi2212 Tc = 91 K
Co-Bi2212 Tc = 78 K
(π,0)
(0,0)
(c)
(π,0)
(0,0)
(d) (π,π)
(0,π)
(π,π)
(0,π) Zn-Bi2212 Tc = 85 K
Ni-Bi2212 Tc = 85 K
(0,0)
(π,0)
(0,0)
(π,0)
Fig. 1. ARPES intensity plot as a function of two-dimensional wave vector for (a) Bi2212 (TcZ91 K), (b) Co–Bi2212 (TcZ78 K), (c) Ni–Bi2212 (TcZ85 K), and (d) Zn–Bi2212 (TcZ85 K). Note that in addition to the main FS centered at (p, p), a replica due to the superlattice is observed around (0, 0).
Fig. 1 shows plot of ARPES intensity at EF as a function of two-dimensional wave vector for pristine and three different impurity-substituted Bi2212. Bright areas correspond to the Fermi surface (FS). We find in Fig. 1 that the shape of the FS, a holelke FS centered at (p, p), is unchanged by the impurity substitution. Further we have estimated the volume of the FS for each compound and found that it is essentially the same, 0.57G0.02 of the Brillouin-zone volume, for all compounds. This indicates that a small amount of impurity (about 1%) does not change the FS shape or the volume. Fig. 2(a) shows ARPES spectra of Co–Bi2212 measured at the superconducting state (40 K) along the FS from near (p, 0) (spectrum 1) to near (p/2, p/2) (spectrum 11), as shown in the inset of Fig. 2(b). It is obvious from Fig. 2(a) that the superconducting gap is anisotropic, about 40 meV near (p, 0) and almost zero near (p/2, p/2). In order to estimate the more exact values of the superconducting gap size as a function of the FS angle (q), we have symmetrized the spectrum with respect to EF to remove the effect from the Fermi-Dirac function [11] and fitted the spectra with Lorentzians. The results for pristine, Co–, Ni–, and Zn–Bi2212 are shown in Fig. 2(b), where we find that the dx2Ky2 gap symmetry is unchanged even in the impurity-substituted Bi2212. However, it is remarked that the gap around the nodal direction (qZ458) seems to be closed in a certain finite momentum region, possibly due to the disorder-induced scattering. We show in Fig. 3(a) the temperature dependence of the coherent peak around (p, 0) in Co–Bi2212. The sharp coherent
(a)
(b) 11 10 9 8 7 6 5 4 3 2 1
Co-Bi2212
100
50
EF
Binding Energy (meV)
Bi2212 Tc= 91 K Co-Bi2212 Tc= 78 K Ni-Bi2212 Tc= 85 K Zn-Bi2212 Tc= 85 K
1
Gap size (meV)
3. Results and discussion
peak gradually loses its spectral weight as increasing temperature and disappears at around Tc. To discuss more quantitatively the temperature dependence of the coherentpeak intensity, we performed numerical fitting to the spectra [12,13] and estimated the normalized intensity of coherent peak Z [13]. Fig. 3(b) shows the temperature dependence of Z in pristine and Co–Bi2212. We clearly find that the temperature dependence of Z is very similar to each other; Z evolves around Tc, and suddenly increases as decreasing temperature in both compounds. This suggests that there is a good correspondence between Z and superfluid density even in the impuritysubstituted Bi2212. Fig. 4(a) shows ARPES spectra of pristine, Co–, Ni–, Zn– Bi2212, and Bi2Sr2Ca2Cu3O10Cd (Bi2223) measured at the (p, 0)–(p, p) crossing point in the superconducting state. The spectral peak, located at 40 meV in pristine Bi2212, is slightly shifted toward lower binding energy in impurity-
Intensity (arb. units)
was referenced to that of a gold film evaporated onto the sample substrate.
30 2
20 (0,π)
10
0
(π,π)
11
11 (0,0)
θ 1 (π,0)
0 10 20 30 40 50 60
Fermi surface angle (θ)
Fig. 2. (a) ARPES spectra at 40 K of Co–Bi2212 measured at various kF-points shown in inset of (b). (b) Superconducting gap size of pristine- and impuritysubstituted Bi2212 as a function of FS angle (q).
K. Terashima et al. / Journal of Physics and Chemistry of Solids 67 (2006) 271–273
30 K 50 K 60 K 70 K 80 K 100 K
(π,π)
(0,π)
(0,0)
(b) 6 5 4
Z (%)
Intensity (arb. units)
(a)
273
3 2 Bi2212
1
Z 200
200
EF
100
150
100
Co-Bi2212
0 50
EF
0
–50
20
40
60
80
100 120
Temperature (K)
Binding Energy (meV)
Fig. 3. (a) Temperature dependence of ARPES spectra of Co–Bi2212 at (p, 0)–(p, p) crossing point. Inset shows the schematic view to estimate the peak intensity Z. (b) Temperature dependence of Z in pristine- and Co–Bi2212.
substituted Bi2212, indicating that the superconducting gap size is reduced by the impurities. We also find in Fig. 4(a) that the normalized peak intensity Z is apparently suppressed by the impurity-substitution. The extent of suppression is different for different impurities, but there is a general trend in Fig. 4(a) that a compound with higher Tc has higher peak intensity. This shows a good agreement with the ‘Uemura plot’ derived by the mSR experiment [14]. In Fig. 4(b), we plot Z as a function of Tc as in the case of Fig. 3. As clearly seen, we find a scaling behavior between Z and Tc for Bi2223, pristine-, Ni–, Co– Bi2212, and Bi2Sr2CuO6Cd (Bi2201). It is noted that estimated Z of Bi2201 is zero because we do not observe a sharp peak feature near EF [15,16]. In spite of a good scaling between Z and Tc among many pristine and impurity-substituted high-Tc superconductors, only Zn–Bi2212 shows a clear deviation from the scaling. This suggests that a non-magnetic Zn atom more effectively suppresses the superconductivity by causing the local pair breaking [4,6,7]. Another interesting experimental result is found in the spectra near EF. Inset of Fig. 4(a) shows an expansion of the ARPES spectra near EF. There is a finite spectral intensity at EF in all the impurity-substituted Bi2212. When we compare the spectral intensity at EF with the coherent peak intensity for each compound, we find a close relation between the two; namely, a compound which has a higher Bi2223 Bi2212 Ni–Bi2212 Zn–Bi2212 Co–Bi2212 Bi2201
10 8 10 5 EF –5 –10 B. E. (meV)
6 4
Bi2223 (Tc = 105 K) Bi2212 (Tc = 91 K) Ni–Bi2212 (Tc = 85 K) Co–Bi2212 (Tc = 78 K) Zn–Bi2212 (Tc = 81 K)
150
4. Summary We performed high-resolution ARPES on impurity-substituted Bi2212 to study the impurity effect on the electronic structure near EF. We measured the topology of Fermi surface, the momentum dependence of superconducting gap, and the spectral lineshape around (p, 0). The overall shape of FS and the symmetry of superconducting gap are unchanged by impurity-substitution. However, the superconducting gap size is slightly reduced, accompanied with the increase of gapless momentum region around the nodal direction. The intensity of the coherent peak is also reduced, indicating that the pair breaking takes places upon the impurity substitution. We found a scaling of the intensity of the coherent peak with Tc for pristine and impurity-substituted Bi2212 except for Zn– Bi2212. The deviation from the scaling of Zn–Bi2212 suggests the strong local pair breaking due to the magnetic interaction. Acknowledgements This work is supported by a grant from the MEXT of Japan. HM thanks a financial support from JSPS.
(b) 12
T = 40 K
Z (%)
Intensity (arb. units)
(a)
coherent peak intensity has a lower intensity at EF. It is inferred that the finite intensity at EF corresponds to the impurityinduced in-gap states reported by STS measurements [7,8].
100
50
Binding energy (meV)
2 0 EF
0
20 40 60 80 100
Tc (K)
Fig. 4. (a) APRES spectra of pristine-, Co–, Ni–, Zn–Bi2212 (TcZ81 K), and Bi2223 measured at (p, 0)–(p, p) crossing point at 40 K. Inset shows an expansion in the vicinity of EF. (b) Intensity of coherent peak Z at 40 K for various samples plotted as a function of Tc. Straight line is a guide for eyes.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]
B. Jayaram, et al., Phys. Rev. B 38 (1988) 2903. K. Mizuhashi, et al., Phys. Rev. B 52 (1995) R3884. M. Akoshima, et al., Phys. Rev. B 57 (1998) 7491. C. Bernhard, et al., Phys. Rev. Lett. 77 (1996) 2304. B. Nachumi, et al., Phys. Rev. Lett. 77 (1996) 5421. D.N. Basov, et al., Phys. Rev. Lett. 81 (1998) 2132. S.H. Pan, et al., Nature 403 (2000) 746. E.W. Hudson, et al., Nature 411 (2001) 920. H. Alloul, et al., Phys. Rev. Lett. 67 (1991) 3140. C. Quitmann, et al., Phys. Rev. B 53 (1996) 6819. L. Perfetti, et al., Phys. Rev. Lett. 90 (2003) 166401–166411. D.L. Feng, et al., Science 289 (2000) 277. H. Ding, et al., Phys. Rev. Lett. 87 (2001) 227001–227011. Y.J. Uemura, et al., Phys. Rev. Lett. 62 (1989) 2317. D.L. Feng, et al., Phys. Rev. Lett. 88 (2002) 107001–107011. T. Sato, et al., Phys. Rev. Lett. 89 (2002) 067005–067015.
Electronic structure of impurity-substituted Bi2Sr2CaCu2O8Cd studied by angle-resolved photoemission spectroscopy K. Terashima a,*, D. Hashimoto a, H. Matsui a, T. Sato a, T. Takahashi a, T. Yamamoto b, K. Kadowaki b b
a Department of Physics, Tohoku University, Sendai 980-8578, Japan Institute of Materials Science, University of Tsukuba 1-1-1, Ten-nodai, Tsukuba, Ibaraki 305-8573, Japan
Abstract We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) on Co-, Ni-, and Zn-substituted Bi2Sr2CaCu2O8Cd (Bi2212) to study the impurity effect on the electronic structure. The shape of Fermi surface and the symmetry of superconducting gap are unchanged by impurities, while the superconducting coherent peak around (p, 0) is remarkably suppressed. The temperature dependence of the coherent-peak intensity shows a good correspondence to the reported superfluid density. The intensity of coherent peak scales well with the Tc in pristine, Co–, and Ni–Bi2212, but not in Zn–Bi2212, suggesting that non-magnetic Zn atoms destroy the superconductivity more strongly than the magnetic impurities. q 2005 Elsevier Ltd. All rights reserved. Keywords: D. Superconductivity
1. Introduction It is well known that even a small amount of impurities strongly suppresses the superconducting transition temperature (Tc) in high-temperature (high-Tc) superconductors. In contrast to the case of conventional BCS superconductors, non-magnetic impurities such as Zn [1] effectively destroy the superconductivity, showing the importance of the magnetic interaction in high-Tc superconductors. Impurity effects have been observed in many physical properties: (1) the residual resisitivity is increased by impurities [2,3]; (2) the suppression of superfluid density indicative of pair-breaking due to the impurity has been observed by mSR [4,5] and optical [6] experiments; (3) scanning tunneling spectroscopy (STS) experiment has revealed the existence of in-gap state as well as the suppression of the superconducting coherent peak [7,8]; (4) NMR experiment [9] suggests that non-magnetic impurity Zn induces an additional magnetic moment on the Cu site. In spite of these extensive experimental studies, there are few ARPES reports to study impurity effect on the electronic states near the Fermi level (EF) [10]. In this paper, we report ARPES results of Co-, Ni-, Znsubstituted Bi 2Sr 2CaCu2O 8Cd (Bi2212). We studied * Corresponding author. E-mail address: [email protected] (K. Terashima).
0022-3697/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2005.10.054
the impurity effect on the Fermi surface (FS), the superconducting gap anisotropy, and the spectral lineshape at the superconducting state. We found that while a small amount of impurities does not change the topology of FS or the d-wave gap symmetry, the coherent-peak intensity around (p, 0) is significantly suppressed and the effect is more pronounced in non-magnetic Zn substitution than in the cases of magnetic impurities Co and Ni. 2. Experiments High quality single crystals of Co-, Ni-, and Zn-substituted BI2212 were grown by the traveling-solvent floating-zone method. The actual content of impurity is estimated to be about 1%. The onset Tcs’ of Co– and Ni–Bi2212 crystals are 78 and 85 K, respectively, while we used two different Zn–Bi2212 crystals with different Tcs’ (81 and 85 K). ARPES measurements were performed using a GAMMADATA-SCIENTA SES-200 spectrometer with a high-flux discharge lamp and a toroidal grating monochrometor as well as at PGM beamline in Synchrotron Radiation Center, Wisconsin. We used the He Ia resonance line (21.218 eV) and 22-eV synchrotron radiation to excite photoelectrons. The energy and angular resolutions were set at 9–20 meV and 0.28, respectively. Clean surface for ARPES measurements was obtained by in situ cleaving of crystal in an ultrahigh vacuum better than 7!10K11 Torr. The Fermi level (EF) of the sample
272
K. Terashima et al. / Journal of Physics and Chemistry of Solids 67 (2006) 271–273
(b)
(a) (π,π)
(0,π)
(π,π)
(0,π)
Bi2212 Tc = 91 K
Co-Bi2212 Tc = 78 K
(π,0)
(0,0)
(c)
(π,0)
(0,0)
(d) (π,π)
(0,π)
(π,π)
(0,π) Zn-Bi2212 Tc = 85 K
Ni-Bi2212 Tc = 85 K
(0,0)
(π,0)
(0,0)
(π,0)
Fig. 1. ARPES intensity plot as a function of two-dimensional wave vector for (a) Bi2212 (TcZ91 K), (b) Co–Bi2212 (TcZ78 K), (c) Ni–Bi2212 (TcZ85 K), and (d) Zn–Bi2212 (TcZ85 K). Note that in addition to the main FS centered at (p, p), a replica due to the superlattice is observed around (0, 0).
Fig. 1 shows plot of ARPES intensity at EF as a function of two-dimensional wave vector for pristine and three different impurity-substituted Bi2212. Bright areas correspond to the Fermi surface (FS). We find in Fig. 1 that the shape of the FS, a holelke FS centered at (p, p), is unchanged by the impurity substitution. Further we have estimated the volume of the FS for each compound and found that it is essentially the same, 0.57G0.02 of the Brillouin-zone volume, for all compounds. This indicates that a small amount of impurity (about 1%) does not change the FS shape or the volume. Fig. 2(a) shows ARPES spectra of Co–Bi2212 measured at the superconducting state (40 K) along the FS from near (p, 0) (spectrum 1) to near (p/2, p/2) (spectrum 11), as shown in the inset of Fig. 2(b). It is obvious from Fig. 2(a) that the superconducting gap is anisotropic, about 40 meV near (p, 0) and almost zero near (p/2, p/2). In order to estimate the more exact values of the superconducting gap size as a function of the FS angle (q), we have symmetrized the spectrum with respect to EF to remove the effect from the Fermi-Dirac function [11] and fitted the spectra with Lorentzians. The results for pristine, Co–, Ni–, and Zn–Bi2212 are shown in Fig. 2(b), where we find that the dx2Ky2 gap symmetry is unchanged even in the impurity-substituted Bi2212. However, it is remarked that the gap around the nodal direction (qZ458) seems to be closed in a certain finite momentum region, possibly due to the disorder-induced scattering. We show in Fig. 3(a) the temperature dependence of the coherent peak around (p, 0) in Co–Bi2212. The sharp coherent
(a)
(b) 11 10 9 8 7 6 5 4 3 2 1
Co-Bi2212
100
50
EF
Binding Energy (meV)
Bi2212 Tc= 91 K Co-Bi2212 Tc= 78 K Ni-Bi2212 Tc= 85 K Zn-Bi2212 Tc= 85 K
1
Gap size (meV)
3. Results and discussion
peak gradually loses its spectral weight as increasing temperature and disappears at around Tc. To discuss more quantitatively the temperature dependence of the coherentpeak intensity, we performed numerical fitting to the spectra [12,13] and estimated the normalized intensity of coherent peak Z [13]. Fig. 3(b) shows the temperature dependence of Z in pristine and Co–Bi2212. We clearly find that the temperature dependence of Z is very similar to each other; Z evolves around Tc, and suddenly increases as decreasing temperature in both compounds. This suggests that there is a good correspondence between Z and superfluid density even in the impuritysubstituted Bi2212. Fig. 4(a) shows ARPES spectra of pristine, Co–, Ni–, Zn– Bi2212, and Bi2Sr2Ca2Cu3O10Cd (Bi2223) measured at the (p, 0)–(p, p) crossing point in the superconducting state. The spectral peak, located at 40 meV in pristine Bi2212, is slightly shifted toward lower binding energy in impurity-
Intensity (arb. units)
was referenced to that of a gold film evaporated onto the sample substrate.
30 2
20 (0,π)
10
0
(π,π)
11
11 (0,0)
θ 1 (π,0)
0 10 20 30 40 50 60
Fermi surface angle (θ)
Fig. 2. (a) ARPES spectra at 40 K of Co–Bi2212 measured at various kF-points shown in inset of (b). (b) Superconducting gap size of pristine- and impuritysubstituted Bi2212 as a function of FS angle (q).
K. Terashima et al. / Journal of Physics and Chemistry of Solids 67 (2006) 271–273
30 K 50 K 60 K 70 K 80 K 100 K
(π,π)
(0,π)
(0,0)
(b) 6 5 4
Z (%)
Intensity (arb. units)
(a)
273
3 2 Bi2212
1
Z 200
200
EF
100
150
100
Co-Bi2212
0 50
EF
0
–50
20
40
60
80
100 120
Temperature (K)
Binding Energy (meV)
Fig. 3. (a) Temperature dependence of ARPES spectra of Co–Bi2212 at (p, 0)–(p, p) crossing point. Inset shows the schematic view to estimate the peak intensity Z. (b) Temperature dependence of Z in pristine- and Co–Bi2212.
substituted Bi2212, indicating that the superconducting gap size is reduced by the impurities. We also find in Fig. 4(a) that the normalized peak intensity Z is apparently suppressed by the impurity-substitution. The extent of suppression is different for different impurities, but there is a general trend in Fig. 4(a) that a compound with higher Tc has higher peak intensity. This shows a good agreement with the ‘Uemura plot’ derived by the mSR experiment [14]. In Fig. 4(b), we plot Z as a function of Tc as in the case of Fig. 3. As clearly seen, we find a scaling behavior between Z and Tc for Bi2223, pristine-, Ni–, Co– Bi2212, and Bi2Sr2CuO6Cd (Bi2201). It is noted that estimated Z of Bi2201 is zero because we do not observe a sharp peak feature near EF [15,16]. In spite of a good scaling between Z and Tc among many pristine and impurity-substituted high-Tc superconductors, only Zn–Bi2212 shows a clear deviation from the scaling. This suggests that a non-magnetic Zn atom more effectively suppresses the superconductivity by causing the local pair breaking [4,6,7]. Another interesting experimental result is found in the spectra near EF. Inset of Fig. 4(a) shows an expansion of the ARPES spectra near EF. There is a finite spectral intensity at EF in all the impurity-substituted Bi2212. When we compare the spectral intensity at EF with the coherent peak intensity for each compound, we find a close relation between the two; namely, a compound which has a higher Bi2223 Bi2212 Ni–Bi2212 Zn–Bi2212 Co–Bi2212 Bi2201
10 8 10 5 EF –5 –10 B. E. (meV)
6 4
Bi2223 (Tc = 105 K) Bi2212 (Tc = 91 K) Ni–Bi2212 (Tc = 85 K) Co–Bi2212 (Tc = 78 K) Zn–Bi2212 (Tc = 81 K)
150
4. Summary We performed high-resolution ARPES on impurity-substituted Bi2212 to study the impurity effect on the electronic structure near EF. We measured the topology of Fermi surface, the momentum dependence of superconducting gap, and the spectral lineshape around (p, 0). The overall shape of FS and the symmetry of superconducting gap are unchanged by impurity-substitution. However, the superconducting gap size is slightly reduced, accompanied with the increase of gapless momentum region around the nodal direction. The intensity of the coherent peak is also reduced, indicating that the pair breaking takes places upon the impurity substitution. We found a scaling of the intensity of the coherent peak with Tc for pristine and impurity-substituted Bi2212 except for Zn– Bi2212. The deviation from the scaling of Zn–Bi2212 suggests the strong local pair breaking due to the magnetic interaction. Acknowledgements This work is supported by a grant from the MEXT of Japan. HM thanks a financial support from JSPS.
(b) 12
T = 40 K
Z (%)
Intensity (arb. units)
(a)
coherent peak intensity has a lower intensity at EF. It is inferred that the finite intensity at EF corresponds to the impurityinduced in-gap states reported by STS measurements [7,8].
100
50
Binding energy (meV)
2 0 EF
0
20 40 60 80 100
Tc (K)
Fig. 4. (a) APRES spectra of pristine-, Co–, Ni–, Zn–Bi2212 (TcZ81 K), and Bi2223 measured at (p, 0)–(p, p) crossing point at 40 K. Inset shows an expansion in the vicinity of EF. (b) Intensity of coherent peak Z at 40 K for various samples plotted as a function of Tc. Straight line is a guide for eyes.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]
B. Jayaram, et al., Phys. Rev. B 38 (1988) 2903. K. Mizuhashi, et al., Phys. Rev. B 52 (1995) R3884. M. Akoshima, et al., Phys. Rev. B 57 (1998) 7491. C. Bernhard, et al., Phys. Rev. Lett. 77 (1996) 2304. B. Nachumi, et al., Phys. Rev. Lett. 77 (1996) 5421. D.N. Basov, et al., Phys. Rev. Lett. 81 (1998) 2132. S.H. Pan, et al., Nature 403 (2000) 746. E.W. Hudson, et al., Nature 411 (2001) 920. H. Alloul, et al., Phys. Rev. Lett. 67 (1991) 3140. C. Quitmann, et al., Phys. Rev. B 53 (1996) 6819. L. Perfetti, et al., Phys. Rev. Lett. 90 (2003) 166401–166411. D.L. Feng, et al., Science 289 (2000) 277. H. Ding, et al., Phys. Rev. Lett. 87 (2001) 227001–227011. Y.J. Uemura, et al., Phys. Rev. Lett. 62 (1989) 2317. D.L. Feng, et al., Phys. Rev. Lett. 88 (2002) 107001–107011. T. Sato, et al., Phys. Rev. Lett. 89 (2002) 067005–067015.