- Email: [email protected]
Spin correlations in electron-doped high-Tc superconductor
ARTICLE IN PRESS
Journal of Physics and Chemistry of Solids 68 (2007) 2035–2038 www.elsevier.com/locate/jpcs
Spin correlations in electron-doped high-T c superconductor M. Fujita Institute for Materials Research, Tohoku University, Sendai, Miyagi 980-8577, Japan
Abstract Spin correlations in the electron-doped Pr1x LaCex CuO4 have been investigated by neutron-scattering and muon rotation/relaxation measurements. The low-enegy spin correlations were found to be in commensurate with the wide superconducting phase, unlike the incommensurate ones in the hole-doped La2x Srx CuO4 . No enhancement of the magnetic order by impurity-doping and applying magnetic fields was observed, although the superconductivity is effectively suppressed, compared to that in the hole-doped system. Distinct impurity and magnetic field effects between the static spin correlation in the electron-doped system and those in the hole-doped systems suggest the different magnetic ground state in the two systems. r 2007 Elsevier Ltd. All rights reserved. Keywords: C. Neutron-scattering; D. mSR measurements
1. Introduction High-transition temperature ðT c Þ superconductivity mediated by spin fluctuations is one of central issues in the strongly correlated electron systems. In the last two decades, extensive neutron scattering measurements on a prototypical superconducting (SC) system of La2x Srx CuO4 (LSCO) have revealed an evolution of spin correlation by doping and its intimate relationship with the superconductivity [1]. For example, spin modulation vector diagonal to Cu–O–Cu direction in the insulating phase changes into parallel direction on crossing the critical concentration for the appearance of superconductivity, xc 0:055. Furthermore, an overall spin excitation in the SC phase of La2x Bax CuO4 (LBCO) with x ¼ 18 [2] and YBa2Cu3O6.6 [3] have a similar fascinating hourglassshaped dispersion. These findings are important steps towards unified understanding of spin correlations and its direct relevance to the high-T c superconductivity. On the other hand, the low-energy spin fluctuations seem to compete with the superconductivity: the magnetic order in superconducting LSCO at x 18 can be enhanced by applying magnetic fields or by impurity substitution onto the CuO2 planes [4–6]. Moreover, in the Tel.: +81 22 215 2037; fax: +81 22 215 2036.
E-mail address: [email protected] 0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2007.08.021
optimally doped LSCO ðx0:15Þ where a spin gap exists, both external magnetic field and Zn-doping induce slow spin fluctuations below the gap, which would be a tendency toward the magnetic order [7,8]. Therefore, the antiferromagnetic (AF) insulator with incommensurate correlations is considered to be the ground state for the system with high Zn-concentrations and/or the under high magnetic fields where the superconductivity vanishes. To understand a novel magnetism in carrier-doped Mott insulators and the role in the high-T c SC mechanism, comparative studies betweeen hole-doped (p-type) and electron-doped (n-type) systems are indispensable. However, there are quite few investigations of spin correlations in the n-type system, possibly due to difficulties in preparing high quality and sufficiently large samples through adequate heat treatments. Such experimental difficulties was overcome by our group and we showed a magnetic and superconducting phase diagram of the n-type Pr1x LaCex CuO4 (PLCCO) [9]. This result provides important challenges to the paradigm established for the hole-doped system. We hence studied spin correlations in the electron-doped system by neutron-scattering and muon spin rotation/relaxation ðmSRÞ measurements. In this paper, I present the typical experimental results obtained for PLCCO system, which is contrastive to the results for LSCO system.
ARTICLE IN PRESS 2036
M. Fujita / Journal of Physics and Chemistry of Solids 68 (2007) 2035–2038
Pr1-x LaCex CuO4 T = 8K, ω = 4meV
2. Experiment
(h h 0)
200 100 0
Count / 7min
Single crystals of Pr1x LaCex CuO4 with x ¼ 0:07, 0.09, 0.11, 0.13, 0.15 and 0.18 were grown by the travelingsolvent floating-zone method. As-grown single crystals were annealed under Ar gas flow at 920–950 C for 10–12 h. The samples with xX0:09 shows bulk superconductivity, while no superconducting transition was observed in the x ¼ 0:07 sample. On the other hand, AF order takes place in the samples with 0:07pxp0:11. Thus, AF order and superconductivity coexist in the vicinity of the AF and SC phase boundary. These results are consistent with the previously obtained results for the powder and small single crystals samples [9]. For the mSR measurements, we furthermore prepared a series of powder samples of Zndoped PLCCO by the solid-state reaction method. The Ce and Zn concentrations are confirmed to be nominal value by the inductively coupled plasma spectrometry technique.
600 400 200 0
Count / 18min
2.1. Sample preparation and characterization
Count/11min
300
100
0 0.40
0.45
0.50 h (r.l.u.)
0.55
0.60
Fig. 1. Inelastic neutron scattering spectra of Pr1x LaCex CuO4 with x ¼ ðaÞ 0.07, (b) 0.11 and (d) 0.18 at o ¼ 4 meV and T ¼ 8 K. The solid lines are fits assuming single Gaussian-shaped peak centered at (0.5,0.5,0).
2.2. Neutron-scattering and mSR measurements Pr0.89 LaCe0.11CuO4
3. Results
200
150
ω (meV)
Low-eneryg ðop12 meVÞ and high-energy ðop180 meVÞ neutron-scattering measurements were performed on the thermal triple-axis spectrometers TOPAN and TAS-1 installed in the reactor of JRR-3 at Japan Atomic Energy Agency and time-of-flight spectrometers MARI and MAPS at the ISIS pulsed spallation neutron source, Rutherford Appleton Laboratory (RAL) in the UK, respectively. Zero-field mSR measurements were also carried out in RIKEN-RAL muon Facility, RAL.
100
50
3.1. spin fluctuations 0
Fig. 1 shows the neutron-scattering spectra with a constant energy of 4 meV for x ¼ 0:07 (AF ordered sample) and 0.11 (optimally doped sample) and 0.18 (overdope sample) measured at 8 K. Commensurate low-energy spin fluctuations were observed in both AF ordered and SC samples. No evidence of drastic change on crossing AF and SC phase boundary was observed, although the peak-width is slightly wider in the SC sample. Single peak in the x ¼ 0:18 sample locating far inside the SC dome suggests that the commensurate spin correlations are robust against electron-doping. In the optimally doped x ¼ 0.11, single peak were confirmed to be centered at ðp; pÞ position even at highenergy region. In Fig. 2, the spin excitation spectrum up to 180 meV for the x ¼ 0:11 sample is shown. Horizontal and vertical axes of the rectangle represents a fitted result of peak-width in full-width at half-width with assuming a single Gaussian function and the integrated energy region for the fitting. The peak broadens in the low-energy region below 60 meV, while the width weakly depends on o at high-energy region above 100 meV. This excitation is far
0.3
0.4
0.5 h (r.l.u.)
0.6
0.7
Fig. 2. Magnetic excitation in the optimally doped Pr0:89 LaCe0:11 CuO4 at 8 K. Horizontal axis of the rectangle represents the peak-width (full-width at half-width) within the energy range show vertical axis. Dashed lines are guides to the eye.
different from that observed in the p-type system showing hourglass-shaped dispersion, suggesting the asymmetric doping effect on the spin correlations against the carrier type. We note that the observed overall spectrum is also different from the conventional spin-wave excitation, although the x ¼ 0:11 sample is located on the AF ordered and superconducting phase boundary. 3.2. Zn impurity and magnetic field effects on the static spin correlation In Fig. 3, Zn concentration (y) dependence of the magnetic ordering temperature ðT m Þ, where the rotation
ARTICLE IN PRESS M. Fujita / Journal of Physics and Chemistry of Solids 68 (2007) 2035–2038
4. Discussion and summary The spin correlations in the n-type PLCCO system show distinct features from those in the p-type LSCO system. First, commensurate low-energy spin fluctuations were confirmed in the wide SC phase, unlike to the incommensurate ones in LSCO. The high-energy spin excitations in the two system also shows qualitative difference. Second, AF order is simply degraded by Zn doping, while the anomalous enhancement of spin correlations was reported for the LSCO system with the adequate Zn concentrations. Pr1-x LaCex Cu1-y Zny O4 150
x=0.06
T (K)
100
x=0.08
50
x=0.10 0 0
0.05 0.10 Zn concentration (y)
Pr1-x LaCex CuO4 , T = 3K 40 (1.5+h 0.5-h 0)
x = 0.11 x = 0.15
20
Count / min
component appears in the mSR time spectrum upon cooling, is shown for x ¼ 0:06, 0.08 and 0.10. T m for all x-fixed samples is monotonically decreases upon increasing y, indicating a degradation of magnetic order. In the SC sample with xX0:12, no enhancement or inducement of AF order was observed even though the superconductivity was suppressed by Zn doping. This behavior seems to be quantitatively different from the competitive relation between the AF order and superconductivity in the p-type LSCO system [6,10]. Similarly, weak or no inducement of magnetic order under magnetic fields was observed in the optimally doped and overdoped samples, respectively. Fig. 4 shows background-subtracted peak profiles for x ¼ 0:11 (closed circles) and x ¼ 0:15 (open circles) under magnetic fields at (a) 0 T, (b) 5 T. Contrast to the no indication of magnetic signal in x ¼ 0:15, the intensity is enhanced by the field of 5 T in the x ¼ 0:11 sample. However, compared with LSCO with x ¼ 0:10, the enhanced intensity is quite weak, although the superconductivity is almost suppressed due to the low critical field for the full suppression of the superconductivity. Thus, the competitive coupling between the AF ordering and superconductivity is much weaker or absent in the n-type system.
2037
0 40
20
0 -0.01
0 h (r.l.u.)
0.01
Fig. 4. Peak profiles for Pr1x LaCex CuO4 with x ¼ 0:11 (closed circles) and x ¼ 0:15 (open circles) at 3 K under the field at (a) 0 T and (b) 6 T. The field-independent background was subtracted. The solid lines are results fitted with a single Gaussian function by convoluting the resolution.
Furthermore, the suppression of superconductivity by Zn-substitution or applying magnetic fields neither enhance nor induce well-defined AF order such as seen in the LSCO system. These experimental facts suggest a different magnetic ground state between the two systems. In the p-type LSCO, there increases the evidence of the spatially segregated spin and change stripe orders. On the other hand, commensurate spin correlations simply suggest no existence of stripe correlations in the n-type system. The nuclear magnetic resonance study by Zheng et al. suggests the Fermi-liquid ground state is a possible ground state in the optimally doped PLCCO system [11] and the metallic conductivity was reported for the doped AF phase of n-type Nd2x Cex CuO4 [12]. Observed high-energy spin excitations persisting at ðp; pÞ position is indeed similar to those in nearly antiferromagnetic metal Cr0.95V0.05 [13]. Weak enhancement of the AF order with suppressing the superconductivity would be originated from the weak effect on the mobile carriers compared to that in the p-type system. To clarify the universal role of spin fluctuations in the mechanism of superconductivity, further comprehensive studies for both systems are important. In conclusion, we studied the spin correlations in the n-type PLCCO system and its response against the Zn-doping and magnetic field. The spin correlations in the PLCCO system is of commensurate in the wide SC phase, unlike to the incommensurate ones in the p-type LSCO. Distinct impurity and magnetic field effects on the the static spin correlation in the n- and p-types suggest the different magnetic ground state in the two systems.
0.15
Fig. 3. Zn concentration (y) dependence of the magnetic ordering temperature for the x ¼ 0:06 (open diamonds), 0.08 (filled circles) and 0.10 (open squares) samples. Dashed lines are guides to the eye.
Acknowledgement I would like to thank my collaborators, H. Goka, K. Kawashima, H. Kimura, T. Kubo, S. Kuroshima,
ARTICLE IN PRESS 2038
M. Fujita / Journal of Physics and Chemistry of Solids 68 (2007) 2035–2038
A. Hino, S.H. Lee, M. Nakagawa, M. Matsuda, T. Takagi, T. Uefuji and K. Yamada for collaborative works on neutron scattering. This work was supported in part by a Grant-In-Aid for Young Scientists A (17684016) and a Grant-in-Aid from the Japanese Ministry of Education, Culture, Sports, Science and Technology.
[6] [7]
[8]
References [1] M. Fujita, K. Yamada, H. Hiraka, P.M. Gehring, S.H. Lee, S. Wakimoto, G. Shirane, Phys. Rev. B 65 (2002) 064505. [2] J.M. Tranquada, H. Woo, T.G. Perring, H. Goka, G.D. Gu, G. Xu, M. Fujita, K. Yamada, Nature 429 (2004) 534. [3] S.M. Hayden, H.A. Mook, P. Dai, T.G. Perring, F. Dog˘an, Nature 429 (2004) 531. [4] S. Katano, M. Sato, K. Yamada, T. Suzuki, T. Fukase, Phys. Rev. B 62 (2000) R14677. [5] B. Lake, H.M. Rønnow, N.B. Christensen, G. Aeppli, K. Lefmann, D.F. McMorrow, P. Vorderwisch, P. Smeibidl, N. Mangkorntong,
[9]
[10] [11] [12] [13]
T. Sasagawa, M. Nohara, H. Takagi, T.E. Mason, Nature (London) 417 (2002) 299. I. Watanabe, T. Adachi, K. Takahashi, S. Yairi, Y. Koike, K. Nagamine, Phys. Rev. B 65 (2002) 180516. B. Lake, G. Aeppli, K.N. Clausen, D.F. McMorrow, K. Lefmann, N.E. Hussey, N. Mangkorntong, M. Nohara, H. Takagi, T.E. Mason, A. Scho¨rder, Science 291 (2001) 1759. M. Kofu, H. Kimura, K. Hirota, Phys. Rev. B 72 (2005) 064502. M. Fujita, T. Kubo, S. Kuroshima, T. Uefuji, K. Kawashima, K. Yamada, I. Watanabe, K. Nagamine, Phys. Rev. B 67 (2003) 014514. T. Adachi, S. Yairi, K. Takahashi, Y. Koike, I. Watanabe, K. Nagamine, Phys. Rev. B 69 (2004) 184507. G.-q. Zheng, T. Sato, Y. Kitaoka, M. Fujita, K. Yamada, Phys. Rev. Lett. 90 (2003) 197005. Y. Onose, Y. Taguchi, K. Ishizaka, Y. Tokura, Phys. Rev. Lett. 87 (2001) 217001. S.M. Hayden, R. Doubble, G. Aeppli, T.G. Perring, E. Fawcett, Phys. Rev. Lett. 84 (2000) 999.
Journal of Physics and Chemistry of Solids 68 (2007) 2035–2038 www.elsevier.com/locate/jpcs
Spin correlations in electron-doped high-T c superconductor M. Fujita Institute for Materials Research, Tohoku University, Sendai, Miyagi 980-8577, Japan
Abstract Spin correlations in the electron-doped Pr1x LaCex CuO4 have been investigated by neutron-scattering and muon rotation/relaxation measurements. The low-enegy spin correlations were found to be in commensurate with the wide superconducting phase, unlike the incommensurate ones in the hole-doped La2x Srx CuO4 . No enhancement of the magnetic order by impurity-doping and applying magnetic fields was observed, although the superconductivity is effectively suppressed, compared to that in the hole-doped system. Distinct impurity and magnetic field effects between the static spin correlation in the electron-doped system and those in the hole-doped systems suggest the different magnetic ground state in the two systems. r 2007 Elsevier Ltd. All rights reserved. Keywords: C. Neutron-scattering; D. mSR measurements
1. Introduction High-transition temperature ðT c Þ superconductivity mediated by spin fluctuations is one of central issues in the strongly correlated electron systems. In the last two decades, extensive neutron scattering measurements on a prototypical superconducting (SC) system of La2x Srx CuO4 (LSCO) have revealed an evolution of spin correlation by doping and its intimate relationship with the superconductivity [1]. For example, spin modulation vector diagonal to Cu–O–Cu direction in the insulating phase changes into parallel direction on crossing the critical concentration for the appearance of superconductivity, xc 0:055. Furthermore, an overall spin excitation in the SC phase of La2x Bax CuO4 (LBCO) with x ¼ 18 [2] and YBa2Cu3O6.6 [3] have a similar fascinating hourglassshaped dispersion. These findings are important steps towards unified understanding of spin correlations and its direct relevance to the high-T c superconductivity. On the other hand, the low-energy spin fluctuations seem to compete with the superconductivity: the magnetic order in superconducting LSCO at x 18 can be enhanced by applying magnetic fields or by impurity substitution onto the CuO2 planes [4–6]. Moreover, in the Tel.: +81 22 215 2037; fax: +81 22 215 2036.
E-mail address: [email protected] 0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2007.08.021
optimally doped LSCO ðx0:15Þ where a spin gap exists, both external magnetic field and Zn-doping induce slow spin fluctuations below the gap, which would be a tendency toward the magnetic order [7,8]. Therefore, the antiferromagnetic (AF) insulator with incommensurate correlations is considered to be the ground state for the system with high Zn-concentrations and/or the under high magnetic fields where the superconductivity vanishes. To understand a novel magnetism in carrier-doped Mott insulators and the role in the high-T c SC mechanism, comparative studies betweeen hole-doped (p-type) and electron-doped (n-type) systems are indispensable. However, there are quite few investigations of spin correlations in the n-type system, possibly due to difficulties in preparing high quality and sufficiently large samples through adequate heat treatments. Such experimental difficulties was overcome by our group and we showed a magnetic and superconducting phase diagram of the n-type Pr1x LaCex CuO4 (PLCCO) [9]. This result provides important challenges to the paradigm established for the hole-doped system. We hence studied spin correlations in the electron-doped system by neutron-scattering and muon spin rotation/relaxation ðmSRÞ measurements. In this paper, I present the typical experimental results obtained for PLCCO system, which is contrastive to the results for LSCO system.
ARTICLE IN PRESS 2036
M. Fujita / Journal of Physics and Chemistry of Solids 68 (2007) 2035–2038
Pr1-x LaCex CuO4 T = 8K, ω = 4meV
2. Experiment
(h h 0)
200 100 0
Count / 7min
Single crystals of Pr1x LaCex CuO4 with x ¼ 0:07, 0.09, 0.11, 0.13, 0.15 and 0.18 were grown by the travelingsolvent floating-zone method. As-grown single crystals were annealed under Ar gas flow at 920–950 C for 10–12 h. The samples with xX0:09 shows bulk superconductivity, while no superconducting transition was observed in the x ¼ 0:07 sample. On the other hand, AF order takes place in the samples with 0:07pxp0:11. Thus, AF order and superconductivity coexist in the vicinity of the AF and SC phase boundary. These results are consistent with the previously obtained results for the powder and small single crystals samples [9]. For the mSR measurements, we furthermore prepared a series of powder samples of Zndoped PLCCO by the solid-state reaction method. The Ce and Zn concentrations are confirmed to be nominal value by the inductively coupled plasma spectrometry technique.
600 400 200 0
Count / 18min
2.1. Sample preparation and characterization
Count/11min
300
100
0 0.40
0.45
0.50 h (r.l.u.)
0.55
0.60
Fig. 1. Inelastic neutron scattering spectra of Pr1x LaCex CuO4 with x ¼ ðaÞ 0.07, (b) 0.11 and (d) 0.18 at o ¼ 4 meV and T ¼ 8 K. The solid lines are fits assuming single Gaussian-shaped peak centered at (0.5,0.5,0).
2.2. Neutron-scattering and mSR measurements Pr0.89 LaCe0.11CuO4
3. Results
200
150
ω (meV)
Low-eneryg ðop12 meVÞ and high-energy ðop180 meVÞ neutron-scattering measurements were performed on the thermal triple-axis spectrometers TOPAN and TAS-1 installed in the reactor of JRR-3 at Japan Atomic Energy Agency and time-of-flight spectrometers MARI and MAPS at the ISIS pulsed spallation neutron source, Rutherford Appleton Laboratory (RAL) in the UK, respectively. Zero-field mSR measurements were also carried out in RIKEN-RAL muon Facility, RAL.
100
50
3.1. spin fluctuations 0
Fig. 1 shows the neutron-scattering spectra with a constant energy of 4 meV for x ¼ 0:07 (AF ordered sample) and 0.11 (optimally doped sample) and 0.18 (overdope sample) measured at 8 K. Commensurate low-energy spin fluctuations were observed in both AF ordered and SC samples. No evidence of drastic change on crossing AF and SC phase boundary was observed, although the peak-width is slightly wider in the SC sample. Single peak in the x ¼ 0:18 sample locating far inside the SC dome suggests that the commensurate spin correlations are robust against electron-doping. In the optimally doped x ¼ 0.11, single peak were confirmed to be centered at ðp; pÞ position even at highenergy region. In Fig. 2, the spin excitation spectrum up to 180 meV for the x ¼ 0:11 sample is shown. Horizontal and vertical axes of the rectangle represents a fitted result of peak-width in full-width at half-width with assuming a single Gaussian function and the integrated energy region for the fitting. The peak broadens in the low-energy region below 60 meV, while the width weakly depends on o at high-energy region above 100 meV. This excitation is far
0.3
0.4
0.5 h (r.l.u.)
0.6
0.7
Fig. 2. Magnetic excitation in the optimally doped Pr0:89 LaCe0:11 CuO4 at 8 K. Horizontal axis of the rectangle represents the peak-width (full-width at half-width) within the energy range show vertical axis. Dashed lines are guides to the eye.
different from that observed in the p-type system showing hourglass-shaped dispersion, suggesting the asymmetric doping effect on the spin correlations against the carrier type. We note that the observed overall spectrum is also different from the conventional spin-wave excitation, although the x ¼ 0:11 sample is located on the AF ordered and superconducting phase boundary. 3.2. Zn impurity and magnetic field effects on the static spin correlation In Fig. 3, Zn concentration (y) dependence of the magnetic ordering temperature ðT m Þ, where the rotation
ARTICLE IN PRESS M. Fujita / Journal of Physics and Chemistry of Solids 68 (2007) 2035–2038
4. Discussion and summary The spin correlations in the n-type PLCCO system show distinct features from those in the p-type LSCO system. First, commensurate low-energy spin fluctuations were confirmed in the wide SC phase, unlike to the incommensurate ones in LSCO. The high-energy spin excitations in the two system also shows qualitative difference. Second, AF order is simply degraded by Zn doping, while the anomalous enhancement of spin correlations was reported for the LSCO system with the adequate Zn concentrations. Pr1-x LaCex Cu1-y Zny O4 150
x=0.06
T (K)
100
x=0.08
50
x=0.10 0 0
0.05 0.10 Zn concentration (y)
Pr1-x LaCex CuO4 , T = 3K 40 (1.5+h 0.5-h 0)
x = 0.11 x = 0.15
20
Count / min
component appears in the mSR time spectrum upon cooling, is shown for x ¼ 0:06, 0.08 and 0.10. T m for all x-fixed samples is monotonically decreases upon increasing y, indicating a degradation of magnetic order. In the SC sample with xX0:12, no enhancement or inducement of AF order was observed even though the superconductivity was suppressed by Zn doping. This behavior seems to be quantitatively different from the competitive relation between the AF order and superconductivity in the p-type LSCO system [6,10]. Similarly, weak or no inducement of magnetic order under magnetic fields was observed in the optimally doped and overdoped samples, respectively. Fig. 4 shows background-subtracted peak profiles for x ¼ 0:11 (closed circles) and x ¼ 0:15 (open circles) under magnetic fields at (a) 0 T, (b) 5 T. Contrast to the no indication of magnetic signal in x ¼ 0:15, the intensity is enhanced by the field of 5 T in the x ¼ 0:11 sample. However, compared with LSCO with x ¼ 0:10, the enhanced intensity is quite weak, although the superconductivity is almost suppressed due to the low critical field for the full suppression of the superconductivity. Thus, the competitive coupling between the AF ordering and superconductivity is much weaker or absent in the n-type system.
2037
0 40
20
0 -0.01
0 h (r.l.u.)
0.01
Fig. 4. Peak profiles for Pr1x LaCex CuO4 with x ¼ 0:11 (closed circles) and x ¼ 0:15 (open circles) at 3 K under the field at (a) 0 T and (b) 6 T. The field-independent background was subtracted. The solid lines are results fitted with a single Gaussian function by convoluting the resolution.
Furthermore, the suppression of superconductivity by Zn-substitution or applying magnetic fields neither enhance nor induce well-defined AF order such as seen in the LSCO system. These experimental facts suggest a different magnetic ground state between the two systems. In the p-type LSCO, there increases the evidence of the spatially segregated spin and change stripe orders. On the other hand, commensurate spin correlations simply suggest no existence of stripe correlations in the n-type system. The nuclear magnetic resonance study by Zheng et al. suggests the Fermi-liquid ground state is a possible ground state in the optimally doped PLCCO system [11] and the metallic conductivity was reported for the doped AF phase of n-type Nd2x Cex CuO4 [12]. Observed high-energy spin excitations persisting at ðp; pÞ position is indeed similar to those in nearly antiferromagnetic metal Cr0.95V0.05 [13]. Weak enhancement of the AF order with suppressing the superconductivity would be originated from the weak effect on the mobile carriers compared to that in the p-type system. To clarify the universal role of spin fluctuations in the mechanism of superconductivity, further comprehensive studies for both systems are important. In conclusion, we studied the spin correlations in the n-type PLCCO system and its response against the Zn-doping and magnetic field. The spin correlations in the PLCCO system is of commensurate in the wide SC phase, unlike to the incommensurate ones in the p-type LSCO. Distinct impurity and magnetic field effects on the the static spin correlation in the n- and p-types suggest the different magnetic ground state in the two systems.
0.15
Fig. 3. Zn concentration (y) dependence of the magnetic ordering temperature for the x ¼ 0:06 (open diamonds), 0.08 (filled circles) and 0.10 (open squares) samples. Dashed lines are guides to the eye.
Acknowledgement I would like to thank my collaborators, H. Goka, K. Kawashima, H. Kimura, T. Kubo, S. Kuroshima,
ARTICLE IN PRESS 2038
M. Fujita / Journal of Physics and Chemistry of Solids 68 (2007) 2035–2038
A. Hino, S.H. Lee, M. Nakagawa, M. Matsuda, T. Takagi, T. Uefuji and K. Yamada for collaborative works on neutron scattering. This work was supported in part by a Grant-In-Aid for Young Scientists A (17684016) and a Grant-in-Aid from the Japanese Ministry of Education, Culture, Sports, Science and Technology.
[6] [7]
[8]
References [1] M. Fujita, K. Yamada, H. Hiraka, P.M. Gehring, S.H. Lee, S. Wakimoto, G. Shirane, Phys. Rev. B 65 (2002) 064505. [2] J.M. Tranquada, H. Woo, T.G. Perring, H. Goka, G.D. Gu, G. Xu, M. Fujita, K. Yamada, Nature 429 (2004) 534. [3] S.M. Hayden, H.A. Mook, P. Dai, T.G. Perring, F. Dog˘an, Nature 429 (2004) 531. [4] S. Katano, M. Sato, K. Yamada, T. Suzuki, T. Fukase, Phys. Rev. B 62 (2000) R14677. [5] B. Lake, H.M. Rønnow, N.B. Christensen, G. Aeppli, K. Lefmann, D.F. McMorrow, P. Vorderwisch, P. Smeibidl, N. Mangkorntong,
[9]
[10] [11] [12] [13]
T. Sasagawa, M. Nohara, H. Takagi, T.E. Mason, Nature (London) 417 (2002) 299. I. Watanabe, T. Adachi, K. Takahashi, S. Yairi, Y. Koike, K. Nagamine, Phys. Rev. B 65 (2002) 180516. B. Lake, G. Aeppli, K.N. Clausen, D.F. McMorrow, K. Lefmann, N.E. Hussey, N. Mangkorntong, M. Nohara, H. Takagi, T.E. Mason, A. Scho¨rder, Science 291 (2001) 1759. M. Kofu, H. Kimura, K. Hirota, Phys. Rev. B 72 (2005) 064502. M. Fujita, T. Kubo, S. Kuroshima, T. Uefuji, K. Kawashima, K. Yamada, I. Watanabe, K. Nagamine, Phys. Rev. B 67 (2003) 014514. T. Adachi, S. Yairi, K. Takahashi, Y. Koike, I. Watanabe, K. Nagamine, Phys. Rev. B 69 (2004) 184507. G.-q. Zheng, T. Sato, Y. Kitaoka, M. Fujita, K. Yamada, Phys. Rev. Lett. 90 (2003) 197005. Y. Onose, Y. Taguchi, K. Ishizaka, Y. Tokura, Phys. Rev. Lett. 87 (2001) 217001. S.M. Hayden, R. Doubble, G. Aeppli, T.G. Perring, E. Fawcett, Phys. Rev. Lett. 84 (2000) 999.