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Pressure-induced superconductivity in CeCoGe3 without inversion symmetry
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 310 (2007) 844–846 www.elsevier.com/locate/jmmm
Pressure-induced superconductivity in CeCoGe3 without inversion symmetry R. Settaia,, I. Sugitania, Y. Okudaa, A. Thamizhavela,1, M. Nakashimab, ¯ nukia, H. Harimac Y. O a
Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan b Faculty of Science, Shinshu University, Matsumoto, Nagano 390-8621, Japan c Department of Physics, Faculty of Science, Kobe University, Kobe 657-8501, Japan Available online 15 November 2006
Abstract We investigated the pressure-induced superconductivity for an antiferromagnet CeCoGe3 without inversion symmetry in the crystal structure. We found the pressure-induced superconductivity in CeCoGe3 with the superconducting transition temperature T sc ¼ 0:7 K at 5.5 GPa. CeCoGe3 belongs to a new type of superconductor without inversion symmetry in the crystal structure as in CePt3 Si, UIr, CeRhSi3 and CeIrSi3 . r 2006 Elsevier B.V. All rights reserved. PACS: 71.27.+a; 74.70.Tx; 74.62.Fj Keywords: CeCoGe3 ; Pressure-induced superconductor; Non-centrosymmetric superconductivity
Recently, non-centrosymmetric superconductivity was observed for CePt3 Si [1], UIr [2], CeRhSi3 [3] and CeIrSi3 [4]. Here we investigated the pressure-induced superconductivity for an antiferromagnet CeCoGe3 . CeCoGe3 crystallizes in the tetragonal BaNiSn3 -type crystal structure (I4 mm), which is the same crystal structure as in CeRhSi3 and CeIrSi3 . The Ce atoms are occupied on the four corners and in the body center of the tetragonal crystal structure, similar to the well known ThCr2 Si2 -type tetragonal crystal structure, while Co and Ge atoms lack inversion symmetry along the [0 0 1] direction (c-axis). CeCoGe3 is known as an antiferromagnet with a Ne´el temperature T N1 ¼ 21 K and undergoes two successive transitions T N2 ¼ 12 K and T N3 ¼ 8 K [5]. We prepared the polycrystal samples of CeCoGe3 , which were grown by arc-melting stoichiometric qualities of 3N Corresponding author. Tel.: +81 6 6850 5371; fax: +81 6 6850 5372.
E-mail address: [email protected] (R. Settai). Present address: Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research Colaba, Mumbai 400 005, India. 1
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.10.717
(99.9%)–Ce, 4N–Co and 6N–Si, which were wrapped in Ta-foil, sealed in a quartz tube under vacuum of 106 Torr and annealed at 850 C for one week. The electrical resistivity was measured using the DC and AC four-probe method. Pressure was applied by using the indenter and Bridgeman cells with Daphe 7373 oil as a pressuretransmitting oil, and pressure was calibrated by the superconducting transition temperature of Pb. Fig. 1 shows the temperature dependence of electrical resistivity under several pressures ranging from 0 to 3.5 GPa, which was obtained using the indenter cell. In the temperature range from the room temperature to about 150 K, the resistivity at ambient pressure is unchanged appreciably but decreases steeply below 100 K. A shoulderlike peak around 150 K is due to the interplay between the crystalline electric field and Kondo effects. The antiferromagnetic ordering is clearly marked at T N1 ¼ 21 K and T N2 ¼ 13.5 K by a change of slope in resistivity, as shown in the inset of Fig. 1. T N3 was not observed in the present sample. The residual resistivity r0 and the residual resistivity ratio are 1:68 mO cm and 54, respectively. When pressure is applied to the sample in the range from 0 to
ARTICLE IN PRESS R. Settai et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 844–846
845
Fig. 2. Electrical resistivity in CeCoGe3 under pressure ranging from 4.3 to 5.5 GPa.
Fig. 1. Electrical resistivity in CeCoGe3 under pressure of 0, 1.8 and 3.5 GPa. The inset indicates the electrical resistivity at low temperature.
3.5 GPa, the overall behavior in resistivity is unchanged appreciably. T N1 decreases, however, monotonically with increasing pressure. Much higher pressures were obtained by using the Bridgeman anvil cell. Fig. 2 shows the electrical resistivity in the pressure range from 4.3 to 5.5 GPa, where the Ne´el temperature T N1 becomes 3.0 K at 4.3 GPa. The electrical resistivity at 4.3 GPa decreases steeply below T sc ¼ 0.6 K. This is due to the onset of superconductivity, which is shown by arrows. With further increasing pressure, the resistivity zero is clearly attained at 5.5 GPa. The Ne´el temperature is not clearly defined at 5.5 GPa. We show in Fig. 3 the pressure phase diagram for the Ne´el temperature T N and the superconducting transition temperature T sc . Here we define T sc as the onset of the superconducting transition. We discuss the present superconductivity and the electronic state in CeCoGe3 without inversion symmetry. In our recent paper on the de Haas–van Alphen (dHvA) experiment, we clarified Fermi surfaces in LaCoGe3 and CeCoGe3 [6]. The dHvA frequencies in CeCoGe3 are similar to those in LaCoGe3 . A characteristic feature in the dHvA experiment and the energy band calculation is that the Fermi surfaces consist of three kinds of nearly closed Fermi surfaces. Furthermore, each Fermi surface is found to consist of two kinds of Fermi surfaces, which are very similar to each other in topology but is slightly different in volume. For example, two kinds of Fermi surfaces are separated in energy of 110–560 K. The spin–orbit interac-
Temperature (K)
20
CeCoGe3
TN1
10
Tsc 0 0
2
4 Pressure (GPa)
6
Fig. 3. Pressure phase diagram in CeCoGe3 .
tion of with 110–560 K is by two orders of magnitude larger than the present superconducting energy gap. This means that the simple spin–triplet Cooper pairing is not realized in CeCoGe3 . In conclusion, we found the pressure-induced superconductivity in CeCoGe3 , which belongs to a new type of superconductor without inversion symmetry in the crystal structure as in CePt3 Si, UIr, CeRhSi3 and CeIrSi3 . The present work was financially supported by the Grants-in-Aid for Creative Scientific Research (15GS0213) and Scientific Research (A) (16204026) from the Japan Society for the Promotion of Science (JSPS), and Scientific
ARTICLE IN PRESS 846
R. Settai et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 844–846
Research on Priority Area ‘‘Skutterudite’’ (15072204) and the 21st Century COE Program named ‘‘Towards a new basic science: depth and synthesis’’ from the Ministry of Education, Culture, Sports, Science and Technology of Japan. R.S. was financially supported by a Grant-in-Aid for Scientific Research (C) (17540325) from JSPS. References [1] E. Bauer, G. Hilscher, H. Michor, Ch. Paul, E.W. Scheidt, A. Gribanov, Yu Seropegin, H. Noe¨l, M. Sigrist, P. Rogl, Phys. Rev. Lett. 92 (2004) 027003.
[2] T. Akazawa, H. Hidaka, H. Kotegawa, T.C. Kobayashi, T. Fujiwara, ¯ nuki, J. Phys. Soc. Japan 73 E. Yamamoto, Y. Haga, R. Settai, Y. O (2004) 3129. [3] N. Kimura, K. Ito, K. Saitoh, Y. Umeda, H. Aoki, T. Terashima, Phys. Rev. Lett. 95 (2005) 247004. [4] I. Sugitani, Y. Okuda, H. Shishido, T. Yamada, A. Thamizhavel, E. Yamamoto, T.D. Matsuda, Y. Haga, T. Takeuchi, R. Settai, Y. ¯ nuki, J. Phys. Soc. Japan 75 (2006) 043703. O [5] A. Thamizhavel, T. Takeuchi, T.D. Matsuda, Y. Haga, R. Settai, Y. ¯ nuki, J. Phys. Soc. Japan 74 (2005) 1858. O [6] A. Thamizhavel, H. Shishido, Y. Okuda, H. Harima, T.D. ¯ nuki, J. Phys. Soc. Japan 75 Matsuda, Y. Haga, R. Settai, Y. O (2006) 044711.
Journal of Magnetism and Magnetic Materials 310 (2007) 844–846 www.elsevier.com/locate/jmmm
Pressure-induced superconductivity in CeCoGe3 without inversion symmetry R. Settaia,, I. Sugitania, Y. Okudaa, A. Thamizhavela,1, M. Nakashimab, ¯ nukia, H. Harimac Y. O a
Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan b Faculty of Science, Shinshu University, Matsumoto, Nagano 390-8621, Japan c Department of Physics, Faculty of Science, Kobe University, Kobe 657-8501, Japan Available online 15 November 2006
Abstract We investigated the pressure-induced superconductivity for an antiferromagnet CeCoGe3 without inversion symmetry in the crystal structure. We found the pressure-induced superconductivity in CeCoGe3 with the superconducting transition temperature T sc ¼ 0:7 K at 5.5 GPa. CeCoGe3 belongs to a new type of superconductor without inversion symmetry in the crystal structure as in CePt3 Si, UIr, CeRhSi3 and CeIrSi3 . r 2006 Elsevier B.V. All rights reserved. PACS: 71.27.+a; 74.70.Tx; 74.62.Fj Keywords: CeCoGe3 ; Pressure-induced superconductor; Non-centrosymmetric superconductivity
Recently, non-centrosymmetric superconductivity was observed for CePt3 Si [1], UIr [2], CeRhSi3 [3] and CeIrSi3 [4]. Here we investigated the pressure-induced superconductivity for an antiferromagnet CeCoGe3 . CeCoGe3 crystallizes in the tetragonal BaNiSn3 -type crystal structure (I4 mm), which is the same crystal structure as in CeRhSi3 and CeIrSi3 . The Ce atoms are occupied on the four corners and in the body center of the tetragonal crystal structure, similar to the well known ThCr2 Si2 -type tetragonal crystal structure, while Co and Ge atoms lack inversion symmetry along the [0 0 1] direction (c-axis). CeCoGe3 is known as an antiferromagnet with a Ne´el temperature T N1 ¼ 21 K and undergoes two successive transitions T N2 ¼ 12 K and T N3 ¼ 8 K [5]. We prepared the polycrystal samples of CeCoGe3 , which were grown by arc-melting stoichiometric qualities of 3N Corresponding author. Tel.: +81 6 6850 5371; fax: +81 6 6850 5372.
E-mail address: [email protected] (R. Settai). Present address: Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research Colaba, Mumbai 400 005, India. 1
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.10.717
(99.9%)–Ce, 4N–Co and 6N–Si, which were wrapped in Ta-foil, sealed in a quartz tube under vacuum of 106 Torr and annealed at 850 C for one week. The electrical resistivity was measured using the DC and AC four-probe method. Pressure was applied by using the indenter and Bridgeman cells with Daphe 7373 oil as a pressuretransmitting oil, and pressure was calibrated by the superconducting transition temperature of Pb. Fig. 1 shows the temperature dependence of electrical resistivity under several pressures ranging from 0 to 3.5 GPa, which was obtained using the indenter cell. In the temperature range from the room temperature to about 150 K, the resistivity at ambient pressure is unchanged appreciably but decreases steeply below 100 K. A shoulderlike peak around 150 K is due to the interplay between the crystalline electric field and Kondo effects. The antiferromagnetic ordering is clearly marked at T N1 ¼ 21 K and T N2 ¼ 13.5 K by a change of slope in resistivity, as shown in the inset of Fig. 1. T N3 was not observed in the present sample. The residual resistivity r0 and the residual resistivity ratio are 1:68 mO cm and 54, respectively. When pressure is applied to the sample in the range from 0 to
ARTICLE IN PRESS R. Settai et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 844–846
845
Fig. 2. Electrical resistivity in CeCoGe3 under pressure ranging from 4.3 to 5.5 GPa.
Fig. 1. Electrical resistivity in CeCoGe3 under pressure of 0, 1.8 and 3.5 GPa. The inset indicates the electrical resistivity at low temperature.
3.5 GPa, the overall behavior in resistivity is unchanged appreciably. T N1 decreases, however, monotonically with increasing pressure. Much higher pressures were obtained by using the Bridgeman anvil cell. Fig. 2 shows the electrical resistivity in the pressure range from 4.3 to 5.5 GPa, where the Ne´el temperature T N1 becomes 3.0 K at 4.3 GPa. The electrical resistivity at 4.3 GPa decreases steeply below T sc ¼ 0.6 K. This is due to the onset of superconductivity, which is shown by arrows. With further increasing pressure, the resistivity zero is clearly attained at 5.5 GPa. The Ne´el temperature is not clearly defined at 5.5 GPa. We show in Fig. 3 the pressure phase diagram for the Ne´el temperature T N and the superconducting transition temperature T sc . Here we define T sc as the onset of the superconducting transition. We discuss the present superconductivity and the electronic state in CeCoGe3 without inversion symmetry. In our recent paper on the de Haas–van Alphen (dHvA) experiment, we clarified Fermi surfaces in LaCoGe3 and CeCoGe3 [6]. The dHvA frequencies in CeCoGe3 are similar to those in LaCoGe3 . A characteristic feature in the dHvA experiment and the energy band calculation is that the Fermi surfaces consist of three kinds of nearly closed Fermi surfaces. Furthermore, each Fermi surface is found to consist of two kinds of Fermi surfaces, which are very similar to each other in topology but is slightly different in volume. For example, two kinds of Fermi surfaces are separated in energy of 110–560 K. The spin–orbit interac-
Temperature (K)
20
CeCoGe3
TN1
10
Tsc 0 0
2
4 Pressure (GPa)
6
Fig. 3. Pressure phase diagram in CeCoGe3 .
tion of with 110–560 K is by two orders of magnitude larger than the present superconducting energy gap. This means that the simple spin–triplet Cooper pairing is not realized in CeCoGe3 . In conclusion, we found the pressure-induced superconductivity in CeCoGe3 , which belongs to a new type of superconductor without inversion symmetry in the crystal structure as in CePt3 Si, UIr, CeRhSi3 and CeIrSi3 . The present work was financially supported by the Grants-in-Aid for Creative Scientific Research (15GS0213) and Scientific Research (A) (16204026) from the Japan Society for the Promotion of Science (JSPS), and Scientific
ARTICLE IN PRESS 846
R. Settai et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 844–846
Research on Priority Area ‘‘Skutterudite’’ (15072204) and the 21st Century COE Program named ‘‘Towards a new basic science: depth and synthesis’’ from the Ministry of Education, Culture, Sports, Science and Technology of Japan. R.S. was financially supported by a Grant-in-Aid for Scientific Research (C) (17540325) from JSPS. References [1] E. Bauer, G. Hilscher, H. Michor, Ch. Paul, E.W. Scheidt, A. Gribanov, Yu Seropegin, H. Noe¨l, M. Sigrist, P. Rogl, Phys. Rev. Lett. 92 (2004) 027003.
[2] T. Akazawa, H. Hidaka, H. Kotegawa, T.C. Kobayashi, T. Fujiwara, ¯ nuki, J. Phys. Soc. Japan 73 E. Yamamoto, Y. Haga, R. Settai, Y. O (2004) 3129. [3] N. Kimura, K. Ito, K. Saitoh, Y. Umeda, H. Aoki, T. Terashima, Phys. Rev. Lett. 95 (2005) 247004. [4] I. Sugitani, Y. Okuda, H. Shishido, T. Yamada, A. Thamizhavel, E. Yamamoto, T.D. Matsuda, Y. Haga, T. Takeuchi, R. Settai, Y. ¯ nuki, J. Phys. Soc. Japan 75 (2006) 043703. O [5] A. Thamizhavel, T. Takeuchi, T.D. Matsuda, Y. Haga, R. Settai, Y. ¯ nuki, J. Phys. Soc. Japan 74 (2005) 1858. O [6] A. Thamizhavel, H. Shishido, Y. Okuda, H. Harima, T.D. ¯ nuki, J. Phys. Soc. Japan 75 Matsuda, Y. Haga, R. Settai, Y. O (2006) 044711.