- Email: [email protected]
Relation between superconductivity and superstructure in Ce2RhIn8
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 310 (2007) e31–e32 www.elsevier.com/locate/jmmm
Relation between superconductivity and superstructure in Ce2RhIn8 Masahito Koedaa,, Tetsuya Fujiwaraa, Masato Hedoa, Yoshiya Uwatokoa, Hajime Sagayamab, Yusuke Wakabayashib, Hiroshi Sawab a
Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan b Institute of Materials Structure Science, KEK, Tsukuba, Ibaraki, 305-0801, Japan Available online 30 October 2006
Abstract We have performed the electrical resistivity measurements on Ce2RhIn8 in the temperature range 0.3–300 K and observed zeroresistance state at ambient pressure on several samples. We have performed synchrotron X-ray diffraction experiment on single crystal of Ce2RhIn8 to investigate relation between superconductivity and crystal structure. Superlattice reflections were observed with modulation wave vector q(0, 0, 1/8) on the superconducting samples at room temperature. r 2006 Elsevier B.V. All rights reserved. PACS: 61.10.i; 71.27.+a; 74.25.Fy; 74.70.Tx Keywords: Ce2RhIn8; Heavy fermion superconductor; Electrical resistivity; Synchrotron X-ray diffraction
1. Introduction The CenTIn3n+2 (T ¼ Co, Rh or In; n ¼ 1, 2 or N) compounds have attracted much attention because of their interesting various physical properties such as heavyfermion, non-fermi liquid behavior, magnetic ordering, unconventional superconductivity and pressure-induced supreconductivity. The majority of CenTIn3n+2 compounds show superconductivity. CeCoIn5, CeIrIn5 and Ce2CoIn8 are superconductor at ambient pressure with Tc ¼ 2.3 K [1], Tc ¼ 0.4 K [2] and Tc ¼ 0.4 K [3], respectively. On the other hand, CeIn3 and CeRhIn5 are antiferromagnets at ambient pressure with TN ¼ 10 K [4] and TN ¼ 3.8 K [5], respectively, however, these compounds show superconductivity under high pressure with Tc ¼ 0.25 K at P ¼ 2.5 GPa [4] and Tc ¼ 2.2 K at P ¼ 2.5 GPa [5], respectively. Ce2RhIn8 is also antiferromagnet with TN ¼ 2.8 K. TN decreases linearly with applying pressure. It was reported that Ce2RhIn8 becomes superconductor under high pressure above 1.1 GPa [6]. On the other hand, it was reported that the resistivity of Ce2RhIn8 becomes zero at ambient pressure by Ref. [7]. Corresponding author. Tel.: +81 4 7136 3518; fax: +81 4 7136 3518.
E-mail address: [email protected] (M. Koeda). 0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.10.073
The crystal structure of Ce2RhIn8 is Ho2CoGa8-type tetragonal structure with lattice constants a ¼ 4:4665 A˚ ˚ in which two cubic CeIn3 and one RhIn2 and c ¼ 12:244 A, layers alternately stacked along the c-axis [8]. We have performed the electrical resistivity measurements on Ce2RhIn8 in the temperature range 0.3–300 K and observed zero-resistance state at ambient pressure on several samples. Thus, we have performed synchrotron X-ray diffraction experiment to investigate relation between superconductivity and crystal structure and to get the information of the superconducting properties of Ce2RhIn8.
2. Experimental Single crystals of Ce2RhIn8 were grown by the In selfflux method. The electrical resistivity measurements were performed at ambient pressure by the standard AC fourprobe method in the temperature range from 0.3 to 300 K with the current direction perpendicular to the crystallographic c-axis. Synchrotron radiation X-ray diffraction experiment was performed using two-dimensional cylindrical imaging-plate detector installed at BL-1 Photon Factory, KEK, Tsukuba, Japan. An incident X-ray beam
ARTICLE IN PRESS e32
M. Koeda et al. / Journal of Magnetism and Magnetic Materials 310 (2007) e31–e32
with the wavelength of 0.688 A˚ produced by Si(1 1 1) monochromator was used. 3. Results and discussion Fig. 1 shows temperature dependence of the electrical resistivity for selected sample #8 and #10 of Ce2RhIn8 at ambient pressure. In both samples, the resistivity shows an inflection point at 2.8 K. It corresponds to TN reported in the previous paper [6]. The residual resistivity (r0) of sample #8 and #10 are about 47 and 40 mO cm, respectively. A residual resistivity ratio is about 1. The resistivity on sample #10 shows abrupt drops at about 0.8 K with decreasing temperature. Below 0.5 K, the resistivity becomes zero indicating the superconductivity. As already reported in Ref. [7], the superconductivity under ambient pressure was only observed for the current along the a-axis, and it is suggested that the superconductivity is not bulk one because the specific heat has no anomaly in this temperature range. In order to investigate a relation between sample dependence in superconductivity and crystal structure, Synchrotron diffraction experiment was performed on these single crystals of Ce2RhIn8 at room temperature. Fig. 2(a) and (b) show X-ray oscillation photograph for sample #10 and #8, respectively. Main X-ray diffraction spots in both pictures can be explained with the tetragonal Ho2CoGa8 structure. For superconducting samples of #10, clear superlattice reflections with modulation wave vector (0, 0, q) (q1/8) and higher harmonic components of them were observed. For instance, superlattice reflections at (3, 71, 23+2q) and (3, 71, 243q) are indicated by the arrow in Fig. 2(a). On the other hand, for non-superconducting samples of #8, no superlattice reflections were observed. As shown in Fig. 2(b), diffuse scattering, which suggests stacking fault along the c-axis were observed. As a result of the electrical resistivity measurements and synchrotron radiation X-ray diffraction experiment, it was
Fig. 2. X-ray diffraction patterns of Ce2RhIn8 for (a) sample #10 and (b) sample #8 at room temperature. Superlattice reflections was observed for sample #10. Arrows indicates one of superlattice reflections.
suggested that relation between superconductivity and superstructure in Ce2RhIn8. However, the superconductivity is not the bulk one as suggested by the specific heat measurements. Since X-ray infiltrate only about 50 mm from surface of the samples, The superstructure structure for sample #10 has been realized only in region near the surface of the sample and the region with the superlattice structure may leads the superconductivity in Ce2RhIn8 at ambient pressure. References
Fig. 1. Low temperature resistivity for Ce2RhIn8 on two different samples #8 and #10. The arrows indicate the TN.
[1] [2] [3] [4] [5] [6] [7] [8]
C. Petrovic, et al., J. Phys.: Condens. Matter 13 (2001) L337. C. Petrovic, et al., Europhys. Lett. 53 (2001) 354. G. Chen, et al., J. Phys. Soc. Japan 71 (2002) 2836. N.D. Mathur, et al., Nature 394 (1998) 39. H. Hegger, et al., Phys. Rev. Lett. 84 (2000) 4986. M. Nicklas, et al., Phys. Rev. B 67 (2003) 020506. T. Ueda, et al., J. Phys. Soc. Japan 73 (2004) 649. W. Bao, et al., Phys. Rev. B 64 (2001) 020401.
Journal of Magnetism and Magnetic Materials 310 (2007) e31–e32 www.elsevier.com/locate/jmmm
Relation between superconductivity and superstructure in Ce2RhIn8 Masahito Koedaa,, Tetsuya Fujiwaraa, Masato Hedoa, Yoshiya Uwatokoa, Hajime Sagayamab, Yusuke Wakabayashib, Hiroshi Sawab a
Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan b Institute of Materials Structure Science, KEK, Tsukuba, Ibaraki, 305-0801, Japan Available online 30 October 2006
Abstract We have performed the electrical resistivity measurements on Ce2RhIn8 in the temperature range 0.3–300 K and observed zeroresistance state at ambient pressure on several samples. We have performed synchrotron X-ray diffraction experiment on single crystal of Ce2RhIn8 to investigate relation between superconductivity and crystal structure. Superlattice reflections were observed with modulation wave vector q(0, 0, 1/8) on the superconducting samples at room temperature. r 2006 Elsevier B.V. All rights reserved. PACS: 61.10.i; 71.27.+a; 74.25.Fy; 74.70.Tx Keywords: Ce2RhIn8; Heavy fermion superconductor; Electrical resistivity; Synchrotron X-ray diffraction
1. Introduction The CenTIn3n+2 (T ¼ Co, Rh or In; n ¼ 1, 2 or N) compounds have attracted much attention because of their interesting various physical properties such as heavyfermion, non-fermi liquid behavior, magnetic ordering, unconventional superconductivity and pressure-induced supreconductivity. The majority of CenTIn3n+2 compounds show superconductivity. CeCoIn5, CeIrIn5 and Ce2CoIn8 are superconductor at ambient pressure with Tc ¼ 2.3 K [1], Tc ¼ 0.4 K [2] and Tc ¼ 0.4 K [3], respectively. On the other hand, CeIn3 and CeRhIn5 are antiferromagnets at ambient pressure with TN ¼ 10 K [4] and TN ¼ 3.8 K [5], respectively, however, these compounds show superconductivity under high pressure with Tc ¼ 0.25 K at P ¼ 2.5 GPa [4] and Tc ¼ 2.2 K at P ¼ 2.5 GPa [5], respectively. Ce2RhIn8 is also antiferromagnet with TN ¼ 2.8 K. TN decreases linearly with applying pressure. It was reported that Ce2RhIn8 becomes superconductor under high pressure above 1.1 GPa [6]. On the other hand, it was reported that the resistivity of Ce2RhIn8 becomes zero at ambient pressure by Ref. [7]. Corresponding author. Tel.: +81 4 7136 3518; fax: +81 4 7136 3518.
E-mail address: [email protected] (M. Koeda). 0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.10.073
The crystal structure of Ce2RhIn8 is Ho2CoGa8-type tetragonal structure with lattice constants a ¼ 4:4665 A˚ ˚ in which two cubic CeIn3 and one RhIn2 and c ¼ 12:244 A, layers alternately stacked along the c-axis [8]. We have performed the electrical resistivity measurements on Ce2RhIn8 in the temperature range 0.3–300 K and observed zero-resistance state at ambient pressure on several samples. Thus, we have performed synchrotron X-ray diffraction experiment to investigate relation between superconductivity and crystal structure and to get the information of the superconducting properties of Ce2RhIn8.
2. Experimental Single crystals of Ce2RhIn8 were grown by the In selfflux method. The electrical resistivity measurements were performed at ambient pressure by the standard AC fourprobe method in the temperature range from 0.3 to 300 K with the current direction perpendicular to the crystallographic c-axis. Synchrotron radiation X-ray diffraction experiment was performed using two-dimensional cylindrical imaging-plate detector installed at BL-1 Photon Factory, KEK, Tsukuba, Japan. An incident X-ray beam
ARTICLE IN PRESS e32
M. Koeda et al. / Journal of Magnetism and Magnetic Materials 310 (2007) e31–e32
with the wavelength of 0.688 A˚ produced by Si(1 1 1) monochromator was used. 3. Results and discussion Fig. 1 shows temperature dependence of the electrical resistivity for selected sample #8 and #10 of Ce2RhIn8 at ambient pressure. In both samples, the resistivity shows an inflection point at 2.8 K. It corresponds to TN reported in the previous paper [6]. The residual resistivity (r0) of sample #8 and #10 are about 47 and 40 mO cm, respectively. A residual resistivity ratio is about 1. The resistivity on sample #10 shows abrupt drops at about 0.8 K with decreasing temperature. Below 0.5 K, the resistivity becomes zero indicating the superconductivity. As already reported in Ref. [7], the superconductivity under ambient pressure was only observed for the current along the a-axis, and it is suggested that the superconductivity is not bulk one because the specific heat has no anomaly in this temperature range. In order to investigate a relation between sample dependence in superconductivity and crystal structure, Synchrotron diffraction experiment was performed on these single crystals of Ce2RhIn8 at room temperature. Fig. 2(a) and (b) show X-ray oscillation photograph for sample #10 and #8, respectively. Main X-ray diffraction spots in both pictures can be explained with the tetragonal Ho2CoGa8 structure. For superconducting samples of #10, clear superlattice reflections with modulation wave vector (0, 0, q) (q1/8) and higher harmonic components of them were observed. For instance, superlattice reflections at (3, 71, 23+2q) and (3, 71, 243q) are indicated by the arrow in Fig. 2(a). On the other hand, for non-superconducting samples of #8, no superlattice reflections were observed. As shown in Fig. 2(b), diffuse scattering, which suggests stacking fault along the c-axis were observed. As a result of the electrical resistivity measurements and synchrotron radiation X-ray diffraction experiment, it was
Fig. 2. X-ray diffraction patterns of Ce2RhIn8 for (a) sample #10 and (b) sample #8 at room temperature. Superlattice reflections was observed for sample #10. Arrows indicates one of superlattice reflections.
suggested that relation between superconductivity and superstructure in Ce2RhIn8. However, the superconductivity is not the bulk one as suggested by the specific heat measurements. Since X-ray infiltrate only about 50 mm from surface of the samples, The superstructure structure for sample #10 has been realized only in region near the surface of the sample and the region with the superlattice structure may leads the superconductivity in Ce2RhIn8 at ambient pressure. References
Fig. 1. Low temperature resistivity for Ce2RhIn8 on two different samples #8 and #10. The arrows indicate the TN.
[1] [2] [3] [4] [5] [6] [7] [8]
C. Petrovic, et al., J. Phys.: Condens. Matter 13 (2001) L337. C. Petrovic, et al., Europhys. Lett. 53 (2001) 354. G. Chen, et al., J. Phys. Soc. Japan 71 (2002) 2836. N.D. Mathur, et al., Nature 394 (1998) 39. H. Hegger, et al., Phys. Rev. Lett. 84 (2000) 4986. M. Nicklas, et al., Phys. Rev. B 67 (2003) 020506. T. Ueda, et al., J. Phys. Soc. Japan 73 (2004) 649. W. Bao, et al., Phys. Rev. B 64 (2001) 020401.