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Pairing and vortex states in Sr2RuO4 studied by Hall probe magnetometry
Physica B 284}288 (2000) 543}544
Pairing and vortex states in Sr RuO studied by Hall probe magnetometry Tsuyoshi Tamegai *, Kamran Behnia , Nobuhiro Okuda , Shuuichi Ooi , Takasada Shibauchi , Zhiqiang Mao , Yoshiteru Maeno Department of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan CREST, Japan Science and Technology Corporation, Kawaguchi, Saitama 332-0012, Japan Department of Physics, Kyoto University, Kyoto 606-8502, Japan
Abstract Nature of the pairing and vortex states are studied in Sr RuO using a Hall probe array. No clear evidence for the spontaneous magnetic "eld, accompanying the time-reversal symmetry breaking states, has been obtained. Magnetization with H #c shows an anomaly close to H and a peak near H "0. We interpret the former to be due to the synchronization peak e!ect. H or change in the vortex lattice structure could be relevant to the latter. 2000 Elsevier Science B.V. All rights reserved. Keywords: Hall probe; Pairing symmetry; Peak e!ect; Sr RuO
Sr RuO is the only superconducting material with layered Perovskite structure other than high-temperature superconductors [1]. Although its ¹ is only 1.5 K, there is increasing interest in this superconductor due to its possible exotic superconducting properties. Theoretical prediction of p-wave symmetry in this superconductor [2] has been recently con"rmed by NMR measurements [3]. Another peculiar feature is the appearance of the spontaneous magnetic "eld (SMF) accompanying breaking of time-reversal symmetry [4]. Domain walls between oppositely magnetized region could play an important role with regard to the nature and the dynamics of vortices in such systems.
* Corresponding author. Tel.: 81-3-5841-6846; fax: #81-35841-8886. E-mail address: [email protected] (T. Tamegai) Also at Laboratoire de Physique des Solides (CNRS), UniversiteH Paris-Sud, 91405 Orsay, France. Present address: National Research Institute for Metals, Sengen 1-2-1, Tsukuba 305-0047, Japan. Present address: IBM T. J. Watson Research Center Box 218, Yorktown Heights, NY 10598, USA.
We apply the highly sensitive Hall probe magnetometry for the study of the pairing and the vortex state in Sr RuO . Crystals used in this study were grown by the #oating-zone method [1]. They are cut into dimensions of 1.0;0.5;0.3 mm and glued on top of a Hall probe array having more than 10 elements with an active area of 5;5 lm, a spacing of 25 lm, and a "eld resolution better than 10 mG. For the detection of SMF, we measure local magnetic induction at several points on the sample under constant applied "elds (H ) close to zero. Fig. 1 shows an example of such measurements in Sr RuO C1 (¹ "1.15 K) by Hall probes near the edge (P2) and close to the center (P1) of the sample, at H "#0.5, 0, and }0.5 Oe. Judging from the measured signal, the actual "eld at the sample position is almost zero at H "!0.5 Oe. Except for the usual Meissner signal, we did not detect any additional signal larger than 0.1 G. In another crystal (Sr RuO C2, ¹ "1.35 K), we also do not detect clear evidence of SMF. There are several possible reasons why we do not detect SMF. If the distance from the Hall probe to the sample edge, where we expect to detect SMF, is much larger than the penetration depth (j (0)&0.19 lm [5]), SMF would vanish rapidly. Fur* thermore, the size of domains with opposite polarities
0921-4526/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 2 1 5 6 - 0
544
T. Tamegai et al. / Physica B 284}288 (2000) 543}544
Fig. 1. Temperature dependence of local magnetic "eld in Sr RuO C1 at H "#0.5, 0, and }0.5 Oe. P2 and P1 locate near the edge and the center of the sample, respectively.
Fig. 2. Local magnetization hysteresis loops in Sr RuO C2 between 0.6 K (largest loop) and 1.55 K (collapsed loop). Two characteristic "elds H and HH can be identi"ed. Inset shows temperature dependence of H , H and HH.
has to be comparable or larger than that of Hall probes. Otherwise, SMF would be averaged out. Measurements with much "ner resolution are needed to resolve this issue. Local magnetization hysteresis loops measured at the center of Sr RuO C2 are shown in Fig. 2. Irreversible magnetization diminishes to zero in temperature-dependent "eld, which can be assigned to H [5]. There are two characteristic features other than H . One is the prominent peak structure near zero "eld (HH). The other is a small anomaly at "elds just below H (H ). HH, H , and H are plotted in the inset of Fig. 2. H could be interpreted as a manifestation of the synchronization peak e!ect, which is expected when the shear modulus becomes small and has been detected when H #ab [6]. HH has similar magnitude to H (0) estimated in Ref. [7] and could be related to H . Another interpretation of this anomaly is the change in the vortex structure, for example, from triangular to square lattices.
Acknowledgements This work is partly supported by Grant-in-Aid for Scienti"c Research from the Ministry of Education, Science, Sports, and Culture, Japan.
References [1] Y. Maeno et al., Nature 372 (1994) 126. [2] T.M. Rice, M. Sigrist, J. Phys.: Condens. Matter 7 (1995) L643. [3] K. Ishida et al., Nature 396 (1998) 658. [4] G.M. Luke et al., Nature 394 (1998) 558. [5] T.M. Riseman et al., Nature 396 (1998) 242. [6] K. Yoshida et al., J. Phys. Soc. Japan 65 (1996) 2220. [7] T. Akima et al., J. Phys. Soc. Japan 68 (1999) 694.
Pairing and vortex states in Sr RuO studied by Hall probe magnetometry Tsuyoshi Tamegai *, Kamran Behnia , Nobuhiro Okuda , Shuuichi Ooi , Takasada Shibauchi , Zhiqiang Mao , Yoshiteru Maeno Department of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan CREST, Japan Science and Technology Corporation, Kawaguchi, Saitama 332-0012, Japan Department of Physics, Kyoto University, Kyoto 606-8502, Japan
Abstract Nature of the pairing and vortex states are studied in Sr RuO using a Hall probe array. No clear evidence for the spontaneous magnetic "eld, accompanying the time-reversal symmetry breaking states, has been obtained. Magnetization with H #c shows an anomaly close to H and a peak near H "0. We interpret the former to be due to the synchronization peak e!ect. H or change in the vortex lattice structure could be relevant to the latter. 2000 Elsevier Science B.V. All rights reserved. Keywords: Hall probe; Pairing symmetry; Peak e!ect; Sr RuO
Sr RuO is the only superconducting material with layered Perovskite structure other than high-temperature superconductors [1]. Although its ¹ is only 1.5 K, there is increasing interest in this superconductor due to its possible exotic superconducting properties. Theoretical prediction of p-wave symmetry in this superconductor [2] has been recently con"rmed by NMR measurements [3]. Another peculiar feature is the appearance of the spontaneous magnetic "eld (SMF) accompanying breaking of time-reversal symmetry [4]. Domain walls between oppositely magnetized region could play an important role with regard to the nature and the dynamics of vortices in such systems.
* Corresponding author. Tel.: 81-3-5841-6846; fax: #81-35841-8886. E-mail address: [email protected] (T. Tamegai) Also at Laboratoire de Physique des Solides (CNRS), UniversiteH Paris-Sud, 91405 Orsay, France. Present address: National Research Institute for Metals, Sengen 1-2-1, Tsukuba 305-0047, Japan. Present address: IBM T. J. Watson Research Center Box 218, Yorktown Heights, NY 10598, USA.
We apply the highly sensitive Hall probe magnetometry for the study of the pairing and the vortex state in Sr RuO . Crystals used in this study were grown by the #oating-zone method [1]. They are cut into dimensions of 1.0;0.5;0.3 mm and glued on top of a Hall probe array having more than 10 elements with an active area of 5;5 lm, a spacing of 25 lm, and a "eld resolution better than 10 mG. For the detection of SMF, we measure local magnetic induction at several points on the sample under constant applied "elds (H ) close to zero. Fig. 1 shows an example of such measurements in Sr RuO C1 (¹ "1.15 K) by Hall probes near the edge (P2) and close to the center (P1) of the sample, at H "#0.5, 0, and }0.5 Oe. Judging from the measured signal, the actual "eld at the sample position is almost zero at H "!0.5 Oe. Except for the usual Meissner signal, we did not detect any additional signal larger than 0.1 G. In another crystal (Sr RuO C2, ¹ "1.35 K), we also do not detect clear evidence of SMF. There are several possible reasons why we do not detect SMF. If the distance from the Hall probe to the sample edge, where we expect to detect SMF, is much larger than the penetration depth (j (0)&0.19 lm [5]), SMF would vanish rapidly. Fur* thermore, the size of domains with opposite polarities
0921-4526/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 2 1 5 6 - 0
544
T. Tamegai et al. / Physica B 284}288 (2000) 543}544
Fig. 1. Temperature dependence of local magnetic "eld in Sr RuO C1 at H "#0.5, 0, and }0.5 Oe. P2 and P1 locate near the edge and the center of the sample, respectively.
Fig. 2. Local magnetization hysteresis loops in Sr RuO C2 between 0.6 K (largest loop) and 1.55 K (collapsed loop). Two characteristic "elds H and HH can be identi"ed. Inset shows temperature dependence of H , H and HH.
has to be comparable or larger than that of Hall probes. Otherwise, SMF would be averaged out. Measurements with much "ner resolution are needed to resolve this issue. Local magnetization hysteresis loops measured at the center of Sr RuO C2 are shown in Fig. 2. Irreversible magnetization diminishes to zero in temperature-dependent "eld, which can be assigned to H [5]. There are two characteristic features other than H . One is the prominent peak structure near zero "eld (HH). The other is a small anomaly at "elds just below H (H ). HH, H , and H are plotted in the inset of Fig. 2. H could be interpreted as a manifestation of the synchronization peak e!ect, which is expected when the shear modulus becomes small and has been detected when H #ab [6]. HH has similar magnitude to H (0) estimated in Ref. [7] and could be related to H . Another interpretation of this anomaly is the change in the vortex structure, for example, from triangular to square lattices.
Acknowledgements This work is partly supported by Grant-in-Aid for Scienti"c Research from the Ministry of Education, Science, Sports, and Culture, Japan.
References [1] Y. Maeno et al., Nature 372 (1994) 126. [2] T.M. Rice, M. Sigrist, J. Phys.: Condens. Matter 7 (1995) L643. [3] K. Ishida et al., Nature 396 (1998) 658. [4] G.M. Luke et al., Nature 394 (1998) 558. [5] T.M. Riseman et al., Nature 396 (1998) 242. [6] K. Yoshida et al., J. Phys. Soc. Japan 65 (1996) 2220. [7] T. Akima et al., J. Phys. Soc. Japan 68 (1999) 694.