自從發現了高溫銅氧平面的超導體，許多學者便致力於尋找具類似性質的金屬氧化物超導體，如鈷氧化物及鎳氧化物超導體，而NaxCoO2•yH2O (x ~ 0.35, y ~ 1.3)則是第一個鈷氧平面的新金屬氧平面超導體。在這篇論文中，我們對此新超導體進行了磁場下的比熱研究，在零磁場下，我們在大約4.7K也就是樣品相轉變溫度附近觀察到其超導特性，並且在低溫區發現其含有αT2的項，明顯表示出其屬於line node的超導體種類。當外加磁場給樣品時，可明顯的看到零磁場下的尖峰隨外加磁場的逐漸增大而逐漸變小。除此之外，Tc也隨著外加磁場在改變，而在實驗數據中我們觀察到有點奇異的H-T曲線，因此發生在混合能態中的多重相轉換的可能性也在討論之列。

Since the discovery of high superconducting transition temperature in layered copper oxides, many researchers have searched for similar behavior in other layered metal oxides, such as cobalt and nickel. The sodium cobalt oxyhydrate is the first cobalt-oxide layered superconductor.
We present the studies of low-temperature specific heat C(T, H) in NaxCoO2•yH2O (x ~ 0.35, y ~ 1.3). At H = 0, a very sharp anomaly was observed at T ~ 4.7 K indicating the existence of bulk superconductivity. There exists an αT2 term in C(T, H=0) in the superconducting state manifesting the line nodal superconducting order parameter. The feature at the superconducting transition is rather sharp, becoming broad and strongly suppressed in an applied magnetic field. The transition temperature also changed in an applied magnetic field. Thus an abrupt change of slope in H vs. Tc curve was observed. Possible scenarios such as the multiple phase transitions in the mixed state are discussed.

Abstract..................................................i
Content.................................................iii
List of Figures..........................................iv
List of Tables...........................................vi

Chapter One: Introduction.................................1

Chapter Two: Theory.......................................7
2.1 Destruction of superconductivity by magnetic fields...7
2.2 Models of the specific heat..........................11

Chapter Three: Experiment Details........................18
3.1 Sample synthesis and characterization................18
3.2 Specific heat system.................................20
3.3 Calibration of the calorimeter.......................39

Chapter Four: Experimental Results and Data Analysis.....43
4.1 Sample handling......................................43
4.2 Analysis of experimental data........................45
4.3 Discussion...........................................63

Chapter Five: Conclusion...............................................66

Reference................................................67

1 H. Kamerlingh Onnes, Akad. Van Wetenschappen (Amsterdam) 14, 113, 818 (1911)
2 J. Bardeen, L. N. Cooper and J. R. Schrieffer, Phys. Rev. 108, 1175 (1957)
3 J. G. Bednorz and K. A. Müller, Z. Phys. B 64, 189 (1986)
4 M. K. Wu, J. R. Ashburn, C. J. Torng, P. H. Hor, R. L. Meng, L. Gao, Z. J. Huang, Y. Q. Wang, and C. W. Chu, Phys. Rev. Lett. 58, 908 (1987)
5 A. Schilling, M. Cantoni, J. D. Guo, and H. R. Ott, Nature 363, 56 (1993)
6 C. W. Chu, L. Gao, F. Chen, Z. J. Huang, R. L. Mrng, and Y. Y. Xue, Nature 362, 226 (1993)
7 K. Takada, H. Sakurai, E. Takayama-Muromachi, F. Izumi, R. A. Dilanian, and T. Sasaki, Nature 422, 53 (2003)
8 Y. Kobayashi, M. Yokoi, and M. Sato, J. Phys. Soc. Jpn. 72, 2161 (2003)
9 T. Waki, C. Michika, M. Kato, K. Yoshimura, K. Takada, H. Sakurai, E. Takayama-Muromachi, and T. Sasaki, cond-mat/0306036
10 T. Fujimoto, G. Q. Zhang, Y. Kitaoka, R. L. Meng, J. Cmaidalka, and C. W. Chu, Phys. Rev. Lett. 92, 047004 (2004)
11 K. Ishida, Y. Ihara, Y. Maeno, C. Michioka, M. Kato, K. Yoshimura, K. Takada, T. Sasaki, H. Sakurai, and E. Takayama-Muromachi, J. Phys. Soc. Jpn. 72, 3041 (2003)
12 I. Terasaki, Y. Sasago, and K. Uchinokura, Phys. Rev. B 56, 12685 (1997)
13 R. E. Schaak, T. Klimczuk, M. K. Foo, and R. J. Cava, Nature 424, 527 (2003)
14 Y. Wang, N. S. Ragodo, R. J. Cava, and N. P. Ong, Nature 423, 425 (2003)
15 N. W. Ashcroft and N. D. Mermin, in Solid State Physics, W. B. Saunders Company, Philadelphia (1976)
16 G. E. Volovik, JETP Lett. 58, 469 (1993)
17 K. Yamada, S. Wakimoto, G.. Shirane, C. H. Lee, M. A. Kastner, S. Hosoya, M. Greven, Y. Endoh, and R. J. Birgeneau, Phys. Rev. Lett. 75, 1626 (1995)
18 X. K. Chen, J. C. Irwin, H. J. Trodahl, T. Kimura, and K. Kishio, Phys. Rev. Lett. 73, 3290 (1994)
19 N. Momono and M. Ido, Physica C 264, 311 (1996)
20 C. Caroli, P. G. deGeens, and J. Matricon, Phys. Lett. 9, 307 (1964)
21 M. Prohammer, A. Perez-Gonzalez, and J. P. Carbotte, Phys. Rev. B 47, 15152 (1993)
22 A. Junod, in Physical Properties of HTSCⅡ, edited by D. Ginsberg
23 N. E. Phillips, R.A. Fisher and J. E. Gordon, in Progress in low temperature Physics, edited by D. F. Brewer, Vol. 13, pp.267-357 (1992)
24 J. P. Emerson, R. A. Fisher, and N. E. Phillips et al., Phys. Rev. B 49, 9256 (1994)
25 D. Sanchez, A. Junod, J. –Y. Genoud, T. Graf, and J. Muller, Physica C 200, 1 (1992)
26 T. E. Mason, G. Appli, S. M. Hayden, A. P. Ramires, and H. A. Mook, Phys. Rev. Lett. 71, 919 (1993)
27 R. A. Fisher and J. E. Gordon et al., Physica C 252, 237 (1995)
28 K. A. Moler, D. L. Sisson, J. S. Urbach, and M. R. Beasley et al., Phys. Rev. B 55, 3954 (1997)
29 C. Kittle, in Introduction to Solid State Physics, edited by J. Wiley, SEA Pte. Ltd., Singapore (1986)
30 S. Nishizaki, Y. Maeno, and Z. Mao, J. Phys. Soc. Jpn. 69, 572 (2000)
31 H. Sakurai, K. Takada, S. Yoshii, T. Sasaki, K. Kindo, and E. Takayama-Muromachi, Phys. Rev. B 68, 132507 (2003)
32 S. J. Chen, C. F. Chang, H. L. Tsay, H. D. Yang, and J. –Y. Lin, Phys. Rev. B 58, R14753 (1998)
33 M. M. Maśaka, M. Mierzejewski, B. Andrzejewski, M. L. Foo, T. Klimczuk, and R. J. Cava, cond-mat/0402503
34 F. Bouquet, R. A. Fisher, N. E. Phillips, D. G. Hinks, and J. D. Jorgensen, Phys. Rev. Lett. 87, 047001 (2001)
35 H. D. Yang J. –Y. Lin, H. H. Li, F. H. Hsu, C. –J. Liu, S. –C. Li, R. –C. Yu, and C. –Q. Jin, Phys. Rev. Lett. 87, 167003 (2001)
36 J. –Y. Lin, P. L. Ho, H. L. Huang, P. H. Lin, Y. –L. Zhang, R. –C. Yu, C. –Q. Jin, and H. D. Yang, Phys. Rev. B 67, 52501 (2003)
37 H. D. Yang and J. –Y. Lin, J. Phys. Chem. Solid. 62, 1861 (2001)
38 B. Lorenz, J. Cmaidalka, R. L. Meng, and C. W. Chu, Physica C 402, 106 (2004)
39 Y. G. Shi, J. Q. Li, H. C. Yu, Y. Q. Zhou, H. R. Zhang, and C. Dong, Supercond. Sci. Technol. 17, 42 (2004)
40 T. Sasaki, P. Badica, N. Yoneyama, K. Yamada, K. Togano, and N. Kobayashi, cond-mat/0402355
41 A. M. Clogston, Phys. Rev. Lett. 9, 266 (1962)
42 B. S. Chandrasekhar, Appl. Phys. Lett. 1, 7 (1962)
43 M. N. Iliev, A. P. Litvinchuk, R. L. Meng, Y. Y. Sun, J. Cmaidalka, and C. W. Chu, Physica C 402, 239 (2004)
44 R. Jin, B. C. Sales, P. Khalifah, and D. Mandrus, Phys. Rev. Lett. 91, 217001 (2003)
45 G. Cao, C. Feng, Y. Xu, W. Lu, J. Shen, M. Fang, and Z. Xu, J. Phys. Condens. Matter 15, L519 (2003)
46 G. Baskaran, Phys. Rev. Lett. 97, 97003 (2003)
47 Q. –H. Wang, D. –H. Lee, and P. A. Lee, Phys. Rev. B 69, 092504 (2004)
48 A. Tanaka and X. Hu, Phys. Rev. Lett. 91, 257006 (2003)