Abstract
The temperature dependence of the ac heat capacity of a molecule-based superconductor κ-(BEDT-TTF)2Cu(NCS)2 under external pressures and with magnetic fields is reported. A peak structure in C p T −1 due to the superconductive transition was observed around 9 K at ambient pressure. This peak is suppressed by applying magnetic fields up to 7 T. The systematic decrease in the transition temperature with the increase in external pressure is confirmed by thermodynamic measurements under 0.15, 0.30 and 0.45 GPa. Through the analysis of the peak shape of the thermal anomaly, it is suggested that the gradual suppression of the coupling strength of the superconductivity occurs with the increase in pressure. This feature is consistent with the argument based on the chemical pressure effect in the superconductive phase of κ-(BEDT-TTF)2 X system, where X denotes mono-valence counter anions. The result demonstrates that the appearance of the Fermi-liquid character produced by applying pressure in the dimer-Mott phase diagram affects the nature and the coupling feature of the superconductivity. Importance of high-pressure heat capacity for molecule-based compounds is emphasized.
Similar content being viewed by others
References
Ishiguro T, Yamaji K, Saito G. Quasi two-dimensional systems. Organic superconductors. Berlin: Springer; 1998. p. 125–219.
Williams JM, Ferraro JR, Thorn RJ, Carlson KD, Geiser U, Wang HH, Kini AM, Whangbo MH. Organic superconductors. New Jersey: Prentice-Hall, Inc.; 1992.
Kagoshima S, Kato R, Fukuyama H, Seo H, Kino H 1999 Interplay of structural and electronic properties. In: Bernier P, Lefrant S, Bidan G, editors. Advances in synthetic metals twenty years of progress in science and technology, Chap. 4. Elsevier: Lausanne; 1999. p. 262–316.
Mori H. Materials viewpoint of organic superconductors. J Phys Soc Jpn. 2006;75:051003-1–15.
Kanoda K. Metal–insulator transition in κ-(ET)2X and (DCNQI)2M: two contrasting manifestation of electron correlation. J Phys Soc Jpn. 2006;75:051007-1–16.
Jérome D. The physics of organic superconductors. Science. 1991;252:1509–14.
Kanoda K. Recent progress in NMR studies on organic conductors. Hyperfine Interact. 1997;104:235–49.
Kanoda K. Electron correlation, metal-insulator transition and superconductivity in quasi-2D organic systems, (ET)2X. Physica C. 1997;287:299–302.
Kagawa F, Miyagawa K, Kanoda K. Unconventional critical behaviour in a quasi-two-dimensional organic conductor. Nature. 2005;436:534–7.
Miyagawa K, Kanoda K, Kawamoto A. NMR studies on two-dimensional molecular conductors and superconductors: Mott transition in κ-(BEDT-TTF)2X. Chem Rev. 2004;104:5635–54.
Arai T, Ichimura K, Nomura K, Takasaki S, Yamada J, Nakatsuji S, Anzai H. Tunneling spectroscopy on the organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 using STM. Phys Rev B. 2001;63:104518-1–5.
Nakazawa Y, Yamashita S. Thermodynamic properties of κ-(BEDT-TTF)2X salts: electron correlations and superconductivity. Crystals. 2012;2:741–61.
Nakazawa Y, Kanoda K. Thermodynamic property of organic superconductor κ-(BEDT-TTF)2X [X = Cu(NCS)2, Cu[N(CN)2]Br]. Phys C. 1997;282–287:1897–8.
Taylor OJ, Carrington A, Schlueter JA. Specific-heat measurements of the gap structure of the organic superconductors κ-(ET)2Cu[N(CN)2]Br and κ-(ET)2Cu(NCS)2. Phys Rev Lett. 2007;99:057001-1–4.
Sorai M, Nakazawa Y, Nakano M, Miyazaki Y. Colorimetric investigation of phase transitions occurring in molecule-based magnets. Chem Rev. 2013;113:PR41–122.
Nakazawa Y, Yoshimoto R, Fukuoka S, Yamashita S. Investigation on electronic states of molecule-based compounds by high-pressure AC calorimetry. Curr Inorg Chem. 2014;4:122–34.
Kubota O, Nakazawa Y. Construction of a low-temperature thermodynamic measurement system for single crystal of molecular compounds under pressures. Rev Sci Instrum. 2008;79:053901-1-6.
Kubota O, Fukuoka S, Nakazawa Y, Nakata K, Yamashita S, Miyasaka H. Thermodynamic investigation of coordination-networked systems of [Mn4] single-molecule magnets under pressure. J Phys: Condens Matter. 2010;22:026007-1–5.
Tokoro N, Kubota O, Yamashita S, Kawamoto A, Nakazawa Y. Thermodynamic study of κ-(BEDT-TTF)2Ag(CN)2H2O under pressures and with magnetic fields. J Phys Conf Ser. 2008;132:012010-1–8.
Tokoro N, Fukuoka S, Kubota O, Nakazawa Y. Low-temperature heat capacity measurements of κ-type organic superconductors under pressure. Phys B. 2010;405:S273–6.
Urayama H, Yamochi H, Saito G, Nozaki K, Sugano T, Kinoshita M, Sato S, Ohshima K, Kawamoto A, Tanaka J. A new ambient pressure organic superconductor based on BEDT-TTF with T c higher than 10 K (T c = 10.4 K). Chem Lett. 1988;17:55–8.
Müller J, Lang M, Helfrich R, Steglich F, Sasaki T. High-resolution ac-calorimetry studies of the quasi-two-dimensional organic superconductor κ-(BEDT-TTF)2Cu(NCS)2. Phys Rev B. 2002;65:140509-1–4.
Yamashita S, Ishikawa T, Fujisaki T, Naito A, Nakazawa Y, Oguni M. Thermodynamic behavior of the 10 K class organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 studied by relaxation calorimetry. Thermochim Acta. 2005;431:123–6.
Katsumoto S, Kobayashi S, Urayama H, Yamochi H, Saito G. Low-temperature specific heat of organic superconductor κ-(BEDT-TTF)2Cu(NCS)2. J Phys Soc Jpn. 1988;57:3672–3.
Andraka B, Kim JS, Stewart GR, Calson KD, Wang HH, Williams JM. Specific heat in high magnetic field of κ-di[bis(ethylenedithio)tetrathiafulvalene]- di(thiocyano)cuprate [κ-(ET)2Cu(NCS)2]: evidence for strong-coupling superconductivity. Phys Rev B. 1989;40:11345–7.
Graebner JE, Haddon RC, Chichester SV, Glarum SH. Specific heat of superconducting κ-(BEDT-TTF)2Cu(NCS)2 near Tc [where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene]. Phys Rev B. 1990;41:4808–10.
Elsinger H, Wosnizta J, Wanka S, Hagel J, Schweitzer D, Strunz W. κ-(BEDT-TTF)2Cu[N(CN)2]Br: a fully gapped strong-coupling superconductor. Phys Rev Lett. 2000;84:6098–101.
Lortz R, Wang Y, Demuer A, Böttger PHM, Bergk B, Zwicknagl G, Nakazawa Y, Wosnitza J. Calorimetric evidence for a Fulde–Ferrell–Larkin–Ovchinnikov superconducting state in the layered organic superconductor κ-(BEDT-TTF)2Cu(NCS)2. Phys Rev Lett. 2007;99:187002-1–4.
Ishikawa T, Yamashita S, Nakazawa Y, Kawamoto A, Oguni M. Calorimetric study of molecular superconductor κ-(BEDT-TTF)2Ag(CN)2H2O which contains water in the anion layers. J Therm Anal Calorim. 2008;92:435–8.
Acknowledgements
The work presented in this paper was partly supported by a Grant-in-Aid for Scientific Research (No. 23110717) from the Ministry of Education, Culture, Sports, Science, and Technology, Japan.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Muraoka, Y., Imajo, S., Yamashita, S. et al. Thermal anomaly around the superconductive transition of κ-(BEDT-TTF)2Cu(NCS)2 with external pressure and magnetic field control. J Therm Anal Calorim 123, 1891–1897 (2016). https://doi.org/10.1007/s10973-016-5246-8
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10973-016-5246-8