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The Low-Temperature Specific Heat of Chalcogen -based FeSe

The Low-Temperature Specific Heat of Chalcogen -based FeSe. 1 Institute of Physics/National Chiao Tung University, Hsinchu 30010, Taiwan 2 Institute of Experimental Mineralogy, Cherngolovka , Moscow Region 142432, Russia

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The Low-Temperature Specific Heat of Chalcogen -based FeSe

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  1. The Low-Temperature Specific Heat of Chalcogen-based FeSe 1 Institute of Physics/National Chiao Tung University, Hsinchu 30010, Taiwan 2Institute of Experimental Mineralogy, Cherngolovka, Moscow Region 142432, Russia 3Department of Low temperature Physics, Moscow State University, Moscow 119991, Russia 4Department of Physics, University of California, Santa Babara, CA 93106, USA 4Department of Physics, National Sun Yat-sen University, Kaohsiung 804, Taiwan J.-Y. Lin,1 Y. S. Hsieh,1D. Chareev,2 A. N. Vasiliev,3 Y. Parsons,4 and H. D. Yang4

  2. Contents • Introduction to Fe-based superconductors • Specific heat as a probe of the superconducting order parameter • Experiments and results • Conclusions

  3. A brief introduction to iron-based superconductors

  4. Structure

  5. The Race to Beat Cuprates? Hg - cuprate ？ TI - cuprate YBCO Fe-based superconductors Cuprates MgB2 LSCO e-doped SmOFeAs Nb3Ge e-doped LaOFeAs Metallic alloys e-doped LaOFeP 70 The crusade of Room Temperature superconductors?

  6. Motivation • The order parameter in Fe-based superconductors remains elusive. To get insight into the pairing mechanism, it is crucial to determine the gap structure in the superconductors like FeSe or pnictides. • Though with lower Tc, FeSe has the simplest structure, and this very simplicity could provide the most appropriate venue of understanding both the order parameter and the superconducting mechanism of Fe-base superconductors.

  7. Johnston, 2010

  8. (Subediet al., 2008)

  9. Specific heat as the probe • Revealing the superconducting order parameter from the specific heat • Information from k-space integration. Non phase-sensitive. • Surprisingly selective if well excuted

  10. FeSe single crystals

  11. FeSe single crystal

  12. FeSe single crystal

  13. n=5.73 mJ/mol K2 =210 Knearly identical to the results of polycrystals from T. M. McQueen et al. (2009)

  14. Weak limit BCS isotropic s-wave: C/nTc=1.43 C/nTc=1.65

  15. C. P. Sun et al. (2004)

  16. =0cos2 =e(1+cos2)

  17. Nicholson et al. (2011)

  18. Quasi-linear (H) in high H was also observed in 122. (J. S. Kim et al. 2010) Hc2=13.1 T? /n=0~0.69

  19. Bang, 2010

  20. Anisotropic Hc2

  21. STM on FeSe C. L. Song et al., 2011

  22. Comparison between FeSe and Fe(Se,Te) FeSe Song et al., 2011 Fe(Se,Te) Hanaguri et al., 2010

  23. The fitting parameters

  24. Conclusions for FeSe • Existence of low-energy excitations more than in an isotropic s-wave. • Gap anisotropy. S + exntendeds. Probably No accidental nodes. • Existence of an isotropic s-wave. • Hc2,H//c13.1 T and Hc2,Hc27.9 T. The anisotropy in Hc2 is about 2.1.

  25. Fig. 4 The specific heat of MgB2. The dashed lines are determined by the conservation of entropy around the anomaly and used to estimate ΔC/Tc. Inset: Entropy difference ΔS by integration of ΔC/T.

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