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Title: Specific heat to H c2: Evidence for nodes or deep minima in the superconducting gap of underdoped and overdoped Ba(Fe 1–xCo x)₂As₂

Low-temperature specific heat, C, in magnetic fields up to H c2 is reported for underdoped Ba(Fe₀.₉₅₅Co₀.₀₄₅)₂As₂ (T c = 8 K) and for three overdoped samples Ba(Fe₁₋ xCo x)₂As₂ (x = 0.103, 0.13, and 0.15; T c = 17.2, 16.5, and 11.7 K, respectively). Previous measurements of thermal conductivity (as a function of temperature and field) and penetration depth on comparable-composition samples gave some disagreement as to whether there was fully gapped/nodal behavior in the under-/overdoped materials, respectively. The present work shows that the measured behavior of the specific heat γ (∝C/T as T → 0, i.e., a measure of the electronic density of states at the Fermi energy) as a function of field approximately obeys γ ∝ H 0.5±0.1, similar to the Volovik effect for nodal superconductors, for both the underdoped and the most overdoped Co samples. However, for the two overdoped compositions x = 0.103 and 0.13, the low-field (H ≤ 10 T) data show a Volovik-like behavior of γ ∝ H 0.3–0.4, followed by an inflection point, followed at higher fields by γ ∝ H¹. We argue that, within the two-band theory of superconductivity, an inflection point may occur if the interband coupling is dominant.
Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Type:
Publisher's Accepted Manuscript
Journal Name:
Physical Review. B, Condensed Matter and Materials Physics
Additional Journal Information:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Volume: 86 Journal Issue: 1; Journal ID: ISSN 1098-0121
Publisher:
American Physical Society
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
OSTI Identifier:
1102896

Kim, J. S., Faeth, B. D., Wang, Y., Hirschfeld, P. J., Stewart, G. R., Gofryk, K., Ronning, F., Sefat, A. S., Choi, K. Y., and Kim, K. H.. Specific heat to Hc2: Evidence for nodes or deep minima in the superconducting gap of underdoped and overdoped Ba(Fe1–xCox)₂As₂. United States: N. p., Web. doi:10.1103/PhysRevB.86.014513.
Kim, J. S., Faeth, B. D., Wang, Y., Hirschfeld, P. J., Stewart, G. R., Gofryk, K., Ronning, F., Sefat, A. S., Choi, K. Y., & Kim, K. H.. Specific heat to Hc2: Evidence for nodes or deep minima in the superconducting gap of underdoped and overdoped Ba(Fe1–xCox)₂As₂. United States. doi:10.1103/PhysRevB.86.014513.
Kim, J. S., Faeth, B. D., Wang, Y., Hirschfeld, P. J., Stewart, G. R., Gofryk, K., Ronning, F., Sefat, A. S., Choi, K. Y., and Kim, K. H.. 2012. "Specific heat to Hc2: Evidence for nodes or deep minima in the superconducting gap of underdoped and overdoped Ba(Fe1–xCox)₂As₂". United States. doi:10.1103/PhysRevB.86.014513.
@article{osti_1102896,
title = {Specific heat to Hc2: Evidence for nodes or deep minima in the superconducting gap of underdoped and overdoped Ba(Fe1–xCox)₂As₂},
author = {Kim, J. S. and Faeth, B. D. and Wang, Y. and Hirschfeld, P. J. and Stewart, G. R. and Gofryk, K. and Ronning, F. and Sefat, A. S. and Choi, K. Y. and Kim, K. H.},
abstractNote = {Low-temperature specific heat, C, in magnetic fields up to Hc2 is reported for underdoped Ba(Fe₀.₉₅₅Co₀.₀₄₅)₂As₂ (Tc = 8 K) and for three overdoped samples Ba(Fe₁₋xCox)₂As₂ (x = 0.103, 0.13, and 0.15; Tc = 17.2, 16.5, and 11.7 K, respectively). Previous measurements of thermal conductivity (as a function of temperature and field) and penetration depth on comparable-composition samples gave some disagreement as to whether there was fully gapped/nodal behavior in the under-/overdoped materials, respectively. The present work shows that the measured behavior of the specific heat γ (∝C/T as T → 0, i.e., a measure of the electronic density of states at the Fermi energy) as a function of field approximately obeys γ ∝ H0.5±0.1, similar to the Volovik effect for nodal superconductors, for both the underdoped and the most overdoped Co samples. However, for the two overdoped compositions x = 0.103 and 0.13, the low-field (H ≤ 10 T) data show a Volovik-like behavior of γ ∝ H0.3–0.4, followed by an inflection point, followed at higher fields by γ ∝ H¹. We argue that, within the two-band theory of superconductivity, an inflection point may occur if the interband coupling is dominant.},
doi = {10.1103/PhysRevB.86.014513},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 1,
volume = 86,
place = {United States},
year = {2012},
month = {7}
}

Works referenced in this record:

Measurement of low‐temperature specific heat
journal, January 1983
  • Stewart, G. R.
  • Review of Scientific Instruments, Vol. 54, Issue 1, p. 1-11
  • DOI: 10.1063/1.1137207