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Specific heat to Hc⁢2: Evidence for nodes or deep minima in the superconducting gap of underdoped and overdoped Ba(Fe1–$$x$$Co$$x$$)2As2

Journal Article · · Physical Review. B, Condensed Matter and Materials Physics
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  1. University of Florida, Gainesville, FL (United States)
  2. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
  3. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
  4. Seoul National University (Korea)
+ Show Author Affiliations
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. Here, we argue that, within the two-band theory of superconductivity, an inflection point may occur if the interband coupling is dominant.
Research Organization:
University of Florida, Gainesville, FL (United States)
Sponsoring Organization:
Ministry of Education, Science and Technology; USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
FG02-05ER46236; FG02-86ER45268
OSTI ID:
2484145
Alternate ID(s):
OSTI ID: 1102896
OSTI ID: 1081962
Journal Information:
Physical Review. B, Condensed Matter and Materials Physics, Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Issue: 1 Vol. 86; ISSN 1098-0121
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English

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