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Title: Specific heat investigation for line nodes in heavily overdoped Ba1-xKxFe2As2

Journal Article · · Physical Review. B, Condensed Matter and Materials Physics
 [1];  [1];  [2];  [3]
  1. Univ. of Florida, Gainesville, FL (United States)
  2. Ames Lab., Ames, IA (United States)
  3. Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States)

Previous research has found that the pairing symmetry in the iron-based superconductor Ba1-xKxFe2As2 changes from nodeless s-wave near optimally doped, x≈0.4-0.55 and Tc>30 K, to nodal (either d-wave or s-wave) at the pure endpoint, x=1 and Tc<4 K. Intense theoretical interest has been focused on this possibility of changing pairing symmetry, where in the transition region both order parameters would be present and time reversal symmetry would be broken. Here we report specific heat measurements in zero and applied magnetic fields down to 0.4 K of three individual single crystals, free of low temperature magnetic anomalies, of heavily overdoped Ba1-xKxFe2As2, x= 0.91, 0.88, and 0.81. The values for Tcmid are 5.6, 7.2 and 13 K and for Hc2≈ 4.5, 6, and 20 T respectively. Furthermore, the data can be analyzed in a two gap scenario, Δ21 ≈ 4, with the magnetic field dependence of γ (=C/T as T→0) showing an anisotropic ‘S-shaped’ behavior vs H, with the suppression of the lower gap by 1 T and γ ≈ H1/2 overall. Although such a non-linear γ vs H is consistent with deep minima or nodes in the gap structure, it is not clear evidence for one, or both, of the gaps being nodal in these overdoped samples. Thus, following the established theoretical analysis of the specific heat of d-wave cuprate superconductors containing line nodes, we present the specific heat normalized by H1/2 plotted vs T/H1/2 of these heavily overdoped Ba1-xKxFe2As2 samples which – thanks to the absence of magnetic impurities in our sample - convincingly shows the expected scaling for line node behavior for the larger gap for all three compositions. There is however no clear observation of the nodal behavior C ∝ αT2 in zero field at low temperatures, with α ≤ 2 mJ/molK3 being consistent with the data. Together with the scaling, this leaves open the possibility of extreme anisotropy in a nodeless larger gap, Δ2, such that the scaling works for fields above 0.25 – 0.5 T (0.2 – 0.4 K in temperature units), where this an estimate for the size of the deep minima in the Δ2 ~ 20-25 K gap. Furthermore, the location of the change from nodeless→nodal gaps between optimally doped and heavily overdoped Ba1-xKxFe2As2 based on the present work may be closer to the KFe2As2 endpoint than x=0.91.

Research Organization:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
AC02-07CH11358
OSTI ID:
1227372
Alternate ID(s):
OSTI ID: 1184356
Report Number(s):
IS-J--8695
Journal Information:
Physical Review. B, Condensed Matter and Materials Physics, Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Issue: 21 Vol. 91; ISSN 1098-0121; ISSN PRBMDO
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English

References (37)

Pairing State with a Time-Reversal Symmetry Breaking in FeAs-Based Superconductors journal May 2009
Electronic specific heat and low-energy quasiparticle excitations in the superconducting state of La 2 − x Sr x Cu O 4 single crystals journal December 2004
Specific heat in KFe 2 As 2 in zero and applied magnetic field journal May 2011
Specific-heat discontinuity Δ C vs. T c in annealed Ba(Fe 1 − x Co x ) 2 As 2 journal August 2012
Comprehensive scenario for single-crystal growth and doping dependence of resistivity and anisotropic upper critical fields in (Ba 1 − x K x )Fe 2 As 2 ( 0.22 ≤ x ≤ 1 ) journal April 2014
Volovik Effect in the ± s -Wave State for the Iron-Based Superconductors journal May 2010
Electronic structure of optimally doped pnictide Ba 0.6 K 0.4 Fe 2 As 2 : a comprehensive angle-resolved photoemission spectroscopy investigation journal March 2011
Upper critical field of high-quality single crystals of KFe 2 As 2 journal April 2013
Simon and Lee Reply: journal June 1997
Specific Heat of Mg 11 B 2 : Evidence for a Second Energy Gap journal July 2001
Superconductivity from repulsion in LiFeAs: Novel s -wave symmetry and potential time-reversal symmetry breaking journal April 2014
Vortex contribution to specific heat of dirty d-wave superconductors: Breakdown of scaling journal February 1998
Specific heat anomalies for T\ll T_{\mathrm {c}} in superconducting single crystal doped BaFe 2 As 2 : comparison of different flux growth methods journal June 2009
Pairing in the iron arsenides: a functional RG treatment journal May 2009
Magnetic-field dependence of the low-temperature specific heat of La 2 − x Sr x CuO 4 journal December 1998
Volovik effect in a highly anisotropic multiband superconductor: Experiment and theory journal November 2011
Microwave Surface-Impedance Measurements of the Magnetic Penetration Depth in Single Crystal Ba 1 − x K x Fe 2 As 2 Superconductors: Evidence for a Disorder-Dependent Superfluid Density journal May 2009
Magnetic Field Dependence of the Density of States of Y Ba 2 Cu 3 O 6.95 as Determined from the Specific Heat journal November 1994
Low temperature specific heat of the hole-doped Ba 0.6 K 0.4 Fe 2 As 2 single crystals journal May 2009
Direct observation and anisotropy of the contribution of gap nodes in the low-temperature specific heat of YBa 2 Cu 3 O 7 journal February 2001
Low-Temperature Specific Heat of YBa 2 Cu 3 O 7 − δ , 0 ≤ δ ≤ 0.2 : Evidence for d -Wave Pairing journal February 1999
Mechanism for Explaining Differences in the Order Parameters of FeAs-Based and FeP-Based Pnictide Superconductors journal May 2011
Measurement of low‐temperature specific heat journal January 1983
Spontaneous currents in a superconductor with s + i s symmetry journal April 2015
Anisotropic thermodynamics of d -wave superconductors in the vortex state journal April 1999
Octet-Line Node Structure of Superconducting Order Parameter in KFe2As2 journal September 2012
Thermodynamic Study of Nodal Structure and Multiband Superconductivity of KFe 2 As 2 journal January 2014
From d-wave to s-wave pairing in the iron-pnictide superconductor (Ba,K)Fe 2 As 2 journal July 2012
Anomalous Change in the Field Dependence of the Electronic Specific Heat of an Electron-Doped Cuprate Superconductor journal August 2004
s + i s state with broken time-reversal symmetry in Fe-based superconductors journal April 2013
Iron-Based Layered Superconductor La[O 1- x F x ]FeAs ( x = 0.05−0.12) with T c = 26 K journal March 2008
Magnetic-field dependence of the low-temperature specific heat of the electron-doped superconductor Pr 1.85 Ce 0.15 Cu O 4 journal December 2005
Effect of delocalized vortex core states on the specific heat of Nb journal April 2006
Superconductivity in iron compounds journal December 2011
Universal Heat Conduction in the Iron Arsenide Superconductor KFe 2 As 2 : Evidence of a d -Wave State journal August 2012
Superconductivity at 38 K in the Iron Arsenide ( Ba 1 − x K x ) Fe 2 As 2 journal September 2008
Scaling of the Quasiparticle Spectrum for d -wave Superconductors journal February 1997

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