Volovik effect in a highly anisotropic multiband superconductor: Experiment and theory

Wang, Yeqing; Kim, J. S.; Stewart, G. R.; Hirschfeld, P. J.; Gräser, S.; Kasahara, S.; Terashima, Takahito; Matsuda, Yuji; Shibauchi, T.; Vekhter, Ilya

doi:10.1103/physrevb.84.184524

Cited by 34 publications

(38 citation statements)

References 44 publications

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“…The exponent is in the range of 0.6 to 0.7 for all three samples. Previous measurements at optimal doping 43 show as well a very similar field dependence for fields up to 4 T, while a crossover to a linear behavior is found at higher fields. This behavior is interpreted in terms of a double gap system, in which the Volovik-like trend at low fields is due to a strongly anisotropic gap, while the linear component at high fields is due to a second isotropic gap.…”

Section: Resultsmentioning

confidence: 73%

Superconducting gap evolution in overdopedBaFe2(As1−xPx)2single crystals through nanocal

et al. 2015

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We report on specific heat measurements on clean overdoped BaFe2(As1−xPx)2 single crystals performed with a high resolution membrane-based nanocalorimeter. A nonzero residual electronic specific heat coefficient at zero temperature γr = C/T |T →0 is seen for all doping compositions, indicating a considerable fraction of the Fermi surface ungapped or having very deep minima. The remaining superconducting electronic specific heat is analyzed through a two-band s-wave α model in order to investigate the gap structure. Close to optimal doping we detect a single zero-temperature gap of ∆0 ∼ 5.3 meV, corresponding to ∆0/kBTc ∼ 2.2. Increasing the phosphorus concentration x, the main gap reduces till a value of ∆0 ∼ 1.9 meV for x = 0.55 and a second weaker gap becomes evident. From the magnetic field effect on γr, all samples however show similar behavior [γr(H) − γr(H = 0) ∝ H n , with n between 0.6 and 0.7]. This indicates that, despite a considerable redistribution of the gap weights, the total degree of gap anisotropy does not change drastically with doping.

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Section: Resultsmentioning

confidence: 73%

Superconducting gap evolution in overdopedBaFe2(As1−xPx)2single crystals through nanocal

et al. 2015

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“…Note that the underdoped sample is in the SDW-SC coexistence phase. In the isovalent analog system BaFe 2 (As 1−x P x ) 2 , an early report of linear-H behavior which appeared inconsistent with penetration depth measurements [223] reporting linear T behavior as discussed above [205], as well as evidence for nodes from NMR [149] and thermal conductivity measurements [205], was recently superseded by a measurement reporting a small Volovik term at low fields crossing over to linear behavior at higher fields [224]. This work underlined the importance of determining on which sheets the nodes occur, since sheets with smaller mass and longer relaxation times will dominate transport, while larger mass alone will determine specific heat.…”

Section: Specific Heatmentioning

confidence: 97%

Gap symmetry and structure of Fe-based superconductors

Hirschfeld¹,

Korshunov²,

Mazin³

2011

Rep. Prog. Phys.

1,199

1,467

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Abstract.The recently discovered Fe pnictide and chalcogenide superconductors display low temperature properties suggesting superconducting gap structures which appear to vary substantially from family to family, and even within family as a function of doping or pressure. We propose that this apparent nonuniversality can actually be understood by considering the predictions of spin fluctuation theory and accounting for the peculiar electronic structure of these systems, coupled with the likely "sign-changing s-wave" (s ± ) symmetry. We review theoretical aspects, materials properties, and experimental evidence relevant to this suggestion, and discuss which further measurements would be useful to settle these issues.

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“…In addition to the C(H, ) measurements (Malone et al [518]) on P-doped BaFe2As2 discussed in section 6.6., where line node behavior was inferred, Wang et al [526] measured the specific heat to 35 T on BaFe2(As0.7P0.3)2. Their low temperature  data varied as H 1/2 only up to ~ 4 T, with linear behavior at higher fields.…”

Section: Specific Heat  Varies As H 1/2 In the Superconducting Statementioning

confidence: 99%

“…Such behavior is indicative of either two s-wave gaps (Bang [83])) or strong anisotropy/possible nodal behavior in a single gap (Wang et al [526]). The calculation of large 2/kBTc values (up to 4.5) by Kasahara et al [636], which they claimed as evidence for an increase in coupling strength with doping above x=0.07, was done using an empirical theory (Padamsee, Neighbor, and Shiffman [637]) that assumed an "isotopically [sic] gapped state," which is questionable based on the evidence from their own (H) data which implied strong anisotropy.…”

Section: Superconducting Properties That Impinge On Possible Ucs -Formmentioning

confidence: 99%

Unconventional superconductivity

Stewart

2017

Advances in Physics

Self Cite

200

165

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Abstract:"Conventional" superconductivity, as used in this review, refers to electron-phonon coupled superconducting electron pairs described by BCS theory. Unconventional superconductivity refers to superconductors where the Cooper pairs are not bound together by phonon-exchange but instead by exchange of some other kind, e. g. spin fluctuations in a superconductor with magnetic order either coexistent or nearby in the phase diagram. Such unconventional superconductivity has been known experimentally since heavy fermion CeCu2Si2, with its strongly correlated 4f electrons, was discovered to superconduct below 0.6 K in 1979. Since the discovery of unconventional superconductivity in the layered cuprates in 1986, the study of these materials saw Tc jump to 164 K by 1994. Further progess in high temperature superconductivity would be aided by understanding the cause of such unconventional pairing. This review compares the fundamental properties of 9 unconventional superconducting classes of materialsfrom 4f-electron heavy fermions to organic superconductors to classes where only three known members exist to the cuprates with over 200 examples -with the hope that common features will emerge to help theory explain (and predict!) these phenomena. In addition, three new emerging classes of superconductors (topological, interfacial -e. g. FeSe on SrTiO3, and H2S under high pressure) are briefly covered, even though their "conventionality" is not yet fully determined.

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Volovik effect in a highly anisotropic multiband superconductor: Experiment and theory

Cited by 34 publications

References 44 publications

Superconducting gap evolution in overdopedBaFe2(As1−xPx)2single crystals through nanocal

Superconducting gap evolution in overdopedBaFe2(As1−xPx)2single crystals through nanocal

Gap symmetry and structure of Fe-based superconductors

Unconventional superconductivity

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