Superconducting gap structure of FeSe

Jiao, Lin; Huang, Chien-Lung; Rößler, Sahana; Koz, Cevriye; Rößler, U.; Schwarz, Ulrich; Wirth, S.

doi:10.1038/srep44024

Cited by 61 publications

(77 citation statements)

References 63 publications

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“…2 (a) and (b). A similar anomaly was also seen in earlier report [20], which however exhibits like a shoulder around 2 K there, and the authors attributed this anomaly to a very small second superconducting gap. Since the low temperature anomaly observed here is a clear jumping step, not a knee like, this excludes the possibility that it is a second superconducting gap of the FeSe system, since a multiband fitting using the same T c would give rise to a "knee" or "hump" here, not as a sharp step.…”

Section: B Measurement On Specific Heat and Fitting With Different Gsupporting

confidence: 56%

“…In that work, a similar anomaly of specific heat appears at around 1.25 K and it strongly depends on the concentration of interstitial Fe. (2) In another earlier study [20], the authors observed a similar specific heat anomaly at around 2-3 K, this is much higher than the critical temperature of Al (T c = 1.17 K). (3) Most importantly, in our low temperature specific heat measurements, we find that this anomaly appears to a magnetic field at least up to 2000 Oe, but the critical field H c of Al is about 99 Oe.…”

Section: Magnetic Field Dependence Of Specific Heat In Low Temperamentioning

confidence: 90%

“…The STS measurements [12,14] suggest that there might be nodes in this system, while the thermal conductivity measurement [15] and the specific heat measurement [20] support a nodeless gap. In order to obtain more information about the gap structure of FeSe, we use BCS formula to fit the electronic specific heat in supercon- ducting state, the formula based on BCS theory is shown below,…”

Section: B Measurement On Specific Heat and Fitting With Different Gmentioning

confidence: 99%

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Highly anisotropic superconducting gaps and possible evidence of antiferromagnetic order in FeSe single crystals

et al. 2017

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Specific heat has been measured in FeSe single crystals down to 0.414 K under magnetic fields up to 16 T. A sharp specific heat anomaly at about 8.2 K is observed and is related to the superconducting transition. Another jump of specific heat is observed at about 1.08 K which may either reflect an antiferromagnetic transition of the system or a superconducting transition arising from Al impurity. We would argue that this anomaly in low temperature region may be the long sought antiferromagnetic transition in FeSe. Global fitting in wide temperature region shows that the models with a single contribution with isotropic s-wave, anisotropic s-wave, and d-wave gap all do not work well, nor the two isotropic s-wave gaps. We then fit the data by a model with two components in which one has the gap function of ∆0(1 + αcos2θ). To have a good global fitting and the entropy conservation for the low temperature transition, we reach a conclusion that the gap minimum should be smaller than 0.15 meV (α = 0.9 to 1), indicating that the superconducting gap(s) are highly anisotropic. Our results are very consistent with the gap structure derived recently from the scanning tunneling spectroscopy measurements and yield specific heat contributions of about 32% weight from the hole pocket and 68% from the electron pockets. Subject Areas: Condensed Matter Physics, SuperconductivityThe iron-selenium (FeSe) is one of the iron based superconductors with the simplest structure [1]. The later effort in enhancing the superconducting transition temperature from about 8.5 K to 37 K by pressure was encouraging [2]. However, the interest has been revived recently by exploring the phase diagram under pressure [3][4][5]. In the normal state under ambient pressure, there is a structural transition from tetragonal to orthorhombic at about 90 K [6]. This transition has been proved to be accompanied by the formation of the nematic electronic state [7]. In contrast, however, there is no evidence of antiferromagnetic long range order found in the system although the normal state is dominated by very strong spin fluctuations [8]. This may help to resolve the disputes about the origin of the nematicity [9]. Under pressure, together with the enhancement of superconducting transition temperature, an antiferromagnetic (AF) order appears [3][4][5]. However, it remains unknown how the AF order extends to the superconducting state in the low pressure region. It might be possible that this AF order is hidden under the superconducting dome and most measurements have been undertaken above the possible AF transition temperature. Angle resolved photoemission (ARPES) [10,11] and scanning tunneling spectroscopy (STS) [12] have revealed the existence of both electron and hole pockets with very small area, showing the approximate semi-metal behavior. The closeness of the band edge to the Fermi energy, or the comparable scales of the Fermi energy E F and the superconducting gap ∆, suggests a possible BCS-BEC crossover [13]. The pairing order parameter has been detected...

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Section: B Measurement On Specific Heat and Fitting With Different Gsupporting

confidence: 56%

Section: Magnetic Field Dependence Of Specific Heat In Low Temperamentioning

confidence: 90%

Section: B Measurement On Specific Heat and Fitting With Different Gmentioning

confidence: 99%

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Highly anisotropic superconducting gaps and possible evidence of antiferromagnetic order in FeSe single crystals

et al. 2017

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“…Experimentally, scanning tunneling spectroscopy (STS) [39], London penetration depth and thermal conductivity [34] claimed nodal superconductivity. However, measurements of the lower critical field [40], low-temperature specific heat [41,42], other STM [42] and other thermal conductivity studies [43,44] are consistent with nodeless superconducting gap. A cross-over from nodal in the bulk to nodeless at the twin boundary is found from STS [45].…”

mentioning

confidence: 96%

Enhancement of superconducting transition temperature by pointlike disorder and anisotropic energy gap in FeSe single crystals

et al. 2016

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“…Interestingly, it was also shown by STS measurements that the tunneling spectra display a full gap at the twin boundaries (). However, our most recent combined STS and specific heat studies conducted on single crystals grown by pure chemical vapor transport () strongly support multigap node‐less superconducting gap structure throughout the FeSe material ().…”

Section: Fesementioning

confidence: 83%

Synthesis, phase stability, structural, and physical properties of 11‐type iron chalcogenides

Rößler

Koz

Wirth

et al. 2016

Physica Status Solidi (b)

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This article reviews recent experimental investigations on two binary Fe-chalcogenides: FeSe and Fe1+yTe. The main focus is on synthesis, single crystal growth, chemical composition, as well as on the effect of excess iron on structural, magnetic, and transport properties of these materials. The structurally simplest Fe-based superconductor Fe1+xSe with a critical temperature Tc ≈ 8.5 K undergoes a tetragonal to orthorhombic phase transition at a temperature Ts ≈ 87 K. No longrange magnetic order is observed down to the lowest measured temperature in Fe1+xSe. On the other hand, isostructural Fe1+yTe displays a complex interplay of magnetic and structural phase transitions in dependence on the tuning parameter such as excess amount of Fe or pressure, but it becomes a superconductor only when Te is substituted by a sufficient amount of Se. We summarize experimental evidence for different competing interactions and discuss related open questions.

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Superconducting gap structure of FeSe

Cited by 61 publications

References 63 publications

Highly anisotropic superconducting gaps and possible evidence of antiferromagnetic order in FeSe single crystals

Highly anisotropic superconducting gaps and possible evidence of antiferromagnetic order in FeSe single crystals

Enhancement of superconducting transition temperature by pointlike disorder and anisotropic energy gap in FeSe single crystals

Synthesis, phase stability, structural, and physical properties of 11‐type iron chalcogenides

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