Close relationship between superconductivity and the bosonic mode in Ba0.6K0.4Fe2As2 and Na(Fe0.975Co0.025)As

Zhen-yu, Wang; Yang, Huan; Fang, Delong; Shen, Bing; Wang, Qiang-Hua; Shan, Lei; Zhang, Chenglin; Dai, Pengcheng; Wen, Hao

doi:10.1038/nphys2478

Cited by 62 publications

(85 citation statements)

References 44 publications

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“…Other data are consistent with these observations [12,27]. It appears that in some pnictides there is a close relationship between the structure seen in the STS data, as an example for Ba 0.6 K 0.4 Fe 2 As 2 and for Na(Fe 0.975 Co 0.025 )As [28], and a magnetic resonance at Ω [28,29,30]. This is reminiscent of the situation in the high T c oxides where coupling to a resonance mode is observed in the optics at Ω OP T R ∼ 6.3 k B T c which is close to the canonical value of the spin resonance seen in neutron scattering Ω [31,32].…”

Section: Introductionsupporting

confidence: 79%

Electron-boson spectral density of LiFeAs obtained from optical data

Hwang

Ćarbotte

Min

et al. 2015

J. Phys.: Condens. Matter

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Abstract. We analyze existing optical data in the superconducting state of LiFeAs at T = 4 K, to recover its electron-boson spectral density. A maximum entropy technique is employed to extract the spectral density I 2 χ(ω) from the optical scattering rate. Care is taken to properly account for elastic impurity scattering which can importantly affect the optics in an s-wave superconductor, but does not eliminate the boson structure. We find a robust peak in I 2 χ(ω) centered about Ω R ∼ = 8.0 meV or 5.3 k B T c (with T c = 17.6 K). Its position in energy agrees well with a similar structure seen in scanning tunneling spectroscopy (STS). There is also a peak in the inelastic neutron scattering (INS) data at this same energy. This peak is found to persist in the normal state at T = 23 K. There is evidence that the superconducting gap is anisotropic as was also found in low temperature angular resolved photoemission (ARPES) data.

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Section: Introductionsupporting

confidence: 79%

Electron-boson spectral density of LiFeAs obtained from optical data

Hwang

Ćarbotte

Min

et al. 2015

J. Phys.: Condens. Matter

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“…They give rise to the frequently observed V-shape of the normal state spectrum closely tied to an overdamped particlehole spectrum as depicted by the blue curve in Figure 2. Such V-shaped background conductances have also been seen in the iron pnictide superconductors [13,24,25]. In the superconducting state inelastic tunneling was discussed in the context of fine structures of the tunneling spectrum that displayed an isotope effect, suggesting the tunneling via apical oxygen states [38].…”

mentioning

confidence: 97%

Tracing the Electronic Pairing Glue in Unconventional Superconductors via Inelastic Scanning Tunneling Spectroscopy

et al. 2017

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Scanning tunneling microscopy (STM) has been shown to be a powerful experimental probe to detect electronic excitations and further allows to deduce fingerprints of bosonic collective modes in superconductors. Here, we demonstrate that the inclusion of inelastic tunnel events is crucial for the interpretation of tunneling spectra of unconventional superconductors and allows to directly probe electronic and bosonic excitations via STM. We apply the formalism to the iron based superconductor LiFeAs. With the inclusion of inelastic contributions, we find strong evidence for a non-conventional pairing mechanism, likely via magnetic excitations.PACS numbers: 74.55.+v, 74.20.Mn, 74.20.Rp, 74.70.Xa Electron tunneling spectroscopy has turned out to be an outstanding tool for the investigation of superconductors. A classical example is the determination of the electron-phonon pairing interaction in conventional superconductors [1,2]. More recently, quasi-particles interference spectroscopy managed to exploit the local resolution of scanning tunneling microscopy (STM) to obtain momentum space information [3][4][5]. Both examples are based on elastic tunneling theory [6,7] where one interprets the low-temperature conductance to be proportional to the electronic density of states (DOS), including renormalizations of the DOS that occur for example within the strong coupling Eliashberg formalism [8]. An energy dependent coupling to phonons or electronic collective modes and the details of these bosonic spectral features lead to a renormalization of the electronic DOS in form of peak-dip features above the superconducting coherence peaks [1]. Such pronounced peak-dip features have also been observed in cuprate and iron-based superconductors [9][10][11][12][13][15][16][17][18][19][20][21][22][23][24][25]. A frequent interpretation is, based on elastic tunneling theory, in terms of a coupling of electrons to a sharp spin resonance mode with frequency ω res and with momentum at the antiferromagnetic ordering vector of the material [26][27][28].In an interacting system the injection of a real electron may cause both, the creation of a fermionic quasiparticle and the excitation of (bosonic) collective modes as depicted in Fig. 1. The strength of the interaction is usually crucial for the relative weight of the low-energy quasiparticle and the cloud of excitations associated with it. The excitation of the quasiparticle corresponds to the above discussed elastic tunneling, while the creation of real collective modes during the tunneling process corresponds to inelastic tunneling.In this paper we demonstrate that such inelastic tunneling events can lead to important and observable modifications of the STM spectrum in unconventional su- perconductors. In addition to fermionic exitations that are visible via elastic tunneling, inelastic tunneling spectroscopy can be used to identify the bosonic excitations of the system. We show that the fine-structures seen in LiFeAs are predominantly due to such inelastic tunneling processes and th...

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“…[37] Recently in some iron based superconductors, the scanning tunneling spectroscopy measurements also reveal a peak outside the superconducting coherence peak, which is explained as the coupling of the quasiparticles with the resonance mode, a simple ratio Ω ≈ 4.3 ± 0.5k B T c was discovered. [38] This strongly suggests that the neutron resonance is indeed closely related to the superconductivity.…”

Section: T/u>>1 T/u 1 T/u<<1mentioning

confidence: 94%

Study on Unconventional Superconductivity after the BCS Paradigm

Wen

2014

Proceedings of the 12th Asia Pacific Physics Conference (APPC12)

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The Bardeen-Cooper-Schrieffer (BCS) theoretical picture has successfully explained the phenomenon of superconductivity in many single element and alloy superconductors. It suggests that the superconductivity is established through quantum condensation of vast number of Copper pairs formed by exchanging phonons between two electrons with opposite momentum and spins near the Fermi energy. This interesting paradigm has dominated the field of superconductivity since 1957. Many superconductors discovered in past three decades, such as the cuprates, iron pnictide/charcogenide and heavy Fermion superconductors seem, however, to violate the BCS picture to some extent. Most of these new superconducting systems seem to get rid of the phonons, instead use the antiferromagnetic spin fluctuations as the pairing gluons. In cuprate superconductors, the origin for the pairing may be even more exotic. In this short report, we will summarize part of these progresses and try to guide readers to possibly new schemes of superconductivity after the BCS paradigm.

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Close relationship between superconductivity and the bosonic mode in Ba0.6K0.4Fe2As2 and Na(Fe0.975Co0.025)As

Cited by 62 publications

References 44 publications

Electron-boson spectral density of LiFeAs obtained from optical data

Electron-boson spectral density of LiFeAs obtained from optical data

Tracing the Electronic Pairing Glue in Unconventional Superconductors via Inelastic Scanning Tunneling Spectroscopy

Study on Unconventional Superconductivity after the BCS Paradigm

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