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Jandke, Jasmin; Wild, P.C.; Schackert, Michael; Suga, S.; Kobayashi, Tatsuya; Miyasaka, S.; Tajima, S.; Wulfhekel, Wulf

doi:10.1103/physrevb.93.104528

Cited by 4 publications

(6 citation statements)

References 43 publications

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“…In STM, the electron current I tunneling between an atomically sharp tip and the sample is recorded. As has been shown recently in the context of conventional [35,36] and unconventional [31] superconductors, the tunneling conductance between a normal conducting tip and a superconducting material consists besides the well-known elastic contributions σ el of significant inelastic contributions σ inel : dI/dU = σ tot = σ el + σ inel . Due to the spatial confinement of the electrons in the tip apex, the wave vector of the tunneling electrons is widely spread.…”

Section: Inelastic Tunneling Spectroscopymentioning

confidence: 97%

“…First of all, the electronic spectrum develops a gap ±∆ around the Fermi energy and at least a bias voltage of ±e∆ needs to be applied to add or remove a single electron from the superconductor by tunneling. Inelastic contributions caused by electron-phonon coupling thus lead to signals on top of the BCS DOS at voltages corresponding to the phonon energy ω ph shifted by the gap ∆ [36,39]. If, however, the bosonic excitations are of electronic nature, additionally the gap in the electronic excitation spectrum needs to be overcome.…”

Section: Inelastic Tunneling Spectroscopymentioning

confidence: 99%

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Unconventional pairing in single FeSe layers

Jandke

Hlobil

et al. 2019

Phys. Rev. B

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The pairing mechanism in iron-based superconductors is believed to be unconventional, i.e. not phonon-mediated. The achieved transition temperatures Tc in these superconductors are still significantly below those of some of the cuprates, with the exception of single layer FeSe films on SrTiO3 showing a Tc between 60 and 100 K, i.e. an order of magnitude larger than in bulk FeSe. This enormous increase of Tc demonstrates the potential of interface engineering for superconductivity, yet the underlying mechanism of Cooper pairing is not understood. Both conventional and unconventional mechanisms have been discussed. Here we report a direct measurement of the electron-boson coupling function in FeSe on SrTiO3 using inelastic electron scattering which shows that the excitation spectrum becomes fully gapped below Tc strongly supporting a predominantly electronic pairing mechanism. We also find evidence for strong electron-phonon coupling of low energy electrons, which is however limited to regions near structural domain boundaries.

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Section: Inelastic Tunneling Spectroscopymentioning

confidence: 97%

Section: Inelastic Tunneling Spectroscopymentioning

confidence: 99%

Unconventional pairing in single FeSe layers

Jandke

Hlobil

et al. 2019

Phys. Rev. B

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“…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].…”

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confidence: 99%

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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“…Using STM/STS offers the possibility to measure IETS at the atomic scale. However, for the moment, this methodology has been limited to a few solid materials, such as graphite/graphene [30,[34][35][36], copper [31,37], gold [31], and the only superconducting material of lead [26,32,33]. The observation in this work extends the field of research to the widely concerned TMDs, an easily tailored system suitable to further study or manipulate EPC.…”

mentioning

confidence: 97%

“…Here, F (ω) is the phonon density of states (DOS) and α the energy-dependent EPC strength. This method, known as IETS, could be utilized to reveal the vibrational spectra of molecules at the interface of a tunneling junction [24,[27][28][29] or, in a few cases, to obtain the collective vibrations or Eliashberg functions in solids [26,[30][31][32][33].…”

mentioning

confidence: 99%

Inelastic Electron Tunneling in 2H−TaxNb1−xSe
Hou
¹
,
Zhang
²
,
Tu
³

et al. 2020
Phys. Rev. Lett.
6
0
0
0
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We report a detailed study of tunneling spectra measured on 2H-TaxNb1−xSe2 (x = 0 ∼ 0.1) single crystals using a low-temperature scanning tunneling microscope. The prominent gap-like feature unintelligible for a long time was found to be accompanied by some "in-gap" fine structures. By investigating the second-derivative spectra and their temperature and magnetic field dependencies, we were able to prove that inelastic electron tunneling is the origin of these features and obtain the Eliashberg function of 2H-TaxNb1−xSe2 at atomic scale, providing a potential way to study the local Eliashberg function and phonon spectra of the related transition-metal dichalcogenides.As a prototype of transition-metal dichalcogenides (TMDs), 2H-NbSe 2 keeps attracting great interest since it provides a platform, both in bulk and in its twodimensional form, to study the mechanism of chargedensity waves (CDWs) [1][2][3], interplay between CDWs and superconductivity (SC) [4][5][6], potential applications in electronic devices [7][8][9], and so on. In recent years, there is growing consensus that it is the wave-vectordependent strong electron-phonon coupling (EPC) that drives CDW formation [10][11][12]. However, unlike the typical strong EPC system of Pb [13], no characteristics of the tunneling spectra of 2H-NbSe 2 have been identified as its EPC function, i.e., the Eliashberg function. The dominant low-energy feature other than the superconducting gap is the kinks at approximately ±35 mV, which has been observed repeatedly by scanning tunneling microscopy/spectroscopy (STM/STS) [14,15]. This well-known gap-like feature was initially regarded as the CDW gap [14], but has not been demonstrated by subsequent measurements of angle-resolved photoelectron spectroscopy (ARPES) [16,17]. A recent STM/STS experiment ascribed it to the combination of a 35-mV electron self-energy effect and a non-symmetric CDW gap of approximately 12 meV [15], which is supported by the later ARPES experiment [5]. Nonetheless, it is confusing to note that no other phonon modes have been noticed by STS, although various modes in addition to the 35-meV one can be observed in the energy-momentum dispersions from ARPES [18].In this work, we performed precise STM/STS measurements for 2H-Ta x Nb 1−x Se 2 single crystals. In addition to the 35-mV gap-like feature, a series of "in-gap" shoulders/steps were observed in all samples. By investigating the second-derivative spectra of d 2 I/dV 2 and its temperature and magnetic field evolutions, we demonstrated that these spectroscopic features, including the long-term incomprehensible 35-mV enigma, originate from the inelastic electron tunneling process instead of a CDW gap [14] or the electron self-energy effect [15]. Meanwhile, a double Fermi-Dirac broadening effect was found to be a convenient way to distinguish an inelastic electron tunneling process. Then, the real-space resolved Eliashberg functions were obtained from inelastic electron tunneling spectroscopy (IETS), which might be extended to the study of other memb...

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Scanning tunneling spectroscopy onSrFe2(As1−xPx)2

Cited by 4 publications

References 43 publications

Unconventional pairing in single FeSe layers

Unconventional pairing in single FeSe layers

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

Inelastic Electron Tunneling in 2H−TaxNb1−xSe
Hou
¹
,
Zhang
²
,
Tu
³

et al. 2020
Phys. Rev. Lett.
6
0
0
0
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Scanning tunneling spectroscopy onSrFe2(As1−xPx)2

Cited by 4 publications

References 43 publications

Unconventional pairing in single FeSe layers

Unconventional pairing in single FeSe layers

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

Inelastic Electron Tunneling in 2H−TaxNb1−xSeHou1, Zhang2, Tu3 et al. 2020Phys. Rev. Lett.6000View full textAdd to dashboardCite

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Product

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About

Inelastic Electron Tunneling in 2H−TaxNb1−xSe
Hou
¹
,
Zhang
²
,
Tu
³

et al. 2020
Phys. Rev. Lett.
6
0
0
0
View full text Add to dashboard Cite