scholarly journals Angle-resolved photoemission spectroscopy of superconducting LiFeAs: Evidence for strong electron-phonon coupling

2011 ◽  
Vol 83 (13) ◽  
Author(s):  
A. A. Kordyuk ◽  
V. B. Zabolotnyy ◽  
D. V. Evtushinsky ◽  
T. K. Kim ◽  
I. V. Morozov ◽  
...  
Keyword(s):  
Photoemission Spectroscopy ◽  
Phonon Coupling ◽  
Strong Electron ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Electron Phonon Coupling

scholarly journals Dichotomy of superconductivity between monolayer FeS and FeSe

2019 ◽  
Vol 116 (49) ◽  
pp. 24470-24474
Author(s):  
Koshin Shigekawa ◽  
Kosuke Nakayama ◽  
Masato Kuno ◽  
Giao N. Phan ◽  
Kenta Owada ◽  
...  
Keyword(s):  
Molecular Beam ◽  
Photoemission Spectroscopy ◽  
Phonon Coupling ◽  
Superconducting Layer ◽  
Iron Based Superconductors ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Electron Phonon Coupling ◽  
Heavy Electron ◽  
Superconducting Pairing

The discovery of high-temperature (Tc) superconductivity in monolayer FeSe on SrTiO3 raised a fundamental question: Whether high Tc is commonly realized in monolayer iron-based superconductors. Tetragonal FeS is a key material to resolve this issue because bulk FeS is a superconductor with Tc comparable to that of isostructural FeSe. However, difficulty in synthesizing tetragonal monolayer FeS due to its metastable nature has hindered further investigations. Here we report elucidation of band structure of monolayer FeS on SrTiO3, enabled by a unique combination of in situ topotactic reaction and molecular-beam epitaxy. Our angle-resolved photoemission spectroscopy on FeS and FeSe revealed marked similarities in the electronic structure, such as heavy electron doping and interfacial electron–phonon coupling, both of which have been regarded as possible sources of high Tc in FeSe. However, surprisingly, high-Tc superconductivity is absent in monolayer FeS. This is linked to the weak superconducting pairing in electron-doped multilayer FeS in which the interfacial effects are absent. Our results strongly suggest that the cross-interface electron–phonon coupling enhances Tc only when it cooperates with the pairing interaction inherent to the superconducting layer. This finding provides a key insight to explore heterointerface high-Tc superconductors.

scholarly journals Evidence for superconductivity in Li-decorated monolayer graphene

2015 ◽  
Vol 112 (38) ◽  
pp. 11795-11799 ◽  
Author(s):  
B. M. Ludbrook ◽  
G. Levy ◽  
P. Nigge ◽  
M. Zonno ◽  
M. Schneider ◽  
...  
Keyword(s):  
Low Temperature ◽  
Photoemission Spectroscopy ◽  
Monolayer Graphene ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
Phonon Coupling ◽  
Temperature Dependent ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Electron Phonon Coupling ◽  
First Time

Monolayer graphene exhibits many spectacular electronic properties, with superconductivity being arguably the most notable exception. It was theoretically proposed that superconductivity might be induced by enhancing the electron–phonon coupling through the decoration of graphene with an alkali adatom superlattice [Profeta G, Calandra M, Mauri F (2012) Nat Phys 8(2):131–134]. Although experiments have shown an adatom-induced enhancement of the electron–phonon coupling, superconductivity has never been observed. Using angle-resolved photoemission spectroscopy (ARPES), we show that lithium deposited on graphene at low temperature strongly modifies the phonon density of states, leading to an enhancement of the electron–phonon coupling of up to λ≃0.58. On part of the graphene-derived π∗-band Fermi surface, we then observe the opening of a Δ≃0.9-meV temperature-dependent pairing gap. This result suggests for the first time, to our knowledge, that Li-decorated monolayer graphene is indeed superconducting, with Tc≃5.9 K.

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