Momentum dependence of the superconducting gap and in-gap states in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">MgB</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>multiband superconductor

Mou, Daixiang; Jiang, Rui; Taufour, Valentin; Bud’ko, Sergey L.; Canfield, Paul C.; Kaminski, Adam

doi:10.1103/physrevb.91.214519

Cited by 23 publications

(20 citation statements)

References 41 publications

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“…The data show a clear 6-fold symmetry as expected, with spectra consistent with previous ARPES studies on the [001] cleavage plane [25][26][27][28][29] . This confirms that we are able to observe the proper bulk band structure Fig.…”

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confidence: 89%

Observation of topological surface states in the high-temperature superconductor MgB2

et al. 2019

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The hunt for the benchmark topological superconductor 1,2 (TSc) has been an extremely active research subject in condensed matter research, with quite a few candidates identified or proposed. However, low transition temperatures (T c ) and/or strong sensitivity to disorder and dopant levels inknown TSc candidates have greatly hampered progress in this field. Here, we use Angle-resolved Photoemission Spectroscopy (ARPES) to show the presence of Dirac Nodal Lines (DNLs) and the corresponding topological surface states (TSS's) on the [010] faces of the T c =39K s-wave BCS superconductor MgB 2. Not only is this nearly triple the current record 3 of superconducting T c among all candidate TSc's, but the nature of these DNL states should make them highly tolerant against disorder and inadvertent doping variations. This makes MgB 2 a promising high temperature platform for the study of topological superconductivity.As its name suggests, a topological superconductor has two essential ingredients: nontrivial topology and the superconducting order. The exploration of topological superconductivity started with pwave superconductors such as Sr 2 RuO 4 4, 5, 6 and the 5/2 quantum Hall state in electron gas systems 7,8,9 , in which the chiral superconducting order parameter is topologically nontrivial by itself. However, these pwave superconductors are extremely sensitive to disorder, very scarce in nature, and have transition temperatures well below liquid helium temperature -each of which imposes great difficulties in the exploration of topological superconductivity. Thanks to the discovery of topological order in band structures 10,11 , it was soon realized 12 that the "topological" part of a TSc can be realized with a topological surface state arising from a topologically nontrivial band-inversion, which can then be gapped by a conventional s-wave superconducting gap. This opens many new pathways to higher T c topological superconductors. One route is to construct topological insulator / superconductor hetero-structures, in which the proximity effect allows the topological surface state of a topological insulator to be gapped by the superconducting gap of a neighboring superconductor 13,14,15 . However, the proximity effect that enables topological superconductivity also imposes a severe constraint on the perfection of the interface between the two materials, which is an even greater problem for higher temperature superconductors that naturally have shorter superconducting coherence lengths. The complication of the interface physics thus becomes a major obstacle which can be naturally circumvented in a singular system, such as the one discussed here. An alternative is to dope a known bulk topological material to make it superconducting, which has seen some success in materials such as Cu-doped Bi 2 Se 3 16, 17, 18 . However, given that the discoveries of high temperature superconductivity have been largely accidental, it is unclear how far this approach can be taken. 3With the explosion of discoveries on numerous topolo...

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confidence: 89%

Observation of topological surface states in the high-temperature superconductor MgB2

et al. 2019

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“…For this reason, we model the superconducting state with the interaction on the Mg atoms Λ M g = 0 and the interaction parameter for the Boron atoms as Λ B = 0.288Ry. This parameter is tuned to fit the experimental zero temperature gap size [5][6][7]. In experimental studies, the smaller gap at zero temperature ranges from 1.8meV [6] to approximately 3meV [5,7], whereas the larger gap is around 7meV.…”

Section: Magnesium Diboridementioning

confidence: 99%

Gap anisotropy in multiband superconductors based on multiple scattering theory

et al. 2020

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We implement the Bogoliubov-de Gennes (BdG) equation in a screened Korringa-Kohn-Rostoker (KKR) method for solving, self-consistently, the superconducting state for 3d crystals. This method combines the full complexity of the underlying electronic structure and Fermi surface geometry with a simple phenomenological parametrisation for the superconductivity. We apply this theoretical framework to the known s-wave superconductors Nb, Pb, and MgB2. In these materials multiple distinct peaks at the gap in the density of states were observed, showing significant gap anisotropy which is in good agreement with experiment. Qualitatively, the results can be explained in terms of the k-dependent Fermi velocities on the Fermi surface sheets exploiting concepts from BCS theory. arXiv:1911.04163v1 [cond-mat.supr-con]

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“…Although MgB 2 is often regarded as a conventional high-T c superconductor, described by the Eliashberg theory for phonon-mediated superconductivity, it displays many peculiar characteristics that make it a unique case. Most remarkable is the anisotropy of the electronic and superconducting properties, where electronic states belonging to the σ bands are strongly coupled to phonons, and display thus large superconducting gaps ∆ σ , whereas electronic states associated with the π bands are only weakly coupled to the lattice, and hence exhibit small superconducting gaps ∆ π [1][2][3][4][5][6][7][8][9][10]. Such electronic anisotropy is also accompanied by a striking anisotropy in the phonon states.…”

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Ultrafast Hot Phonon Dynamics in MgB2 Driven by Anisotropic Electron-Phonon Coupling

et al. 2020

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The zone-center E2g modes play a crucial role in MgB2, controlling the scattering mechanisms in the normal state as well the superconducting pairing. Here, we demonstrate via first-principles quantum-field theory calculations that, due to the anisotropic electron-phonon interaction, a hotphonon regime where the E2g phonons can achieve significantly larger effective populations than other modes, is triggered in MgB2 by the interaction with an ultra-short laser pulse. Spectral signatures of this scenario in ultrafast pump-probe Raman spectroscopy are discussed in detail, revealing also a fundamental role of nonadiabatic processes in the optical features of the E2g mode.Although MgB 2 is often regarded as a conventional high-T c superconductor, described by the Eliashberg theory for phonon-mediated superconductivity, it displays many peculiar characteristics that make it a unique case. Most remarkable is the anisotropy of the electronic and superconducting properties, where electronic states belonging to the σ bands are strongly coupled to phonons, and display thus large superconducting gaps ∆ σ , whereas electronic states associated with the π bands are only weakly coupled to the lattice, and hence exhibit small superconducting gaps ∆ π [1-10]. Such electronic anisotropy is also accompanied by a striking anisotropy in the phonon states. The electron-phonon (e-ph) coupling is indeed strongly concentrated in few in-plane E 2g phonons modes along the Γ − A path of the Brillouin zone [4,11,12], whereas the remaining e-ph coupling is spread over all other lattice modes in the Brillouin zone.Due to its pivotal role in ruling e-ph based many-body effects and in the superconducting pairing, the properties of the long-wavelength E 2g mode have been extensively investigated, both theoretically and experimentally [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. On the experimental side, Raman spectroscopy has proven particularly suitable for providing fundamental information on the lattice dynamics and on the manybody e-ph processes. Particularly debated is the origin of the large phonon linewidth Γ E2g ≈ 25 meV, and of the temperature dependence of both the phonon frequency and linewidth [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. The complexity of identifying the quantum-mechanical origin of these phenomena arises from the concomitance of the e-ph interaction, non-adiabaticity, and lattice anharmonicities, in turn responsible for phonon-phonon scattering and thermal expansion. A possible path for tuning selectively only one of these processes is thus highly desirable, in order to disentangle the different mechanisms in action.Ultrafast time-resolved optical characterizations of MgB 2 with a pump-probe setup were presented in Refs. [31][32][33], where two different relaxation times were identified in the normal states. In particular, the ob-served anomalous blueshift at a short time scale of the in-plane plasmon was qualitatively explained in Ref. [33] by assumin...

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Momentum dependence of the superconducting gap and in-gap states inMgB2multiband superconductor

Cited by 23 publications

References 41 publications

Observation of topological surface states in the high-temperature superconductor MgB2

Observation of topological surface states in the high-temperature superconductor MgB2

Gap anisotropy in multiband superconductors based on multiple scattering theory

Ultrafast Hot Phonon Dynamics in MgB2 Driven by Anisotropic Electron-Phonon Coupling

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