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	Author	Bekaert, J.; Petrov, M.; Aperis, A.; Oppeneer, P.M.; Milošević, M.V.
	Title	Hydrogen-induced high-temperature superconductivity in two-dimensional materials : the example of hydrogenated monolayer MgB₂			Type	A1 Journal article
	Year	2019	Publication	Physical review letters	Abbreviated Journal	Phys Rev Lett
	Volume	123	Issue	7	Pages	077001
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Hydrogen-based compounds under ultrahigh pressure, such as the polyhydrides H3S and LaH10, superconduct through the conventional electron-phonon coupling mechanism to attain the record critical temperatures known to date. Here we exploit the intrinsic advantages of hydrogen to strongly enhance phonon-mediated superconductivity in a completely different system, namely, a two-dimensional material with hydrogen adatoms. We find that van Hove singularities in the electronic structure, originating from atomiclike hydrogen states, lead to a strong increase of the electronic density of states at the Fermi level, and thus of the electron-phonon coupling. Additionally, the emergence of high-frequency hydrogen-related phonon modes in this system boosts the electron-phonon coupling further. As a concrete example, we demonstrate the effect of hydrogen adatoms on the superconducting properties of monolayer MgB2, by solving the fully anisotropic Eliashberg equations, in conjunction with a first-principles description of the electronic and vibrational states, and their coupling. We show that hydrogenation leads to a high critical temperature of 67 K, which can be boosted to over 100 K by biaxial tensile strain.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000480611900017	Publication Date	2019-08-14
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0031-9007	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	8.462	Times cited	42	Open Access
	Notes	; This work was supported by TOPBOF-UAntwerp, Research Foundation-Flanders (FWO), the Swedish Research Council (VR), the Rontgen-Angstrom Cluster, and the EU-COST Action CA16218. J.B. acknowledges support of a postdoctoral fellowship of the FWO. The computational resources and services used for the first principles calculations in this work were provided by the VSC (Flemish Supercomputer Center), funded by the FWO and the Flemish Government-department EWI. Eliashberg theory calculations were supported through the Swedish National Infrastructure for Computing (SNIC). We would also like to acknowledge useful discussions with Bart Partoens, Jacques Tempere, and Matthieu Verstraete. ;			Approved	Most recent IF: 8.462
	Call Number	UA @ admin @ c:irua:161816			Serial	5415
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	Author	Bekaert, J.; Aperis, A.; Partoens, B.; Oppeneer, P.M.; Milošević, M.V.
	Title	Advanced first-principles theory of superconductivity including both lattice vibrations and spin fluctuations : the case of FeB₄			Type	A1 Journal article
	Year	2018	Publication	Physical review B	Abbreviated Journal	Phys Rev B
	Volume	97	Issue	1	Pages	014503
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	<script type='text/javascript'>document.write(unpmarked('We present an advanced method to study spin fluctuations in superconductors quantitatively and entirely from first principles. This method can be generally applied to materials where electron-phonon coupling and spin fluctuations coexist. We employ it here to examine the recently synthesized superconductor iron tetraboride (FeB4) with experimental T-c similar to 2.4 K [H. Gou et al., Phys. Rev. Lett, 111, 157002 (2013)]. We prove that FeB4 is particularly prone to ferromagnetic spin fluctuations due to the presence of iron, resulting in a large Stoner interaction strength, I = 1.5 eV, as calculated from first principles. The other important factor is its Fermi surface that consists of three separate sheets, among which two are nested ellipsoids. The resulting susceptibility has a ferromagnetic peak around q = 0, from which we calculated the repulsive interaction between Cooper pair electrons using the random phase approximation. Subsequently, we combined the electron-phonon interaction calculated from first principles with the spin fluctuation interaction in fully anisotropic Eliashberg theory calculations. We show that the resulting superconducting gap spectrum is conventional, yet very strongly depleted due to coupling to the spin fluctuations. The critical temperature decreases from T-c = 41 K, if they are not taken into account, to T-c = 1.7 K, in good agreement with the experimental value.'));
	Address
	Corporate Author				Thesis
	Publisher	American Physical Society	Place of Publication	New York, N.Y	Editor
	Language		Wos	000419229100004	Publication Date	2018-01-04
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	2469-9969; 2469-9950	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	23	Open Access
	Notes	; This work was supported by TOPBOF-UAntwerp, Research Foundation Flanders (FWO), the Swedish Research Council (VR), and the Rontgen-Angstrom Cluster. The computational resources and services used in this work were provided by the VSC (Flemish Supercomputer Center), funded by the Research Foundation Flanders (FWO) and the Flemish Government-department EWI. Anisotropic Eliashberg theory calculations were supported through the Swedish National Infrastructure for Computing (SNIC). ;			Approved	Most recent IF: 3.836
	Call Number	UA @ lucian @ c:irua:148447UA @ admin @ c:irua:148447			Serial	4866
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	Author	Bekaert, J.; Bignardi, L.; Aperis, A.; van Abswoude, P.; Mattevi, C.; Gorovikov, S.; Petaccia, L.; Goldoni, A.; Partoens, B.; Oppeneer, P.M.; Peeters, F.M.; Milošević, M.V.; Rudolf, P.; Cepek, C.
	Title	Free surfaces recast superconductivity in few-monolayer MgB₂ : combined first-principles and ARPES demonstration			Type	A1 Journal article
	Year	2017	Publication	Scientific reports	Abbreviated Journal	Sci Rep-Uk
	Volume	7	Issue		Pages	14458
	Keywords	A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
	Abstract	<script type='text/javascript'>document.write(unpmarked('Two-dimensional materials are known to harbour properties very different from those of their bulk counterparts. Recent years have seen the rise of atomically thin superconductors, with a caveat that superconductivity is strongly depleted unless enhanced by specific substrates, intercalants or adatoms. Surprisingly, the role in superconductivity of electronic states originating from simple free surfaces of two-dimensional materials has remained elusive to date. Here, based on first-principles calculations, anisotropic Eliashberg theory, and angle-resolved photoemission spectroscopy (ARPES), we show that surface states in few-monolayer MgB2 make a major contribution to the superconducting gap spectrum and density of states, clearly distinct from the widely known, bulk-like sigma-and pi-gaps. As a proof of principle, we predict and measure the gap opening on the magnesium-based surface band up to a critical temperature as high as similar to 30 K for merely six monolayers thick MgB2. These findings establish free surfaces as an unavoidable ingredient in understanding and further tailoring of superconductivity in atomically thin materials.'));
	Address
	Corporate Author				Thesis
	Publisher	Nature Publishing Group	Place of Publication	London	Editor
	Language		Wos	000414231000059	Publication Date	2017-10-25
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	2045-2322	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	4.259	Times cited	27	Open Access
	Notes	; This work was supported by TOPBOF-UAntwerp, Research Foundation Flanders (FWO), the Foundation for Fundamental Research on Matter (FOM)-part of the Netherlands Organisation for Scientific Research, the Swedish Research Council (VR) and the Rontgen-Angstrom Cluster. P.v.A. acknowledges an Ubbo Emmius fellowship for his PhD studies. The computational resources and services used for the first-principles calculations in this work were provided by the VSC (Flemish Supercomputer Center), funded by the Research Foundation Flanders (FWO) and the Flemish Government – department EWI. Eliashberg theory calculations were supported through the Swedish National Infrastructure for Computing (SNIC). We thank D. Lonza for technical assistance in the experimental part. ;			Approved	Most recent IF: 4.259
	Call Number	UA @ lucian @ c:irua:147426			Serial	4875
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	Author	Bekaert, J.; Aperis, A.; Partoens, B.; Oppeneer, P.M.; Milošević, M.V.
	Title	Evolution of multigap superconductivity in the atomically thin limit : strain-enhanced three-gap superconductivity in monolayer MgB₂			Type	A1 Journal article
	Year	2017	Publication	Physical review B	Abbreviated Journal	Phys Rev B
	Volume	96	Issue	9	Pages	094510
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Starting from first principles, we show the formation and evolution of superconducting gaps in MgB2 at its ultrathin limit. Atomically thin MgB2 is distinctly different from bulk MgB2 in that surface states become comparable in electronic density to the bulklike sigma and pi bands. Combining the ab initio electron-phonon coupling with the anisotropic Eliashberg equations, we showthat monolayer MgB2 develops three distinct superconducting gaps, on completely separate parts of the Fermi surface due to the emergent surface contribution. These gaps hybridize nontrivially with every extra monolayer added to the film owing to the opening of additional coupling channels. Furthermore, we reveal that the three-gap superconductivity in monolayer MgB2 is robust over the entire temperature range that stretches up to a considerably high critical temperature of 20 K. The latter can be boosted to >50K under biaxial tensile strain of similar to 4%, which is an enhancement that is stronger than in any other graphene-related superconductor known to date.
	Address
	Corporate Author				Thesis
	Publisher	American Physical Society	Place of Publication	New York, N.Y	Editor
	Language		Wos	000410166800008	Publication Date	2017-09-11
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	2469-9969; 2469-9950	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	56	Open Access
	Notes	; This work was supported by TOPBOF-UAntwerp, Research Foundation-Flanders (FWO), the Swedish Research Council (VR), and the Rontgen-Angstrom Cluster. The first-principles calculations have been carried out on the HPC infrastructure of the University of Antwerp (CalcUA), a division of the Flemish Supercomputer Centre (VSC), supported financially by the Hercules Foundation and the Flemish Government (EWI Department). Eliashberg theory calculations were supported through the Swedish National Infrastructure for Computing (SNIC). ;			Approved	Most recent IF: 3.836
	Call Number	UA @ lucian @ c:irua:145623			Serial	4741
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