Proximity two bands Eliashberg theory of electrostatic field-effect doping in a superconducting film of MgB<sub>2</sub>

Ummarino, Giovanni; Romanin, Davide

doi:10.1088/1361-648x/aaef6b

Cited by 6 publications

(14 citation statements)

References 31 publications

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“…The theoretical approach we used, which has already given successful results in Pb and

{MgB}_{2}

, is able to reproduce experimental results of Glover and Sherrill . As a consequence, the Thomas–Fermi approximation is justified.…”

Section: Discussionmentioning

confidence: 67%

“…For the computation of

Δ T_{normalc}

as a function of increasing electron doping, we considered three different film thicknesses of

d = 3,5,7 nm

and a junction area of

A {= 10}^{- 6} {normalm}^{2}

. The results of proximity‐coupled Eliashberg calculations are shown in Figure , where we assume that the Thomas–Fermi model always holds (

d_{normals} = d_{TF}

).…”

Section: Resultsmentioning

confidence: 99%

“…Usually, the thickness of the surface layer is difficult to determine a priori, and a suitable model for field‐effect geometry should be used in DFT computations . However in the weak electric field limit, we can set

d_{normals}

equal to the Thomas–Fermi screening length

d_{TF}

, thus getting rid of any free parameter …”

Section: Discussionmentioning

confidence: 99%

“…The induced charge in the material is treated assuming that the additional carriers spread uniformly inside the surface layer of thickness

d_{normals}

, which is justified for not too high values of the applied electric field. Indeed, in this case, Thomas–Fermi approximation is still valid and the thickness of the perturbed surface layer is taken to be of the order of the Thomas–Fermi screening length (i.e., weak‐field limit). As a matter of fact, in a field‐effect device, it is possible to modulate the carrier density per unit surface ,

n_{2 D}

, by tuning the polarization of the gate electrode.…”

Section: Ab Initio Calculation Of αS(b)2ffalse(ωfalse) δEnormalf Anmentioning

confidence: 99%

“…[24][25][26] In this work, we show instead a theoretical treatment to properly describe the effect of an electrostatic field on the superconductive properties of more complex materials developed in the framework of Eliashberg theory and successfully applied to Pb and MgB 2 . [28,29] Further development of such a theoretical framework and its validation on different classes of superconductive materials are important to suggest a priori experimental conditions (e.g., number of carriers to induce, device thickness, and so on) for an optimal modulation of superconductive properties in the field-effect architecture [30] and quantitatively describe future experimental results.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Theoretical Explanation of Electric Field‐Induced Superconductive Critical Temperature Shifts in Indium Thin Films

Ummarino

Romanin

2020

Physica Status Solidi (b)

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Herein, ab initio density functional theory computations and the self‐consistent solution of one‐band s‐wave generalized Eliashberg equations with proximity effect are combined to explain 60 years old experimental data on how a static electric field can affect the superconductive critical temperature of indium thin films. Although electronic densities of states, Fermi energy shifts, and Eliashberg spectral functions can be computed ab initio, the only parameter in the theory that cannot be determined a priori is the thickness of the surface layer affected by the electric field. However, it is shown that in the weak electrostatic field limit, Thomas–Fermi approximation is valid and, therefore, no free parameters are left, as this perturbed layer is known to have a thickness of the order of the Thomas–Fermi screening length. Moreover, it is shown that the theoretical model can reproduce experimental data, even when the magnitudes of the induced charge densities are so small to be usually neglected.

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“…The theoretical approach we used, which has already given successful results in Pb and

{MgB}_{2}

, is able to reproduce experimental results of Glover and Sherrill . As a consequence, the Thomas–Fermi approximation is justified.…”

Section: Discussionmentioning

confidence: 67%

“…For the computation of

Δ T_{normalc}

as a function of increasing electron doping, we considered three different film thicknesses of

d = 3,5,7 nm

and a junction area of

A {= 10}^{- 6} {normalm}^{2}

. The results of proximity‐coupled Eliashberg calculations are shown in Figure , where we assume that the Thomas–Fermi model always holds (

d_{normals} = d_{TF}

).…”

Section: Resultsmentioning

confidence: 99%

d_{normals}

equal to the Thomas–Fermi screening length

d_{TF}

, thus getting rid of any free parameter …”

Section: Discussionmentioning

confidence: 99%

“…The induced charge in the material is treated assuming that the additional carriers spread uniformly inside the surface layer of thickness

d_{normals}

n_{2 D}

, by tuning the polarization of the gate electrode.…”

Section: Ab Initio Calculation Of αS(b)2ffalse(ωfalse) δEnormalf Anmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Theoretical Explanation of Electric Field‐Induced Superconductive Critical Temperature Shifts in Indium Thin Films

Ummarino

Romanin

2020

Physica Status Solidi (b)

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Mapping multi-valley Lifshitz transitions induced by field-effect doping in strained MoS₂ nanolayers

Piatti

Romanin

Gonnelli

2019

J. Phys.: Condens. Matter

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Gate-induced superconductivity at the surface of nanolayers of semiconducting transition metal dichalcogenides (TMDs) has attracted a lot of attention in recent years, thanks to the sizeable transition temperature, robustness against in-plane magnetic fields beyond the Pauli limit, and hints to a non-conventional nature of the pairing. A key information necessary to unveil its microscopic origin is the geometry of the Fermi surface hosting the Cooper pairs as a function of field-effect doping, which is dictated by the filling of the inequivalent valleys at the K/K ′ and Q/Q ′ points of the Brillouin Zone. Here, we achieve this by combining Density Functional Theory calculations of the bandstructure with transport measurements on ion-gated 2H-MoS2 nanolayers. We show that, when the number of layers and the amount of strain are set to their experimental values, the Fermi level crosses the bottom of the high-energy valleys at Q/Q ′ at doping levels where characteristic kinks in the transconductance are experimentally detected. We also develop a simple 2D model which is able to quantitatively describe the broadening of the kinks observed upon increasing temperature. We demonstrate that this combined approach can be employed to map the dependence of the Fermi surface of TMD nanolayers on field-effect doping, detect Lifshitz transitions, and provide a method to determine the amount of strain and spin-orbit splitting between sub-bands from electric transport measurements in real devices.

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Special issue on novel superconducting and magnetic materials

Bernardini

Boeri

Floris

et al. 2019

J. Phys.: Condens. Matter

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Superconductivity and magnetism-and their entanglement in a single material-are among the most studied phenomena in condensed matter physics and continue to pose new challenges for fundamental research and exciting opportunities for technological applications. The last decade has witnessed groundbreaking discoveries in both fields: high-temperature superconductivity in compressed hydrides 1-3 , unconventional superconductivity in iron-based materials 4,5 and new types of magnetic states in spin-orbit coupled materials with topological and nematic characteristics 6. The prediction of material-specific properties and the interpretation of superconducting and magnetic phase transitions have been crucially aided by advances in ab-initio electronic structure methods within the density functional theory and its extensions 7. This special issue gathers together selected theoretical and experimental contributions on novel aspects of superconductivity and magnetism, collected in memory of Prof. Sandro Massidda. The collection aims to provide an updated view on timing issues and challenges in this active research field that have been at the hearth of Sandro's scientific interests. As commemorated in the obituary by Continenza and Colombo 8 , Sandro has dedicated his scientific work to the development and application of ab-initio computational and theoretical methods, yet never losing focus to the ultimate goal of theoretical and computational physics, that is to support, complement and understand the experimental observations.

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Proximity two bands Eliashberg theory of electrostatic field-effect doping in a superconducting film of MgB₂

Cited by 6 publications

References 31 publications

Theoretical Explanation of Electric Field‐Induced Superconductive Critical Temperature Shifts in Indium Thin Films

Theoretical Explanation of Electric Field‐Induced Superconductive Critical Temperature Shifts in Indium Thin Films

Mapping multi-valley Lifshitz transitions induced by field-effect doping in strained MoS₂ nanolayers

Special issue on novel superconducting and magnetic materials

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Proximity two bands Eliashberg theory of electrostatic field-effect doping in a superconducting film of MgB2

Cited by 6 publications

References 31 publications

Theoretical Explanation of Electric Field‐Induced Superconductive Critical Temperature Shifts in Indium Thin Films

Theoretical Explanation of Electric Field‐Induced Superconductive Critical Temperature Shifts in Indium Thin Films

Mapping multi-valley Lifshitz transitions induced by field-effect doping in strained MoS2 nanolayers

Special issue on novel superconducting and magnetic materials

Contact Info

Product

Resources

About

Proximity two bands Eliashberg theory of electrostatic field-effect doping in a superconducting film of MgB₂

Mapping multi-valley Lifshitz transitions induced by field-effect doping in strained MoS₂ nanolayers