On the calculation of the inverse isotope effect in PdH(D): A Migdal-Eliashberg theory approach

Villa-Cortés, S.; Baquero, R.

doi:10.1016/j.jpcs.2018.03.025

Cited by 13 publications

(10 citation statements)

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“…Yussouff et al [7] extended this discovery on palladium-hydrogen-deuterium-tritium system (PdHx-PdDx-PdTx). This reverse isotope effect in PdHx-PdDx-PdTx system is still under wide discussion [8,9]. In regard of considered in this paper ThH-ThD system, detailed studied by Caton and Satterthwaite [10] showed that superconductors in thorium-hydrogen-deuterium (ThH-ThD) system have reverse isotope effect, and Dietrich et al [11] showed that transition temperature, Tc, of the Th4H15 phase has linear positive ramp of 0.42 K/GPa versus applied external pressure.…”

Section: Introductionmentioning

confidence: 85%

Classifying Superconductivity in ThH-ThD Superhydrides

Talantsev¹

2019

Preprint

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Satterthwaite and Toepke (1970 Phys. Rev. Lett. 25 741) discovered that Th4H15-Th4D15 superhydrides exhibit superconductivity and have no isotope effect. The latter is fundamental contradiction with the concept of electron-phonon mediated superconductivity of Bardeen-Cooper-Schrieffer (BCS) theory. Soon after this work, Stritzker and Buckel (1972 Zeitschrift für Physik A Hadrons and nuclei 257 1-8) reported that superconductors in PdHx-PdDx system exhibit reverse isotope effect. Yussouff et al (1995 Solid State Communications 94 549) extended this finding on PdHx-PdDx-PdTx system. Recent interest to hydrogen- and deuterium-rich superconductors is based on the discovery of near-room-temperature superconductivity in highly-compressed H3S (Drozdov et al. 2015 Nature 525 73) and LaH10 (Somayazulu et al 2019 Phys. Rev. Lett. 122 027001). To date, there is no clarity about isotope effect in H3S-D3S system, because thorough examination of available experimental data reported by Drozdov et al (2015 Nature 525 73) shows that H3S-D3S system perhaps has reverse isotope effect. In attempt to reaffirm/disprove our primary idea that the mechanism for near-room-temperature superconductivity in hydrogen-rich superconductors is not BCS electron-phonon interaction, we analyse the upper critical field data, Bc2(T), in Th4H15-Th4D15 phases (Satterthwaite and Toepke 1970 Phys. Rev. Lett. 25 741) and two recently discovered high-pressure hydrogen-rich phases of ThH9 and ThH10 (Semenok et al 2019 arXiv:1902.10206). As the result, it is found that all known to date thorium super-hydrides/deuterides are unconventional superconductors which have Tc/TF ratios within a range of 0.008 < Tc/TF < 0.120, where Tc is the superconducting transition temperature and TF is the Fermi temperature.

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Section: Introductionmentioning

confidence: 85%

Classifying Superconductivity in ThH-ThD Superhydrides

Talantsev¹

2019

Preprint

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“…where R (ω) is given by and the T c functional derivative respect to the Eliashberg function is expressed as [46,47,49,50]…”

Section: Computational Detailsmentioning

confidence: 99%

Superconductivity on ScH$_{3}$ and YH$_{3}$ hydrides: Effects of applied pressure in combination with electron- and hole-doping on the electron-phonon coupling properties

Villa-Cortés,

De la Peña-Seaman

2021

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The implementation of electron-and hole-doping, in conjunction to applied pressure, is analyzed as a mechanism to induce or enhance the superconducting state on fcc YH3 and ScH3. In particular, the evolution of their structural, electronic, and lattice dynamical properties, as well as the electron-phonon coupling and superconducting critical temperature (Tc) is presented and discussed, as a function of the electron-and hole-doping content as well as applied pressure. The study was performed within the density functional perturbation theory, taking into account the effects of zero-point energy through the quasi-harmonic approximation, while the doping was implemented by means of the construction of the Sc1−xMxH3 (M=Ca,Ti) and Y1−xMxH3 (M=Sr,Zr) solid solutions modeled with the virtual crystal approximation (VCA). We found that the ScH3 and YH3 hydrides shown a significant improvement of their electron-phonon coupling properties under hole-doping (M=Ca,Sr) and at pressure values close to dynamical instabilities. Instead, by electron-doping (M=Ti,Zr), the systems do not improve such properties, whatever value of applied pressure is considered. Then, as a result, Tc rapidly increases as a function of x on the hole-doping region, reaching its maximum value of 92.7(67.9) K and 84.5(60.2) K at x = 0.3 for Sc1−xCaxH3 at 10.8 GPa and Y1−xSrxH3 at 5.8 GPa respectively, with µ * = 0(0.15), while for both, electron-and hole-doping, Tc decreases as a function of the applied pressure, mainly due to phonon hardening. By the thorough analysis of the electron-phonon properties as a function of doping and pressure, we can conclude that the tuning of the lattice dynamics is a promising path for improving the superconductivity on both systems.

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“…For LaH 10 a value of α ∼ = 0.47 at 150 GPa has been observed 10 , whereas in H 3 S it has a very large value of α ∼ = 2.37 at 130 GPa, decreasing it rapidly as pressure increases up to 230 GPa (α ∼ = 0.29). While for PdH there are in literature several theoretical and experimental publications studying and discussing the nature of its inverse isotope effect [34][35][36][37][38] , for H 3 S there are just a few theoretical reports that address this topic 14,20,[39][40][41][42] , but without a proper discussion of the nature of such interesting phenomena or quantitative analysis of α.…”

Section: Introductionmentioning

confidence: 99%

“…For α, we take into account the changes in the electron-electron interaction coming from the isotope mass substitution, in addition to the electron-phonon interaction. Then, the isotope coefficient is splitted into two contributions, each of them to their corresponding interaction 34,35,51 . This formalism has successfully explained the inverse isotope effect in PdH at ambient pressure 35 , as well as its behavior under pressure 34 .…”

Section: Introductionmentioning

confidence: 99%

“…Then, the isotope coefficient is splitted into two contributions, each of them to their corresponding interaction 34,35,51 . This formalism has successfully explained the inverse isotope effect in PdH at ambient pressure 35 , as well as its behavior under pressure 34 . For the electron-phonon contribution we use a generalization of the work of Rainer and Culleto on the differential isotope effect coefficient of β (ω) that includes energy dependence in N (ε) 47,52 .…”

Section: Introductionmentioning

confidence: 99%

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Effect of van Hove singularity on the isotope effect and critical temperature of H$_{3}$S hydride superconductor as a function of pressure

Villa-Cortés,

De la Peña-Seaman

2021

Preprint

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We have performed density functional calculations in conjunction with the linearized Migdal-Eliashberg equations and the functional derivative approach, which takes into account the energyrange dependence of the density of states at the Fermi level (N (ε) variable on the scale of phonon energy), to determine the evolution of the critical temperature (Tc) and the isotope effect coefficient (α) of H3S as a function of pressure on its lm 3m crystal-structure range (from 162 to 250 GPa). Such approach, in comparison with N (ε)=N (0)=const., improves the agreement of Tc with available experiments on the whole range of studied pressure. Considering for α two main contributions: one positive coming from the electron-phonon (el-ph) and the other negative from the electron-electron interaction (el-el), we obtained a monotonic decrement as a function of pressure, independent of applied scheme (N (ε) or N (0)). However, when N (ε) is taken into account, an important renormalization occurs on both contributions, el-ph and el-el, improving the agreement with experimental data, specially for the high-pressure regime. The observed evolution of Tc and α as a function of pressure indicates, thus, the crucial role of the energy-dependence on N (ε) for the proper analysis and description of the superconducting state on high-Tc metal hydrides as H3S, by considering the role of its van Hove singularities.

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On the calculation of the inverse isotope effect in PdH(D): A Migdal-Eliashberg theory approach

Cited by 13 publications

References 55 publications

Classifying Superconductivity in ThH-ThD Superhydrides

Classifying Superconductivity in ThH-ThD Superhydrides

Superconductivity on ScH$_{3}$ and YH$_{3}$ hydrides: Effects of applied pressure in combination with electron- and hole-doping on the electron-phonon coupling properties

Effect of van Hove singularity on the isotope effect and critical temperature of H$_{3}$S hydride superconductor as a function of pressure

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