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Breakdown of the Migdal approximation at Lifshitz transitions with giant zero-point motion in the H3S superconductor.

Jarlborg T, Bianconi A - Sci Rep (2016)

Bottom Line: The other Lifshitz-transition (of type 1) for the appearing of a new Fermi surface occurs at 130 GPa where new Fermi surfaces appear at the Γ point of the Brillouin zone here the Migdal-approximation breaks down and the zero-point-motion induces large fluctuations.The maximum Tc = 203 K occurs at 160 GPa where EF/ω0 = 1 in the small Fermi surface pocket at Γ.A Feshbach-like resonance between a possible BEC-BCS condensate at Γ and the BCS condensate in different k-space spots is proposed.

View Article: PubMed Central - PubMed

Affiliation: DPMC, University of Geneva, 24 Quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland.

ABSTRACT
While 203 K high temperature superconductivity in H3S has been interpreted by BCS theory in the dirty limit here we focus on the effects of hydrogen zero-point-motion and the multiband electronic structure relevant for multigap superconductivity near Lifshitz transitions. We describe how the topology of the Fermi surfaces evolves with pressure giving different Lifshitz-transitions. A neck-disrupting Lifshitz-transition (type 2) occurs where the van Hove singularity, vHs, crosses the chemical potential at 210 GPa and new small 2D Fermi surface portions appear with slow Fermi velocity where the Migdal-approximation becomes questionable. We show that the neglected hydrogen zero-point motion ZPM, plays a key role at Lifshitz transitions. It induces an energy shift of about 600 meV of the vHs. The other Lifshitz-transition (of type 1) for the appearing of a new Fermi surface occurs at 130 GPa where new Fermi surfaces appear at the Γ point of the Brillouin zone here the Migdal-approximation breaks down and the zero-point-motion induces large fluctuations. The maximum Tc = 203 K occurs at 160 GPa where EF/ω0 = 1 in the small Fermi surface pocket at Γ. A Feshbach-like resonance between a possible BEC-BCS condensate at Γ and the BCS condensate in different k-space spots is proposed.

No MeSH data available.


Related in: MedlinePlus

The total DOS for H3S with variable lattice constants between 5.6 and 6.2 a.u.
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f3: The total DOS for H3S with variable lattice constants between 5.6 and 6.2 a.u.

Mentions: We show the electronic self-consistent paramagnetic bands for the bcc BZ in Fig. 1 and in Fig. 2 for the sc BZ. In this last picture the simple cubic unit cell contains 8 sites totally. The calculations have been performed by the linear muffin-tin orbital (LMTO) method46 and the local spin-density approximation (LSDA) in the frame of standard methods47484950. The basis set goes up through  = 2 for S and for H. We have found that the S-2p core levels are always far below the valence band region at these pressures (about 12.2 Ry below EF). The Wigner-Seitz (WS) radii are 0.38a for S and 0.278a for H. The k-point mesh corresponds to 11 points between Γ and X, or 1331 points totally in 1/8 of the BZ, or with finer k-point mesh for plots of the bands along symmetry lines. One spin-polarized calculation is made for the largest volume starting from an imposed ferro-magnetic (FM) configuration. All local FM moments converge to zero, which shows that FM and FM spin fluctuations are unlikely. The low-lying s-band on S is very similar to the Si-s band in the A15-compound V3Si47, but the high pressure in H3S makes it to overlap with the S-p band. In contrast, the Si-p band in V3Si is separated from the Si-s band. The separation is never complete in H3S, but it is visible as a dip in the DOS at 13 eV below EF for the largest lattice constants, see Fig. 3.


Breakdown of the Migdal approximation at Lifshitz transitions with giant zero-point motion in the H3S superconductor.

Jarlborg T, Bianconi A - Sci Rep (2016)

The total DOS for H3S with variable lattice constants between 5.6 and 6.2 a.u.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837402&req=5

f3: The total DOS for H3S with variable lattice constants between 5.6 and 6.2 a.u.
Mentions: We show the electronic self-consistent paramagnetic bands for the bcc BZ in Fig. 1 and in Fig. 2 for the sc BZ. In this last picture the simple cubic unit cell contains 8 sites totally. The calculations have been performed by the linear muffin-tin orbital (LMTO) method46 and the local spin-density approximation (LSDA) in the frame of standard methods47484950. The basis set goes up through  = 2 for S and for H. We have found that the S-2p core levels are always far below the valence band region at these pressures (about 12.2 Ry below EF). The Wigner-Seitz (WS) radii are 0.38a for S and 0.278a for H. The k-point mesh corresponds to 11 points between Γ and X, or 1331 points totally in 1/8 of the BZ, or with finer k-point mesh for plots of the bands along symmetry lines. One spin-polarized calculation is made for the largest volume starting from an imposed ferro-magnetic (FM) configuration. All local FM moments converge to zero, which shows that FM and FM spin fluctuations are unlikely. The low-lying s-band on S is very similar to the Si-s band in the A15-compound V3Si47, but the high pressure in H3S makes it to overlap with the S-p band. In contrast, the Si-p band in V3Si is separated from the Si-s band. The separation is never complete in H3S, but it is visible as a dip in the DOS at 13 eV below EF for the largest lattice constants, see Fig. 3.

Bottom Line: The other Lifshitz-transition (of type 1) for the appearing of a new Fermi surface occurs at 130 GPa where new Fermi surfaces appear at the Γ point of the Brillouin zone here the Migdal-approximation breaks down and the zero-point-motion induces large fluctuations.The maximum Tc = 203 K occurs at 160 GPa where EF/ω0 = 1 in the small Fermi surface pocket at Γ.A Feshbach-like resonance between a possible BEC-BCS condensate at Γ and the BCS condensate in different k-space spots is proposed.

View Article: PubMed Central - PubMed

Affiliation: DPMC, University of Geneva, 24 Quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland.

ABSTRACT
While 203 K high temperature superconductivity in H3S has been interpreted by BCS theory in the dirty limit here we focus on the effects of hydrogen zero-point-motion and the multiband electronic structure relevant for multigap superconductivity near Lifshitz transitions. We describe how the topology of the Fermi surfaces evolves with pressure giving different Lifshitz-transitions. A neck-disrupting Lifshitz-transition (type 2) occurs where the van Hove singularity, vHs, crosses the chemical potential at 210 GPa and new small 2D Fermi surface portions appear with slow Fermi velocity where the Migdal-approximation becomes questionable. We show that the neglected hydrogen zero-point motion ZPM, plays a key role at Lifshitz transitions. It induces an energy shift of about 600 meV of the vHs. The other Lifshitz-transition (of type 1) for the appearing of a new Fermi surface occurs at 130 GPa where new Fermi surfaces appear at the Γ point of the Brillouin zone here the Migdal-approximation breaks down and the zero-point-motion induces large fluctuations. The maximum Tc = 203 K occurs at 160 GPa where EF/ω0 = 1 in the small Fermi surface pocket at Γ. A Feshbach-like resonance between a possible BEC-BCS condensate at Γ and the BCS condensate in different k-space spots is proposed.

No MeSH data available.


Related in: MedlinePlus