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Pressure Induced Enhancement of Superconductivity in LaRu2P2.

Li B, Lu P, Liu J, Sun J, Li S, Zhu X, Wen HH - Sci Rep (2016)

Bottom Line: The ab-initio calculation shows that the superconductivity in LaRu2P2 at ambient pressure can be explained by the McMillan's theory with strong electron-phonon coupling.Detailed analysis of the pressure induced evolution of resistivity and upper critical field Hc2(T) reveals that the increase of Tc with pressure may be accompanied by the involvement of extra electron-boson interaction.This suggests that the Ru-based system has some commonality as the Fe-based superconductors.

View Article: PubMed Central - PubMed

Affiliation: National Laboratory of Solid State Microstructures and Department of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.

ABSTRACT
To explore new superconductors beyond the copper-based and iron-based systems is very important. The Ru element locates just below the Fe in the periodic table and behaves like the Fe in many ways. One of the common thread to induce high temperature superconductivity is to introduce moderate correlation into the system. In this paper, we report the significant enhancement of superconducting transition temperature from 3.8 K to 5.8 K by using a pressure only of 1.74 ± 0.05 GPa in LaRu2P2 which has an iso-structure of the iron-based 122 superconductors. The ab-initio calculation shows that the superconductivity in LaRu2P2 at ambient pressure can be explained by the McMillan's theory with strong electron-phonon coupling. However, it is difficult to interpret the enhancement of Tc versus pressure within this picture. Detailed analysis of the pressure induced evolution of resistivity and upper critical field Hc2(T) reveals that the increase of Tc with pressure may be accompanied by the involvement of extra electron-boson interaction. This suggests that the Ru-based system has some commonality as the Fe-based superconductors.

No MeSH data available.


Pressure enhanced superconductivity and theoretical calculations.(a) Transition temperature Tc versus pressure for the LaRu2P2 single crystal obtained by the electrical resistivity measurement (black squares). Theoretical calculation results (red circles) are presented in the same graph for comparison, which is based on the McMillan’s theory for the case of strong electron-phonon coupling. (b) First principle calculation values of the maximum phonon frequency ωlog and the electron-phonon coupling constant λe−ph under different pressures. The calculation is based on the Density Functional Theory, using ultrasoft pseudopotentials, Generalized Gradient Approximation (PBE) functionals.
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f2: Pressure enhanced superconductivity and theoretical calculations.(a) Transition temperature Tc versus pressure for the LaRu2P2 single crystal obtained by the electrical resistivity measurement (black squares). Theoretical calculation results (red circles) are presented in the same graph for comparison, which is based on the McMillan’s theory for the case of strong electron-phonon coupling. (b) First principle calculation values of the maximum phonon frequency ωlog and the electron-phonon coupling constant λe−ph under different pressures. The calculation is based on the Density Functional Theory, using ultrasoft pseudopotentials, Generalized Gradient Approximation (PBE) functionals.

Mentions: At a pressure higher than 1.74 ± 0.05 GPa, the Tc seems getting lower, as shown in Fig. 2a. The Tc at 2.25 ± 0.05 GPa is not presented in this graph since we cannot precisely determine the Tc at that pressure because of the broadening of resistive transition. Since there is only one confirmed point at 1.97 ± 0.05 GPa above the pressure with a maximum Tc, we are not sure whether there is a dome like Tc-p phase diagram. This behavior is not contradicted, but slightly different from that in the previously reported AC susceptibility measurements with hydrostatic pressures23, which reveals also an enhanced Tc, but superconductivity suddenly disappears above 2.1 GPa. In the magnetic susceptibility measurements23, above about 2.1 GPa, the magnetic susceptibility vs. temperature curve becomes very smooth with a very strange background. Therefore it is very difficult to judge whether the superconductivity is really absent or just invisible due to the huge unknown background. In order to understand the superconductivity mechanism, we performed ab-initio calculations for the electron-phonon coupling in the frame work of density functional perturbation theory24, details of the calculations were provided in the Method section and Supplementary Information. Based on the McMillan theory for strong electron-phonon coupling, Tc can be estimated as:


Pressure Induced Enhancement of Superconductivity in LaRu2P2.

Li B, Lu P, Liu J, Sun J, Li S, Zhu X, Wen HH - Sci Rep (2016)

Pressure enhanced superconductivity and theoretical calculations.(a) Transition temperature Tc versus pressure for the LaRu2P2 single crystal obtained by the electrical resistivity measurement (black squares). Theoretical calculation results (red circles) are presented in the same graph for comparison, which is based on the McMillan’s theory for the case of strong electron-phonon coupling. (b) First principle calculation values of the maximum phonon frequency ωlog and the electron-phonon coupling constant λe−ph under different pressures. The calculation is based on the Density Functional Theory, using ultrasoft pseudopotentials, Generalized Gradient Approximation (PBE) functionals.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4834477&req=5

f2: Pressure enhanced superconductivity and theoretical calculations.(a) Transition temperature Tc versus pressure for the LaRu2P2 single crystal obtained by the electrical resistivity measurement (black squares). Theoretical calculation results (red circles) are presented in the same graph for comparison, which is based on the McMillan’s theory for the case of strong electron-phonon coupling. (b) First principle calculation values of the maximum phonon frequency ωlog and the electron-phonon coupling constant λe−ph under different pressures. The calculation is based on the Density Functional Theory, using ultrasoft pseudopotentials, Generalized Gradient Approximation (PBE) functionals.
Mentions: At a pressure higher than 1.74 ± 0.05 GPa, the Tc seems getting lower, as shown in Fig. 2a. The Tc at 2.25 ± 0.05 GPa is not presented in this graph since we cannot precisely determine the Tc at that pressure because of the broadening of resistive transition. Since there is only one confirmed point at 1.97 ± 0.05 GPa above the pressure with a maximum Tc, we are not sure whether there is a dome like Tc-p phase diagram. This behavior is not contradicted, but slightly different from that in the previously reported AC susceptibility measurements with hydrostatic pressures23, which reveals also an enhanced Tc, but superconductivity suddenly disappears above 2.1 GPa. In the magnetic susceptibility measurements23, above about 2.1 GPa, the magnetic susceptibility vs. temperature curve becomes very smooth with a very strange background. Therefore it is very difficult to judge whether the superconductivity is really absent or just invisible due to the huge unknown background. In order to understand the superconductivity mechanism, we performed ab-initio calculations for the electron-phonon coupling in the frame work of density functional perturbation theory24, details of the calculations were provided in the Method section and Supplementary Information. Based on the McMillan theory for strong electron-phonon coupling, Tc can be estimated as:

Bottom Line: The ab-initio calculation shows that the superconductivity in LaRu2P2 at ambient pressure can be explained by the McMillan's theory with strong electron-phonon coupling.Detailed analysis of the pressure induced evolution of resistivity and upper critical field Hc2(T) reveals that the increase of Tc with pressure may be accompanied by the involvement of extra electron-boson interaction.This suggests that the Ru-based system has some commonality as the Fe-based superconductors.

View Article: PubMed Central - PubMed

Affiliation: National Laboratory of Solid State Microstructures and Department of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.

ABSTRACT
To explore new superconductors beyond the copper-based and iron-based systems is very important. The Ru element locates just below the Fe in the periodic table and behaves like the Fe in many ways. One of the common thread to induce high temperature superconductivity is to introduce moderate correlation into the system. In this paper, we report the significant enhancement of superconducting transition temperature from 3.8 K to 5.8 K by using a pressure only of 1.74 ± 0.05 GPa in LaRu2P2 which has an iso-structure of the iron-based 122 superconductors. The ab-initio calculation shows that the superconductivity in LaRu2P2 at ambient pressure can be explained by the McMillan's theory with strong electron-phonon coupling. However, it is difficult to interpret the enhancement of Tc versus pressure within this picture. Detailed analysis of the pressure induced evolution of resistivity and upper critical field Hc2(T) reveals that the increase of Tc with pressure may be accompanied by the involvement of extra electron-boson interaction. This suggests that the Ru-based system has some commonality as the Fe-based superconductors.

No MeSH data available.