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Theory of nodal s ± -wave pairing symmetry in the Pu-based 115 superconductor family.

Das T, Zhu JX, Graf MJ - Sci Rep (2015)

Bottom Line: The spin-fluctuation mechanism of superconductivity usually results in the presence of gapless or nodal quasiparticle states in the excitation spectrum.Our calculation demonstrates that the s(±) wave pairing strength is stronger than the previously thought d-wave pairing; and more importantly, this pairing state allows for the existence of nodal quasiparticles.Finally, we predict the shape of the momentum- and energy-dependent magnetic resonance spectrum for the identification of this pairing symmetry.

View Article: PubMed Central - PubMed

Affiliation: Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.

ABSTRACT
The spin-fluctuation mechanism of superconductivity usually results in the presence of gapless or nodal quasiparticle states in the excitation spectrum. Nodal quasiparticle states are well established in copper-oxide, and heavy-fermion superconductors, but not in iron-based superconductors. Here, we study the pairing symmetry and mechanism of a new class of plutonium-based high-Tc superconductors and predict the presence of a nodal s(±) wave pairing symmetry in this family. Starting from a density-functional theory (DFT) based electronic structure calculation we predict several three-dimensional (3D) Fermi surfaces in this 115 superconductor family. We identify the dominant Fermi surface "hot-spots" in the inter-band scattering channel, which are aligned along the wavevector Q = (π, π, π), where degeneracy could induce sign-reversal of the pairing symmetry. Our calculation demonstrates that the s(±) wave pairing strength is stronger than the previously thought d-wave pairing; and more importantly, this pairing state allows for the existence of nodal quasiparticles. Finally, we predict the shape of the momentum- and energy-dependent magnetic resonance spectrum for the identification of this pairing symmetry.

No MeSH data available.


Related in: MedlinePlus

Fermi surfaces and hot-spots from first-principles electronic band structure calculations.(a)–(c) FS topologies in the momentum space of the Brillouin zone for all three Pu-115 materials, plotted separately in three columns. An intensity colormap is used to depict the values of the JDOS on the FSs at Q = (π, π, π). For better visualization a quadrant of the holelike FS of band 2 was clipped. The JDOS gives a qualitative estimate of the static susceptibility (Eq. (1)) for nesting vector Q. These images help identify the strongest nesting between bands 1 and 2 (in the vicinity of the kz = 0-plane) to bands 3 and 4 (near the kz = π-plane). (d)–(f) The full momentum (q) dependence of the static bare bubble susceptibility χ(q, ω = 0) is visualized in three-dimensional volume rendering. The highest intensity (red color) is in the vicinity of q ~ (π, π, qz). (g)–(i) Top views of FSs (same as in Fig. 1a–c) with corresponding colormaps of the magnitude of the Fermi velocities (or inverse normal-state density of states) from low (blue) to high (red). The green solid lines denote the nodal planes of the SC  pairing symmetry. (j)–(l) Same as above, but now the green solid lines denote the nodal planes of the SC s±-wave pairing symmetry. Note, only the holelike FS of band 2 has nodes in the gap function on the cross-arms near the zone boundary.
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f1: Fermi surfaces and hot-spots from first-principles electronic band structure calculations.(a)–(c) FS topologies in the momentum space of the Brillouin zone for all three Pu-115 materials, plotted separately in three columns. An intensity colormap is used to depict the values of the JDOS on the FSs at Q = (π, π, π). For better visualization a quadrant of the holelike FS of band 2 was clipped. The JDOS gives a qualitative estimate of the static susceptibility (Eq. (1)) for nesting vector Q. These images help identify the strongest nesting between bands 1 and 2 (in the vicinity of the kz = 0-plane) to bands 3 and 4 (near the kz = π-plane). (d)–(f) The full momentum (q) dependence of the static bare bubble susceptibility χ(q, ω = 0) is visualized in three-dimensional volume rendering. The highest intensity (red color) is in the vicinity of q ~ (π, π, qz). (g)–(i) Top views of FSs (same as in Fig. 1a–c) with corresponding colormaps of the magnitude of the Fermi velocities (or inverse normal-state density of states) from low (blue) to high (red). The green solid lines denote the nodal planes of the SC pairing symmetry. (j)–(l) Same as above, but now the green solid lines denote the nodal planes of the SC s±-wave pairing symmetry. Note, only the holelike FS of band 2 has nodes in the gap function on the cross-arms near the zone boundary.

Mentions: We begin by evaluating the nature of enhanced FS scattering or hot-spots, and the electronic fingerprints of s±-, and -wave pairing symmetries for three known Pu-115 superconductors PuCoIn5 (Tc = 2.5 K)21, PuCoGa5 (Tc = 18.5 K)14, and PuRhGa5 (Tc = 8 K)22. The low-energy electronic states of these compounds consist of four pairs of spin-orbit split energy bands cut by the Fermi level, as shown in Fig. 1a–c823. We note that these results are in agreement with similar electronic structure calculations performed independently by other groups17242526. We estimate the strength of the band-dependent scattering enhancement by computing the bare bubble two-particle response function from first-principles band structure aswhere is the DFT-derived Bloch dispersion with wavevector k and band index n, and is the corresponding fermion occupation number. Figure 1d–f shows the computed static susceptibilities in a colormap plot in the three-dimensional momentum transfer q space. The location of the maximum of is primarily in the vicinity of Q ~ (π, π, π), with additional weights spread all along qz. This suggests that the dominant FS instability occurs between the FSs separated by Q in the Brillouin zone. For this value of Q, we identify the locations of the electronic hot-spots or the highest joint-density of states (JDOS), which satisfy , where and are the Fermi momenta in the initial and final states of bands n and m, respectively. The hot-spots are superimposed on the FSs using an intensity colormap as shown in Figs. 1a–c. The intensity is determined from the approximate , where is the Fermi speed in band m. We immediately see a consistent scenario for all three materials, namely that the hot-spots connect bands 1 or 2 near the plane with kz = 0 to bands 3 or 4 lying in the plane with kz = ±π. The locations of the hot-spots dictate a pairing symmetry, which favors sign reversal for Q. In Fig. 1g–l the same FS topologies are shown in top view with nodal lines for -wave (top row) and s±-wave (bottom row) pairing symmetries superimposed by green solid lines. Based on the correspondence between topology of the FSs and the dominant hot-spot nesting vector, it is now possible to conjecture that the Pu-115 system may favor s±-wave pairing. Wang et al.27 attained very similar results for χnm(q, 0), however, they emphasized the nesting at Q ~ (π, π, 0).


Theory of nodal s ± -wave pairing symmetry in the Pu-based 115 superconductor family.

Das T, Zhu JX, Graf MJ - Sci Rep (2015)

Fermi surfaces and hot-spots from first-principles electronic band structure calculations.(a)–(c) FS topologies in the momentum space of the Brillouin zone for all three Pu-115 materials, plotted separately in three columns. An intensity colormap is used to depict the values of the JDOS on the FSs at Q = (π, π, π). For better visualization a quadrant of the holelike FS of band 2 was clipped. The JDOS gives a qualitative estimate of the static susceptibility (Eq. (1)) for nesting vector Q. These images help identify the strongest nesting between bands 1 and 2 (in the vicinity of the kz = 0-plane) to bands 3 and 4 (near the kz = π-plane). (d)–(f) The full momentum (q) dependence of the static bare bubble susceptibility χ(q, ω = 0) is visualized in three-dimensional volume rendering. The highest intensity (red color) is in the vicinity of q ~ (π, π, qz). (g)–(i) Top views of FSs (same as in Fig. 1a–c) with corresponding colormaps of the magnitude of the Fermi velocities (or inverse normal-state density of states) from low (blue) to high (red). The green solid lines denote the nodal planes of the SC  pairing symmetry. (j)–(l) Same as above, but now the green solid lines denote the nodal planes of the SC s±-wave pairing symmetry. Note, only the holelike FS of band 2 has nodes in the gap function on the cross-arms near the zone boundary.
© Copyright Policy - open-access
Related In: Results  -  Collection

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f1: Fermi surfaces and hot-spots from first-principles electronic band structure calculations.(a)–(c) FS topologies in the momentum space of the Brillouin zone for all three Pu-115 materials, plotted separately in three columns. An intensity colormap is used to depict the values of the JDOS on the FSs at Q = (π, π, π). For better visualization a quadrant of the holelike FS of band 2 was clipped. The JDOS gives a qualitative estimate of the static susceptibility (Eq. (1)) for nesting vector Q. These images help identify the strongest nesting between bands 1 and 2 (in the vicinity of the kz = 0-plane) to bands 3 and 4 (near the kz = π-plane). (d)–(f) The full momentum (q) dependence of the static bare bubble susceptibility χ(q, ω = 0) is visualized in three-dimensional volume rendering. The highest intensity (red color) is in the vicinity of q ~ (π, π, qz). (g)–(i) Top views of FSs (same as in Fig. 1a–c) with corresponding colormaps of the magnitude of the Fermi velocities (or inverse normal-state density of states) from low (blue) to high (red). The green solid lines denote the nodal planes of the SC pairing symmetry. (j)–(l) Same as above, but now the green solid lines denote the nodal planes of the SC s±-wave pairing symmetry. Note, only the holelike FS of band 2 has nodes in the gap function on the cross-arms near the zone boundary.
Mentions: We begin by evaluating the nature of enhanced FS scattering or hot-spots, and the electronic fingerprints of s±-, and -wave pairing symmetries for three known Pu-115 superconductors PuCoIn5 (Tc = 2.5 K)21, PuCoGa5 (Tc = 18.5 K)14, and PuRhGa5 (Tc = 8 K)22. The low-energy electronic states of these compounds consist of four pairs of spin-orbit split energy bands cut by the Fermi level, as shown in Fig. 1a–c823. We note that these results are in agreement with similar electronic structure calculations performed independently by other groups17242526. We estimate the strength of the band-dependent scattering enhancement by computing the bare bubble two-particle response function from first-principles band structure aswhere is the DFT-derived Bloch dispersion with wavevector k and band index n, and is the corresponding fermion occupation number. Figure 1d–f shows the computed static susceptibilities in a colormap plot in the three-dimensional momentum transfer q space. The location of the maximum of is primarily in the vicinity of Q ~ (π, π, π), with additional weights spread all along qz. This suggests that the dominant FS instability occurs between the FSs separated by Q in the Brillouin zone. For this value of Q, we identify the locations of the electronic hot-spots or the highest joint-density of states (JDOS), which satisfy , where and are the Fermi momenta in the initial and final states of bands n and m, respectively. The hot-spots are superimposed on the FSs using an intensity colormap as shown in Figs. 1a–c. The intensity is determined from the approximate , where is the Fermi speed in band m. We immediately see a consistent scenario for all three materials, namely that the hot-spots connect bands 1 or 2 near the plane with kz = 0 to bands 3 or 4 lying in the plane with kz = ±π. The locations of the hot-spots dictate a pairing symmetry, which favors sign reversal for Q. In Fig. 1g–l the same FS topologies are shown in top view with nodal lines for -wave (top row) and s±-wave (bottom row) pairing symmetries superimposed by green solid lines. Based on the correspondence between topology of the FSs and the dominant hot-spot nesting vector, it is now possible to conjecture that the Pu-115 system may favor s±-wave pairing. Wang et al.27 attained very similar results for χnm(q, 0), however, they emphasized the nesting at Q ~ (π, π, 0).

Bottom Line: The spin-fluctuation mechanism of superconductivity usually results in the presence of gapless or nodal quasiparticle states in the excitation spectrum.Our calculation demonstrates that the s(±) wave pairing strength is stronger than the previously thought d-wave pairing; and more importantly, this pairing state allows for the existence of nodal quasiparticles.Finally, we predict the shape of the momentum- and energy-dependent magnetic resonance spectrum for the identification of this pairing symmetry.

View Article: PubMed Central - PubMed

Affiliation: Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.

ABSTRACT
The spin-fluctuation mechanism of superconductivity usually results in the presence of gapless or nodal quasiparticle states in the excitation spectrum. Nodal quasiparticle states are well established in copper-oxide, and heavy-fermion superconductors, but not in iron-based superconductors. Here, we study the pairing symmetry and mechanism of a new class of plutonium-based high-Tc superconductors and predict the presence of a nodal s(±) wave pairing symmetry in this family. Starting from a density-functional theory (DFT) based electronic structure calculation we predict several three-dimensional (3D) Fermi surfaces in this 115 superconductor family. We identify the dominant Fermi surface "hot-spots" in the inter-band scattering channel, which are aligned along the wavevector Q = (π, π, π), where degeneracy could induce sign-reversal of the pairing symmetry. Our calculation demonstrates that the s(±) wave pairing strength is stronger than the previously thought d-wave pairing; and more importantly, this pairing state allows for the existence of nodal quasiparticles. Finally, we predict the shape of the momentum- and energy-dependent magnetic resonance spectrum for the identification of this pairing symmetry.

No MeSH data available.


Related in: MedlinePlus