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Brian M Andersen - One of the best experts on this subject based on the ideXlab platform.
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pairing symmetry of the one band hubbard model in the paramagnetic weak coupling limit a numerical rpa study
Physical Review B, 2015Co-Authors: A T Romer, Andreas Kreisel, Ilya Eremin, M A Malakhov, Thomas Maier, P J Hirschfeld, Brian M AndersenAbstract:We study the Spin-Fluctuation-mediated superconducting pairing gap in a weak-coupling approach to the Hubbard model for a two-dimensional square lattice in the paramagnetic state. Performing a comprehensive theoretical study of the phase diagram as a function of filling, we find that the superconducting gap exhibits transitions from $p$-wave at very low electron fillings to ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wave symmetry close to half filling in agreement with previous reports. At intermediate filling levels, different gap symmetries appear as a consequence of the changes in the Fermi surface topology and the associated structure of the Spin susceptibility. In particular, the vicinity of a Van Hove singularity in the electronic structure close to the Fermi level has important consequences for the gap structure in favoring the otherwise subdominant triplet solution over the singlet $d$-wave solution. By solving the full gap equation, we find that the energetically favorable triplet solutions are chiral and break time-reversal symmetry. Finally, we also calculate the detailed angular gap structure of the quasiparticle spectrum, and show how Spin-Fluctuation-mediated pairing leads to significant deviations from the first harmonics both in the singlet ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ gap as well as the chiral triplet gap solution.
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pairing symmetry of the one band hubbard model in the paramagnetic weak coupling limit a numerical rpa study
Physical Review B, 2015Co-Authors: A T Romer, Andreas Kreisel, Ilya Eremin, M A Malakhov, Thomas Maier, P J Hirschfeld, Brian M AndersenAbstract:We study the Spin-Fluctuation-mediated superconducting pairing gap in a weak-coupling approach to the Hubbard model for a two dimensional square lattice in the paramagnetic state. Performing a comprehensive theoretical study of the phase diagram as a function of filling, we find that the superconducting gap exhibits transitions from p-wave at very low electron fillings to d_{x^2-y^2}-wave symmetry close to half filling in agreement with previous reports. At intermediate filling levels, different gap symmetries appear as a consequence of the changes in the Fermi surface topology and the associated structure of the Spin susceptibility. In particular, the vicinity of a van Hove singularity in the electronic structure close to the Fermi level has important consequences for the gap structure in favoring the otherwise sub-dominant triplet solution over the singlet d-wave solution. By solving the full gap equation, we find that the energetically favorable triplet solutions are chiral and break time reversal symmetry. Finally, we also calculate the detailed angular gap structure of the quasi-particle spectrum, and show how Spin-Fluctuation-mediated pairing leads to significant deviations from the first harmonics both in the singlet d_{x^2-y^2} gap as well as the chiral triplet gap solution.
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doping asymmetry of superconductivity coexisting with antiferromagnetism in Spin Fluctuation theory
New Journal of Physics, 2015Co-Authors: A T Romer, Ilya Eremin, Brian M Andersen, W Rowe, P J HirschfeldAbstract:We generalize the theory of Cooper-pairing by Spin excitations in the metallic antiferromagnetic state to include situations with electron and/or hole pockets. We show that Cooper-pairing arises from transverse Spin waves and from gapped longitudinal Spin Fluctuations of comparable strength. However, each of these interactions, projected on a particular symmetry of the superconducting gap, acts primarily within one type of pocket. We find a nodeless -wave state is supported primarily by the longitudinal Fluctuations on the electron pockets, and both transverse and longitudinal Fluctuations support nodal -wave symmetry on the hole pockets. Our results may be relevant to the asymmetry of the AF/SC coexistence state in the cuprate phase diagram.
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doping asymmetry of superconductivity coexisting with antiferromagnetism in Spin Fluctuation theory
arXiv: Superconductivity, 2013Co-Authors: A T Romer, Ilya Eremin, Brian M Andersen, W Rowe, P J HirschfeldAbstract:We generalize the theory of Cooper pairing by Spin excitations in the metallic antiferromagnetic state to include situations with electron and/or hole pockets. We show that Cooper pairing arises from transverse Spin waves and from gapped longitudinal Spin Fluctuations of comparable strength. However, each of these interactions, projected on a particular symmetry of the superconducting gap, acts primarily within one type of pocket. We find a nodeless $d_{x^2-y^2}$-wave state is supported primarily by the longitudinal Fluctuations on the electron pockets, and both transverse and longitudinal Fluctuations support nodeless odd-parity Spin singlet $p-$wave symmetry on the hole pockets. Our results may be relevant to the asymmetry of the AF/SC coexistence state in the cuprate phase diagram, as well as for the "nodal gap" observed recently for strongly underdoped cuprates.
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local modulations of the Spin Fluctuation mediated pairing interaction by impurities in d wave superconductors
Physical Review B, 2012Co-Authors: A T Roemer, P J Hirschfeld, S Graser, Tamara S Nunner, Brian M AndersenAbstract:We present a self-consistent real space formulation of Spin-Fluctuation mediated $d$-wave pairing. By calculating all relevant inhomogeneous Spin and charge susceptibilities in real space within the random phase approximation (RPA), we obtain the effective pairing interaction and study its spatial dependence near both local potential and hopping impurities. A remarkably large enhancement of the pairing interaction may be obtained near the impurity site. We discuss the relevance of our result to inhomogeneities observed by scanning tunneling spectroscopy on the surface of cuprate superconductors.
P J Hirschfeld - One of the best experts on this subject based on the ideXlab platform.
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pairing symmetry of the one band hubbard model in the paramagnetic weak coupling limit a numerical rpa study
Physical Review B, 2015Co-Authors: A T Romer, Andreas Kreisel, Ilya Eremin, M A Malakhov, Thomas Maier, P J Hirschfeld, Brian M AndersenAbstract:We study the Spin-Fluctuation-mediated superconducting pairing gap in a weak-coupling approach to the Hubbard model for a two dimensional square lattice in the paramagnetic state. Performing a comprehensive theoretical study of the phase diagram as a function of filling, we find that the superconducting gap exhibits transitions from p-wave at very low electron fillings to d_{x^2-y^2}-wave symmetry close to half filling in agreement with previous reports. At intermediate filling levels, different gap symmetries appear as a consequence of the changes in the Fermi surface topology and the associated structure of the Spin susceptibility. In particular, the vicinity of a van Hove singularity in the electronic structure close to the Fermi level has important consequences for the gap structure in favoring the otherwise sub-dominant triplet solution over the singlet d-wave solution. By solving the full gap equation, we find that the energetically favorable triplet solutions are chiral and break time reversal symmetry. Finally, we also calculate the detailed angular gap structure of the quasi-particle spectrum, and show how Spin-Fluctuation-mediated pairing leads to significant deviations from the first harmonics both in the singlet d_{x^2-y^2} gap as well as the chiral triplet gap solution.
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pairing symmetry of the one band hubbard model in the paramagnetic weak coupling limit a numerical rpa study
Physical Review B, 2015Co-Authors: A T Romer, Andreas Kreisel, Ilya Eremin, M A Malakhov, Thomas Maier, P J Hirschfeld, Brian M AndersenAbstract:We study the Spin-Fluctuation-mediated superconducting pairing gap in a weak-coupling approach to the Hubbard model for a two-dimensional square lattice in the paramagnetic state. Performing a comprehensive theoretical study of the phase diagram as a function of filling, we find that the superconducting gap exhibits transitions from $p$-wave at very low electron fillings to ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wave symmetry close to half filling in agreement with previous reports. At intermediate filling levels, different gap symmetries appear as a consequence of the changes in the Fermi surface topology and the associated structure of the Spin susceptibility. In particular, the vicinity of a Van Hove singularity in the electronic structure close to the Fermi level has important consequences for the gap structure in favoring the otherwise subdominant triplet solution over the singlet $d$-wave solution. By solving the full gap equation, we find that the energetically favorable triplet solutions are chiral and break time-reversal symmetry. Finally, we also calculate the detailed angular gap structure of the quasiparticle spectrum, and show how Spin-Fluctuation-mediated pairing leads to significant deviations from the first harmonics both in the singlet ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ gap as well as the chiral triplet gap solution.
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doping asymmetry of superconductivity coexisting with antiferromagnetism in Spin Fluctuation theory
New Journal of Physics, 2015Co-Authors: A T Romer, Ilya Eremin, Brian M Andersen, W Rowe, P J HirschfeldAbstract:We generalize the theory of Cooper-pairing by Spin excitations in the metallic antiferromagnetic state to include situations with electron and/or hole pockets. We show that Cooper-pairing arises from transverse Spin waves and from gapped longitudinal Spin Fluctuations of comparable strength. However, each of these interactions, projected on a particular symmetry of the superconducting gap, acts primarily within one type of pocket. We find a nodeless -wave state is supported primarily by the longitudinal Fluctuations on the electron pockets, and both transverse and longitudinal Fluctuations support nodal -wave symmetry on the hole pockets. Our results may be relevant to the asymmetry of the AF/SC coexistence state in the cuprate phase diagram.
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doping asymmetry of superconductivity coexisting with antiferromagnetism in Spin Fluctuation theory
arXiv: Superconductivity, 2013Co-Authors: A T Romer, Ilya Eremin, Brian M Andersen, W Rowe, P J HirschfeldAbstract:We generalize the theory of Cooper pairing by Spin excitations in the metallic antiferromagnetic state to include situations with electron and/or hole pockets. We show that Cooper pairing arises from transverse Spin waves and from gapped longitudinal Spin Fluctuations of comparable strength. However, each of these interactions, projected on a particular symmetry of the superconducting gap, acts primarily within one type of pocket. We find a nodeless $d_{x^2-y^2}$-wave state is supported primarily by the longitudinal Fluctuations on the electron pockets, and both transverse and longitudinal Fluctuations support nodeless odd-parity Spin singlet $p-$wave symmetry on the hole pockets. Our results may be relevant to the asymmetry of the AF/SC coexistence state in the cuprate phase diagram, as well as for the "nodal gap" observed recently for strongly underdoped cuprates.
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superconducting gap in lifeas from three dimensional Spin Fluctuation pairing calculations
Physical Review B, 2013Co-Authors: Yan Wang, Andreas Kreisel, Thomas Maier, P J Hirschfeld, S V Borisenko, V B Zabolotnyy, B Buchner, D J ScalapinoAbstract:The lack of nesting of the electron and hole Fermi-surface sheets in the Fe-based superconductor LiFeAs, with a critical temperature of 18 K, has led to questions as to whether the origin of superconductivity in this material might be different from other Fe-based superconductors. Both angle-resolved photoemission and quasiparticle interference experiments have reported fully gapped superconducting order parameters with significant anisotropy. The system is also of interest because relatively strong correlations seem to be responsible for significant renormalization of the hole bands. Here we present calculations of the superconducting gap and pairing in the random-phase approximation using Fermi surfaces derived from measured photoemission spectra. The qualitative features of the gaps obtained in these calculations are shown to be different from previous two-dimensional theoretical works and in good agreement with experiment on the main Fermi-surface pockets. We analyze the contributions to the pairing vertex thus obtained and show that the scattering processes between electron and hole pockets that are believed to dominate the pairing in other Fe-based superconductors continue to do so in LiFeAs despite the lack of nesting, leading to gaps with anisotropic ${s}_{\ifmmode\pm\else\textpm\fi{}}$ structure. Some interesting differences relating to the enhanced ${d}_{xy}$ orbital content of the LiFeAs Fermi surface are noted.
I I Mazin - One of the best experts on this subject based on the ideXlab platform.
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ferromagnetic Spin Fluctuation induced superconductivity in sr 2 ruo 4
Physical Review Letters, 1997Co-Authors: I I Mazin, David J SinghAbstract:We propose a quantitative model for triplet superconductivity in ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ based on first principles calculations for the electronic structure and magnetic susceptibility. The superconductivity is due to ferromagnetic Spin Fluctuations that are strong at small wave vectors. The calculated effective mass renormalization, renormalized susceptibility, and superconducting critical temperature are all in good agreement with experiment. The order parameter is of comparable magnitude on all three sheets of the Fermi surface.
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s wave superconductivity from an antiferromagnetic Spin Fluctuation model for bilayer materials
Physical Review Letters, 1995Co-Authors: A I Liechtenstein, I I Mazin, O K AndersenAbstract:It is usually believed that the Spin-Fluctuation mechanism for high-temperature superconductivity results in $d$-wave pairing, and that it is destructive for the conventional phonon-mediated pairing. We show that in bilayer materials, due to nearly perfect antiferromagnetic Spin correlations between the planes, the stronger instability is with respect to a superconducting state whose order parameters in the even and odd plane bands have opposite signs, while having both two-dimensional $s$ symmetry. The interaction of electrons with Raman- (infrared-) active phonons enhances (suppresses) the instability.
A T Romer - One of the best experts on this subject based on the ideXlab platform.
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pairing symmetry of the one band hubbard model in the paramagnetic weak coupling limit a numerical rpa study
Physical Review B, 2015Co-Authors: A T Romer, Andreas Kreisel, Ilya Eremin, M A Malakhov, Thomas Maier, P J Hirschfeld, Brian M AndersenAbstract:We study the Spin-Fluctuation-mediated superconducting pairing gap in a weak-coupling approach to the Hubbard model for a two-dimensional square lattice in the paramagnetic state. Performing a comprehensive theoretical study of the phase diagram as a function of filling, we find that the superconducting gap exhibits transitions from $p$-wave at very low electron fillings to ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wave symmetry close to half filling in agreement with previous reports. At intermediate filling levels, different gap symmetries appear as a consequence of the changes in the Fermi surface topology and the associated structure of the Spin susceptibility. In particular, the vicinity of a Van Hove singularity in the electronic structure close to the Fermi level has important consequences for the gap structure in favoring the otherwise subdominant triplet solution over the singlet $d$-wave solution. By solving the full gap equation, we find that the energetically favorable triplet solutions are chiral and break time-reversal symmetry. Finally, we also calculate the detailed angular gap structure of the quasiparticle spectrum, and show how Spin-Fluctuation-mediated pairing leads to significant deviations from the first harmonics both in the singlet ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ gap as well as the chiral triplet gap solution.
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pairing symmetry of the one band hubbard model in the paramagnetic weak coupling limit a numerical rpa study
Physical Review B, 2015Co-Authors: A T Romer, Andreas Kreisel, Ilya Eremin, M A Malakhov, Thomas Maier, P J Hirschfeld, Brian M AndersenAbstract:We study the Spin-Fluctuation-mediated superconducting pairing gap in a weak-coupling approach to the Hubbard model for a two dimensional square lattice in the paramagnetic state. Performing a comprehensive theoretical study of the phase diagram as a function of filling, we find that the superconducting gap exhibits transitions from p-wave at very low electron fillings to d_{x^2-y^2}-wave symmetry close to half filling in agreement with previous reports. At intermediate filling levels, different gap symmetries appear as a consequence of the changes in the Fermi surface topology and the associated structure of the Spin susceptibility. In particular, the vicinity of a van Hove singularity in the electronic structure close to the Fermi level has important consequences for the gap structure in favoring the otherwise sub-dominant triplet solution over the singlet d-wave solution. By solving the full gap equation, we find that the energetically favorable triplet solutions are chiral and break time reversal symmetry. Finally, we also calculate the detailed angular gap structure of the quasi-particle spectrum, and show how Spin-Fluctuation-mediated pairing leads to significant deviations from the first harmonics both in the singlet d_{x^2-y^2} gap as well as the chiral triplet gap solution.
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doping asymmetry of superconductivity coexisting with antiferromagnetism in Spin Fluctuation theory
New Journal of Physics, 2015Co-Authors: A T Romer, Ilya Eremin, Brian M Andersen, W Rowe, P J HirschfeldAbstract:We generalize the theory of Cooper-pairing by Spin excitations in the metallic antiferromagnetic state to include situations with electron and/or hole pockets. We show that Cooper-pairing arises from transverse Spin waves and from gapped longitudinal Spin Fluctuations of comparable strength. However, each of these interactions, projected on a particular symmetry of the superconducting gap, acts primarily within one type of pocket. We find a nodeless -wave state is supported primarily by the longitudinal Fluctuations on the electron pockets, and both transverse and longitudinal Fluctuations support nodal -wave symmetry on the hole pockets. Our results may be relevant to the asymmetry of the AF/SC coexistence state in the cuprate phase diagram.
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doping asymmetry of superconductivity coexisting with antiferromagnetism in Spin Fluctuation theory
arXiv: Superconductivity, 2013Co-Authors: A T Romer, Ilya Eremin, Brian M Andersen, W Rowe, P J HirschfeldAbstract:We generalize the theory of Cooper pairing by Spin excitations in the metallic antiferromagnetic state to include situations with electron and/or hole pockets. We show that Cooper pairing arises from transverse Spin waves and from gapped longitudinal Spin Fluctuations of comparable strength. However, each of these interactions, projected on a particular symmetry of the superconducting gap, acts primarily within one type of pocket. We find a nodeless $d_{x^2-y^2}$-wave state is supported primarily by the longitudinal Fluctuations on the electron pockets, and both transverse and longitudinal Fluctuations support nodeless odd-parity Spin singlet $p-$wave symmetry on the hole pockets. Our results may be relevant to the asymmetry of the AF/SC coexistence state in the cuprate phase diagram, as well as for the "nodal gap" observed recently for strongly underdoped cuprates.
Thomas Maier - One of the best experts on this subject based on the ideXlab platform.
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pairing symmetry of the one band hubbard model in the paramagnetic weak coupling limit a numerical rpa study
Physical Review B, 2015Co-Authors: A T Romer, Andreas Kreisel, Ilya Eremin, M A Malakhov, Thomas Maier, P J Hirschfeld, Brian M AndersenAbstract:We study the Spin-Fluctuation-mediated superconducting pairing gap in a weak-coupling approach to the Hubbard model for a two-dimensional square lattice in the paramagnetic state. Performing a comprehensive theoretical study of the phase diagram as a function of filling, we find that the superconducting gap exhibits transitions from $p$-wave at very low electron fillings to ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wave symmetry close to half filling in agreement with previous reports. At intermediate filling levels, different gap symmetries appear as a consequence of the changes in the Fermi surface topology and the associated structure of the Spin susceptibility. In particular, the vicinity of a Van Hove singularity in the electronic structure close to the Fermi level has important consequences for the gap structure in favoring the otherwise subdominant triplet solution over the singlet $d$-wave solution. By solving the full gap equation, we find that the energetically favorable triplet solutions are chiral and break time-reversal symmetry. Finally, we also calculate the detailed angular gap structure of the quasiparticle spectrum, and show how Spin-Fluctuation-mediated pairing leads to significant deviations from the first harmonics both in the singlet ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ gap as well as the chiral triplet gap solution.
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pairing symmetry of the one band hubbard model in the paramagnetic weak coupling limit a numerical rpa study
Physical Review B, 2015Co-Authors: A T Romer, Andreas Kreisel, Ilya Eremin, M A Malakhov, Thomas Maier, P J Hirschfeld, Brian M AndersenAbstract:We study the Spin-Fluctuation-mediated superconducting pairing gap in a weak-coupling approach to the Hubbard model for a two dimensional square lattice in the paramagnetic state. Performing a comprehensive theoretical study of the phase diagram as a function of filling, we find that the superconducting gap exhibits transitions from p-wave at very low electron fillings to d_{x^2-y^2}-wave symmetry close to half filling in agreement with previous reports. At intermediate filling levels, different gap symmetries appear as a consequence of the changes in the Fermi surface topology and the associated structure of the Spin susceptibility. In particular, the vicinity of a van Hove singularity in the electronic structure close to the Fermi level has important consequences for the gap structure in favoring the otherwise sub-dominant triplet solution over the singlet d-wave solution. By solving the full gap equation, we find that the energetically favorable triplet solutions are chiral and break time reversal symmetry. Finally, we also calculate the detailed angular gap structure of the quasi-particle spectrum, and show how Spin-Fluctuation-mediated pairing leads to significant deviations from the first harmonics both in the singlet d_{x^2-y^2} gap as well as the chiral triplet gap solution.
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superconducting gap in lifeas from three dimensional Spin Fluctuation pairing calculations
Physical Review B, 2013Co-Authors: Yan Wang, Andreas Kreisel, Thomas Maier, P J Hirschfeld, S V Borisenko, V B Zabolotnyy, B Buchner, D J ScalapinoAbstract:The lack of nesting of the electron and hole Fermi-surface sheets in the Fe-based superconductor LiFeAs, with a critical temperature of 18 K, has led to questions as to whether the origin of superconductivity in this material might be different from other Fe-based superconductors. Both angle-resolved photoemission and quasiparticle interference experiments have reported fully gapped superconducting order parameters with significant anisotropy. The system is also of interest because relatively strong correlations seem to be responsible for significant renormalization of the hole bands. Here we present calculations of the superconducting gap and pairing in the random-phase approximation using Fermi surfaces derived from measured photoemission spectra. The qualitative features of the gaps obtained in these calculations are shown to be different from previous two-dimensional theoretical works and in good agreement with experiment on the main Fermi-surface pockets. We analyze the contributions to the pairing vertex thus obtained and show that the scattering processes between electron and hole pockets that are believed to dominate the pairing in other Fe-based superconductors continue to do so in LiFeAs despite the lack of nesting, leading to gaps with anisotropic ${s}_{\ifmmode\pm\else\textpm\fi{}}$ structure. Some interesting differences relating to the enhanced ${d}_{xy}$ orbital content of the LiFeAs Fermi surface are noted.
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origin of gap anisotropy in Spin Fluctuation models of the iron pnictides
Physical Review B, 2009Co-Authors: Thomas Maier, S Graser, D J Scalapino, P J HirschfeldAbstract:We discuss the large gap anisotropy found for the ${A}_{1g}$ ($s$ wave) state in random-phase approximation Spin Fluctuation and functional renormalization-group calculations and show how the simple arguments leading to isotropic sign-switched $s$-wave states in these systems need to be supplemented by a consideration of pair scattering within Fermi-surface sheets and between the individual electron sheets as well. In addition, accounting for the orbital makeup of the states on the Fermi surface is found to be crucial.