The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Ingrid Mertig - One of the best experts on this subject based on the ideXlab platform.
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absence of strong skew scattering in crystals with multi sheeted Fermi Surfaces
Journal of Physics: Condensed Matter, 2019Co-Authors: Albert Honemann, Christian Herschbach, Dmitry V Fedorov, Martin Gradhand, Ingrid MertigAbstract:We consider an extrinsic contribution to the anomalous and spin Hall effect in dilute alloys based on Fe, Co, Ni, and Pt hosts with different substitutional impurities. It is shown that a strong skew-scattering mechanism is absent in such crystals with multi-sheeted Fermi Surfaces. Based on this finding, we conclude on the mutual exclusion of strong intrinsic and skew-scattering contributions to the considered transport phenomena. It also allows us to draw general conclusions in which materials with a giant anomalous Hall effect caused by the skew scattering can be achieved.
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absence of strong skew scattering in crystals with multi sheeted Fermi Surfaces
arXiv: Mesoscale and Nanoscale Physics, 2018Co-Authors: Albert Honemann, Christian Herschbach, Dmitry V Fedorov, Martin Gradhand, Ingrid MertigAbstract:We consider an extrinsic contribution to the anomalous and spin Hall effect in dilute alloys based on Fe, Co, Ni, and Pt hosts with different substitutional impurities. It is shown that a strong skew-scattering mechanism is absent in such crystals with multi-sheeted Fermi Surfaces. Based on this finding, we conclude on the mutual exclusion of strong intrinsic and skew-scattering contributions to the considered transport phenomena. It also allows us to draw general conditions for materials where the anomalous Hall effect caused by the skew scattering can be achieved giant.
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spin polarization on Fermi Surfaces of metals by the kkr method
Physical Review B, 2009Co-Authors: Dmitry V Fedorov, Martin Gradhand, Ingrid Mertig, Michael Czerner, Peter Zahn, Bogdan Yu Yavorsky, L SzunyoghAbstract:With the implementation of a relativistic Korringa-Kohn-Rostoker Green's function and band-structure method, we analyze the spin-expectation value of the electron states on the Fermi surface of nonmagnetic as well as magnetic metals. It is shown that for relatively light elements such as Cu the spin states are well defined. A separation of all electron states to ``up'' and ``down'' spin-polarized states can be done even in the case of quite heavy but monovalent elements such as Au. In contrast, for heavy polyvalent metals such as Pt, the expectation value of the spin operator can be close to zero in large regions of the Fermi surface. In this case the nonrelativistic language of well-defined ``spin-up'' and ``spin-down'' states is not valid anymore. For magnetic materials, the relativistic Fermi Surfaces change their topology with respect to the nonrelativistic majority and minority sheets because of spin-orbit driven avoided crossings of the bands. As a result, regions with vanishing spin polarization appear.
Carsten Timm - One of the best experts on this subject based on the ideXlab platform.
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distortional weak coupling instability of bogoliubov Fermi Surfaces
Physical Review B, 2021Co-Authors: Carsten Timm, P M R Brydon, D F AgterbergAbstract:Centrosymmetric multiband superconductors which break time-reversal symmetry generically have two-dimensional nodes, i.e., Fermi Surfaces of Bogoliubov quasiparticles. We show that the coupling of the electrons to the lattice always leads to a weak-coupling instability of such a state toward spontaneous breaking of inversion symmetry at low temperatures. This instability is driven by a Cooper logarithm in the internal energy but the order parameter is not superconducting but distortional. We present a comprehensive symmetry analysis and introduce a measure that allows us to compare the strengths of competing distortional instabilities. Moreover, we discuss the instability using an effective single-band model. This framework reveals a duality mapping of the effective model which maps the distortional order parameter onto a superconducting one, providing a natural explanation for the Cooper logarithm and the weak-coupling nature of the instability. Finally, we consider the possibility of a pair-density wave state when inversion symmetry is broken. We find that it can indeed exist but does not affect the instability itself.
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Experimental consequences of Bogoliubov Fermi Surfaces
Physical Review B, 2020Co-Authors: Clara J. Lapp, Georg Börner, Carsten TimmAbstract:Superconductors involving electrons with internal degrees of freedom beyond spin can have internally anisotropic pairing states that are impossible in single-band superconductors. As a case in point, in even-parity multiband superconductors that break time-reversal symmetry, nodes of the superconducting gap are generically inflated into two-dimensional Bogoliubov Fermi Surfaces. The detection and characterization of these quasiparticle Fermi Surfaces requires the understanding of their experimental consequences. In this paper, we derive the low-energy density of states for a broad range of possible nodal structures. Based on this, we calculate the low-temperature form of observables that are commonly employed for the characterization of nodal superconductors, i.e., the single-particle tunneling rate, the electronic specific heat and Sommerfeld coefficient, the thermal conductivity, the magnetic penetration depth, and the NMR spin-lattice relaxation rate, in the clean limit. We also address the question whether the topological invariant of the Bogoliubov Fermi Surfaces is associated with topologically protected surface states, with negative results. This work is meant to serve as a guide for experimental searches for Bogoliubov Fermi Surfaces in time-reversal-symmetry-breaking superconductors.
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bogoliubov Fermi Surfaces stabilized by spin orbit coupling
Physical Review B, 2019Co-Authors: Henri Menke, Carsten Timm, P M R BrydonAbstract:It was recently understood that centrosymmetric multiband superconductors that break time-reversal symmetry generically show Fermi Surfaces of Bogoliubov quasiparticles. We investigate the thermodynamic stability of these Bogoliubov Fermi Surfaces in a paradigmatic model. To that end, we construct the mean-field phase diagram as a function of spin-orbit coupling and temperature. It confirms the prediction that a pairing state with Bogoliubov Fermi Surfaces can be stabilized at moderate spin-orbit coupling strengths. The multiband nature of the model also gives rise to a first-order phase transition, which can be explained by the competition of intra- and interband pairing and is strongly affected by cubic anisotropy. For the state with Bogoliubov Fermi Surfaces, we also discuss experimental signatures in terms of the residual density of states and the induced magnetic order. Our results show that Bogoliubov Fermi Surfaces of experimentally relevant size can be thermodynamically stable.
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bogoliubov Fermi Surfaces general theory magnetic order and topology
Physical Review B, 2018Co-Authors: P M R Brydon, Henri Menke, D F Agterberg, Carsten TimmAbstract:The authors present a general theory for Fermi Surfaces of Bogoliubov quasiparticles in superconductors with broken time-reversal symmetry. These Fermi Surfaces form two-dimensional nodes of the superconducting gap, which are unique to pairing states with a ``nonunitary'' structure. This generates a nonsuperconducting magnetic order intertwined with superconductivity, which is responsible for inflating the expected zero- or one-dimensional nodes into Bogoliubov Fermi Surfaces. Such Fermi Surfaces should be present in a large class of superconductors that break time-reversal symmetry.
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bogoliubov Fermi Surfaces in superconductors with broken time reversal symmetry
Physical Review Letters, 2017Co-Authors: D F Agterberg, Philip Brydon, Carsten TimmAbstract:Predictions indicate that certain nodal superconductors with broken time-reversal symmetry have Fermi Surfaces made up of charge-neutral broken Cooper pairs. This is a departure from earlier theory that accounted for the electronic structure of these superconductors via point or line nodes of the superconducting gap.
P M R Brydon - One of the best experts on this subject based on the ideXlab platform.
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distortional weak coupling instability of bogoliubov Fermi Surfaces
Physical Review B, 2021Co-Authors: Carsten Timm, P M R Brydon, D F AgterbergAbstract:Centrosymmetric multiband superconductors which break time-reversal symmetry generically have two-dimensional nodes, i.e., Fermi Surfaces of Bogoliubov quasiparticles. We show that the coupling of the electrons to the lattice always leads to a weak-coupling instability of such a state toward spontaneous breaking of inversion symmetry at low temperatures. This instability is driven by a Cooper logarithm in the internal energy but the order parameter is not superconducting but distortional. We present a comprehensive symmetry analysis and introduce a measure that allows us to compare the strengths of competing distortional instabilities. Moreover, we discuss the instability using an effective single-band model. This framework reveals a duality mapping of the effective model which maps the distortional order parameter onto a superconducting one, providing a natural explanation for the Cooper logarithm and the weak-coupling nature of the instability. Finally, we consider the possibility of a pair-density wave state when inversion symmetry is broken. We find that it can indeed exist but does not affect the instability itself.
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bogoliubov Fermi Surfaces stabilized by spin orbit coupling
Physical Review B, 2019Co-Authors: Henri Menke, Carsten Timm, P M R BrydonAbstract:It was recently understood that centrosymmetric multiband superconductors that break time-reversal symmetry generically show Fermi Surfaces of Bogoliubov quasiparticles. We investigate the thermodynamic stability of these Bogoliubov Fermi Surfaces in a paradigmatic model. To that end, we construct the mean-field phase diagram as a function of spin-orbit coupling and temperature. It confirms the prediction that a pairing state with Bogoliubov Fermi Surfaces can be stabilized at moderate spin-orbit coupling strengths. The multiband nature of the model also gives rise to a first-order phase transition, which can be explained by the competition of intra- and interband pairing and is strongly affected by cubic anisotropy. For the state with Bogoliubov Fermi Surfaces, we also discuss experimental signatures in terms of the residual density of states and the induced magnetic order. Our results show that Bogoliubov Fermi Surfaces of experimentally relevant size can be thermodynamically stable.
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bogoliubov Fermi Surfaces general theory magnetic order and topology
Physical Review B, 2018Co-Authors: P M R Brydon, Henri Menke, D F Agterberg, Carsten TimmAbstract:The authors present a general theory for Fermi Surfaces of Bogoliubov quasiparticles in superconductors with broken time-reversal symmetry. These Fermi Surfaces form two-dimensional nodes of the superconducting gap, which are unique to pairing states with a ``nonunitary'' structure. This generates a nonsuperconducting magnetic order intertwined with superconductivity, which is responsible for inflating the expected zero- or one-dimensional nodes into Bogoliubov Fermi Surfaces. Such Fermi Surfaces should be present in a large class of superconductors that break time-reversal symmetry.
A Fujimori - One of the best experts on this subject based on the ideXlab platform.
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orbital character and electron correlation effects on two and three dimensional Fermi Surfaces in kfe2as2 revealed by angle resolved photoemission spectroscopy
Frontiers in Physics, 2014Co-Authors: T Yoshida, I Nishi, A Fujimori, Zhixun Shen, K Kihou, S Ideta, Robert C Moore, Z Hussain, C H Lee, A IyoAbstract:We have investigated orbital character and electron correlation effects on Fermi Surfaces in the hole-overdoped iron pnictide superconductor KFe2As2, which shows a low Tc of ~4 K, by angle-resolved photoemission spectroscopy. From the polarization-dependence of the ARPES spectra, we have determined the orbital character of each Fermi surface. Electron mass renormalization of each band is quantitatively consistent with de Haas-van Alphen results. The outer beta and middle zeta Fermi Surfaces show large renormalization factor of m*/mb ~6-7, while the inner Fermi surface has a smaller factor m*/mb ~2. Middle hole Fermi surface zeta has strong three-dimensionality compared to other Fermi Surfaces, indicating the d3z2-r2 orbital character, which may be related to the "octet-line nodes" recently observed by laser ARPES. The observed orbital-dependent mass renormalization would give constraints on the pairing mechanism with line nodes of this system.
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Fermi Surfaces and quasi particle band dispersions of the iron pnictides superconductor kfe2as2 observed by angle resolved photoemission spectroscopy
Journal of Physics and Chemistry of Solids, 2011Co-Authors: T Yoshida, I Nishi, A Fujimori, R G Moore, Zhixun Shen, K Kihou, Parasharam M Shirage, Hijiri Kito, Chulho Lee, A IyoAbstract:Abstract We have performed an angle-resolved photoemission study of the iron pnictide superconductor KFe2As2 with T c ∼ 4 K . Most of the observed Fermi Surfaces show almost two-dimensional shapes, while one of the quasi-particle bands near the Fermi level has a strong dispersion along the kz direction, consistent with the result of a band-structure calculation. However, hole Fermi Surfaces α and ζ are smaller than those predicted by the calculation while other Fermi Surfaces are larger. These observations are consistent with the result of a de Haas–van Alphen study and a theoretical prediction on inter-band scattering, possibly indicating many body effects on the electronic structure.
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4f derived Fermi Surfaces of ceru2 si1 xgex 2 near the quantum critical point resonant soft x ray arpes study
Physical Review Letters, 2009Co-Authors: T Okane, Hiroshi Yamagami, A Fujimori, Takuo Ohkochi, Yukiharu Takeda, S I Fujimori, Akira Yasui, Y SaitohAbstract:Angle-resolved photoelectron spectroscopy in the Ce $3d\ensuremath{\rightarrow}4f$ excitation region was measured for the paramagnetic state of ${\mathrm{CeRu}}_{2}{\mathrm{Si}}_{2}$, ${\mathrm{CeRu}}_{2}({\mathrm{Si}}_{0.82}{\mathrm{Ge}}_{0.18}{)}_{2}$, and ${\mathrm{LaRu}}_{2}{\mathrm{Si}}_{2}$ to investigate the changes of the $4f$ electron Fermi Surfaces around the quantum critical point. While the difference of the Fermi Surfaces between ${\mathrm{CeRu}}_{2}{\mathrm{Si}}_{2}$ and ${\mathrm{LaRu}}_{2}{\mathrm{Si}}_{2}$ was experimentally confirmed, a strong $4f$-electron character was observed in the band structures and the Fermi Surfaces of ${\mathrm{CeRu}}_{2}{\mathrm{Si}}_{2}$ and ${\mathrm{CeRu}}_{2}({\mathrm{Si}}_{0.82}{\mathrm{Ge}}_{0.18}{)}_{2}$, consequently indicating a delocalized nature of the $4f$ electrons in both compounds. The absence of Fermi surface reconstruction across the critical composition suggests that SDW quantum criticality is more appropriate than local quantum criticality in ${\mathrm{CeRu}}_{2}({\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}{)}_{2}$.
Martin Gradhand - One of the best experts on this subject based on the ideXlab platform.
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absence of strong skew scattering in crystals with multi sheeted Fermi Surfaces
Journal of Physics: Condensed Matter, 2019Co-Authors: Albert Honemann, Christian Herschbach, Dmitry V Fedorov, Martin Gradhand, Ingrid MertigAbstract:We consider an extrinsic contribution to the anomalous and spin Hall effect in dilute alloys based on Fe, Co, Ni, and Pt hosts with different substitutional impurities. It is shown that a strong skew-scattering mechanism is absent in such crystals with multi-sheeted Fermi Surfaces. Based on this finding, we conclude on the mutual exclusion of strong intrinsic and skew-scattering contributions to the considered transport phenomena. It also allows us to draw general conclusions in which materials with a giant anomalous Hall effect caused by the skew scattering can be achieved.
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absence of strong skew scattering in crystals with multi sheeted Fermi Surfaces
arXiv: Mesoscale and Nanoscale Physics, 2018Co-Authors: Albert Honemann, Christian Herschbach, Dmitry V Fedorov, Martin Gradhand, Ingrid MertigAbstract:We consider an extrinsic contribution to the anomalous and spin Hall effect in dilute alloys based on Fe, Co, Ni, and Pt hosts with different substitutional impurities. It is shown that a strong skew-scattering mechanism is absent in such crystals with multi-sheeted Fermi Surfaces. Based on this finding, we conclude on the mutual exclusion of strong intrinsic and skew-scattering contributions to the considered transport phenomena. It also allows us to draw general conditions for materials where the anomalous Hall effect caused by the skew scattering can be achieved giant.
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spin polarization on Fermi Surfaces of metals by the kkr method
Physical Review B, 2009Co-Authors: Dmitry V Fedorov, Martin Gradhand, Ingrid Mertig, Michael Czerner, Peter Zahn, Bogdan Yu Yavorsky, L SzunyoghAbstract:With the implementation of a relativistic Korringa-Kohn-Rostoker Green's function and band-structure method, we analyze the spin-expectation value of the electron states on the Fermi surface of nonmagnetic as well as magnetic metals. It is shown that for relatively light elements such as Cu the spin states are well defined. A separation of all electron states to ``up'' and ``down'' spin-polarized states can be done even in the case of quite heavy but monovalent elements such as Au. In contrast, for heavy polyvalent metals such as Pt, the expectation value of the spin operator can be close to zero in large regions of the Fermi surface. In this case the nonrelativistic language of well-defined ``spin-up'' and ``spin-down'' states is not valid anymore. For magnetic materials, the relativistic Fermi Surfaces change their topology with respect to the nonrelativistic majority and minority sheets because of spin-orbit driven avoided crossings of the bands. As a result, regions with vanishing spin polarization appear.