Based on the scattering theory, we calculate the Josephson current in a junction between two ferromagnetic super-conductors as a function of the interface potential z. We consider the ferromagnetic superconductor (FS...Based on the scattering theory, we calculate the Josephson current in a junction between two ferromagnetic super-conductors as a function of the interface potential z. We consider the ferromagnetic superconductor (FS) in three different Cooper pairing states: spin singlet s-wave pairing (SWP) state, spin triplet opposite spin pairing (OSP) state, and spin triplet equal spin pairing (ESP) state. We find that the critical Josephson current as a function of z shows clear differences among the SWP, OSP, and ESP states. The obtained results can be used as a useful tool for determining the pair symmetry of the ferromagnetic superconductors.展开更多
The heavy fermion physics arises from the complex interplay of nearly localized 4f/5f electrons and itinerant band- like ones, yielding heavy quasiparticles with an effective mass about 100 times (or more) of the ba...The heavy fermion physics arises from the complex interplay of nearly localized 4f/5f electrons and itinerant band- like ones, yielding heavy quasiparticles with an effective mass about 100 times (or more) of the bare electrons, Recently, experimental and theoretical investigations point out a localized and delocalized dual nature in actinide compounds, where itinerant quasiparticles account for the unconventional superconductivity in the vicinity of a magnetic instability. Here we report the strong coupling between localized 5f moments and itinerant quasiparticles in the ferromagnetic superconductor UGe2. The coupling is nearly antiferromagnetic. As embedded in the ferromagnetic matrix of localized 5f moments below Tc ~ 52 K, this coupling leads to short-range dynamic correlations of heavy quasiparticles, characterized by fluctuations of magnetic clusters. Those cluster-like spins of itinerant quasiparticles show a broad hump of magnetization at Tx≈28 K, which is typical for the spin-glass freezing. Thus, our results present the direct observation of itinerant quasiparticles coexisting with localized 5f moments by conventional magnetic measurements, providing a new route into the coexistence between ferromagnetism and superconductivity in heavy fermion systems.展开更多
Alternating-current losses in a two-layer superconducting cable, each layer being composed of 15 closely-spaced rectangular wires made up of second-generation superconductors when the ends of wires are coated by eithe...Alternating-current losses in a two-layer superconducting cable, each layer being composed of 15 closely-spaced rectangular wires made up of second-generation superconductors when the ends of wires are coated by either a non-magnetic or strong ferromagnetic material having a U profile is numerically investigated. Computations are carried out through the finite-element method. The alternating-current losses do not increase significantly if the relative permeability of the coating is increased three orders of magnitude, provided that the current amplitude is less than half of the critical current in a superconducting wire. However, the losses are much higher for ferromagnetic coating if the amplitude of the applied current oscillating at 50 Hz is close to the critical current. The ferromagnetic coating is seen to accumulate the magnetic field lines normally on its surfaces, while the field lines are parallel to the long axes of the wires, leading to more significant flux penetration in the coated regions. This facilitates a uniform low-loss current flow in the uncoated regions of the wires. In contrast, coating with a non-magnetic material gives rise to a considerably smaller current flow in the uncoated regions, whereas the low-loss flow is maintained in the coated regions. Moreover, the current flows in opposite directions in the coated and uncoated regions, where the direction in each region is converse for the two materials.展开更多
Superconductors and ferromagnets are highly non-compatible materials due to the natures of their respective electronic states.But when artificially brought together,they develop interesting characteristics,one of whic...Superconductors and ferromagnets are highly non-compatible materials due to the natures of their respective electronic states.But when artificially brought together,they develop interesting characteristics,one of which,vortex clustering,is discussed here in this paper.Phase-field and micromagnetic simulations are performed to investigate the superconductor and ferromagnet bilayer,respectively.The ferromagnet with uniaxial anisotropy is observed to develop the maze domain,whereas the superconductor subjected to the influence of the ferromagnetic stray field displays a vortex pattern.Clustered vortices in superconductors at certain locations are observed to be precisely located over magnetic domain bifurcations.The enhanced out-of-plane stray field at bifurcations around the curved domain walls and the convergent Lorentz force due to screening currents in superconductor are attributed to the formation of clusters at bifurcation sites.Segregation of the inter-vortex spacing between straight and bifurcated domain is clearly observed.More importantly,inter-vortex spacing is predicted to serve as a precise tool to map local ferromagnet domain shapes.展开更多
This paper solves a self-consistent equation for the d-wave superconducting gap and the effective exchange field in the mean-field approximation, and studies the Zeeman effects on the d-wave superconducting gap and th...This paper solves a self-consistent equation for the d-wave superconducting gap and the effective exchange field in the mean-field approximation, and studies the Zeeman effects on the d-wave superconducting gap and thermodynamic potential. The Josephson currents in the d-wave superconductor(S)/insulating layer(I)/d-wave S junctions are calculated as a function of the temperature, exchange field, and insulating barrier strength under a Zeeman magnetic field on the two d-wave Ss. It is found that the Josephson critical currents in d-wave S/d-wave S junction to a great extent depend on the relative orientation of the effective exchange field of the two S electrodes, and the crystal orientation of the d-wave S. The exchange field under certain conditions can enhance the Josephson critical current in a d-wave S/I/d-wave S junction.展开更多
We study Andreev tunneling through a ferromagnet/quantum-dot (QD)/superconductor system. By usingnonequilibrum Green function method, the averaged occupation of electrons in QD and the Andreev tunneling currentare stu...We study Andreev tunneling through a ferromagnet/quantum-dot (QD)/superconductor system. By usingnonequilibrum Green function method, the averaged occupation of electrons in QD and the Andreev tunneling currentare studied. Comparing to the norma-metal/quantum-dot/superconductor, the system shows significant changes: (i)The averaged occupations of spin-up and spin-down electrons are not equal. (ii) With the increase of the polarizationof ferromagnetic lead, the Andreev reflection current decreases. (iii) However, even the ferromagnetic lead reaches fullpolarization, the averaged occupation of spin-down electrons is not zero. The physics of these changes is discussed.展开更多
We extend the Blonder, Tinkham and Klapwijk theory to the study of the inverse proximity effects in the normal mental/superconductor/ferromagnet structures. In the superconducting film, there are the gapless supercond...We extend the Blonder, Tinkham and Klapwijk theory to the study of the inverse proximity effects in the normal mental/superconductor/ferromagnet structures. In the superconducting film, there are the gapless superconductivity and the spin-dependent density of states both within and without the energy gap. It indicates an appearance of the inverse-proximity-effect-induced ferromagnetism and a coexistence of ferromagnetism and superconductivity near the interface. The influence of exchange energy in the ferromagnet and barrier strength at the superconductor/ferromagnet interface on the inverse proximity effects is discussed.展开更多
The dc Josephson effect in superconductor / insulator / normal metal / insulator/ferromagnetic superconductor junctions has been studied. We calculate the de Josephson current based on the Bogoliubov de Gennes equatio...The dc Josephson effect in superconductor / insulator / normal metal / insulator/ferromagnetic superconductor junctions has been studied. We calculate the de Josephson current based on the Bogoliubov de Gennes equation. The Josephson current is derived as a function of exchange field in ferromagnetic superconductor, normal metal thickness and insulating barrier strength. It is found that there exists an oscillation relation between the critical Josephson current and the normal metal thickness. The oscillation amplitude decreases as the thickness of the normal metal increases or the exchange field augments.展开更多
基金Project supported by the Iran National Science Foundation(INSF)
文摘Based on the scattering theory, we calculate the Josephson current in a junction between two ferromagnetic super-conductors as a function of the interface potential z. We consider the ferromagnetic superconductor (FS) in three different Cooper pairing states: spin singlet s-wave pairing (SWP) state, spin triplet opposite spin pairing (OSP) state, and spin triplet equal spin pairing (ESP) state. We find that the critical Josephson current as a function of z shows clear differences among the SWP, OSP, and ESP states. The obtained results can be used as a useful tool for determining the pair symmetry of the ferromagnetic superconductors.
基金Project supported by the National Natural Science Foundation of China(Grant No.11404297)the Science Challenge Project(Grant No.TZ2016004)the Science and Technology Foundation of China Academy of Engineering Physics(Grant Nos.2013B0301050 and 2014A0301013)
文摘The heavy fermion physics arises from the complex interplay of nearly localized 4f/5f electrons and itinerant band- like ones, yielding heavy quasiparticles with an effective mass about 100 times (or more) of the bare electrons, Recently, experimental and theoretical investigations point out a localized and delocalized dual nature in actinide compounds, where itinerant quasiparticles account for the unconventional superconductivity in the vicinity of a magnetic instability. Here we report the strong coupling between localized 5f moments and itinerant quasiparticles in the ferromagnetic superconductor UGe2. The coupling is nearly antiferromagnetic. As embedded in the ferromagnetic matrix of localized 5f moments below Tc ~ 52 K, this coupling leads to short-range dynamic correlations of heavy quasiparticles, characterized by fluctuations of magnetic clusters. Those cluster-like spins of itinerant quasiparticles show a broad hump of magnetization at Tx≈28 K, which is typical for the spin-glass freezing. Thus, our results present the direct observation of itinerant quasiparticles coexisting with localized 5f moments by conventional magnetic measurements, providing a new route into the coexistence between ferromagnetism and superconductivity in heavy fermion systems.
基金Project supported by the Fund from the Scientific and Technological Research Council of Turkey(TüB˙ITAK)(Grant No.110T876)
文摘Alternating-current losses in a two-layer superconducting cable, each layer being composed of 15 closely-spaced rectangular wires made up of second-generation superconductors when the ends of wires are coated by either a non-magnetic or strong ferromagnetic material having a U profile is numerically investigated. Computations are carried out through the finite-element method. The alternating-current losses do not increase significantly if the relative permeability of the coating is increased three orders of magnitude, provided that the current amplitude is less than half of the critical current in a superconducting wire. However, the losses are much higher for ferromagnetic coating if the amplitude of the applied current oscillating at 50 Hz is close to the critical current. The ferromagnetic coating is seen to accumulate the magnetic field lines normally on its surfaces, while the field lines are parallel to the long axes of the wires, leading to more significant flux penetration in the coated regions. This facilitates a uniform low-loss current flow in the uncoated regions of the wires. In contrast, coating with a non-magnetic material gives rise to a considerably smaller current flow in the uncoated regions, whereas the low-loss flow is maintained in the coated regions. Moreover, the current flows in opposite directions in the coated and uncoated regions, where the direction in each region is converse for the two materials.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51972028 and 12004036)the National Key Research and Development Program of China(Grant No.2019YFA0307900)。
文摘Superconductors and ferromagnets are highly non-compatible materials due to the natures of their respective electronic states.But when artificially brought together,they develop interesting characteristics,one of which,vortex clustering,is discussed here in this paper.Phase-field and micromagnetic simulations are performed to investigate the superconductor and ferromagnet bilayer,respectively.The ferromagnet with uniaxial anisotropy is observed to develop the maze domain,whereas the superconductor subjected to the influence of the ferromagnetic stray field displays a vortex pattern.Clustered vortices in superconductors at certain locations are observed to be precisely located over magnetic domain bifurcations.The enhanced out-of-plane stray field at bifurcations around the curved domain walls and the convergent Lorentz force due to screening currents in superconductor are attributed to the formation of clusters at bifurcation sites.Segregation of the inter-vortex spacing between straight and bifurcated domain is clearly observed.More importantly,inter-vortex spacing is predicted to serve as a precise tool to map local ferromagnet domain shapes.
基金supported by the Natural Science Foundation of Education Bureau of Jiangsu Province of China (Grant No 05KJB140008)the '333' Project Funds of Jiangsu Province of China
文摘This paper solves a self-consistent equation for the d-wave superconducting gap and the effective exchange field in the mean-field approximation, and studies the Zeeman effects on the d-wave superconducting gap and thermodynamic potential. The Josephson currents in the d-wave superconductor(S)/insulating layer(I)/d-wave S junctions are calculated as a function of the temperature, exchange field, and insulating barrier strength under a Zeeman magnetic field on the two d-wave Ss. It is found that the Josephson critical currents in d-wave S/d-wave S junction to a great extent depend on the relative orientation of the effective exchange field of the two S electrodes, and the crystal orientation of the d-wave S. The exchange field under certain conditions can enhance the Josephson critical current in a d-wave S/I/d-wave S junction.
基金The project supported by National Natural Science Foundation of China under Grant Nos. 10074001 and 90103027 and the State KeyLaboratory for Mesoscopic Physics in Peking University
文摘We study Andreev tunneling through a ferromagnet/quantum-dot (QD)/superconductor system. By usingnonequilibrum Green function method, the averaged occupation of electrons in QD and the Andreev tunneling currentare studied. Comparing to the norma-metal/quantum-dot/superconductor, the system shows significant changes: (i)The averaged occupations of spin-up and spin-down electrons are not equal. (ii) With the increase of the polarizationof ferromagnetic lead, the Andreev reflection current decreases. (iii) However, even the ferromagnetic lead reaches fullpolarization, the averaged occupation of spin-down electrons is not zero. The physics of these changes is discussed.
基金Project supported by the Special Funds of the National Natural Science Foundation of China(Grant Nos.10847132 and 10847133)the Natural Science Foundation of Education Bureau of Jiangsu Province,China(Grant No.07KJD140024)
文摘We extend the Blonder, Tinkham and Klapwijk theory to the study of the inverse proximity effects in the normal mental/superconductor/ferromagnet structures. In the superconducting film, there are the gapless superconductivity and the spin-dependent density of states both within and without the energy gap. It indicates an appearance of the inverse-proximity-effect-induced ferromagnetism and a coexistence of ferromagnetism and superconductivity near the interface. The influence of exchange energy in the ferromagnet and barrier strength at the superconductor/ferromagnet interface on the inverse proximity effects is discussed.
基金Project supported by the Natural Science Foundation of Jiangsu Higher Education Institutions, China (Grant No 06KJB140009).
文摘The dc Josephson effect in superconductor / insulator / normal metal / insulator/ferromagnetic superconductor junctions has been studied. We calculate the de Josephson current based on the Bogoliubov de Gennes equation. The Josephson current is derived as a function of exchange field in ferromagnetic superconductor, normal metal thickness and insulating barrier strength. It is found that there exists an oscillation relation between the critical Josephson current and the normal metal thickness. The oscillation amplitude decreases as the thickness of the normal metal increases or the exchange field augments.