Crystal-momentum dispersion of ultrafast spin change in fcc Co.
Nearly twenty years ago, Beaurepaire and coworkers showed that when an ultrafast laser impinges on a ferromagnet, its spin moment undergoes a dramatic change, but how it works remains a mystery. While the current experiment is still unable to resolve the minute details of the spin change, crystal momentum-resolved techniques have long been used to analyze the charge dynamics in superconductors and strongly correlated materials. Here we extend it to probe spin moment change in the entire three-dimensional Brillouin zone for fcc Co. Our results indeed show a strong spin activity along the Δ line, supporting a prior experimental finding. The spin active pockets coalesce into a series of spin surfaces that follow the Fermi surfaces. We predict two largest spin change pockets which have been elusive to experiments: one pocket is slightly below the Δ line and the other is along the Λ line and close to the L point. Our theory presents an opportunity for the time-, spin- and momentum-resolve photoemission technique.
1] Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000, China [2] Department of Physics, Indiana State University, Terre Haute, Indiana 47809, USA.
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Si
Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000, China.
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JY
Li
Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000, China.
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DZ
Yang
Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000, China.
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Xue
Department of Physics, Indiana State University, Terre Haute, Indiana 47809, USA.
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Zhang