Spin Berry points as crucial for ultrafast demagnetization

Abstract

Laser-induced ultrafast demagnetization has puzzled researchers around the world for over two decades. Intrinsic complexity in electronic, magnetic, and phononic subsystems is difficult to understand microscopically. So far it is not possible to explain demagnetization using a single mechanism, which suggests a crucial piece of information still missing. In this paper, we return to a fundamental aspect of physics: spin and its change within each band in the entire Brillouin zone. We employ fcc Ni as an example and use an extremely dense {\bf k} mesh to map out spin changes for every band close to the Fermi level along all the high symmetry lines. To our surprise, spin angular momentum at some special {\bf k} points abruptly changes from $\pm \hslash /2$ to $\mp \hslash /2$ simply by moving from one crystal momentum point to the next. This explains why intraband transitions, which the spin superdiffusion model is based upon, can induce a sharp spin moment reduction, and why electric current can change spin orientation in spintronics. These special {\bf k} points, which are called spin Berry points, are not random and appear when several bands are close to each other, so the Berry potential of spin majority states is different from that of spin minority states. Although within a single band, spin Berry points jump, when we group several neighboring bands together, they form distinctive smooth spin Berry lines. It is the band structure that disrupts those lines. Spin Berry points are crucial to laser-induced ultrafast demagnetization and spintronics.

arXiv comment19 pages and nine figures, Invited paper to Modern Physics Letters B

References in corpus (10)

• Super-Diffusive Spin-Transport as a Mechanism of Ultrafast Demagnetization
• The Ultrafast Einstein-De Haas Effect
• Quasiparticle dynamics and spin-orbital texture of the SrTiO3 two-dimensional electron gas
• Experimental determination of the Berry phase in a superconducting charge pump
• Many-body theory of ultrafast demagnetization and angular momentum transfer in ferromagnetic transition metals
• Femtosecond x-ray absorption spectroscopy of spin and orbital angular momentum in photoexcited Ni films during ultrafast demagnetization
• Resolving photon-shortage mystery in femtosecond magnetism
• Laser-induced ultrafast transport and demagnetization at the earliest time: First-principles and real-time investigation
• Spin-orbit torque-mediated spin-wave excitation as an alternative paradigm for femtomagnetism
• Spin Berry phase in a helical edge state: Sz nonconservation and transport signatures

Cited by in corpus (1)

• Ultrafast magnetization reversal in ferromagnetic spin-valves: an s-d model perspective