The microscopic Einstein-de Haas effect

Area of Science:

• Solid-state physics
• Quantum mechanics
• Materials science

Background:

• The Einstein-de Haas (EdH) effect demonstrates the transfer of electron spin angular momentum to atomic mechanical angular momentum.
• A semiclassical explanation exists, but modern electronic structure methods have not been applied to model this phenomenon.
• Understanding the microscopic origins of the EdH effect is crucial for advancements in spintronics and quantum computing.

Purpose of the Study:

• To investigate the microscopic origins of the Einstein-de Haas effect using modern computational methods.
• To model the EdH effect in an O2 dimer, incorporating spin-orbit coupling and magnetic fields.
• To differentiate the EdH effect from other torque contributions in time-varying magnetic fields.

Main Methods:

• Utilized a noncollinear tight-binding model for an O2 dimer.
• Incorporated spin-orbit coupling, external magnetic field coupling, and vector Stoner exchange.
• Analyzed torque generation by varying an external magnetic field and observing spin evolution.

Main Results:

• Validated the presence of the EdH effect by generating torque on the dimer via a time-varying magnetic field and spin-orbit coupling.
• Identified avoided energy level crossings and the rate of magnetic field change as key factors in spin evolution.
• Discovered additional torque contributions beyond the EdH effect, including field-induced orbital angular momentum changes and Faraday electric fields.

Conclusions:

• The study provides a microscopic understanding of the Einstein-de Haas effect using advanced electronic structure methods.
• The findings highlight the complex interplay of spin-orbit coupling, magnetic fields, and electronic structure in generating torque.
• This research offers new insights into the fundamental physics of spin-orbit interactions and their macroscopic consequences.