Advancing orbitronics by pushing electron orbital angular momentum to terahertz speed

Introduction

The spin angular momentum (S) of the electron has significantly extended conventional electronics, which relies on the electron charge (C), by new, so-called spintronic functionalities. Examples include magnetization switching, the transport of S and its detection, even down to femtosecond time scales.

Orbital Angular Momentum

To boost the efficiency of spintronics, the so far neglected yet equally fascinating and important orbital angular momentum (L) of electrons is considered to be a powerful pathway. Orbitronic phenomena such as L-based transport, torques, and magneto-optic effects have much larger magnitudes than their S counterparts and may, thus, efficiently complement or even replace spintronic functionalities.

Microscopically, L is completely different from S. Its dynamics involves new physics that needs to be understood, in particular on ultrafast time scales.

Project Goals

In the ORBITERA project, my team and I will obtain unprecedented insights into L dynamics by using femtosecond optical pulses and terahertz (THz) electric fields, which couple directly to the motion of conduction electrons at their natural frequencies and relaxation rates.

Key Challenges

We will tackle important challenges of general orbitronics, including:

1. Separating L- and S-based effects despite their identical macroscopic symmetry properties.
2. Building ultrafast generators and detectors of exclusively L currents.
3. Revealing the nature of L transport (e.g., ballistic, diffusive, tunneling).
4. Measuring the magnetic moments forming an L current.
5. Probing the interaction of L with the crystal lattice.
6. Temporally resolving L-S and L-C interconversion.
7. Applying THz L torque to ultimately switch magnetic order ultrafast.

Methodology and Applications

By establishing THz orbitronics, new methodologies (such as ultrafast drivers of L currents and L-conductance spectroscopy at 0.1-50 THz) and applications (such as the detection of THz electric fields without relying on the weak spin-orbit coupling) will be developed that can be used by a community beyond specialized THz labs.