[Paper Review] Petahertz Spintronics

Florian Siegrist, Julia Anthea Gessner+13 more|arXiv (Cornell University)|Dec 18, 2018

Quantum optics and atomic interactions33 references66 citations

TL;DR

The paper demonstrates attosecond-scale control of spin dynamics in ferromagnetic layers using near-single-cycle laser pulses, introducing attosecond magnetic circular dichroism (atto-MCD) to reveal optically induced spin and orbital momentum transfer and enabling petahertz clock-rate spintronics.

ABSTRACT

The enigmatic coupling between electronic and magnetic phenomena was one of the riddles propelling the development of modern electromagnetism. Today, the fully controlled electric field evolution of ultrashort laser pulses permits the direct and ultrafast control of electronic properties of matter and is the cornerstone of light-wave electronics. In sharp contrast, because there is no first order interaction between light and spins, the magnetic properties of matter can only be affected indirectly on the much slower tens-of-femtosecond timescale in a sequence of optical excitation followed by the rearrangement of the spin structure. Here we record an orders of magnitude faster magnetic switching with sub-femtosecond response time by initiating optical excitations with near-single-cycle laser pulses in a ferromagnetic layer stack. The unfolding dynamics are tracked in real-time by a novel attosecond time-resolved magnetic circular dichroism (atto-MCD) detection scheme revealing optically induced spin and orbital momentum transfer (OISTR) in synchrony with light field driven charge relocation. In tandem with ab-initio quantum dynamical modelling, we show how this mechanism provides simultaneous control over electronic and magnetic properties that are at the heart of spintronic functionality. This first incarnation of attomagnetism observes light field coherent control of spin-dynamics in the initial non-dissipative temporal regime and paves the way towards coherent spintronic applications with Petahertz clock rates.

Motivation & Objective

• Motivate the pursuit of ultrafast light-wave control of magnetic properties beyond tens of femtoseconds.
• Demonstrate sub-femtosecond magnetic switching in a ferromagnetic stack driven by ultrashort laser fields.
• Develop and apply attosecond time-resolved magnetic circular dichroism (atto-MCD) to track spin and orbital momentum transfer in real time.

Proposed method

• Excite a ferromagnetic layer stack with near-single-cycle laser pulses to initiate optical excitation.
• Track the ensuing dynamics in real time using attosecond time-resolved magnetic circular dichroism (atto-MCD).
• Combine experimental attosecond measurements with ab-initio quantum dynamical modelling to interpret spin and orbital momentum transfer (OISTR).
• Analyze the coupling between light-field driven charge relocation and magnetic response to understand spintronic functionality.

Experimental results

Research questions

• RQ1 Can light-field coherent control of spin-dynamics be achieved in the initial non-dissipative temporal regime?
• RQ2 How does optically induced spin and orbital momentum transfer occur in synchrony with charge relocation under ultrafast excitation?
• RQ3 What are the implications of OISTR for simultaneous control of electronic and magnetic properties relevant to spintronics?

Key findings

• Sub-femtosecond magnetic switching is observed in a ferromagnetic layer stack.
• Attosecond time-resolved MCD detects optically induced spin and orbital momentum transfer (OISTR) synchronous with light-field driven charge relocation.
• Ab-initio quantum dynamical modelling supports a mechanism linking electronic and magnetic property control.
• Demonstrates a first incarnation of attomagnetism with light-field coherent control of spin dynamics in the initial non-dissipative regime.
• Paves the way for coherent spintronic applications operating at petahertz clock rates.