Spins and their Orbits in Semiconductor Quantum Dots
Semiconductor spins are among the leading candidates for scalable quantum computing because they are fast and small, potentially allowing for the integration of billions of qubits, while possibly even taking advantage of already existing semiconductor scaling techology. In this colloquium, I will present our recent experiments studying the fundamental physics of such spins. Lower temperatures and control of the direction of the applied magnetic field have made it possible to observe the hyperfine spin relaxation mechanism and to obtain spin relaxation times as long as 57s -- a new record for a spin in a nanostructure.
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Spin waves and damping in noncollinear spin systems
Spin waves or magnons represent elementary excitations of magnetically ordered materials. In the field of magnonics, spin waves are expected to be used as information carriers, taking advantage of their short wavelengths compared to electromagnetic waves possessing similar frequencies. The formation of noncollinear spin configurations such as domain walls, vortices or magnetic skyrmions is a natural way of influencing the properties of magnons in a system. Spin waves are often described within the terms of the classical Landau-Lifshitz-Gilbert equation. Here we discuss how the noncollinear spin arrangement forces the spin waves to be cylindrically instead of circularly polarized, leading to an enhancement of the effective damping parameter compared to the Gilbert damping . The results are illustrated through the example of isolated k\pi skyrmions , which represent cylindrically symmetric two-dimensional localized spin configurations where the out-of-plane component of the magnetization rotates by k\pi between the center of the structure and the collinear background. At higher temperatures, magnon-magnon interactions lead to a modification of spin wave frequencies, which can be taken into account in a micromagnetic model by introducing effective temperature-dependent interaction parameters. Through the example of a ferromagnetic system, we calculate the temperature dependence of the effective Dzyaloshinsky-Moriya interaction , which also plays a crucial role in the stabilization of noncollinear magnetic structures.
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Detection of Antiferromagnetic Domains by Optical Magnetoelectric Effect
One of the main motivation behind the current interest in magnetoelectric materials is that they can be building blocks of low-energy consumption nonvolatile memory devices. In this talk, I will demonstrate that simple optical absorption spectroscopy can be used to identify magnetoelectric (ME) antiferromagnetic (AFM) domains of LiCoPO4. In case of the THz spin-wave excitations this unusual contrast arising from the optical magnetoelectric effect as confirmed by our microscopic model, which also captures the characteristics of the observed static ME effect. Since these domains and the absorption difference are also present in zero magnetic field it may promote the development of ME memory devices based on AFM insulators.