Investigation of spin stiffness in spin-depolarized states of two-dimensional electron systems with time-resolved Kerr rotation

Abstract

An experimental technique based on time-resolved Kerr rotation allows a comparison of the spin stiffnesses of different spin-polarized and depolarized states in a two-dimensional electron system. With this technique, a new spin-correlated phase that has no known analogues was discovered. the new spin-depolarized phase is characterized by high spin stiffness equal to that of a spin-polarized quantum Hall ferromagnet.Recently, much attention has been devoted to technological applications based on the manipulation of spin degree of freedom, which has particularly boosted the development of magnonics, the use of spin waves (magnons) for signal transfer 1-3 . More exotic applications entail the involvement of skyrmions, which are spin vortex textures that are topological charge carriers, in spin dynamics. Experimental work on the manipulation of skyrmions and measurement of their mass and characteristic drift length in crossed magnetic and electric fields has been reported 4 .Most of the aforementioned experimental achievements in manipulation of spins and their textures have been for three-dimensional magnetic systems. In contrast, for a two-dimensional electron system (2DES) in a magnetic field, which has given rise to spin-texture physics, the experimental progress is not so impressive. This is largely due to the absence of reliable experimental techniques revealing the local properties of 2DES spin subsystems, such as Lorentz transmission electron microscopy 5 . Setting aside the transport techniques that are not very sensitive to spin ordering, the key method for the characterization of a spin subsystem involves the measurement of the 2DES magnetization as a function of temperature and filling factor and comparison of the experimental data with those obtained from existing theories 6,7 . A quantum Hall ferromagnet (QHF) with a filling factor of ν = 1 is chosen as a reference point of a fully spin-polarized state with maximum achievable spin stiffness. However, for a spin depolarized 2DES, little experimental opportunities for revealing the physical reason for this depolarization exist.A breakthrough in description of spin-depolarized states was achieved when experimentalists focused on the investigation of the spin relaxation processes in a 2DES determined by the local properties of the spin subsystem. The pioneering works on nuclear spin relaxation via a contact interaction with the spins of an electron system led to the concept of skyrmions and skyrmion crystal 8,9,10 . Although the theory of skyrmion crystals was developed for two-dimensional electron systems, the actual formation of a skyrmion crystal lattice was found in three-dimensional MnSi ferromagnetic films and similar compounds with Dzyaloshinskii-Moriya interaction 5,11,12 . Thus far, there has been no compelling evidence on the existence of a skyrmion crystal in a 2DES formed by either lack or excess of electron density in a quantum Hall ferromagnet. Moreover, observations of spin excitation spectra using the inelastic light scattering technique ena...

Damping via the hyperfine interaction of a spin-rotation mode in a two-dimensional strongly magnetized electron plasma

“…( 33) the values of the parameters whose estimates are given above, we find T 2 ≃ 10 ns, which is in agreement with the experimental data. 2,3 V. DISCUSSION…”

“…This influence can be considered in terms of an addition to the effective electron Zeeman energy. Recent experimental data 3 show that under some conditions this mechanism of hyperfine coupling with correlated nuclei is the main one, or at least can compete with that considered before. 4 The reason for the appearance of the spatial correlation of nuclear spins in the quantum well is related to the features of the experimental technique.…”

“…Kerr rotation monitoring is a convenient tool and so far probably the only way to investigate spin stiffness of such quantum Hall (QH) magnetics at different filling factors and temperatures. 3 The discussion presented in the recent work 4 shows that, in general, a macroscopic approach can be applied to a QH ferromagnet (similar to the study of the Kerr rotation effect in common dielectric ferromagnets), however, in this case the Landau-Lifshitz equation hardly is applicable. This is due to the existence of an elementary stochastization process in the magnetized 2DES which saves both Zeemann and exchange energies but results in decreasing total spin S, component S z remaining unchanged.…”

Особенности Когерентной Спиновой Динамики Двумерного Электронного Газа В Режиме Холловского Ферромагнетика

“…1). Подробное описание установки можно найти в работе [2]. С помощью циркулярно-поляризованного импульса накачки в исследуемом образце создавалась спиновая ориентация двумерных электронов вблизи основного состояния электронной системы (нижний спиновый подуровень Ландау), которая регистрировалась по углу поворота плоскости поляризации отраженного от образца линейно поляризованного пучка зондирования с помощью специального балансного фотодетектора.…”

“…При низкой температуре добавляется вклад пространственных флуктуаций эффективного магнитного поля, действующего на электроны, от неравновесной поляризации ядерных спинов. Эти флуктуации не только существенно укорачивают время затухания сигнала керровского вращения, но и приводят к появлению дополнительных пиков в фурье-образе сигнала керровского вращения, соответствующих дополнительному эффективному магнитному полю на уровне 0.1 Тл (подробнее это обсуждается в работе [2]). Таким образом, пространственные флуктуации g-фактора и эффективного магнитного поля, действующего на электроны со стороны ядерных спинов через контактное взаимодействие, усиливаются при понижении температуры, что приводит к более быстрому затуханию спиновой прецессии 2ДЭС.…”