Spin transference and magnetoresistance amplification in a transistor

A current problem in semiconductor spin-based electronics is the difficulty of experimentally expressing the effect of spin-polarized current in electrical circuit measurements. We present a theoretical solution with the principle of transference of the spin diffusion effects in the semiconductor channel of a system with three magnetic terminals. A notable result of technological consequences is the room temperature amplification of the magneto-resistive effect, integrable with electronics circuits, demonstrated by computation of current dependence on magnetization configuration in such a system with currently achievable parameters.Comment: 4 pages, 3 figures, revised version, changed title, new figure

Low-frequency spin qubit energy splitting noise in highly purified 28Si/SiGe

We identify the dominant source for low-frequency spin qubit splitting noise in a highly isotopically-purified silicon device with an embedded nanomagnet and a spin echo decay time Techo2 = 128 µs. The power spectral density (PSD) of the charge noise explains both, the clear transition from a 1/f2- to a 1/f-dependence of the splitting noise PSD as well as the experimental observation of a decreasing time-ensemble spin dephasing time, from T∗2≈ 20 µs, with increasing measurement time over several hours. Despite their strong hyperfine contact interaction, the few 73Ge nuclei overlapping with the quantum dot in the barrier do not limit T∗2, likely because their dynamics is frozen on a few hours measurement scale. We conclude that charge noise and the design of the gradient magnetic field are the key to further improve the qubit fidelity in isotopically purified 28Si/SiGe

Ultrafast demagnetization in the sp-d model: A theoretical study

We propose and analyze a theoretical model of ultrafast light-induced magnetization dynamics in systems of localized spins that are coupled to carriers' spins by sp-d exchange interaction. A prominent example of a class of materials falling into this category are ferromagnetic (III, Mn)V semiconductors, in which ultrafast demagnetization has been recently observed. In the proposed model, light excitation heats up the population of carriers, taking it out of equilibrium with the localized spins. This triggers the process of energy and angular momentum exchange between the two spin systems, which lasts for the duration of the energy relaxation of the carriers. We derive the master equation for the density matrix of a localized spin interacting with the hot carriers and couple it with a phenomenological treatment of the carrier dynamics. We develop a general theory within the sp-d model and we apply it to the ferromagnetic semiconductors, taking into account the valence band structure of these materials. We show that the fast spin relaxation of the carriers can sustain the flow of polarization between the localized and itinerant spins leading to significant demagnetization of the localized spin system, observed in (III, Mn)V materials

Ultrafast demagnetization in the sp-d model: A theoretical study

We propose and analyze a theoretical model of ultrafast light-induced magnetization dynamics in systems of localized spins that are coupled to carriers' spins by sp-d exchange interaction. A prominent example of a class of materials falling into this category are ferromagnetic (III, Mn)V semiconductors, in which ultrafast demagnetization has been recently observed. In the proposed model, light excitation heats up the population of carriers, taking it out of equilibrium with the localized spins. This triggers the process of energy and angular momentum exchange between the two spin systems, which lasts for the duration of the energy relaxation of the carriers. We derive the master equation for the density matrix of a localized spin interacting with the hot carriers and couple it with a phenomenological treatment of the carrier dynamics. We develop a general theory within the sp-d model and we apply it to the ferromagnetic semiconductors, taking into account the valence band structure of these materials. We show that the fast spin relaxation of the carriers can sustain the flow of polarization between the localized and itinerant spins leading to significant demagnetization of the localized spin system, observed in (III, Mn)V materials

Appearance of objectivity for NV centers interacting with dynamically polarized nuclear environment

Quantum-to-classical transition still eludes a full understanding. Out of its multiple aspects, one has recently gained an increased attention - the appearance of objective world out of the quantum. One particular idea is that objectivity appears thanks to specific quantum state structures formation during the evolution, known as spectrum broadcast structures (SBS). Despite that quite some research was already performed on this strong and fundamental form of objectivity, the practical realization of SBS in a concrete physical medium has not been explicitly analyzed so far. In this work, we study the possibility to simulate objectivization process via SBS formation using widely studied nitrogen-vacancy centers in diamonds. Assuming achievable limits of dynamical polarization technique, we show that for high, but experimentally viable polarizations (p > 0.5) of nuclear spins and for magnetic fields lower than ≈20 G the state of the NV center and its nearest polarized environment approaches an SBS state reasonably well. QID/Taminiau LabQuTec

Amtliche Mineraloeldaten fuer die Bundesrepublik Deutschland. November 1989

SIGLEAvailable from Bundesamt fuer Gewerbliche Wirtschaft, Eschborn (DE) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman