Search results for "500 Naturwissenschaften und Mathematik::530 Physik::530 Physik"
showing 8 items of 8 documents
The 2020 magnetism roadmap
2020
Following the success and relevance of the 2014 and 2017 Magnetism Roadmap articles, this 2020 Magnetism Roadmap edition takes yet another timely look at newly relevant and highly active areas in magnetism research. The overall layout of this article is unchanged, given that it has proved the most appropriate way to convey the most relevant aspects of today's magnetism research in a wide variety of sub-fields to a broad readership. A different group of experts has again been selected for this article, representing both the breadth of new research areas, and the desire to incorporate different voices and viewpoints. The latter is especially relevant for thistype of article, in which one's fi…
Transition of laser-induced terahertz spin currents from torque- to conduction-electron-mediated transport
2022
Spin transport is crucial for future spintronic devices operating at bandwidths up to the terahertz range. In F|N thin-film stacks made of a ferromagnetic/ferrimagnetic layer F and a normal-metal layer N, spin transport is mediated by (1) spin-polarized conduction electrons and/or (2) torque between electron spins. To identify a crossover from (1) to (2), we study laser-driven spin currents in F|Pt stacks where F consists of model materials with different degrees of electrical conductivity. For the magnetic insulators yttrium iron garnet, gadolinium iron garnet (GIG) and γ−Fe2O3, identical dynamics is observed. It arises from the terahertz interfacial spin Seebeck effect (SSE), is fully det…
Broadband Terahertz Probes of Anisotropic Magnetoresistance Disentangle Extrinsic and Intrinsic Contributions
2021
Anisotropic magnetoresistance (AMR) is a ubiquitous and versatile probe of magnetic order in contemporary spintronics research. Its origins are usually ascribed to extrinsic effects (i.e. spin-dependent electron scattering), whereas intrinsic (i.e. scattering-independent) contributions are neglected. Here, we measure AMR of polycrystalline thin films of the standard ferromagnets Co, Ni, Ni81Fe19 and Ni50Fe50 over the frequency range from DC to 28 THz. The large bandwidth covers the regimes of both diffusive and ballistic intraband electron transport and, thus, allows us to separate extrinsic and intrinsic AMR components. Analysis of the THz response based on Boltzmann transport theory revea…
Antenna-coupled spintronic terahertz emitters driven by a 1550 nm femtosecond laser oscillator
2019
We demonstrate antenna-coupled spintronic terahertz (THz) emitters excited by 1550 nm, 90 fs laser pulses. Antennas are employed to optimize THz outcoupling and frequency coverage of ferromagnetic/nonmagnetic metallic spintronic structures. We directly compare the antenna-coupled devices to those without antennas. Using a 200 μm H-dipole antenna and an ErAs:InGaAs photoconductive receiver, we obtain a 2.42-fold larger THz peak-peak signal, a bandwidth of 4.5 THz, and an increase in the peak dynamic range (DNR) from 53 dB to 65 dB. A 25 μm slotline antenna offered 5 dB larger peak DNR and a bandwidth of 5 THz. For all measurements, we use a comparatively low laser power of 45 mW from a comme…
Time-energy filtering of single electrons in ballistic waveguides
2019
Characterizing distinct electron wave packets is a basic task for solid-state electron quantum optics with applications in quantum metrology and sensing. A important circuit element for this task is a non-stationary potential barrier than enables backscattering of chiral particles depending on their energy and time of arrival. Here we solve the quantum mechanical problem of single-particle scattering by a ballistic constriction in an fully depleted quantum Hall system under spatially uniform but time-dependent electrostatic potential modulation. The result describes electrons distributed in time-energy space according to a modified Wigner quasiprobability distribution and scattered with an …
The classical two-dimensional Heisenberg model revisited: An $SU(2)$-symmetric tensor network study
2021
The classical Heisenberg model in two spatial dimensions constitutes one of the most paradigmatic spin models, taking an important role in statistical and condensed matter physics to understand magnetism. Still, despite its paradigmatic character and the widely accepted ban of a (continuous) spontaneous symmetry breaking, controversies remain whether the model exhibits a phase transition at finite temperature. Importantly, the model can be interpreted as a lattice discretization of the $O(3)$ non-linear sigma model in $1+1$ dimensions, one of the simplest quantum field theories encompassing crucial features of celebrated higher-dimensional ones (like quantum chromodynamics in $3+1$ dimensio…
Protein dynamics observed by tunable mid-IR quantum cascade lasers across the time range from 10 ns to 1 s
2017
We have developed a spectrometer based on tunable quantum cascade lasers (QCLs) for recording time-resolved absorption spectra of proteins in the mid-infrared range. We illustrate its performance by recording time-resolved difference spectra of bacteriorhodopsin in the carboxylic range (1800–1700 cm− 1) and on the CO rebinding reaction of myoglobin (1960–1840 cm− 1), at a spectral resolution of 1 cm− 1. The spectrometric setup covers the time range from 4 ns to nearly a second with a response time of 10–15 ns. Absorption changes as low as 1 × 10− 4 are detected in single-shot experiments at t > 1 μs, and of 5 × 10− 6 in kinetics obtained after averaging 100 shots. While previous time-res…
Fundamental bounds on qubit reset
2020
Qubit reset is a basic prerequisite for operating quantum devices, requiring the export of entropy. The fastest and most accurate way to reset a qubit is obtained by coupling the qubit to an ancilla on demand. Here, we derive fundamental bounds on qubit reset in terms of maximum fidelity and minimum time, assuming control over the qubit and no control over the ancilla. Using the Cartan decomposition of the Lie algebra of qubit plus two-level ancilla, we identify the types of interaction and controls for which the qubit can be purified. For these configurations, we show that a time-optimal protocol consists of purity exchange between qubit and ancilla brought into resonance, where the maximu…