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Results for “KERR EFFECT”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Modified self-Kerr-nonlinearity in a four-level N-type atomic system

The self-Kerr-nonlinearity of a four-level N-type atomic system is studied both experimentally and theoretically. The self-Kerr-nonlinear coefficient n{sub 2} of the probe beam is greatly enhanced near atomic resonance, and can be dramatically modified by changing the switching laser power. With an increasing switching laser power, the slope of the Kerr nonlinear coefficient n{sub 2} around the atomic resonance changes from negative to positive, and the value of n{sub 2} varies from {approx}-4 x 10{sup -6} to 4 x 10{sup -6} cm{sup 2}/W at certain near-resonant probe frequency detunings. Such controllable Kerr nonlinearity can find applications in optoelectronic devices, such as all-optical switching and logic gates.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Bright spatial solitons in defocusing Kerr media with PT-symmetric potentials

We show that defocusing Kerr media with parity-time-symmetric potentials can support one- and two-dimensional bright spatial solitons. These solitons are found to be stable over the wide range where they exist. More importantly, we discover an exact one-dimensional solution and a closed two-dimensional solution in the structure.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Optical vortex interaction and generation via nonlinear wave mixing

Optical vortex beams are made to interact via degenerate two-wave mixing in a Kerr-like nonlinear medium. Vortex mixing is shown to occur inside the medium, leading to exchange of topological charge and cascaded generation of vortex beams. A mean-field model is developed and is shown to account for the selection rules of the topological charges observed after the wave-mixing process. Fractional charges are demonstrated to follow the same rules as for integer charges.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Nearly Quantum-Limited Josephson-Junction Frequency-Comb Synthesizer

While coherently driven Kerr microcavities have rapidly matured as a platform for frequency-comb formation, such microresonators generally possess weak Kerr coefficients; consequently, triggering comb generation requires millions of photons to be circulating inside the cavity. This suppresses the role of quantum fluctuations in the dynamics of the comb. In this paper, we realize a minimal version of coherently driven Kerr-mediated microwave-frequency combs in the circuit quantum electrodynamics (cQED) architecture, where the fluctuations of the quantum vacuum are the primary limitation on comb coherence. We achieve a comb phase coherence of up to 35 μs, approaching the theoretical device quantum limit of 55 μs and vastly longer than the inherent lifetimes of the modes, of 13 ns. The ability within cQED to engineer stronger nonlinearities than optical microresonators, together with operation at cryogenic temperatures, and the excellent agreement of comb dynamics with quantum theory indicates a promising platform for the study of complex dynamics of quantum nonlinear systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Observation of Defect-Assisted Magnetic Vortex Core Reversal at Ultralow Critical Velocity

The stability of structures with nontrivial topology is a subject of great interest, both from fundamental and technological perspectives. The topology of a magnetic vortex, for example, results in high stability of the vortex core polarity, which is attractive for applications. This high stability, however, greatly impedes the required deterministic polarity switching, which is typically only achieved with large magnetic fields or strong dynamic driving. Here, we show that the interaction between the vortex core and manufactured nanoscale defects in the magnetic material lowers the required driving strength for core polarity reversal by more than an order of magnitude. We excite vortex dynamics in thin permalloy disks, and map the twodimensional (2D) vortex core trajectory using 3D time-resolved Kerr microscopy. In pristine samples, we observe normal gyrotropic motion of the vortex core. After laser-induced generation of defects, however, we observe repeated vortex core reversal at much-reduced driving strength. Micromagnetic simulations reveal how local reduction of exchange coupling and saturation magnetization can create vortex core reversal sites for deterministic vortex core switching.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Superconducting Coupler with Exponentially Large On:Off Ratio

Tunable two-qubit couplers offer an avenue to mitigate errors in multiqubit superconducting quantum processors. However, most couplers achieve this by fine tuning circuit parameters and often target specific couplings, such as the spurious ZZ interaction. We introduce a superconducting coupler that alleviates these limitations by suppressing all two-qubit interactions with an exponentially large on:off ratio and without the need for fine tuning. Our approach is based on a bus mode supplemented by an ancillary nonlinear resonator mode. Driving the ancillary mode leads to a coupler-state-dependent field displacement in the resonator that, in turn, results in an exponential suppression of real and virtual two-qubit interactions with respect to the drive power. A superconducting circuit implementation supporting the proposed mechanism is presented.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Independence of the spin current from the Néel vector orientation in antiferromagnet CoO

Spin pumping from ferromagnetic Fe into antiferromagnetic CoO across a Ag spacer layer was studied using ferromagnetic resonance (FMR) in Py/CoO/Ag/Fe/Ag(001). The thin Py film on top of CoO permits an alignment of the CoO Neél vector through field cooling in two otherwise equivalent [110] and [110] crystalline axes which are parallel and perpendicular to the Fe magnetization direction, respectively. Fe FMR linewidth is measured as a function of Ag thickness in 10-20-GHz frequency range and in 180-330 K temperature range. Furthermore, we find that there exists an anisotropy in the Fe FMR damping for parallel and perpendicular alignment of the Fe and CoO spins. However, such anisotropic damping exists only at thin Ag thickness where there exists a magnetic interlayer coupling between Fe and CoO, and vanishes at thick Ag thickness where the interlayer coupling becomes negligible but permitting spin-current transmission into CoO. Our result indicates the absence of anisotropic spin current for parallel and perpendicular alignment of the Fe and CoO spin axes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Antiferromagnetic domain switching modulated by an ultrathin Co interlayer in the Fe/Co/CoO/MgO(001) system

Using a combination of hysteresis loop, Kerr microscope, and x-ray magnetic circular dichroism measurements, in this study we investigated the antiferromagnetic (AFM) domain switching process modulated by the sub-nm thick Co inserting layer in a single crystalline Fe/Co/CoO/MgO(001). The CoO AFM domain switching occurs at lower temperature for the thicker Co interlayer, and the activation energy barrier of CoO AFM domain switching decreases as the Co interlayer thickness increases. The exchange coupling strength between the AFM spins in CoO layer and the ferromagnetic spins in the Fe/Co bilayer is found to be independent of the Co layer thickness. Our results suggest an approach to modulate the dynamic properties of AFM domains with an interfacial modification.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Parameter-free treatment of a layered correlated van der Waals magnet: CrPS 4

The electronic and magnetic structure of CrPS 4 , a two-dimensional (2D) magnetic semiconductor is examined by employing the SCAN meta-GGA density functional. We find the resulting magnetic moment and band gap are in excellent agreement with experiment. From the bulk magnetic configurations, we confirm the experimentally observed A-type antiferromagnetic (A-AFM) ordered ground state with a magnetic moment of 2.78 µ B per chromium atom and band gap of 1.34 eV. To gain insight into the evolution of the ground state with layers, the total energy of each magnetic configuration is calculated for a variety of thicknesses. Monolayer CrPS 4 is predicted to be a ferromagnetic insulator with a band gap of 1.37 eV, and A-AFM for bilayer and trilayer, with band gaps of 1.35 and 1.30 eV, respectively. The electronic structure is reported for the single-, two-, and three-layer and bulk CrPS 4 . Finally, we explore the optical properties of the 2D structure and report the dielectric tensor components and Kerr parameters for the monolayer.

2-dimensional systems↗
DOE OSTI2017

Temporal and spatial valley dynamics in two-dimensional semiconductors probed via Kerr rotation

Monolayer transition metal dichalcogenides (TMDCs) offer a tantalizing platform for control of both spin and valley degrees of freedom, which may enable future optoelectronic devices with enhanced and novel functionalities. In this work, we investigate the valley dynamics of two prototypical members of TMDCs, namely Mo S 2 and WS e 2 , using time-resolved Kerr rotation (TRKR) at temperatures from 10 K to 300 K. This pump-probe technique enables sub-picosecond temporal resolution, providing insight into ultrafast valley dynamics, which is inaccessible by polarized and time-resolved photoluminescence spectroscopy. Bi-exponential decay dynamics were observed for both materials at low temperatures, and the fast decay component indicated a rapid exciton valley depolarization time (< 10 ps) due to strong Coulomb exchange interactions between the K valleys. However, the slow decay components (several tens of picoseconds) were attributed to different origins in the two materials, which were further elucidated by temperature-dependent TRKR measurements. Moreover, the spatial dependence of the TRKR intensity across Mo S 2 monolayer flakes indicated a weaker valley polarization near the edges, which is likely associated with quenched excitons near the grain boundaries or a disordered edge region in chemical vapor deposition–grown monolayers. These temporal and spatial TRKR measurements reveal insight into the complex dynamics of valley excitonic states, which will be critical for valleytronic applications of monolayer TMDCs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Nonuniform carrier density in Cd 3 As 2 evidenced by optical spectroscopy

In this paper, we report the detailed optical properties of Cd 3 As 2 crystals in a wide parameter space: temperature, magnetic field, carrier concentration, and crystal orientation. We investigate high-quality crystals synthesized by three different techniques. In all the studied samples, independently of how they were prepared and how they were treated before the optical experiments, our data indicate conspicuous fluctuations in the carrier density (up to 30%). These charge puddles have a characteristic scale of 100 μm, they become more pronounced at low temperatures, and possibly, they become enhanced by the presence of crystal twinning. The Drude response is characterized by very small scattering rates (~1 meV) for as-grown samples. Mechanical treatment, such as cutting or polishing, influences the optical properties of single crystals, by increasing the Drude scattering rate and also modifying the high-frequency optical response. Finally, magnetoreflectivity and Kerr rotation are consistent with electronlike charge carriers and a spatially nonuniform carrier density.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Induced versus intrinsic magnetic moments in ultrafast magnetization dynamics

Ferromagnetic metal alloys are today commonly used in spintronic and magnetic data storage devices. These multicompound structures consist of several magnetic sublattices exhibiting both intrinsic and induced magnetic moments. Here, we study the response of the element-specific magnetization dynamics for thin film systems based on purely intrinsic (CoFeB) and partially induced (FePt) magnetic moments using extreme ultraviolet pulses from high-harmonic generation (HHG) as an element-sensitive probe. In FePt, on the one hand, we observe an identical normalized transient magnetization for Fe and Pt throughout both the ultrafast demagnetization and the subsequent remagnetization. On the other hand, Co and Fe show a clear difference in the asymptotic limit of the remagnetization process in CoFeB, which is supported by calculations for the temperature-dependent behavior of the equilibrium magnetization using a dynamic spin model. Furthermore, in this work, we provide a vital step toward a comprehensive understanding of ultrafast light-induced magnetization dynamics in ferromagnetic alloys with sublattices of intrinsic and induced magnetic moments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Optically Induced Anisotropy in Time-Resolved Scattering: Imaging Molecular-Scale Structure and Dynamics in Disordered Media with Experiment and Theory

Time-resolved scattering experiments enable imaging of materials at the molecular scale with femtosecond time resolution. However, in disordered media they provide access to just one radial dimension thus limiting the study of orientational structure and dynamics. Here we introduce a rigorous and practical theoretical framework for predicting and interpreting experiments combining optically induced anisotropy and time-resolved scattering. Using impulsive nuclear Raman and ultrafast x-ray scattering experiments of chloroform and simulations, we demonstrate that this framework can accurately predict and elucidate both the spatial and temporal features of these experiments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Exploring possible ferromagnetism of the LaAl O 3 / SrTi O 3 interface

We report on extensive investigations of magnetism at the n -type LaAl O 3 / SrTi O 3 interface performed by utilizing a spectrum of local and integrative analytical techniques: Scanning superconducting quantum interference device microscopy, polar Kerr magnetometry, ferromagnetic resonance, and magnetic torque magnetometry. The samples originated from the same wafers. For nominally fully oxidized samples, we find that the mere presence of the conducting interface does not induce magnetism to values exceeding already present magnetic signals originating from the substrates, irrespective of the measurement technique. With the controlled introduction of oxygen vacancies, however, the different analytical techniques with their inherently different sensitivities and potential interactions with possible magnetic moments in the samples yield different results concerning the existence of magnetism. These unexpected differences obtained with the various measurement techniques are a possible source of the disagreement in the literature about the existence of ferromagnetism at LaAl O 3 / SrTi O 3 interfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Structural and magnetic properties of Pt/Co/Mn-based multilayers

Magnetic multilayers are a rich class of material systems with numerous highly tunable physical parameters that determine both their magnetic and electronic properties. Here, we present a comprehensive experimental study of the system Pt/Co/Mn, which extends the group of Pt / Co / X ( X = metal) multilayers that have been investigated thus far. We demonstrate that an increasing Co layer thickness changes the magnetic anisotropy from out of plane to in plane, whereas the deposition of thicker Mn layers leads to a decrease in the saturation magnetization. Temperature-dependent magnetometry measurements reinforce the hypothesis of antiferromagnetic coupling at the Co/Mn interfaces being responsible for the observed Mn thickness dependence of the magnetization reversal. Moreover, magneto-optical imaging experiments indicate systematic changes in magnetic domain patterns as a function of the Co and Mn layer thickness, suggesting the existence of bubblelike domains—potentially even magnetic skyrmions—in the case of sufficiently thick Mn layers, which are expected to contribute to a sizable Dzyaloshinskii-Moriya interaction in the multilayer stacks. As a result, we identify Pt/Co/Mn as a highly complex multilayer system with strong potential for further fundamental studies and possible applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Antiferromagnetic V 2 ⁢O 3 based exchange coupling

Vanadium sesquioxide (V 2 ⁢O 3 ) is a strongly correlated electronic material that famously undergoes a triple coupled first-order transition where it transitions from a paramagnetic metal with a rhombohedral structure at high temperature to an antiferromagnetic insulator with a monoclinic structure. While several studies have used one of both electronic and structural transitions to control the properties of a heterostructure, evidence of magnetic coupling has notoriously yet to be found. In this paper, we report on a robust magnetic coupling between the antiferromagnetic (AFM) V 2 ⁢O 3 and ferromagnetic (FM) Permalloy (Py) layers that results in a significant exchange bias and strain-induced coercivity enhancement. We provide a temperature and angle-dependent study of magnetic properties, which clearly indicates exchange bias at the AFM/FM interface that appears at the onset of the metal-insulator transition. The magnitude of the exchange bias is strongest when the field is applied along the [001] V 2 ⁢O 3 crystallographic orientation which corresponds to an AFM spin configuration on the [110] surface. Here, this opens the door to designing and implementing novel functionalities in transition metal oxide-based computing using the connection between magnetism and the metal-insulator transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗