Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “high magnetic fields”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Structural characterization of neutron irradiated hexagonal boron-10 nitride-15 single crystals

The negatively charged boron vacancy ($V$$^{–}_{⁠B}$⁠) in hexagonal boron nitride (hBN) is a promising quantum defect that can be used to sense pressure, temperature, and magnetic field with high spatial resolution. hBN enriched with the boron-10 and nitrogen-15 isotopes, denoted h 10 B 15 N, has good contrast and coherence for quantum sensing because nitrogen-15 has nuclear spin (1/2), reducing hyperfine interactions. Boron vacancies can be generated by neutron irradiation, which causes the transmutation of the boron-10 isotope to lithium-7. In this study, the ancillary structural, compositional, and mechanical properties of h 10 B 15 N crystals that have been subjected to neutron irradiation fluences from 1.4 × 10 16 to 8.4 × 10 17 n/cm 2 were thoroughly characterized. Besides creating $V$$^{–}_{⁠B}$⁠, the process also induces other defects that generate strain in the crystal lattice. In turn, the mechanical properties of these crystals change drastically. Investigated here are the visual changes, lattice integrity, composition, crystal strain, and elastic constants (C 33 and C 66 ) to assess how these characteristics change as a function of neutron fluence.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Covalent 2D Cr 2 Te 3 ferromagnet

To broaden the scope of van der Waals 2D magnets, we report the synthesis and magnetism of covalent 2D magnetic Cr 2 Te 3 with a thickness down to one-unit-cell. The 2D Cr 2 Te 3 crystals exhibit robust ferromagnetism with a Curie temperature of 180 K, a large perpendicular anisotropy of 7 × 10 5 J m -3 , and a high coercivity of ~4.6 kG at 20 K. First principles calculations further show a transition from canted to collinear ferromagnetism, a transition from perpendicular to in-plane anisotropy, and emergent half-metallic behavior in atomically-thin Cr 2 Te 3 , suggesting its potential application for injecting carriers with high spin polarization into spintronic devices.

2D magnets↗
DOE OSTI2020

Electron–phonon coupling enhancement and displacive magnetostructural transition in SrCr 2 As 2 under magneto-Raman spectroscopy

Here, a Raman spectroscopy study on high quality single crystals of SrCr 2 A s 2 (SCA) in the temperature T range 4 K < T < 300 K and high applied magnetic fields up to H = 9 T is presented. The chromium B 1g phonon analysis reveals two anomalous shifts in the frequency, the first below T = 250 K at H = 0 T in the saturated AFM G -type order likely due to an enhanced electron–phonon coupling by the magnetic order, whereas the second anomaly occurs above H = 4 T at T = 4 K likely as a consequence of a magnetostructural displacive transition. Renormalization of the electronic Raman spectra in both studies reveals a decrease in the electronic density of states with decreasing T and increasing H , respectively, with consequent changes in the Fermi surface, which are intrinsically related to the observed anomalies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Proximity-enhanced valley Zeeman splitting at the WS 2 /graphene interface

The valley Zeeman physics of excitons in monolayer transition metal dichalcogenides provides valuable insight into the spin and orbital degrees of freedom inherent to these materials. Being atomically-thin materials, these degrees of freedom can be influenced by the presence of adjacent layers, due to proximity interactions that arise from wave function overlap across the 2D interface. Here, we report 60 T magnetoreflection spectroscopy of the A- and B- excitons in monolayer WS 2 , systematically encapsulated in monolayer graphene. While the observed variations of the valley Zeeman effect for the A- exciton are qualitatively in accord with expectations from the bandgap reduction and modification of the exciton binding energy due to the graphene-induced dielectric screening, the valley Zeeman effect for the B- exciton behaves markedly different. We investigate prototypical WS 2 /graphene stacks employing first-principles calculations and find that the lower conduction band of WS 2 at the <?CDATA $K/K^{^{\prime}}$?> K / K ′ valleys (the <:tex-math><?CDATA $\mathrm{CB}^-$?> C B − band) is strongly influenced by the graphene layer on the orbital level. Specifically, our detailed microscopic analysis reveals that the conduction band at the Q point of WS 2 mediates the coupling between <?CDATA $\mathrm{CB}^-$?> C B − and graphene due to resonant energy conditions and strong coupling to the Dirac cone. This leads to variations in the valley Zeeman physics of the B- exciton, consistent with the experimental observations. Our results therefore expand the consequences of proximity effects in multilayer semiconductor stacks, showing that wave function hybridization can be a multi-step energetically resonant process, with different bands mediating the interlayer interactions. Such effects can be further exploited to resonantly engineer the spin-valley degrees of freedom in van der Waals and moiré heterostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Squeezing quantum states in three-dimensional twisted crystals

Bloch's theorem provides a conventional starting point for describing wave propagation in periodic media, but in ordered materials where competing spatial periods coexist it is rendered ineffective, often with dramatic consequences. Here we develop an alternate approach that uses coherent free-particle vortex states to study quantum states in supertwisted crystals: three-dimensional stacks of atomically thin two-dimensional layers. Here, this formalism leads naturally to the representation of the spectrum using squeezed coherent states, and it reveals the crucial role of a Coriolis coupling in the equations of motion. This identifies an underlying noncommutative geometry and novel edge state structure in a family of complex ordered structures.

36 MATERIALS SCIENCE↗
DOE OSTI2022

High-Cooperativity Coupling of Rare-Earth Spins to a Planar Superconducting Resonator

The interfacing of a superconducting microwave resonator with rare-earth-doped crystals presents a promising hybrid quantum system for applications including spin-assisted transducers and memories. The coupling strength between the spins of the rare-earth ions and the microwave photons is characterized by the cooperativity. Here, we report an ultrahigh cooperativity of C~650 between rare-earth spins and a planar superconducting microwave resonator that features a highly uniform magnetic field for harnessing the strong anisotropic coupling strength of erbium-doped yttrium orthosilicate. This cooperativity rivals that from a bulk dielectric resonator and may pave a path for efficient coupling of spins with microwave photons on an integrated platform.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Isotropically conducting (hidden) quantum Hall stripe phases in a two-dimensional electron gas

Quantum Hall stripe (QHS) phases, predicted by the Hartree-Fock theory, are manifested in GaAs-based two-dimensional electron gases as giant resistance anisotropies. In this communication, we predict a “hidden” QHS phase which exhibits isotropic resistivity whose value, determined by the density of states of QHS, is independent of the Landau index $N$ and is inversely proportional to the Drude conductivity at zero magnetic field. At high enough $N$, this phase yields to an Ando-Unemura-Coleridge-Zawadski-Sachrajda phase in which the resistivity is proportional to 1/$N$ and to the ratio of quantum and transport lifetimes. Experimental observation of this border should allow one to find the quantum relaxation time.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Local magnetic moments due to loop currents in metals

We present Hartree-Fock calculations on a simple model to obtain the conditions of formation of local magnetic moments due to loop currents $L$ $o$ and spin-loop currents $L$ $s$ and compare them to the conditions of formation of local spin moments $M$ which were given long ago in a similar approximation by Anderson. A model with three degenerate orbitals sitting on an equilateral triangle, with on-site and nearest-neighbor repulsions $U$ and $V$, respectively, and intersite kinetic energy, hybridizing with conduction electrons with a parameter $Δ$ is investigated. $L$ $o$ and $L$ $s$ are promoted by large $V$/$Δ$ and their magnitude is relatively unaffected by $U$/$Δ$. Spin-magnetic moments $M$ promoted by large $U$/$Δ$ on the other hand are adversely affected by $V$/$Δ$. In this model, $L$ $o$ for $V$ multiplied by the number of neighbors is approximately the same as the $M$ promoted by $U$ in Anderson’s local model for $M$. $L$ $o$ and $L$ $s$ are degenerate if exchange interactions and Hund’s rule are neglected but $L$ $o$ is favored when they are included. Many of the qualitative results are visible in an expression for the Hartree-Fock ground state energy derived as a function of small $L$ $o$ , $L$ $s$ , and $M$. Numerical minimization of the Hartree-Fock energy is presented for larger values. Additionally, we also briefly discuss the connection and differences of the interaction-generated orbital currents and spin currents discussed here and generalized to a lattice with the topological states in metals and semiconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Strongly correlated itinerant magnetism near superconductivity in NiTa 4 Se 8

Metallic ferromagnets with strongly interacting electrons often exhibit remarkable electronic phases such as ferromagnetic superconductivity, complex spin textures, and nontrivial topology. Here, in this report, we discuss the synthesis of a layered magnetic metal NiTa 4 Se 8 (or Ni 1/4 TaSe 2 ) with a Curie temperature of 58 Kelvin. Magnetization data and density functional theory calculations indicate that the nickel atoms host uniaxial ferromagnetic order of about 0.7µ B per atom, while an even smaller moment is generated in the itinerant tantalum conduction electrons. Strong correlations are evident in flat bands near the Fermi level, a high heat capacity coefficient, and a high Kadowaki-Woods ratio. Density functional theory calculations suggest that electron and hole Fermi surfaces in the ferromagnetic phase are associated with opposite spin polarization. When the system is diluted of magnetic ions, the samples become superconducting below about 2 Kelvin. We discuss possible mechanisms for superconductivity in this family.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Anomalous temperature-dependent magnetization in the nearly collinear antiferromagnet Y 2 Co 3

Y 2 Co 3 is a newly discovered antiferromagnetic (AFM) compound with distorted kagome layers. Here, previous investigations via bulk magnetization measurements suggested a complex non-collinear magnetic behavior, with magnetic moments primarily anti-aligned along the b axis and some canting towards the ac plane. In this study, we report the magnetic structure of Y 2 Co 3 to be an A-type AFM structure with ferromagnetic (FM) interactions within the distorted kagome plane and an inter-plane antiferromagnetic interaction, as determined by single crystal neutron diffraction. The magnetic moments align along the b axis, with minimal canting towards the c axis, at odds with the previous interpretation of bulk magnetization measurements. The magnetic moments on the two distinct Co sites are (0, -0.68, 0) μB and (0, 1.25, 0.07) μ B . We attribute the previously reported ”non-collinear” behavior to the considerable temperature dependence of itinerant AFM exchange interactions, induced by thermal contraction along the b axis. Additionally, our examination of lattice constants through pressure studies reveals compensating effects on FM and AFM interactions, resulting in negligible pressure dependence of T N .

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Three Jahn-Teller States of Matter in Spin-Crossover System Mn(taa)

Three high-spin phases recently discovered in the spin-crossover system Mn(taa) are identified through analysis by a combination of first-principles calculations and Monte Carlo simulation as a low-temperature Jahn-Teller ordered (solid) phase, an intermediate-temperature dynamically correlated (liquid) phase, and an uncorrelated (gas) phase. In particular, the Jahn-Teller liquid phase arises from competition between mixing with low-spin impurities, which drive the disorder, and intermolecular strain interactions. Additionally, the latter are a key factor in both the spin-crossover phase transition and the magnetoelectric coupling. Jahn-Teller liquids may exist in other spin-crossover materials and materials that have multiple equivalent Jahn-Teller axes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Optical Detection of Long Electron Spin Transport Lengths in a Monolayer Semiconductor

Using a spatially resolved optical pump-probe experiment, we measure the lateral transport of spin-valley polarized electrons over very long distances (tens of micrometers) in a single WSe 2 monolayer. By locally pumping the Fermi sea of 2D electrons to a high degree of spin-valley polarization (up to 75%) using circularly polarized light, the lateral diffusion of the electron polarization can be mapped out via the photoluminescence induced by a spatially separated and linearly polarized probe laser. In this work, up to 25% spin-valley polarization is observed at pump-probe separations up to 20 μm. Characteristic spin-valley diffusion lengths of 18 ± 3 μm are revealed at low temperatures. The dependence on temperature, pump helicity, pump intensity, and electron density highlight the key roles played by spin relaxation time and pumping efficiency on polarized electron transport in monolayer semiconductors possessing spin-valley locking.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Six-Body and Eight-Body Exciton States in Monolayer WSe 2

In the archetypal monolayer semiconductor WSe 2 , the distinct ordering of spin-polarized valleys (low-energy pockets) in the conduction band allows for studies of not only simple neutral excitons and charged excitons (i.e., trions), but also more complex many-body states that are predicted at higher electron densities. We discuss magneto-optical measurements of electron-rich WSe 2 monolayers and interpret the spectral lines that emerge at high electron doping as optical transitions of six-body exciton states (“hexcitons”) and eight-body exciton states (“oxcitons”). Additionally, these many-body states emerge when a photoexcited electron-hole pair interacts simultaneously with multiple Fermi seas, each having distinguishable spin and valley quantum numbers. In addition, we explain the relations between dark trions and satellite optical transitions of hexcitons in the photoluminescence spectrum.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Revealing a 3D Fermi Surface Pocket and Electron-Hole Tunneling in UTe 2 with Quantum Oscillations

Spin triplet superconductor UTe 2 is widely believed to host a quasi-two-dimensional Fermi surface, revealed by first-principles calculations, photoemission and quantum oscillation measurements. An outstanding question still remains as to the existence of a three-dimensional Fermi surface pocket, which is crucial for our understanding of the exotic superconducting and topological properties of UTe 2 . This 3D Fermi surface pocket appears in various theoretical models with different physics origins, but has not been unambiguously detected in experiment. Here, in this study, for the first time we provide concrete evidence for a relatively isotropic, small Fermi surface pocket of UTe 2 via quantum oscillation measurements. In addition, we observed high frequency quantum oscillations corresponding to electron-hole tunneling between adjacent electron and hole pockets. The coexistence of 2D and 3D Fermi surface pockets, as well as the breakdown orbits, provides a test bed for theoretical models and aid the realization of a unified understanding of superconducting state of UTe 2 from the first-principles approach.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Quasi-1D Coulomb Drag in the Nonlinear Regime

One-dimensional Coulomb drag has been an essential tool to probe the physics of interacting Tomonaga-Luttinger liquids. To date, most experimental work has focused on the linear regime while the predictions for Luttinger liquids beyond the linear response theory remain largely untested. In this Letter, we report measurements of reciprocal momentum transfer induced Coulomb drag between vertically coupled quasi-one-dimensional quantum wires in the nonlinear regime. Measurements were performed at ultralow temperatures between wires only 15 nm apart. Our results reveal a nonlinear dependence of the drag voltage as a function of the drive current superimposed with an oscillatory contribution, in agreement with theoretical predictions for Coulomb drag between Tomonaga-Luttinger liquids. Additionally, the observed current-voltage characteristics exhibit a nonmonotonic temperature dependence, further corroborating the presence of non-Fermi-liquid behavior in our system. In conclusion, these findings are observed both in the single and in the multiple subband regimes and in the presence of disorder, extending the onset of this behavior beyond the clean single channel Tomonaga-Luttinger regime where the predictions were originally formulated.

1-dimensional systems↗