We use electronic transport and atom-probe tomography to study $\mathrm{Zn}\mathrm{O}:\mathrm{Al}/{\mathrm{Si}\mathrm{O}}_2/\mathrm{Si}$ Schottky diodes on lightly doped $n$- and $p$-type Si. We vary the carrier concentration in the $\mathrm{ZnO}:\mathrm{Al}$ films by 2 orders of magnitude, but the Schottky barrier height remains nearly constant. Atom-probe tomography shows that Al segregates to the interface, so that the $\mathrm{ZnO}:\mathrm{Al}$ at the junction is likely to be metallic even when the bulk of the $\mathrm{ZnO}:\mathrm{Al}$ film is semiconducting. We hypothesize that the observed Fermi-level pinning is connected to the insulator-metal transition in doped ZnO. This implies that tuning the band alignment at oxide/Si interfaces may be achieved by controlling the transition between localized and extended states in the oxide, thereby changing the orbital hybridization across the interface.

One important attribute of graphene that makes it attractive for high-performance electronics is its inherently large thermal conductivity ($\kappa$) for the purposes of thermal management. Using a combined density-functional theory and classical molecular-dynamics approach, we predict that the $\kappa$ of graphene supported on hexagonal boron nitride ($h$-BN) can be as large as 90% of the $\kappa$ of suspended graphene, in contrast to the significant suppression of $\kappa$ (more than 70% reduction) on amorphous silica. Interestingly, we find that this enhanced thermal transport is largely attributed to increased lifetimes of the in-plane acoustic phonon modes, which is a notable contrast from the dominant contribution of out-of-plane acoustic modes in suspended graphene. This behavior is possible due to the charge polarization throughout graphene that induces strong interlayer adhesion between graphene and $h$-BN. These findings highlight the potential benefit of layered dielectric substrates such as $h$-BN for graphene-based thermal management, in addition to their electronic advantages. Furthermore, our study brings attention to the importance of understanding the interlayer interactions of graphene with layered dielectric materials which may offer an alternative technological platform for substrates in electronics.

A powerful technique is introduced for simulating mechanical and electromechanical properties of one-dimensional nanostructures under arbitrary combinations of bending, twisting, and stretching. The technique is based on an unconventional control of periodic symmetry which eliminates artifacts due to deformation constraints and quantum finite-size effects and allows transparent electronic-structure analysis. Via density-functional tight-binding implementation, the technique demonstrates its utility by predicting nonlinear electromechanical properties in carbon nanotubes and abrupt behavior in the structural yielding of ${\mathrm{Au}}_7$ and ${\mathrm{Mo}}_6{\mathrm{S}}_6$ nanowires. The technique drives simulations markedly closer to the realistic modeling of these slender nanostructures under experimental conditions.

In this paper, we study the Schottky transport in a narrow-gap semiconductor and few-layer graphene in which the energy dispersions are highly nonparabolic. We propose that the contrasting current-temperature scaling relation of $J\propto T^2$ in the conventional Schottky interface and $J\propto T^3$ in graphene-based Schottky interface can be reconciled under Kane’s $\mathbf{k}·\mathbf{p}$ nonparabolic band model for narrow-gap semiconductors. Our model suggests a more general form of $J\propto (T^2+\gamma k_B{T}^3)$, where the nonparabolicty parameter $\gamma$ provides a smooth transition from $T^2$ to $T^3$ scaling. For few-layer graphene, we find that $N$-layer graphene with $ABC$ stacking follows $J\propto T^{2/N+1}$, while $ABA$ stacking follows a universal form of $J\propto T^3$ regardless of the number of layers. Intriguingly, the Richardson constant extracted from the Arrhenius plot using an incorrect scaling relation disagrees with the actual value by 2 orders of magnitude, suggesting that correct models must be used in order to extract important properties for many Schottky devices.

Autocatalytic fibril nucleation has recently been proposed to be a determining factor for the spread of neurodegenerative diseases, but the same process could also be exploited to amplify minute quantities of protein aggregates in a diagnostic context. Recent advances in microfluidic technology allow the analysis of protein aggregation in micron-scale samples, potentially enabling such diagnostic approaches, but the theoretical foundations for the analysis and interpretation of such data are, so far, lacking. Here, we study computationally the onset of protein aggregation in small volumes and show that the process is ruled by intrinsic fluctuations whose volume-dependent distribution we also estimate theoretically. Based on these results, we develop a strategy to quantify in silico the statistical errors associated with the detection of aggregate-containing samples. Our work explores a different perspective on the forecasting of protein aggregation in asymptomatic subjects.

We fabricate magnetic tunnel junctions with fully epitaxial $\mathrm{Fe}(001)/{\mathrm{GaO}}_x(001)/\mathrm{Fe}(001)$ structure, where the ${\mathrm{GaO}}_x$ is a wide band-gap semiconductor with a cubic spinel-type crystal structure. Tunneling magnetoresistance ratios up to 92% (125%) are observed at room temperature (20 K), which evidently indicates the existence of a spin-polarized coherent tunneling. The observed MR ratio is the highest among the reported magnetic tunnel junctions with a semiconducting tunnel barrier and ferromagnetic metal electrodes. Such a single-crystalline semiconductor tunnel barrier that shows a high MR ratio is an essential building block for a vertical-type spin field-effect transistor.

The behavior of a nanoparticle in solution depends strongly on the particle’s physical and chemical characteristics, most notably the particle size and the surface properties. Accurately characterizing these properties is critical for quality control in a wide variety of industries. To understand a complex and polydisperse nanoparticle suspension, however, ensemble averaging is not sufficient, and there is a great need for direct measurements of size and surface properties at the individual nanoparticle level. In this work, we present an analysis technique for simultaneous characterization of particle-surface interactions and size using near-field light scattering and verify it using Brownian-dynamics simulations. Using a nanophotonic waveguide, single particles can be stably held near the waveguide’s surface by strongly localized optical forces. By tracking the dynamic 3D motion of the particle under the influence of these forces using an optical microscope, it is possible to extract the particle-surface interaction forces, as well as to estimate the size and refractive index of the nanoparticle. Because of the strong light-scattering signal, this method is viable for high-throughput characterization of particles as small as 100 nm in only a few seconds each.

We report a comprehensive study of the emission from Gd and Tb laser-produced plasmas in the 6.5–6.7-nm wavelength region for a broad range of laser-irradiation parameters using a single $\lambda =1030\mathrm{nm}$ laser with tunable pulse duration in the 120-ps-to-4-ns range. The results are of interest for beyond-extreme-ultraviolet (BEUV) lithography of integrated circuits. BEUV emission spectra are measured as a function of laser-pulse duration, emission angle, and spatial location within the plasma. Images of the BEUV-emitting plasma region at the BEUV wavelength are obtained as a function of irradiation parameters. The emission spectrum is observed to broaden and to shift to a longer wavelength as the duration of the driver laser pulses is shortened from nanoseconds to hundreds of picoseconds. Transient self-consistent hydrodynamic and atomic physics simulations show that the picosecond irradiation creates significantly hotter plasmas in which the dominant emission originates from more highly ionized species. Gd-plasma emission driven by nanosecond laser pulses spectrally best matches the responsivity of the energy monitors used, centered near $\lambda =6.74\mathrm{nm}$. Spatially resolved spectra of the Gd plasma are acquired for different laser-pulse durations. The conversion efficiency (CE) of $\mathrm{Gd}/\mathrm{Tb}$ plasma into a 0.6% bandwidth in a $2\pi$ solid angle is determined by integrating angularly resolved measurements obtained using an array of calibrated energy monitors. Similar maximum CEs of about 0.47% for both the Gd and Tb plasmas are obtained. The source size is measured to approximately match the spot size of the laser on target, in agreement with simulations.

We present two pulse schemes to actively deplete measurement photons from a readout resonator in the nonlinear dispersive regime of circuit QED. One method uses digital feedback conditioned on the measurement outcome, while the other is unconditional. In the absence of analytic forms and symmetries to exploit in this nonlinear regime, the depletion pulses are numerically optimized using the Powell method. We speed up photon depletion by more than six inverse resonator linewidths, saving approximately 1650 ns compared to depletion by waiting. We quantify the benefit by emulating an ancilla qubit performing repeated quantum-parity checks in a repetition code. Fast depletion increases the mean number of cycles to a spurious error detection event from order 1 to 75 at a $1\text{−}\mu \mathrm{s}$ cycle time.

We study the spin Hall magnetoresistance (SMR) in Pt grown in situ on ${\mathrm{CoFe}}_2{\mathrm{O}}_4$ (CFO) ferrimagnetic insulating films. A careful analysis of the angle-dependent and field-dependent longitudinal magnetoresistance indicates that the SMR contains a contribution that does not follow the bulk magnetization of CFO, but it is a fingerprint of the complex magnetism at the surface of the CFO layer, thus signaling SMR as a tool for mapping surface magnetization. A systematic study of the SMR for different temperatures and CFO thicknesses gives us information impossible to obtain with any standard magnetometry technique. On one hand, the surface magnetization behaves independently of the CFO thickness and does not saturate up to high fields, evidencing that the surface has its own anisotropy. On the other hand, characteristic zero-field magnetization steps are not present at the surface while they are relevant in the bulk, strongly suggesting that antiphase boundaries are responsible for such intriguing features. In addition, a contribution from the ordinary magnetoresistance of Pt is identified, which is distinguishable only due to the low resistivity of the in situ grown Pt.

We develop a concept of the traveling-wave Josephson parametric amplifier exploiting quadratic nonlinearity of a serial array of one-junction superconducting quantum interference devices (SQUIDs) embedded in a superconducting transmission line. The external magnetic flux applied to the SQUIDs makes it possible to efficiently control the shape of their current-phase relation and, hence, the balance between quadratic and cubic (Kerr-like) nonlinearities. This property allows us to operate in the favorable three-wave-mixing mode with a minimal phase mismatch, an exponential dependence of the power gain on number of sections $N$, a large bandwidth, a high dynamic range, and substantially separated signal (${\omega }_s$) and pump (${\omega }_p$) frequencies obeying the relation ${\omega }_s+{\omega }_i={\omega }_p$, where ${\omega }_i$ is the idler frequency. An estimation of the amplifier characteristics with typical experimental parameters, a pump frequency of 12 GHz, and $N=300$ yields a flat gain of 20 dB in the bandwidth of 5.6 GHz.

The recent maturation of hybrid quantum devices has led to significant enhancements in the functionality of a wide variety of quantum systems. In particular, harnessing mechanical resonators for manipulation and control has expanded the use of two-level systems in quantum-information science and quantum sensing. Here, we report on a monolithic hybrid quantum device in which strain fields associated with resonant vibrations of a diamond cantilever dynamically control the optical transitions of a single nitrogen-vacancy (NV) defect center in diamond. We quantitatively characterize the strain coupling to the orbital states of the NV center and, with mechanical driving, we observe NV-strain couplings exceeding 10 GHz. Furthermore, we use this strain-mediated coupling to match the frequency and polarization dependence of the zero-phonon lines of two spatially separated and initially distinguishable NV centers. The experiments demonstrated here mark an important step toward engineering a quantum device capable of realizing and probing the dynamics of nonclassical states of mechanical resonators, spin systems, and photons.

Mixed-valence manganites ${\mathrm{La}}_{1-x}{A}_x{\mathrm{MnO}}_3$ ($A=\mathrm{Sr}$, Ca) with $x\approx 0.5$ can be driven from a ferromagnetic-metallic to an antiferromagnetic-insulating state by a small modification ($\mathrm{\Delta }x$) of the carrier density ($\mathrm{\Delta }x/x<1$). For this reason, these oxides have received renewed attention due to their potentially advantageous integration in ferroelectric tunnel junctions of adjustable tunnel barrier width. Interestingly, in thin films, epitaxial strain can modify the electronic and magnetic ground state strongly affecting their magnetotransport properties. Here we exploit the extreme sensitivity of linearly and circularly polarized x-ray absorption to orbital anisotropy and magnetic ordering to explore the role of structural distortions and electronic bandwidth on the orbital occupancy and spin ordering of $\mathrm{Mn}\hspace{0.17em}3d$ states in ${\mathrm{La}}_{0.5}{A}_{0.5}{\mathrm{MnO}}_3$ films under various strain states. ${}^{55}\mathrm{Mn}$ NMR experiments are used to get information about the electronic and magnetic phase separation and orbital ordering occurring in these films. These results combined with the corresponding structural, magnetic, and electrical characterization allow us to map the strain-dependent orbital and magnetic phase diagrams of half-doped manganites and its dependence on the electronic bandwidth.

Understanding quantitatively the heating dynamics in magnetic tunnel junctions submitted to current pulses is very important in the context of spin-transfer-torque magnetic random-access memory development. Here we provide a method to probe the heating of magnetic tunnel junctions using the Ruderman-Kittel-Kasuya-Yoshida coupling of a synthetic ferrimagnetic storage layer as a thermal sensor. The temperature increase versus applied bias voltage is measured thanks to the decrease of the spin-flop field with temperature. This method allows distinguishing spin-transfer torque effects from the influence of temperature on the switching field. The heating dynamics is then studied in real time by probing the conductance variation due to spin-flop rotation during heating. This approach provides a method for measuring fast heating in spintronic devices, particularly magnetic random-access memory using thermally assisted or spin-transfer torque writing.

We study the formation and the dynamics of dipolar rings composed by microscopic ferromagnetic ellipsoids, which self-assemble in water by switching the direction of the applied field. We show how to manipulate these fragile structures and control their shape via the application of external static and oscillating magnetic fields. We introduce a theoretical framework which describes the ring deformation under an applied field, allowing us to understand the underlying physical mechanism. Our microscopic rings are finally used to capture, entrap, and later release a biological cell via a magnetic command, i.e., performing a simple operation which can be implemented in other microfluidic devices which make use of ferromagnetic particles.

Point defects in solids promise precise measurements of various quantities. Especially magnetic field sensing using the spin of point defects has been of great interest recently. When optical readout of spin states is used, point defects achieve optical magnetic imaging with high spatial resolution at ambient conditions. Here, we demonstrate that genuine optical vector magnetometry can be realized using the silicon vacancy in SiC, which has an uncommon $S=3/2$ spin. To this end, we develop and experimentally test sensing protocols based on a reference field approach combined with multifrequency spin excitation. Our work suggests that the silicon vacancy in an industry-friendly platform, SiC, has the potential for various magnetometry applications under ambient conditions.

Coupling mechanical degrees of freedom to single well-controlled quantum systems has become subject to intense research recently. Here, we report on the design, fabrication, and characterization of a diamond architecture consisting of a high-quality thin circular diamond membrane with embedded near-surface nitrogen-vacancy centers (NVCs). To demonstrate this architecture, we employ the NVCs by means of their optical and spin interfaces as nanosensors of the motion of the membrane under static pressure and in-resonance vibration. We also monitor the static residual stress within the membrane using the same method. Driving the membrane at its fundamental resonance mode, we observe coupling of this vibrational mode to the spin of the NVCs. Our realization of this architecture can manifest the applications of diamond structures in 3D piezometry such as mechanobiology and vibrometry, as well as mechanically mediated spin-spin coupling in quantum-information science.

We theoretically demonstrate that core-shell particles with a designed cloaking shell can be unresponsive to acoustic radiation force in an inviscid fluid. The core-shell particles’ size is assumed to be much smaller than the incident wavelength, i.e., the long-wavelength limit. The cloaking shell should have an optimal thickness with which the radiation force is drastically attenuated or even totally suppressed. We show that absorbing shells (polymer type) do not yield neutrality under the radiation force of traveling waves. Such a restriction does not appear in the case of standing waves. In addition, we establish the conditions for the suppression of the acoustic interaction forces (secondary radiation forces) between two or more cloaked particles.

We use neutron dark-field imaging to visualize and interpret the response of bulk magnetic domain walls to static and dynamic magnetic excitations in (110)-Goss textured iron silicon high-permeability steel alloy. We investigate the domain-wall motion under the influence of an external alternating sinusoidal magnetic field. In particular, we perform scans combining varying levels of ${\mathrm{dc}}_{\text{offset}}$ $(0–30\mathrm{A}/\mathrm{m})$, oscillation amplitude $A_{\mathrm{ac}}$ $(0–1500\mathrm{A}/\mathrm{m})$, and frequency $f_{\mathrm{ac}}$ ($(0–200\mathrm{Hz})$. By increasing amplitude $A_{\mathrm{ac}}$ while maintaining constant values of ${\mathrm{dc}}_{\text{offset}}$ and $f_{\mathrm{ac}}$, we record the transition from a frozen domain-wall structure to a mobile one. Vice versa, increasing $f_{\mathrm{ac}}$ while keeping $A_{\mathrm{ac}}$ and ${\mathrm{dc}}_{\text{offset}}$ constant led to the reverse transition from a mobile domain-wall structure into a frozen one. We show that varying both $A_{\mathrm{ac}}$ and $f_{\mathrm{ac}}$ shifts the position of the transition region. Furthermore, we demonstrate that higher frequencies require higher oscillation amplitudes to overcome the freezing phenomena. The fundamental determination and understanding of the frequency-induced freezing process in high-permeability steel alloys is of high interest to the further development of descriptive models for bulk macromagnetic phenomena. Likewise, the efficiency of transformers can be improved based on our results, since these alloys are used as transformer core material.