High-intensity laser irradiation can effectively couple to practically all kinds of materials, causing modification of their physical properties due to laser-induced phase transformations. This gives rise to a broad field of laser micro- and nanofabrication with its various technological applications. We demonstrate that, in a 40-nm-thick film of ${\mathrm{Fe}}_{60}{\mathrm{Al}}_{40}$ alloy, a short laser pulse is capable of (re)writing the ferromagnetism observed at room temperature (RT). The energy of the pulse generating a ferromagnetic region has to be sufficiently high to induce melting of the ${\mathrm{Fe}}_{60}{\mathrm{Al}}_{40}$ layer, while the ferromagnetic state can be erased by various kinds of lower-intensity thermal treatment. This cycling of RT ferromagnetism can be explained in terms of the chemical order (B2)-disorder (A2) phase transition in the ${\mathrm{Fe}}_{60}{\mathrm{Al}}_{40}$ crystal lattice, which is affected by laser-induced melting and rapid resolidification. Our finding has implications for the development of a magnetic memory technology that would use the reversibility of the modulus of the magnetization vector instead of its direction. This promises to circumvent the problem of the superparamagnetic limit for magnetic data storage density.

Two-dimensional (2D) semiconductors, e.g., $\mathrm{Mo}{\mathrm{S}}_2$ and phosphorene, are promising candidates for the channel materials of next-generation field-effect transistors (FETs). Although 2D $\mathrm{Mo}{\mathrm{S}}_2$ FETs with the gate length $L_g$ scaled down to 1 nm have been fabricated with a quite small threshold swing, they suffer from a rather low ON current and are unsuitable for a high-performance device. Herein, we simulate sub-5-nm monolayer (ML) phosphorene MOSFETs using ab initio quantum-transport simulations. We predict that the ON current, delay time, and power dissipation indicator of the sub-5-nm double-gated ML phosphorene MOSFETs with proper underlap structure can fulfill the requirements of the international technology roadmap for semiconductors for both high-performance (along both the armchair and zigzag directions) and low-power (along the zigzag direction) devices in 2028 until $L_g$ is scaled down to 2 nm. Therefore, phosphorene is more suitable for ultrascaled FETs than 2D $\mathrm{Mo}{\mathrm{S}}_2$ in the post-silicon era as far as the ON current is concerned.

Tritium diffusion in the nuclear fusion reactor breeder material ${\mathrm{Li}}_2\mathrm{Ti}{\mathrm{O}}_3$ is a fundamentally important process for tritium-release kinetics. The energy barrier of tritium diffusion in ${\mathrm{Li}}_2\mathrm{Ti}{\mathrm{O}}_3$ has been reported with a considerable uncertainty in previous experiments. Here, we perform systematic density-functional-theory (DFT) studies for the diffusion processes of positively charged tritium, which is the preferential charge state of the tritium interstitial in a single ${\mathrm{Li}}_2\mathrm{Ti}{\mathrm{O}}_3$ crystal. By calculating various local-diffusion minimum-energy paths, we find that the diffusion of tritium is strongly anisotropic along different crystalline directions. The most favorable diffusion paths appear within a ${\mathrm{Li}}_6$ atomic single layer of ${\mathrm{Li}}_2\mathrm{Ti}{\mathrm{O}}_3$ and the corresponding DFT diffusion barrier is 0.334 eV, while the diffusion barrier for the most favorable diffusion paths crossing a ${\mathrm{Li}}_2{\mathrm{Ti}}_4$ atomic layer is 1.006 eV.

Free-space communication links are severely affected by atmospheric turbulence, which causes degradation in the transmitted signal. One of the most common solutions to overcome this is to exploit diversity. In this approach, information is sent in parallel over different paths using two or more transmitters that are spatially separated, with each beam therefore experiencing different atmospheric turbulence, lowering the probability of a receive error. In this work we propose and experimentally demonstrate a alternative method of diversity based on spatial modes of light, which we call modal diversity. We remove the need for a physical separation of the transmitters by exploiting the fact that spatial modes of light experience different perturbations, even when traveling along the same path. For this proof-of-principle, we select identical radius modes from the Hermite-Gaussian and Laguerre-Gaussian basis sets and demonstrate an improvement in bit error rate by up to 54% without increasing the total transmit power or receive aperture radius.

We propose a realizable circuit QED architecture for engineering states of a superconducting resonator off-resonantly coupled to an ancillary superconducting qubit. The qubit-resonator dispersive interaction together with a microwave drive applied to the qubit gives rise to a Kerr resonator with two-photon driving that enables us to efficiently engineer the quantum state of the resonator, such as generation of the Schrödinger cat states for resonator-based universal quantum computation. Moreover, the presented architecture is easily scalable for solving an optimization problem mapped into the Ising spin-glass model and thus serves as a platform for quantum annealing. Although various scalable architectures with superconducting qubits have been proposed for realizing a quantum annealer, the existing annealers are currently limited to the coherent time of the qubits. Here, based on the protocol for realizing a two-photon driven Kerr resonator in three-dimensional circuit QED (3D cQED), we propose a flexible and scalable hardware for implementing a quantum annealer that combines the advantage of the long coherence times attainable in 3D cQED and the recently proposed resonator-based Lechner-Hauke-Zoller (LHZ) scheme. In the proposed resonator-based LHZ annealer, each spin is encoded in the subspace formed by two coherent states of the 3D microwave superconducting resonator with opposite phase and thus the fully connected Ising model is mapped onto the network of the resonator with local tunable three-resonator interaction. This hardware architecture provides a promising physical platform for realizing a quantum annealer with improved coherence.

We present how to physically realize the recently introduced active plasmon-injection loss compensation scheme. Particularly, we show that the characteristics of the auxiliary source described in the active plasmon-injection scheme, including tunable narrow band and selective amplification via convolution, can be realized by using a hyperbolic metamaterial functioning as a near-field spatial filter. Besides loss compensation, the proposed approach with the near-field spatial filter can be useful for enhanced near-field superlensing and real-time high-resolution edge detection.

The interaction between a rapidly oscillating atomic-force-microscope tip and a soft-material surface is described with use of both elastic and viscous forces in a moving-surface model. We present the simplest form of this model, motivating our derivation with the models ability to capture the impact dynamics of the tip and sample with an interaction consisting of two components: interfacial or surface force, and bulk or volumetric force. Analytic solutions to the piecewise linear model identify characteristic time constants, providing a physical explanation for the hysteresis observed in the measured dynamic-force-quadrature curves. Numerical simulation is used to fit the model to experimental data, and excellent agreement is found with a variety of different samples. The model parameters form a dimensionless impact-rheology factor, giving a quantitative physical number to characterize a viscoelastic surface that does not depend on the tip shape or cantilever frequency.

Motivated by the need to control the resistance of metal-graphene interfaces, we have simulated the structural and transport properties of edge contacts upon their formation. Our first-principles calculations reveal that the contacts evolve in a nontrivial way depending on the type of metal and the chemical contamination of the graphene edge. In particular, our results indicate that the origin of the low experimental resistance of chromium-graphene edge contacts is related to their weaker variation upon contamination and defect formation. In summary, by analyzing the distance dependence of the graphene-metal interaction and the relation between the reactivity and forces at the graphene edge, we shed new light on the mechanisms responsible for the diverse performance of experimentally fabricated graphene edge contacts.

We propose a single-photon detector based on a superconducting quantum interference device (SQUID) with superconductor–normal-metal–superconductor Josephson weak links. One of the two Josephson junctions is connected to an antenna, and is heated when a photon is absorbed. The increase of the weak-link temperature exponentially suppresses the Josephson critical current, thereby inducing an asymmetry in the SQUID. This generates a voltage pulse across the SQUID that can be measured with a threshold detector. Realized with realistic parameters, the device can be used as a single-photon detector—and as a calorimeter, since it is able to discriminate photon frequencies above $5\mathrm{THz}$ with a signal-to-noise ratio larger than $20$. The performance of the detector is robust with respect to working temperatures between $0.1$ and $0.5\mathrm{K}$, and with respect to thermal noise perturbation.

We evaluate the sensitivity of large gadolinium-doped water detectors to antineutrinos released by nuclear-fission explosions, using updated signal and background models and taking advantage of the capacity for seismic observations to provide an analysis trigger. Under certain realistic conditions, the antineutrino signature of a 250-kton pure-fission explosion could be identified several hundred kilometers away, in a detector about the size of the largest module currently proposed for a basic physics experiment. In principle, such an observation could provide rapid confirmation that the seismic signal coincided with a fission event, possibly useful for international monitoring of nuclear-weapon tests. We discuss the limited potential for seismically cued antineutrino observations to constrain fission yield, differentiate pure fission from fusion-enhanced weapon tests, indicate that the seismic evidence of an explosion had been intentionally masked, or verify the absence of explosive testing in a targeted area. We conclude that advances in seismic monitoring and neutrino physics have made the detection of explosion-derived antineutrinos more conceivable than previously asserted, but the size and cost of sufficiently sensitive detectors continue to limit applications.

Magnetization switching utilizing the spin-orbit torque of heavy metals is a promising alternative to spin-transfer torque for a faster and more energy-efficient write mechanism for magnetic random-access memory. We report spin-orbit-torque switching in 20-nm-diameter ${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}\text{−}\mathrm{Mg}\mathrm{O}$-based perpendicular magnetic tunnel junctions with a thermal stability factor of ∼47. Conductive atomic force microscopy was used to measure the tunnel magnetoresistance before and after current pulses through the heavy metal underlayer, and magnetostatic shifts in the minor loops provided evidence of spin-orbit-torque switching. Comparison of estimated critical current densities and write energies suggests that spin-orbit torque can be used as an effective switching mechanism for small and thermally stable perpendicular magnetic tunnel junctions.

Hierarchical structures with constituents over multiple length scales are found in various natural materials like bones, shells, spider silk and others, all of which display enhanced quasistatic mechanical properties, such as high specific strength, stiffness, and toughness. At the same time, the role of hierarchy on the dynamic behavior of metamaterials remains largely unexplored. This study numerically and experimentally assesses the effect of bioinspired hierarchical organization as well as of viscoelasticity on the wave attenuation properties of continuous elastic metamaterials. We consider single-phase metamaterials formed by self-similar unit cells with different hierarchical levels and types of hierarchy. Two types of structures are considered: a hub-spoke geometry with thin connecting elements and nested hierarchical organization, and a crosslike porous geometry with external hierarchical organization. In the first, hierarchical elements occur at similar size scales, while in the second they differ by one order of magnitude. Results highlight a number of advantages through the introduction of structural hierarchy. Band gaps relative to the corresponding nonhierarchical structures are mostly preserved in both types of structures, but additional hierarchically-induced band gaps also appear, and the hierarchical configuration allows the tuning of band-gap frequencies to lower frequencies in the crosslike porous geometry, with a simultaneous significant reduction of the global structural weight. We show that even small viscoelastic effects are essential in determining the overall attenuation behavior, including between band gaps. Finally, we verify the numerically-predicted multifrequency band gaps by experimental characterization of the transmission properties of crosslike structures. The approach we propose allows the incorporation of hierarchical organization in existing metamaterial configurations, with the corresponding improvement of wave-damping properties, thus extending application possibilities for elastic metamaterials to multiple frequency scales.

We investigate a hybrid quantum system where an ensemble of nitrogen-vacancy (NV) centers in diamond is interfaced with a piezomagnetic superlattice that supports surface-phonon polaritons (SPHPs). We show that the strong magnetic coupling between the collective spin waves in the NV spin ensemble and the quantized SPHPs can be realized, due to the subwavelength nature of the SPHPs and relatively long spin-coherence times. The magnon-polariton coupling allows different modes of the SPHPs to be mapped and orthogonally stored in different spatial modes of excitation in the solid medium. Because of its easy implementation and high tunability, the proposed hybrid structure with NV spins and piezoactive superlattices could be used for quantum memory and quantum computation.

This paper is a contribution to the Physical Review Applied collection in memory of Mildred S. Dresselhaus.

We discuss the origin and the influence of autocatalytic kinetics on the structure-property relationship in the evolution of macromolecular structure during self-organized growth of vertically aligned carbon-nanotube arrays by chemical vapor deposition of acetylene. Real-time thickness measurements consistent with postgrowth structural characterization show that the rate of carbon incorporation governs not just the length of individual nanotubes, but also cooperative properties such as packing density, alignment, and order in the arrays, which profoundly affect the mechanical strength and the thermal and electrical conductivity of the assembly. Our analysis shows that the autocatalytic kinetics points to radical chain polymerization of acetylene as the most likely mechanism capable of producing the large variations in carbon-addition rates revealed by real-time data. This fresh insight provides alternative approaches for targeting specific array properties using the polymerization reaction framework for creating novel applications in high-density energy storage, advanced interconnects, and high-efficiency heat dissipation.

Thermoelasticity and acoustic velocities of polycrystalline magnetite are studied at simultaneously high pressures and temperatures up to 8.6 GPa and 1123 K using ultrasonic interferometry in conjunction with in situ x-ray techniques. Here, we report temperature-driven anomalies in the shear behavior at temperatures up to ∼450 K, together with pressure-induced softening in the shear properties. Fitting the current data to finite strain equations, we obtain the bulk and shear moduli, as well as their pressure and temperature dependences, namely $B_{S0}=173.2(5)\mathrm{GPa}$, $G_0=55.5(2)\mathrm{GPa}$, $\mathrm{\partial }{B}_S/\mathrm{\partial }P=2.99(9)$, $\mathrm{\partial }G/\mathrm{\partial }P=-0.23(3)$, $\mathrm{\partial }{B}_S/\mathrm{\partial }T=-0.0209(10)\mathrm{GPa}/\mathrm{K}$, $\mathrm{\partial }G/\mathrm{\partial }T=0.0042(4)\mathrm{GPa}/\mathrm{K}$, $({\mathrm{\partial }}^2{B}_S/\mathrm{\partial }{T}^2{)}_P=-1.7(1)\times {10}^{-5}{\mathrm{GPa}}^2/{\mathrm{K}}^2$, and $({\mathrm{\partial }}^{2}G/\mathrm{\partial }{T}^2{)}_P=-2.5(1)\times {10}^{-5}{\mathrm{GPa}}^2/{\mathrm{K}}^2$. The origin of the thermally induced anomaly in the shear modulus for ${\mathrm{Fe}}_3{\mathrm{O}}_4$ magnetite is ascribed to the coupling of local atomic distortions and short-range charge ordering of sixfold-coordinated ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ ions at the octahedral sites in the inverse-spinel structure. These findings or results provide high-P thermoelasticity data of magnetite and present an opportunity to gain a good understanding of the underlying mechanism of temperature-driven anomalies in magnetite-based solid solutions and spinel-structured materials for their applications in extreme conditions.

The magnetoelectronic field effects in organic semiconductors at high magnetic fields are described by field-dependent mixing between singlet and triplet states of weakly bound charge-carrier pairs due to small differences in their Landé $g$ factors that arise from the weak spin-orbit coupling in the material. In this work, we corroborate theoretical models for the high-field magnetoresistance of organic semiconductors, in particular of diodes made of the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) at low temperatures, by conducting magnetoresistance measurements along with multifrequency continuous-wave electrically detected magnetic-resonance experiments. The measurements are performed on identical devices under similar conditions in order to independently assess the magnetic-field-dependent spin-mixing mechanism, the so-called $\mathrm{\Delta }g$ mechanism. An understanding of the microscopic origin of magnetoresistance in organic semiconductors is crucial for developing reliable magnetometer devices capable of operating over a broad range of magnetic fields of order ${10}^{-7}-10\mathrm{T}$.

The energetic properties of electron transport in mesoscopic and nanoscale conductors are of considerable interest at present. Here, we theoretically investigate the possibility of probing charge- and heat-current fluctuations as well as their mixed correlations via the temperature and electrochemical potential fluctuations of a probe coupled to the conductor. Our particular interest is devoted to the charge and energy noise stemming from time-dependently-driven nanoelectronic systems designed for the controlled emission of single electrons, even though our setup is appropriate for more general ac-driving schemes. We employ a Boltzmann-Langevin approach in order to relate the bare charge- and energy-current fluctuations emitted from the electron source to frequency-dependent electrochemical potential and temperature fluctuations, which the former induce in the probe. We apply our findings to the prominent example of an on-demand single-electron source, realized by a driven mesoscopic capacitor in the quantum Hall regime. We show that neither the background fluctuations of the probe in the absence of the working source, nor the fluctuations induced by the probe hinder the access to the sought-after direct source noise for a large range of parameters.

In this work, we experimentally demonstrate the phenomenon of nonlinearity-activated intermodal tunneling in a periodic elastic metamaterial waveguide with internal resonators and we show how this effect can be exploited to achieve conspicuous energy localization and trapping. The architecture of the waveguide is deliberately designed to promote tunneling from flexurally dominated to axially dominated modes, in order to accentuate the functional complementarity that can be harnessed during tunneling. 3D laser vibrometry at different scales of spatial refinement is employed to capture global and local in-plane features of the wavefield. The measured response naturally yields an experimental reconstruction of the band diagram of the waveguide and reveals unequivocally the spectral signature of the high-frequency modes that are activated by tunneling. Finally, a detailed scan of selected cells highlights a strong and persistent axial activation of the resonators, which displays subwavelength deformation features that are unattainable, for the axial mode, by exciting at the same frequency in a linear regime. This result demonstrates the viability of tuning strategies based on nonlinearity and paves the way for the design of metastructures with enhanced energy-trapping and harvesting capabilities.

Intersubband (ISB) transitions are of high significance for light-emitting and light-detecting devices in the infrared and, when involving large electron densities, for plasmonics and strong light-matter coupling physics. Here it is observed that the simultaneously occurring fundamental and excited-state ISB transitions in highly-doped, m-plane $\mathrm{Zn}\mathrm{O}/{\mathrm{Mg}}_x{\mathrm{Zn}}_{1-x}\mathrm{O}$ multiple quantum wells, couple into a single collective oscillation: the multisubband plasmon (MSP). With 2D electron densities up to $4\times {10}^{13}{\mathrm{cm}}^{-2}$, an outstanding regime is reached in which the observed MSP frequency is three times larger than that of the fundamental ISB transition as a result of depolarization. This effect is analyzed using a dielectric tensor for $\mathrm{Zn}\mathrm{O}$ including the interaction of the light with the lattice, the in-plane free electrons, and the off-plane MSP. The impact of the broadening of the MSP and its interaction with phonons is discussed. The results presented here show the potential of $\mathrm{Zn}\mathrm{O}/{\mathrm{Mg}}_x{\mathrm{Zn}}_{1-x}\mathrm{O}$ for infrared optoelectronic applications, which can be extended to the THz range with appropriate design of the quantum wells.

We study the effects of thermal fluctuation on voltage-driven magnetization switching in perpendicularly magnetized magnetic tunnel junctions by combining an experiment and a numerical simulation. The thermal agitation of magnetization is found to affect not only the minimum value of write-error rate (WER) but also the dependence of the WER on the write-voltage pulse width. The WER exhibits a clear local maximum for a certain pulse width, which is explained well by taking into account the thermally induced transition of magnetization between the precession orbits surrounding the energy minima. We show that the increase of WER resulting from the unwanted orbit transition can be avoided by choosing a proper pulse width.