Determining the optimal arrangement of superconducting layers to withstand large-amplitude ac magnetic fields is important for certain applications such as superconducting radio-frequency cavities. In this paper, we evaluate the shielding potential of the superconducting-film–insulating-film–superconductor (${\mathrm{SIS}}^{\prime }$) structure, a configuration that could provide benefits in screening large ac magnetic fields. After establishing that, for high-frequency magnetic fields, flux penetration must be avoided, the superheating field of the structure is calculated in the London limit both numerically and, for thin films, analytically. For intermediate film thicknesses and realistic material parameters, we also solve numerically the Ginzburg-Landau equations. It is shown that a small enhancement of the superheating field is possible, on the order of a few percent, for the ${\mathrm{SIS}}^{\prime }$ structure relative to a bulk superconductor of the film material, if the materials and thicknesses are chosen appropriately.

We investigate radiative coupling between emitters in quantum-dot (QD) nanolasers. For typical systems with tens to hundreds of active emitters, a strong impact of sub- and superradiance on steady-state properties is demonstrated. In a device-relevant parameter regime, it is shown that radiative coupling enhances spontaneous emission such that significantly fewer emitters are required to reach the lasing threshold. The formation of QD-QD correlations can seemingly change the $\beta$ factor by an order of magnitude. The results provide insight into an unconventional kind of lasing in a highly efficient regime dominated by cavity-QED effects. Calculations are based on a microscopic laser theory for the coupled multi-QD-cavity-photon system that provides access to the photon autocorrelation function $g^{(2)}(0)$.

${\mathrm{Cu}}_2{\mathrm{SnS}}_3$ is a promising absorber material that has attracted significant interest in recent years. However, similar to ${\mathrm{Cu}}_2\mathrm{ZnSn}(\mathrm{S},\mathrm{Se}{)}_4$ (CZTS), ${\mathrm{Cu}}_2{\mathrm{SnS}}_3$ displays cation disorder, which complicates the scientific understanding and technological applications of these materials. In this work, we use postdeposition annealing to convert disordered ${\mathrm{Cu}}_2{\mathrm{SnS}}_3$ thin films to the ordered structure. After annealing, we observe crystal structure changes and detect improvements in the majority carrier (hole) transport. However, when the minority carrier (electron) transport is investigated by using optical-pump terahertz-probe spectroscopy, minimal differences are observed in the lifetimes of the photoexcited charge carriers in the ordered and disordered ${\mathrm{Cu}}_2{\mathrm{SnS}}_3$. By combining the experimental data with theoretical results from first-principles calculations and Monte Carlo simulations, we are able to conclude that even ostensibly “ordered” ${\mathrm{Cu}}_2{\mathrm{SnS}}_3$ displays minority carrier transport properties corresponding to the disordered structure. Transmission electron microscopy investigations reveal only a very low density of planar defects (stacking faults and/or twins) in the annealed film, suggesting that these imperfections can dominate minority carrier transport even at low levels. The results of this study highlight some of the challenges in the development of ${\mathrm{Cu}}_2{\mathrm{SnS}}_3$-based photovoltaics and have implications for other disordered multinary semiconductors such as CZTS.

We present an exhaustive theoretical analysis of charge and thermoelectric transport in a normal-metal–ferromagnetic-insulator–superconductor junction and explore the possibility of its use as a sensitive thermometer. We investigate the transfer functions and the intrinsic noise performance for different measurement configurations. A common feature of all configurations is that the best temperature-noise performance is obtained in the nonlinear temperature regime for a structure based on an Europium chalcogenide ferromagnetic insulator in contact with a superconducting Al film structure. For an open-circuit configuration, although the maximal intrinsic temperature sensitivity can achieve $10\mathrm{nK}{\mathrm{Hz}}^{-1/2}$, a realistic amplifying chain will reduce the sensitivity up to $10\mu \mathrm{K}{\mathrm{Hz}}^{-1/2}$. To overcome this limitation, we propose a measurement scheme in a closed-circuit configuration based on state-of-the-art superconducting-quantum-interference-device detection technology in an inductive setup. In such a case, we show that temperature-noise can be as low as $35\mathrm{nK}{\mathrm{Hz}}^{-1/2}$. We also discuss a temperature-to-frequency converter where the obtained thermovoltage developed over a Josephson junction operated in the dissipative regime is converted into a high-frequency signal. We predict that the structure can generate frequencies up to approximately 120 GHz and transfer functions up to $200\mathrm{GHz}/\mathrm{K}$ at around 1 K. If operated as an electron thermometer, the device may provide temperature-noise lower than $35\mathrm{nK}{\mathrm{Hz}}^{-1/2}$ thereby being potentially attractive for radiation-sensing applications.

A new approach to detect absolute radio-frequency (rf) electric fields (E-fields) that uses Rydberg atoms at room temperature in vapor cells has been demonstrated recently. The large-transition dipole moments between energetically adjacent Rydberg states enable this technique to make traceable E-field measurements with high sensitivity over a large frequency range from 1 GHz to 1 THz. In this paper, we experimentally investigate how the vapor-cell geometry affects the accuracy of the measurements. We find that the effects of the vapor cell on the measured rf E-field are minimized by making the vapor-cell size small compared to the wavelength of the rf E-field.

The effect of polarization rotation on the performance of metal-oxide-semiconductor field-effect transistors is investigated with a Landau-Ginzburg-Devonshire theory-based model. In this analytical model, the depolarization field, polarization rotations, and electrostatic properties of the doped silicon substrate are considered to illustrate the size effect of ferroelectric oxides and the stability of polarization in each direction. Based on this model, we provide guidance in designing electronic logic devices with low operating voltages and low active-energy consumption: First, we demonstrate that MOSFET operation could be achieved by polarization reorientation with a low operating voltage, if the thickness of the ferroelectric oxide is properly selected. Polarization reorientation can boost the surface potential of the silicon substrate, leading to a subthreshold swing $S$ lower than $60\mathrm{mV}/\mathrm{decade}$. We also demonstrate that, compared with polarization inversion, polarization rotation offers significant advantages, including a lower energy barrier and a wider range of transferability in nanoelectronic devices.

For improving the temporal resolution in ultrafast pump-probe electron or x-ray diffraction, we report a laser-electron synchronization concept via direct microwave extraction from the laser frequency comb combined with phase detection by fiber-loop interferometry, in situ drift correction via electron-energy analysis, and laser-electron streaking for final timing metrology. We achieve a laser-electron jitter below 5 fs (rms) integrated between 8 min and Nyquist period (400 ns). Slower drifts are also below 5 fs (rms) after active compensation. This result helps advance femtosecond crystallography with electrons or x rays to the regime of fundamental atomic-scale dynamics and light-matter interaction.

We propose hitherto unexplored and fully analytical insights into laminate elastic materials in a true condensed-matter-physics spirit. Pure mechanical surface waves that decay as evanescent waves from the interface are discussed, and we demonstrate how these designer Scholte waves are controlled by the geometry as opposed to the material alone. The linear surface wave dispersion is modulated by the crystal filling fraction such that the degree of confinement can be engineered without relying on narrow-band resonances but on effective stiffness moduli. In the same context, we provide a theoretical recipe for designing Bloch oscillations in classical plate structures and show how mechanical Bloch oscillations can be generated in arrays of solid plates when the modal wavelength is gradually reduced. The design recipe describes how Bloch oscillations in classical structures of arbitrary dimensions can be generated, and we demonstrate this numerically for structures with millimeter and centimeter dimensions in the kilohertz to megahertz range. Analytical predictions agree entirely with full wave simulations showing how elastodynamics can mimic quantum-mechanical condensed-matter phenomena.

Epsilon-near-zero (ENZ) modes arising from condensed-matter excitations such as phonons and plasmons are a new path for tailoring light-matter interactions at the nanoscale. Complex spectral shaping can be achieved by creating such modes in nanoscale semiconductor layers and controlling their interaction with multiple, distinct, dipole resonant systems. Examples of this behavior are presented at midinfrared frequencies for ENZ modes that are strongly coupled to metamaterial resonators and simultaneously strongly coupled to semiconductor phonons or quantum-well intersubband transitions (ISTs), resulting in double- and triple-polariton branches in transmission spectra. For the double-polariton branch case, we find that the best strategy to maximize the Rabi splitting is to use a combination of a doped layer supporting an ENZ feature and a layer supporting ISTs, with overlapping ENZ and IST frequencies. This design flexibility renders this platform attractive for low-voltage tunable filters, light-emitting diodes, and efficient nonlinear composite materials.

Semiconductor nanowires have emerged as an important enabling technology and are today used in many advanced device architectures, with an impact both for what concerns fundamental science and in view of future applications. One of the key challenges in the development of nanowire-based devices is the fabrication of reliable nanoscale contacts. Recent developments in the creation of metal-semiconductor junctions by thermal annealing of metallic electrodes offer promising perspectives. Here, we analyze the optoelectronic properties of nano-Schottky barriers obtained thanks to the controlled formation of metallic AuGa regions in GaAs nanowire. The junctions display a rectifying behavior and their transport characteristics are analyzed to extract the average ideality factor and barrier height in the current architecture. The presence, location, and properties of the Schottky junctions are cross-correlated with spatially resolved photocurrent measurements. Broadband light emission is reported in the reverse breakdown regime; this observation, combined with the absence of electroluminescence at forward bias, is consistent with the device unipolar nature.

Silicon-on-insulator nanowire transistors of very small dimensions exhibit electrostatic or quantum effects like Coulomb blockade or single-dopant transport at low temperature. The same process also yields excellent field-effect transistors (FETs) for larger dimensions, allowing us to design integrated circuits. Using the same process, we cointegrate a FET-based ring oscillator circuit operating at cryogenic temperature which generates a radio-frequency (rf) signal on the gate of a nanoscale device showing Coulomb oscillations. We observe rectification of the rf signal, in good agreement with modeling.

In this paper, a mesoscopic model based on the nonequilibrium Green’s function formalism for a tight-binding-like effective Hamiltonian is used to investigate a selectively contacted quantum-dot array designed for operation as a single-junction quantum-dot solar cell. By establishing a direct relation between nanostructure configuration and optoelectronic properties, the investigation reveals the influence of interdot and dot-contact coupling strengths on the rates of charge-carrier photogeneration, radiative recombination, and extraction at contacts, and, consequently, on the ultimate performance of photovoltaic devices with finite quantum-dot arrays as the active medium. For long carrier lifetimes, the dominant configuration effects originate in the dependence of the joint density of states on the interdot coupling in terms of band width and effective band gap. In the low-carrier-lifetime regime, where recombination competes with carrier extraction, the extraction efficiency shows a critical dependence on the dot-contact coupling.

An alternate approach of analyzing immittance spectra with electrical equivalent circuits, which not only eliminates circuit ambiguity but also directly extracts the system-specific parameters of the selected physical models, is proposed. To understand the underlying mechanisms, a fundamental electrical equivalent circuit, representing Maxwell’s equations, is derived. Allowing nonlinear characteristics for the elements in the circuit results in a universal immittance that is neither limited to the fundamental frequency nor to linear response functions. Process-specific physical models with their intrinsic, potentially nonlinear, dependencies on external parameters are introduced as components of the circuit. This allows the extraction of the system-specific parameters of the models instead of single values for idealized components like resistors and capacitors. The resulting electrical equivalent circuits are unambiguous and can be fitted to measured immittance data for a whole set of varied external parameters instead of the frequency of the applied stimulus only. Furthermore, the different dependencies of the physical models on external parameters automatically weight the regions of their dominance. Exemplarily, for a well-known system, the impedance of a depletion layer in silicon is calculated by using models for the resistance and capacitance that are both dependent on the external parameters voltage and temperature. In addition to a detailed comparison with conventional electrical equivalent circuits, differences between the presented approach and analytical Poisson-Nernst-Planck models are discussed.

Elastically deformable materials can be created from rigid sheets through patterning appropriate meshes which can locally bend and flex. We demonstrate how microaccordion patterns can be fabricated across large areas using three-beam interference lithography. Our resulting mesh induces a large and robust elasticity within any rigid material film. Gold coating the microaccordion produces stretchable conducting films. Conductivity changes are negligible when the sample is stretched reversibly up to 30% and no major defects are introduced, in comparison to continuous sheets which quickly tear. Scaling analysis shows that our method is suited to further miniaturization and large-scale fabrication of stretchable functional films. It thus opens routes to stretchable interconnects in electronic, photonic, and sensing applications, as well as a wide variety of other deformable structures.

Confinement of flowing liquid threads by solid walls makes them stable with respect to the Rayleigh-Plateau instability. We demonstrate here that light can break this stability by forcing locally the deformation of the liquid interface through thermally induced Marangoni stresses. Depending upon the confining conditions and fluid properties, this optocapillary deformation either pinches or inflates the thread, which may, in both cases, lead to its localized fragmentation into droplets. In the pinching regime, the laser beam behaves as a wall-free constriction that flow focuses the thread, leading to successive regimes of single and multiple periodicity. Light-driven local Marangoni stresses may prove an elegant contactless alternative to control reversibly the thread-to-droplet transition for digital microfluidics.

Measuring local magnetization dynamics and its spatial variation is essential for advancements in spintronics and relevant applications. Here we demonstrate a phase-sensitive imaging technique for studying patterned magnetic structures based on picosecond laser heating. With the time-resolved anomalous Nernst effect (TRANE) and extensions, we simultaneously image the dynamic magnetization and rf driving current density. The stroboscopic detection implemented in TRANE microscopy provides access to both amplitude and phase information of the ferromagnetic resonance (FMR) and rf current. Using this approach, we measure the spatial variation of the Oersted driving field angle across a uniform channel. In a spatially nonuniform sample with a cross shape, a strong spatial variation for the rf current as well as FMR precession is observed. We find that both the amplitude and the phase of local FMR precession are closely related to those of the rf current.

We propose and analyze a hybrid device by integrating a microscale diamond beam with a single built-in nitrogen-vacancy ($NV$) center spin to a superconducting coplanar waveguide (CPW) cavity. We find that under an ac electric field the quantized motion of the diamond beam can strongly couple to the single cavity photons via a dielectric interaction. Together with the strong spin-motion interaction via a large magnetic-field gradient, it provides a hybrid quantum device where the diamond resonator can strongly couple both to the single microwave-cavity photons and to the single $NV$ center spin. This enables coherent information transfer and effective coupling between the $NV$ spin and the CPW cavity via mechanically dark polaritons. This hybrid spin-electromechanical device, with tunable couplings by external fields, offers a realistic platform for implementing quantum information with single $NV$ spins, diamond mechanical resonators, and single microwave photons.

As the operation of organic thin-film transistors relies exclusively on injected charge carriers, the gate-induced field assumes a dual role: It is responsible for charge-carrier accumulation and, provided that an injection barrier at the contact-semiconductor interface is present, aids charge-carrier injection across this barrier. Besides the gate-source bias, the thickness of the insulator and its dielectric constant influence the gate field. Here, we explore the impact of the capacitance of the gate dielectric on the performance of organic thin-film transistors utilizing drift-diffusion-based simulations comprising a self-consistent consideration of injection. Upon varying the capacitance of the insulating layer, we observe a conceptually different behavior for top-contact and bottom-contact architectures. Top-contact devices possess a nearly constant contact voltage in the linear regime leading to an apparent mobility lowering. In strong contrast, bottom-contact architectures possess non-Ohmic contact resistances in the linear regime due to a contact voltage whose value depends strongly on both the gate-source bias and the capacitance. Counterintuitively, this is accompanied by a mobility being apparently unaffected by the substantial contact resistance. Additionally, threshold-voltage shifts appear due to gate-limited injection. The latter is particularly dominant in bottom-contact architectures, where the threshold voltages steeply increase with the thickness of the insulating layer.

The field of spintronics, or magnetic electronics, is maturing and giving rise to new subfields. These new directions involve the study of collective spin excitations and couplings of the spin system to additional degrees of freedom of a material, as well as metastable phenomena due to perturbations that drive the system far from equilibrium. The interactions lead to possibilities for future applications within the realm of energy-efficient information technologies. Examples discussed herein include research opportunities associated with (i) various spin-orbit couplings, such as spin Hall effects, (ii) couplings to the thermal bath of a system, such as in spin Seebeck effects, (iii) spin-spin couplings, such as via induced and interacting magnon excitations, and (iv) spin-photon couplings, such as in ultrafast magnetization switching due to coherent photon pulses. These four basic frontier areas of research are giving rise to new applied disciplines known as spin orbitronics, spin caloritronics, magnonics, and spin photonics, respectively. These topics are highlighted in order to stimulate interest in the new directions that spintronics research is taking and to identify open issues to pursue.

Néel walls in soft magnetic NiFe/NiFeGa hybrid stripe structures surrounded by a NiFe film are investigated by high-resolution Lorentz transmission-electron-microscopic imaging. An antiparallel orientation of magnetization in 1000-nm-wide neighboring unirradiated-irradiated stripes is observed by forming high-angle domain walls during magnetization reversal. Upon downscaling the stripe structure size from 1000 to 200 nm, a transition from a discrete domain pattern to an effective magnetic medium is observed for external magnetic-field reversal. This transition is associated with the vanishing ability of hosting high-angle domain walls between adjacent stripes.