Nonequilibrium Green’s function modeling of the structure used for III-V quantum cascade lasers emitting at approximately 5-$\mu \mathrm{m}$ wavelength is performed to get insight into and analyze the processes that determine the linewidth of the optical (inter-sub-band) transition. Theoretical results are compared with electroluminescence data collected for real structures. Excellent agreement is found for both the transition energy of approximately $234\mathrm{meV}$ and the linewidth of approximately $32\mathrm{meV}$, typical for this sort of device. Careful inspection of simulation data shows that, for these structures, the interface-roughness (IR) scattering contributes to the optical linewidth $\cong 50\mathrm{\%}$. The decreased broadening due to IR scattering is not due to very smooth interfaces, but rather due to the finite carrier concentration and the decreased population of final states ${\mathbf{k}}^{{}^{\prime }}$ available for the initial state $\mathbf{k}$ in the limit of vanishing in-plane momentum $\mathbf{k}\to 0$. Further line narrowing is caused by nonparabolicity coupled with the highly nonthermal occupation of the lower laser sub-band, which destroys the population inversion for the hot carriers.

We investigate how a combination of a nonmagnetic impurity scattering rate $\gamma$ and finite subgap states parametrized by Dynes $\mathrm{\Gamma }$ affects various physical quantities relevant to superconducting devices made from extreme type-II $s$-wave superconductors. All the calculations are based on the Eilenberger formalism of the BCS theory. It is well known that the optimum impurity concentration minimizes the surface resistance $R_s$. We find the optimum $\mathrm{\Gamma }$ can also reduce $R_s$ by one order of magnitude for a clean superconductor ($\gamma /{\mathrm{\Delta }}_0<1$) and a few tens of % for a dirty superconductor ($\gamma /{\mathrm{\Delta }}_0>1$). Here, ${\mathrm{\Delta }}_0$ is the pair potential for the idealized ($\mathrm{\Gamma }\to 0$) BCS superconductor for $T\to 0$. Also, we find a nearly ideal ($\mathrm{\Gamma }/{\mathrm{\Delta }}_0\ll 1$) clean-limit superconductor exhibits a frequency-independent $R_s$ for a broad range of frequency $\omega$, which can significantly improve $Q$ of a compact cavity with a few tens of GHz frequency. As $\mathrm{\Gamma }$ or $\gamma$ increases, $R_s$ obeys the ${\omega }^2$ dependence. The subgap-state-induced residual surface resistance $R_{\mathrm{res}}$ is also studied, which can be detected by a high-$Q$ three-dimensional resonator. We calculate the kinetic inductance $L_k(\gamma ,\mathrm{\Gamma },T)$ and the depairing current density $J_d(\gamma ,\mathrm{\Gamma },T)$, which are monotonic increasing and decreasing functions of $(\gamma ,\mathrm{\Gamma },T)$, respectively. Measurements of $(\gamma ,\mathrm{\Gamma })$ of device materials can give helpful information on improving $Q$, engineering $L_k$, and ameliorating $J_d$ via materials processing.

In this paper we study the electromagnetic scattering, absorption, and performance bounds for short time modulated pulses that impinge on a time-varying lossy layer that is sandwiched between vacuum and a perfect electric conductor. The electric characteristics of the layer, namely, the conductivity, permittivity, and permeability, are assumed to change abruptly or gradually in time. We demonstrate numerically that a time-varying absorbing layer that undergoes temporal switching of its permittivity and conductance can absorb the power of a modulated, ultrawideband, as well as a quasimonochromatic, pulsed wave beyond what is dictated by the time-invariant Rozanov bound when integrating over the whole frequency spectrum. We suggest and simulate a practical metamaterial realization that is constructed as a three-dimensional array of resistor loaded dipoles. By switching only the dipole’s load resistance, desired effective media properties are obtained. Furthermore, we show that Rozanov’s bound can be bypassed with abrupt and a more practical gradual, soft, switching, thus overcoming some possible causality issues in abrupt switching.

Single-crystalline α-$\mathrm{Sn}$ films on the wafer scale are epitaxially grown on $\mathrm{In}\mathrm{Sb}(001)$ substrates by molecular-beam epitaxy. The Berry phase for α-$\mathrm{Sn}$ is extracted to be −0.64π from the quantum oscillations of the magnetoconductivity. Angle- and temperature-dependent Shubnikov–de Haas oscillations substantiate that the α-$\mathrm{Sn}$ film has a spherical Fermi surface and small effective mass (0.039$m_0$; $m_0$ is the resting mass of an electron), which are in agreement with the features of three-dimensional Dirac semimetals. In addition, an extremely large magnetoresistance of over $4.5\times {10}^5\mathrm{\%}$ at 1.5 K is observed. These α-$\mathrm{Sn}$ films, with wafer-scale dimensions and extremely large magnetoresistance, may pave the way for device applications of topological materials.

Electrical currents flowing through magnetic domain walls tend to encounter additional extraordinary resistance. At the thin-wall limit, the occurrence of anomalous-field antisymmetric magnetoresistance breaks Onsager symmetry, which seems to be determined by the combination of single-wall and perpendicular-current-injection geometry. However, the delicate magnetic structure and measurement configuration are hard to implement, and the abnormal transport properties observed in multidomain structures are not fully understood. Here, we report the observation of antisymmetric magnetoresistance due to domain-wall tilting in a multidomain structure controlled by a magnetic field gradient. We demonstrate, both experimentally and theoretically, that the anomalous magnetoresistance arises from the nonequilibrium current in the vicinity of tilting domain walls, which are basically governed by the geometry factor of the tilting walls.

Selective shielding of surfaces from flow and diffusion is essential in many domains of physics and engineering. We propose and characterize experimentally a framework to shield both flow and diffusion simultaneously within a reshapable fluid volume. To do so, we directly use flow singularities to generate conformal transforms of the diffusion profile, taking inspiration from classical cloaking devices. The properties of microfluidic surface shields as open-space diffusion filters (O-filters) are further investigated. An analytical model is provided, which yields an outstanding match with experimental measurements of both flow and tracer diffusion. Via conformal mapping, these measurements reveal a strong topological link with classical H-filters in microfluidics.

Perovskite oxides are extremely interesting for their possible use in high-mobility thin-film transistors (TFTs) suitable for high-performance large-area circuits. Here we present a semianalytical model of a recently fabricated TFT based on ${\mathrm{La}\text{−}\mathrm{Ba}\mathrm{Sn}\mathrm{O}}_3$, and explore the possibilities for technology optimization and the intrinsic potential of the device concept for applications in transparent and flexible electronics. We show that ${\mathrm{La}\text{−}\mathrm{Ba}\mathrm{Sn}\mathrm{O}}_3$ TFTs can outperform existing TFT device technologies through a detailed benchmarking exercise, and that these devices can be promising for display electronics and for a broader range of applications.

Absorption spectroscopy has long been hailed as an absolute necessity for detecting the properties of complex chemical and biological samples. While conventional spectroscopy using classical light is severely limited by shot noise and lacks robustness against experimental imperfections, quantum light offers an avenue to perform absorption spectroscopy with provable advantages in the technical operations and the measurement precision. Here, we present an experimental approach to implement entanglement-based absorption spectroscopy with the assistance of Hong-Ou-Mandel interference. Since the temporal interference fringe is determined by the spectrum pattern, a maximum-likelihood decision is sufficient for revealing the relevant quantum information about the absorptive properties of the test samples. These experimental results may significantly facilitate the use of quantum interferometric spectroscopy to practical applications, which may be particularly relevant for photon-sensitive biological and chemical samples.

The nitrogen-vacancy ($\mathrm{N}$-$V$) defect in diamond is a versatile quantum sensor, being able to measure physical quantities such as magnetic field, electric field, temperature, and pressure. In the present work, we demonstrate multiplexed sensing of magnetic field and temperature using a N-V ensemble in diamond. The dual-frequency-driving technique we employ is based on frequency-division multiplexing, which enables the sensing of both measurables in real time. The pair of $\mathrm{N}$-$V$ resonance frequencies for dual-frequency driving must be selected to avoid coherent population trapping of $\mathrm{N}$-$V$ spin states. With enhanced optical collection efficiency higher than 50% and a type 1b diamond crystal with a natural abundance of ${}^{13}\mathrm{C}$ spins, we achieve sensitivities of about $70\mathrm{pT}/\sqrt{\mathrm{Hz}}$ and $25\mu \mathrm{K}/\sqrt{\mathrm{Hz}}$ simultaneously. We demonstrate a high isolation factor of 34 dB in the $\mathrm{N}$-$V$ thermometry signal against the magnetic field; and we provide a theoretical description for the isolation factor. This work paves the way for extending the application of $\mathrm{N}$-$V$ diamond sensors into more demanding conditions.

The Ising machine is an unconventional computing architecture that can be used to solve NP-hard combinatorial optimization problems more efficiently than traditional von Neumann architectures. Fast, compact oscillator networks that provide programmable connectivities among arbitrary pairs of nodes are highly desirable for the development of practical oscillator-based Ising machines. Here we propose using an electrically coupled array of gigahertz spin Hall nano-oscillators to realize such a network. By developing a general analytical framework that describes injection locking of spin Hall oscillators with large precession angles, we explicitly show the mapping between the coupled oscillators’ properties and the Ising model. We integrate our analytical model into a versatile Verilog-A device that can emulate the coupled dynamics of spin Hall oscillators in circuit simulators. With this abstract model, we analyze the performance of the spin Hall oscillator network at the circuit level using conventional electronic components and considering phase noise and scalability. Our results provide design insights and analysis tools toward the realization of a CMOS-integrated spin Hall oscillator Ising machine operating with a high degree of time, space, and energy efficiency.

We report microwave spectroscopy of co-trapped ${}^9$$\mathrm{Be}$${}^{+}$ and ${}^{40}$$\mathrm{Ca}$${}^{+}$ ions within a compact permanent-magnet-based Penning ion trap. The trap is constructed with a reconfigurable array of $\mathrm{Nd}$-$\mathrm{Fe}$-$\mathrm{B}$ rings providing a 0.654-T magnetic field that is near the 0.6774-T magnetic-field-insensitive hyperfine transition in ${}^9$$\mathrm{Be}$${}^{+}$. Performing Ramsey spectroscopy on this hyperfine transition, we demonstrate nuclear spin coherence with a contrast decay time of >1 s. The ${}^9$$\mathrm{Be}$${}^{+}$ is sympathetically cooled by a Coulomb crystal of ${}^{40}$$\mathrm{Ca}$${}^{+}$, which minimizes ${}^9$$\mathrm{Be}$${}^{+}$ illumination and thus mitigates reactive loss. Introducing a unique high-magnetic-field optical-detection scheme for ${}^{40}$$\mathrm{Ca}$${}^{+}$, we perform spin-state readout without a 729-nm shelving laser. We record a fractional trap magnetic field instability below 20 ppb (<13 nT) at 43 s of averaging time with no magnetic shielding and only passive thermal isolation. We discuss potential applications of this compact reconfigurable Penning trap.

Ising machines (IMs) are physical systems designed to find solutions to combinatorial optimization (CO) problems mapped onto the IM via the coupling strengths between its binary spins. Using its intrinsic dynamics and different annealing schemes, the IM relaxes over time to its lowest-energy state, which is the solution to the CO problem. IMs have been implemented on different platforms, and interacting nonlinear oscillators are particularly promising candidates. Here we demonstrate a pathway towards an oscillator-based IM using arrays of nanoconstriction spin Hall nano-oscillators (SHNOs). We show how SHNOs can be readily phase binarized and how their resulting microwave power corresponds to well-defined global phase states. To distinguish between degenerate states, we use phase-resolved Brillouin-light-scattering microscopy and directly observe the individual phase of each nanoconstriction. Micromagnetic simulations corroborate our experiments and confirm that our proposed IM platform can solve CO problems, showcased by how the phase states of a $2\times 2$ SHNO array are solutions to a modified max-cut problem. Compared with the commercially available D-Wave ${\mathrm{Advantage}}^{\mathrm{TM}}$, our architecture holds significant promise for faster sampling, substantially reduced power consumption, and a dramatically smaller footprint.

By measuring the elastic slow dynamics behavior of various consolidated granular materials and metallic alloys, we show that the evolution of the wave velocity as a function of time can be reproduced by using a continuous relaxation-time spectrum, whose main features can be extracted from the experiments. Here we propose to adopt a Weibull distribution of the relaxation times, that we find to display a maximum, which is related to the material grain size and independent of the conditioning amplitude. These results show that the role of the grain-size distribution is fundamental to quantify slow dynamics effects, as well as to clarify its mesoscopic physical origin. Moreover, they can pave the way for the implementation of advanced characterization methods or nondestructive testing techniques capable of retrieving information on the different spatial scales or defects in the materials under investigation.