We consider strongly correlated quantum circuits where a dc drive is added on top of an initial out-of-equilibrium (OE) stationary state. Within a perturbative approach, we derive unifying OE fluctuation relations for high-frequency current noise, shown to be completely determined by zero-frequency noise and dc current. We apply them to the fractional quantum Hall effect at arbitrary incompressible filling factors, driven by OE sources, without knowledge of the underlying model. We show that such OE relations provide robust methods for an unambiguous determination of the fractional charge or of key interaction parameters entering in the exploration of anyonic statistics within an anyon collider.

We report a current scaling study of a quantum phase transition between a quantum anomalous Hall insulator and a trivial insulator on the surface of a heterostructure film of magnetic topological insulators. The transition was observed by tilting the magnetization while measuring the Hall conductivity ${\sigma }_{xy}$. The transition curves of ${\sigma }_{xy}$ taken under various excitation currents cross each other at a single point, exemplifying a quantum critical behavior of the transition. The slopes of the transition curves follow a power-law dependence of the excitation current, giving a scaling exponent. Combining with the result of the previous temperature scaling study, critical exponents $\nu$ for the localization length and $p$ for the coherence length are separately evaluated as $\nu =2.8\pm 0.3$ and $p=3.3\pm 0.3$.

Topological charges are the winding numbers of polarization vectors around the vortex centers of far-field radiation. In this work, the topological charge of photonic crystal modes is theoretically analyzed using an envelope function approach. A group of modes is discovered with unique polarization properties dictated by their nontrivial envelope functions. Experimentally, lasing operation on such a mode is demonstrated in an electrically pumped midinfrared photonic crystal surface-emitting laser with high slope efficiency. The topological charge is directly observed from the polarization properties of single-mode laser emission. Furthermore, it is shown that envelope functions may bring a new possibility to control the polarization profiles of photonic crystal lasers.

We theoretically investigate the curvature of the confinement potential in quantum point contacts (QPCs) under a background disorder potential with Gaussian correlation functions using a noninteracting one-dimensional tight-binding model. The curvature of the potential is evaluated from the gate voltage dependence of the conductance, and the statistical average of the fitting curvature is calculated. The fitting curvature is insensitive to the original QPC confinement curvature when the characteristic length of the QPC potential is larger than the characteristic length of the disorder. In addition, the fitting curvature can be enhanced as the QPC curvature is decreased. Accidental double barrier potential formation on the top of the QPC induces enhancement of the fitting curvature. Finite-temperature effects under the disorder potential are also discussed. Similar results hold in a two-dimensional QPC tight-binding model.

We consider a lateral heterojunction where the left and right leads are made of monolayer graphene and the middle region is made of a gapped tilted Dirac material (borophene or quinoid graphene) illuminated with off-resonant circularly polarized radiation. The tilt parameter $v_t$ makes the band gap indirect and smaller in magnitude as compared to Dirac materials without tilt. Exposure to radiation makes the band gaps of the central region valley dependent, which show their signatures as valley-polarized charge and thermal currents, thereby causing a valley Seebeck effect. We study the variation of the valley-polarized electrical conductance, thermal conductance, thermopower, and figure of merit of this junction with chemical potential $\mu$ and a tunable gap parameter $\eta$. For nonzero $\eta$, all the valley-polarized quantities are peaked at certain values of chemical potential and then vanish asymptotically. An increase in the gap parameter enhances the valley thermopower and valley figure of merit, whereas the valley conductances (electrical and thermal) show nonmonotonic behavior with $\eta$. We also compare the valley-polarized quantities with their corresponding charge counterparts (effective contribution from both valleys). The charge thermopower and the charge figure of merit behave nonmonotonically with $\eta$ and the charge conductances (electrical and thermal) depict a decreasing trend with $\eta$. Furthermore, the tilt parameter reduces the effective transmission of carriers through the junction, thereby diminishing all the charge- and valley-polarized quantities. As the gaps in the dispersion can be adjusted by varying the intensity of light as well as the Semenoff mass, the tunability of this junction with regard to its thermoelectric properties may be experimentally realizable.

Coherent diffraction imaging is a form of microscopy that permits high resolution imaging of atomic displacements from equilibrium where the use of conventional optics is not feasible. Approaches to date for the recovery of atomic displacements from equilibrium and subsequently strain information occur after phase reconstruction of the complex real-space images from at least three independent Bragg diffraction amplitude measurements. While this is a more accessible and effective approach to recover strain information, there is potential for erroneous results if the recovered phase information is not carefully treated. Here we present a strategy for imaging strain with coherent x rays that eliminates the technical challenges that exist in conventional approaches by constructing the strain field concurrently during the phase retrieval process of recovering phase information.

We theoretically study the effect of Dzyaloshinskii-Moriya interaction on the focusing of a spin-wave lens that is constructed by a circular interface between two magnetic films. We analytically derive the generalized Snell's law in the curved geometry and the position of the focal point which exhibits a peculiar off-axial focusing behavior. We uncover a strong dependence of the focal point on both the material parameters and the frequency of incident spin waves. Full micromagnetic simulations compare well with theoretical predictions. Our findings would be helpful to manipulate spin waves in chiral magnets and to design functional magnonic devices.

We report anisotropic magnetocaloric effect and magnetic critical behavior in the van der Waals crystal ${\mathrm{CrCl}}_3$. The maximum magnetic entropy change $-\mathrm{\Delta }{S}_M^{\max }\sim 14.6$ J ${\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$ and the relative cooling power $\text{RCP}\sim 340.3$ J ${\mathrm{kg}}^{-1}$ near $T_c$ with a magnetic field change of 5 T are much larger when compared to ${\mathrm{CrI}}_3$ or ${\mathrm{CrBr}}_3$. The rescaled $\mathrm{\Delta }{S}_M(T,H)$ curves collapse onto a universal curve, confirming the second-order ferromagnetic transition. Further critical behavior analysis around $T_c$ presents a set of critical exponents $\beta =0.28\left(1\right)$ with $T_c=19.4\left(2\right)\mathrm{K}$, $\gamma =0.89\left(1\right)$ with $T_c=18.95\left(8\right)\mathrm{K}$, and $\delta =4.6\left(1\right)$ at $T_c=19\mathrm{K}$, which are close to those of the theoretical tricritical mean-field model.

We report anisotropic magnetocaloric effect and critical behavior in a quasi-one-dimensional ferromagnetic ${\mathrm{CrSbSe}}_3$ single crystal. The maximum magnetic entropy change $-\mathrm{\Delta }{S}_M^{\max }$ is 2.16 J ${\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$ for the easy $a$ axis (2.03 J ${\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$ for the hard $b$ axis) and the relative cooling power RCP is 163.1 J ${\mathrm{kg}}^{-1}$ for the easy $a$ axis (142.1 J ${\mathrm{kg}}^{-1}$ for the hard $b$ axis) near $T_c$ with a magnetic field change of 50 kOe. The magnetocrystalline anisotropy constant $K_u$ is estimated to be 148.5 kJ ${\mathrm{m}}^{-3}$ at 10 K, decreasing to 39.4 kJ ${\mathrm{m}}^{-3}$ at 70 K. The rescaled $\mathrm{\Delta }{S}_M(T,H)$ curves along all three axes collapse onto a universal curve, respectively, confirming the second-order ferromagnetic transition. Further critical behavior analysis around $T_c\sim 70\mathrm{K}$ gives that the critical exponents $\beta =0.26\left(1\right)$, $\gamma =1.32\left(2\right)$, and $\delta =6.17\left(9\right)$ for $H\parallel a$, while $\beta =0.28\left(2\right)$, $\gamma =1.02\left(1\right)$, and $\delta =4.14\left(16\right)$ for $H\parallel b$. The determined critical exponents suggest that the anisotropic magnetic coupling in ${\mathrm{CrSbSe}}_3$ is strongly dependent on orientations of the applied magnetic field.

The interaction between superconductivity and ferromagnetism in thin film superconductor/ferromagnet heterostructures is usually reflected by a change in superconductivity of the S layer set by the magnetic state of the F layers. Here we report the converse effect: transformation of the magnetocrystalline anisotropy of a single Fe(001) layer, and thus its preferred magnetization orientation, driven by the superconductivity of an underlying V layer through a spin-orbit coupled MgO interface. We attribute this to an additional contribution to the free energy of the ferromagnet arising from the controlled generation of triplet Cooper pairs, which depends on the relative angle between the exchange field of the ferromagnet and the spin-orbit field. This is fundamentally different from the commonly observed magnetic domain modification by Meissner screening or domain wall-vortex interaction, and it offers the ability to fundamentally tune magnetic anisotropies using superconductivity—a key step in designing future cryogenic magnetic memories.

Spin waves are discussed as promising information carrier for beyond complementary metal-oxide semiconductor data processing. One major challenge is guiding and steering of spin waves in a uniform film. Here, we explore the use of diffractive optics for these tasks by nanoscale real-space imaging using x-ray microscopy and careful analysis with micromagnetic simulations. We discuss the properties of the focused caustic beams that are generated by a Fresnel-type zone plate and demonstrate control and steering of the focal spot. Thus, we present a steerable and intense nanometer-sized spin-wave source. Potentially, this could be used to selectively illuminate magnonic devices like nano-oscillators.

Magnetization dynamics in a cylindrical Permalloy nanowire under simultaneously applied electric current and field is investigated by means of micromagnetic simulations. The reversal process starts with the creation of open vortex structures with different rotation senses at the nanowire ends. Our results conclude that the current alone enlarges or reduces the size of these vortex structures according to the rotational sense of the associated Oersted field. Large current intensity creates a vortex structure which covers the whole nanowire surface. At the same time the magnetization in the nanowire core remains the same, i.e., no complete magnetization reversal is possible in the absence of external field. The simultaneous action of the current and field allows for the complete control of the vortex structures in terms of setting the polarity and vorticity. The state diagram for the minimum field and current required for the vorticity and axial magnetization switching is presented. This control is essential for future information technologies based on three-dimensional vertical structures, and the presented state diagram will become very useful for future experiments on current-induced domain wall dynamics in cylindrical magnetic nanowires.

$\beta \text{−}{\mathrm{TeVO}}_4$ is a frustrated spin-1/2 zig-zag chain system, where spin-density-wave (SDW), vector-chiral (VC) and an exotic dynamic spin-stripe phase compete at low temperatures. Here we use torque magnetometry to study the anisotropy of these phases in magnetic fields of up to 5 T. Our results show that the magnetic-field-induced spin reorientation occurs in the SDW and in the spin-stripe phases for ${\mu }_{0}H\ge 2$ T. The observed spin reorientation is another element of the anisotropic phase diagram for the field directions in the $ac$ and $a^{*}b$ crystallographic planes. The presented results should help establishing the model of anisotropic magnetic interactions, which are responsible for the formation of complex magnetic phases in $\beta \text{−}{\mathrm{TeVO}}_4$ and similar low-dimensional quantum spin systems.

We have experimentally and theoretically investigated the electron spin transport and spin distribution at room temperature in a Si two-dimensional inversion channel of back-gate-type spin metal-oxide-semiconductor field-effect transistors (spin MOSFETs). The magnetoresistance ratio of the spin MOSFET with a channel length of 0.4 μm was increased by a factor of 6 from that in our previous paper [Phys. Rev. B 99, 165301 (2019)] by lowering the parasitic resistances at the source/drain junctions with highly phosphorus-doped $n^{+}\text{−}\mathrm{Si}$ regions and by increasing the lateral electric field in the channel along the electron transport, called “spin drift.” Clear Hanle signals with several oscillation peaks were observed for the spin MOSFET with a channel length of 10 μm under the lateral electric field, indicating that the effective spin diffusion length is dramatically enhanced by the spin drift. By taking into account the $n^{+}\text{−}\mathrm{Si}$ regions and the spin drift in the channel, one-dimensional analytic functions were derived for analyzing the effect of the spin drift on the spin transport through the channel and these functions were found to explain almost all the experimental results. From the calculated spin accumulation and spin current distribution, it was revealed that almost all the spins are unflipped during the spin-drift-assisted transport through the 0.4-μm-long inversion channel, but the most part of the injected spins from the source electrode are relaxed in the $n^{+}\text{−}\mathrm{Si}$ regions of both the source and drain junctions. This means that the spin drift is useful and precise design of the device structure is essential to obtain a higher magnetoresistance ratio. Furthermore, we showed that the effective spin resistances that are introduced in this study are very helpful to understand how to improve the magnetoresistance ratio of spin MOSFETs for practical use by optimizing the source/drain junctions and channel structure. The most remarkable finding is that the design guideline for spin MOSFETs utilizing electron spin transport is different from that for the ordinary MOSFETs utilizing electron charge transport.

Plasmon-plasmon interactions are key in controlling light at the nanoscale and in the development of high-performance plasmonic devices. Sophisticated design and efficient dynamic control of such devices requires a precise description of both spectral responses and ultrafast temporal dynamics in plasmon-plasmon coupling systems. Here, a microscopic model based on the Heisenberg-Langevin formalism is developed for generic plasmon-plasmon interacting systems. The validity of the model was experimentally supported by precisely reproducing the output spectra of interacting plasmons in a one-dimensional plasmonic crystal. We discussed the inheritance from an initial phase to the Rabi phase, which is accompanied by the vacuum fluctuations dephasing the incoherent coupling channel. We further derived the generalized Rabi frequency between two coupled plasmonic modes. We demonstrate that the interplay between the Rabi phase and the coupling-induced incoherent damping process modulates the ultrafast dynamics of the polariton modes, resulting in distinctly different spectral responses including the degeneracy and reversing in the polariton branches. Our model can be readily extended to any other bosonic coupling systems such as interacting nanoparticles and photonic/plasmonic cavities, thus holding great promise and potential applications in nanocircuits and cavity QED.

Diagrammatic perturbation theory is a powerful tool for the investigation of interacting many-body systems, the self-energy operator $\mathrm{\Sigma }$ encoding all the variety of scattering processes. In the simplest scenario of correlated electrons described by the $GW$ approximation for the electron self-energy, a particle transfers a part of its energy to neutral excitations. Higher-order (in screened Coulomb interaction $W$) self-energy diagrams lead to improved electron spectral functions (SFs) by taking more complicated scattering channels into account and by adding corrections to lower order self-energy terms. However, they also may lead to unphysical negative spectral functions. The resolution of this difficulty has been demonstrated in our previous works. The main idea is to represent the self-energy operator in a Fermi golden rule form which leads to a manifestly positive definite SF and allows for a very efficient numerical algorithm. So far, the method has only been applied to the three-dimensional electron gas, which is a paradigmatic system, but a rather simple one. Here we systematically extend the method to two dimensions including realistic systems such as monolayer and bilayer graphene. We focus on one of the most important vertex function effects involving the exchange of two particles in the final state. We demonstrate that it should be evaluated with the proper screening and discuss its influence on the quasiparticle properties.

Nanotechnology has not only provided us the possibility of developing quantum machines but also noncanonical power sources able to drive them. Here we focus on studying the performance of quantum machines driven by arbitrary combinations of equilibrium reservoirs and a form of engineered reservoirs consisting of noninteracting particles but whose distribution functions are nonthermal. We provide the expressions for calculating the maximum efficiency of those machines without needing any knowledge of how the nonequilibrium reservoirs were actually made. The formulas require the calculation of a quantity that we term entropy current, which we also derive. We illustrate our methodology through a solvable toy model where heat “spontaneously” flows against the temperature gradient.