We propose an electronic bipartite system consisting of a working substance, in which a refrigeration process is implemented, and of a nonthermal resource region, containing a combination of different thermal baths. In the working substance, heat is extracted from the coldest of two electronic reservoirs (refrigeration) via heat transport and particle transport through a quantum dot. This quantum dot of the working substance is capacitively coupled to the resource region. In such a setup, a finite cooling power can be obtained in the working substance, while the energy exchange with the resource region exactly cancels out, on average. At the same time, information is always exchanged, even on average, due to the capacitive coupling between the two parts of the bipartite system. The proposed system therefore implements an autonomous demon with fully vanishing heat extraction from the resource. Unlike macroscopic machines, nanoscale machines exhibit large fluctuations in performance, so precision becomes an important performance quantifier. We give a comprehensive description of the thermodynamic performance of the proposed autonomous demon in terms of stochastic trajectories and of full counting statistics and demonstrate that the precision of the cooling power strongly depends on the operation principle of the device. More specifically, the interplay of information flow and counterbalancing heat flows dramatically impacts the trade-off between cooling power, efficiency, and precision. We expect this insight to be of relevance for guiding the design of energy-conversion processes exploiting nonthermal resources.

Although hydrogen is almost always present in the growth environments of two-dimensional (2D) transition metal dichalcogenides (TMDs), there is a lack of global structure search of hydrogen atoms on different TMDs as well as the corresponding electronic properties variation and the underlying mechanisms for the different electronic properties. A hydrogen atom in/on monolayer (ML) H-phase $M{X}_2$ ($M$ = Mo, W; $X$ = S, Se, Te) can be an interstitial atom in $M{X}_2$ (${\mathrm{H}}_{\mathrm{Int}}$) or as an adatom on $M{X}_2$ either vertically on (${\mathrm{H}}_{\mathrm{Vert}}$) or tilted above (${\mathrm{H}}_{\mathrm{Tilt}}$) an $X$ atom. In this paper, a global scanning of adsorption structures of hydrogen atom on/in $M{X}_2$'s shows that the most stable structure with $\mathrm{Mo}{\mathrm{S}}_2$ and $\mathrm{W}{\mathrm{S}}_2$ is the ${\mathrm{H}}_{\mathrm{Tilt}}$ structure due to the repulsion between the lone-pair electrons of sulfur atoms and the hydrogen-sulfur bonding electrons, while with $\mathrm{MoS}{\mathrm{e}}_2, \mathrm{WS}{\mathrm{e}}_2$, and $\mathrm{MoT}{\mathrm{e}}_2$, the ${\mathrm{H}}_{\mathrm{Int}}$ structure becomes favored due to the larger lattice constant of these TMDs. Both ${\mathrm{H}}_{\mathrm{Tilt}}$ and ${\mathrm{H}}_{\mathrm{Int}}$ structures introduce fully spin-polarized levels close to the conduction band but have different origins of spin polarization of $M$ atoms, with $M$ atoms gaining and losing electrons in ${\mathrm{H}}_{\mathrm{Tilt}}$ and ${\mathrm{H}}_{\mathrm{Int}}$ structures, respectively. The special case is hydrogen in $\mathrm{MoT}{\mathrm{e}}_2$, which does not exhibit spin polarization due to electron delocalization. Moreover, diffusion barrier analyses for hydrogen adatoms with $\mathrm{Mo}{\mathrm{S}}_2$ indicate that the transition from ${\mathrm{H}}_{\mathrm{Tilt}}$ to ${\mathrm{H}}_{\mathrm{Int}}$ is a relatively slow process at room temperature. In this paper, we broaden the understanding of TMDs with hydrogen atoms and clarify several interaction mechanisms of hydrogen with different $M{X}_2$'s. These insights are of vital importance for the various applications of TMDs such as in (opto)electronics, spintronics, and catalysis.

The practical difficulty in distinguishing the impact of magnetic circular dichroism and the inverse Faraday effect fuels intense debates over which mechanism predominantly drives the process of helicity dependent all-optical switching of magnetization in ferromagnets. Here, we quantitatively measure the efficiency of the switching process in a Pt/Co/Pt multilayer stack using visible- to near-infrared optical pulses. We find that the switching efficiency increases by a factor of 8.6 upon increasing the pumping wavelength from 0.5 to 1.1 μm, becoming 100% efficient at even longer wavelengths up to 2.0 μm. Our experimental results can be successfully explained by the phenomenon of magnetic circular dichroism, making a significant step towards resolving the long-standing controversy over the origin of the all-optical process of magnetization reversal in ferromagnets.

NP-hard computational problems can be efficiently recast as finding the ground state of an effective spin model. However, to date no convenient setup exists that can universally simulate all of them, even for a fixed problem size. Here we present such a setup, the universal homogeneous spin simulator (UHSS) using a series of optical (or polaritonic) resonators arranged in a chain using the geometry based on the one introduced in [Phys. Rev. Appl. 21, 024057 (2024)]. We demonstrate by example how the simulator solves Hamiltonian cycle and traveling salesman problems, and show that it generalizes to any NP-hard problem of arbitrary size. This approach works because it allows arbitrary long-range interactions in the spin model to be mapped on an optical system with only nearest-neighbor physical interactions.

It has been found previously that the presence or absence of topological edge states in the Su-Schrieffer-Heeger (SSH) model has a huge impact on harmonic generation spectra. More specifically, the yield of harmonics for harmonic orders that correspond to photon energies below the band gap is many orders of magnitude different in the trivial and topological phases. It is shown in this work that this effect is still present if electron-electron interaction is taken into account, i.e., if a Hubbard term is added to the SSH Hamiltonian. To that end, finite SSH-Hubbard chains at half filling are considered that are short enough to be accessible to exact diagonalization but already show edge states in the topological phase. We show that the huge difference in the harmonic yield between the trivial and topological phases can be reproduced with few-level models employing only the many-body ground state and a few excited many-body states.

Magnetic ordering of $\mathrm{PbMnTe}{\mathrm{O}}_6$ crystallizing in the chiral noncentrosymmetric $P312$ space group has been experimentally investigated by high-resolution neutron powder diffraction (NPD) and theoretically by high-temperature expansion, density matrix renormalization group, and linear spin-wave theory approaches. Processing of low-temperature NPD data showed that, to describe the rather complex spin ordering in $\mathrm{PbMnTe}{\mathrm{O}}_6$, two incommensurate modulations determined by the propagation vectors ${\mathbf{k}}_1$ and ${\mathbf{k}}_2$ should be used. The observed ground state with ${\mathbf{k}}_1=(\frac{1}{3},\frac{1}{3},0.4077)$ is a noncollinear ${120}^{\circ }$ spin structure, which is helically ordered along the layer stacking direction with a characteristic spiral period of $\sim 13.2\AA$. Additionally, the second incommensurate modulation for magnetic structure with the propagation vector ${\mathbf{k}}_2=(\frac{1}{3}+{\delta }_1,\frac{1}{3}+{\delta }_1,{\delta }_2)$ was also observed. An effective spin model for explaining the observed magnetic characteristics in $\mathrm{PbMnTe}{\mathrm{O}}_6$ was also constructed from numerical calculations. The dominant nearest-neighbor interaction was estimated as $J_1=12\pm 2$ K by fits of magnetic susceptibility, the magnetization curve, and the magnetic part of the specific heat between experimental and numerical results. It is shown that spiral ordering along the layers stacking direction can be attributed to frustrated interlayer couplings or the presence of an interlayer Dzyaloshinskii-Moriya interaction. Also, the incommensurate modulation of the propagation vector in the $ab$ plane can be reproduced by introducing a subtle anisotropic distortion of triangular lattice.

We present a method for detecting the chirality $\chi$ of a ($d_{zx}+i\chi d_{yz}$)-wave superconductor through the analysis of the local density of states (LDOS) at the vortex core. Employing the quasiclassical Eilenberger theory, we examine the LDOS in a semi-infinite superconductor with a quantum vortex penetrating the surface perpendicularly. We show that $\mathrm{sgn}\left[\chi \right]$ changes completely the LDOS at the core-surface intersection. Remarkably, the difference between LDOS for the $\chi =1$ and $\chi =-1$ states becomes more prominent when the surface is dirtier, meaning that one does not need to pay close attention to the surface quality of the sample. The difference between these two states arises from the symmetry of the subdominant Cooper pairs induced at the core-surface intersection: whether the subdominant $s$-wave Cooper pairs are present or not. Due to the unique nature of this phenomenon in the ($d_{zx}+i\chi d_{yz}$)-wave superconductor, one can potentially demonstrate the realization of the ($d_{zx}+i\chi d_{yz}$)-wave superconductivity and determine its chirality by, for instance, through scanning-tunneling spectroscopy experiments.

Van der Waals (vdW) antiferromagnets are exceptional platforms for exploring the spin dynamics of antiferromagnetic materials owing to their weak interlayer exchange coupling. In this study, we examined the antiferromagnetic resonance spectra of anisotropic van der Waals antiferromagnet CrSBr. In addition to the ordinary resonance modes, we observed a dipolar spin wave mode when the microwave field was oriented perpendicular to the in-plane easy axis of CrSBr. Furthermore, our results uncovered a pronounced dependency of various resonant modes on the orientation of the microwave field, which is pivotal for the accurate determination of exchange coupling constants. Numerical simulations have elucidated that this orientation dependence of spin dynamics arises from the magnetostatic effect. This discovery underscores the previously underappreciated significance of dipolar interactions in shaping the dynamical properties of two-dimensional antiferromagnetic materials, thereby enhancing our understanding of the intrinsic dynamic properties of vdW magnets.

Majorana zero modes have been shown to be the simplest quasiparticles exhibiting pure odd-frequency pairing, an effect that has so far been theoretically established in the static regime. In this paper, we investigate the formation of Majorana modes and odd-frequency pairing in $p$-wave spin-polarized superconductors under a time-dependent drive. We first show that the driven system hosts multiple Majorana modes emerging at zero and $\pi$, whose formation can be controlled by an appropriate tuning of the drive frequency and chemical potential, in agreement with previous studies. Then we explore the induced pair correlations and find that odd-frequency spin-polarized $s$-wave pairing is broadly induced, acquiring large values in the presence of Majorana modes. We discover that, while odd-frequency pairing is proportional to $\sim 1/\omega$ in the presence of Majorana zero modes, it is proportional to $\sim 1/(\omega -\pi \hslash /T)$ in the presence of Majorana $\pi$ modes, where $T$ is the periodicity of the drive. Furthermore, we find that the amount of odd-frequency pairing becomes larger when multiple Majorana modes appear but the overall divergent profile as a function of frequency remains. We also show that the divergent odd-frequency pairing is robust against scalar disorder. Notably, we establish a bulk-boundary correspondence between the amount of boundary odd-$\omega$ pairing and the bulk topological invariants in driven chiral systems, which we show to be protected by chiral symmetry and is thus robust against disorder. Our paper thus paves the way for understanding the emergent pair correlations in driven topological superconductors.

We explore a large $N$ generalization of the Kitaev model on the honeycomb lattice with a simple nearest-neighbor interacting Hamiltonian. In particular, we focus on the ${\mathbb{Z}}_4$ case with isotropic couplings, which is characterized by an exact ${\mathbb{Z}}_4$ 1-form symmetry. Guided by symmetry considerations and an analytical study in the single-chain limit, on infinitely long cylinders, we find the model is gapped with an extremely short correlation length. Combined with the ${\mathbb{Z}}_4$ 1-form symmetry, this suggests the model is topologically ordered. To pin down the nature of this phase, we further study the model on both finite and infinitely long strips, where we consistently find a $c=1$ conformal field theory (CFT) description, suggesting the existence of chiral edge modes described by a free boson CFT. Further evidence is found by studying the dimer correlators on infinitely long strips. We find the dimer correlation functions show a power-law decay with the exponent close to 2 on the boundary of the strip, while decaying much faster in the bulk. Combined with the topological entanglement entropy extracted from cylinder geometry, we identify the phase as a chiral spin liquid with a $\mathrm{U}{\left(1\right)}_{-8}$ chiral topological order. A unified perspective for all ${\mathbb{Z}}_N$ type Kitaev models is also discussed.

We report our theoretical results on the emergence of a nonlinear frequency-asymmetric optical response characteristic of chiral crystal systems with neither spatial inversion symmetry nor mirror symmetry. Based on the group theoretical analysis, we show that the chirality-related second-order nonlinear optical response occurs for two different input frequencies when the low-energy model Hamiltonian includes a time-reversal-even pseudoscalar quantity, i.e., the electric toroidal monopole. We demonstrate its emergence by investigating a fundamental microscopic model with the chiral-type antisymmetric spin-orbit interaction on a simple cubic lattice. By analyzing the behavior of nonlinear optical conductivity based on the Kubo formula, we find that the response is largely enhanced when one of the frequencies is set to 0 and the other is set to a resonant frequency. We also discuss the relaxation time dependence of the response.

We propose an arbitrary vector beam (VB) generation scheme in a thin disk-shaped quantum dot (QD) medium considering phonon interaction. The QD biexciton system exhibits the interplay between first- and third-order nonlinear susceptibility between two orthogonal circular polarization transitions. Three QD transitions are coupled with one applied weak and two strong control orbital angular momentum (OAM) carrying fields. Therefore, the applied field experiences absorption, and a new field with the desired OAM is generated via four-wave mixing (FWM). These two orthogonal field superpositions produce VB at the QD medium end. We also demonstrate the polarization rotation of a VB by changing only the relative control field phase. Additionally, we analyze the effect of temperature on the VB generation.

The engineering of electromagnetic waves in rf driving platforms is advancing rapidly, driven by advancements in topological photonics and waveguide technologies. However, challenges remain in achieving precise control over frequency diffraction and mode coupling in practical applications. Our work addresses these challenges by introducing an approach that incorporates a voltage-controlled, time-dependent varactor diode within a microwave spoof plasmonic waveguide. By employing periodic voltage modulations through square, sinusoidal, and sawtooth waveforms, we explore their distinct effects on discrete frequency diffraction, sideband suppression, and directional nondiffraction frequency shifts. Our findings demonstrate the efficacy of extended coupled mode equations, which include higher-order coupling terms, in facilitating harmonic control over electromagnetic spectra. Our research highlights potential applications in communication systems and signal processing technologies, paving the way for enhanced manipulation of electromagnetic waves in future integrated photonic devices.

We report experimental studies of coherent population trapping (CPT) and spin relaxation in a temperature range 4 K–100 mK in a silicon vacancy ($\text{Si}V$) center subject to a transverse magnetic field. The spin linewidth, which is determined by spin dephasing, is extracted from power dependent CPT linewidths. Near and below 1 K, phonon-induced spin dephasing becomes negligible compared with that induced by the spin bath of naturally abundant ${}^{13}\mathrm{C}$ atoms. The temperature dependence of the spin dephasing rates agrees with the theoretical expectation that phonon-induced spin dephasing arises primarily from orbital relaxation induced by first order electron-phonon interactions. A nearly 100-fold increase in spin lifetime is observed when the temperature is lowered from 4 K to slightly below 1 K, indicating that two-phonon spin-flip transitions play an essential role in the spin relaxation of $\text{Si}V$ ground states.

The optical conductivity and the relevant electronic excitation processes are investigated in topologically nontrivial MXenes ${\mathrm{Mo}}_2{\mathrm{HfC}}_2{\mathrm{O}}_2$ and ${\mathrm{W}}_2{\mathrm{HfC}}_2{\mathrm{O}}_2$ utilizing first-principles calculation and effective model analysis. The numerical calculation based on the first-principles band structure reveals the presence of several characteristic features in the spectrum of optical conductivity as a function of photon energy. The drastic dependence on the photon polarization angle is also presented in terms of apparent features. In this paper, an effective model is also generated referring to the crystal symmetries and applied to reveal the microscopic origin of the characteristics. Then, it is shown that some features are strongly related to parity inversion between the conduction and valence bands, the key signature in electronic structures of topologically nontrivial insulators.

The altermagnet is a distinctive magnet phase that has a spin-split energy band but with zero net magnetic moment. In this paper we propose that altermagnets behave the spin splitting Nernst effect: under a longitudinal temperature gradient, the electrons with opposite spins tend to split oppositely in the transverse direction, thus generating a transverse spin current. The spin splitting Nernst effect is understood from the contribution of the longitudinal wave vector to the transverse group velocity. Using the nonequilibrium Green's function method, we calculate the spin-dependent transmission coefficient in the four-terminal altermagnet device. From the spin-dependent transmission coefficient, the nonzero transverse spin current from the longitudinal temperature gradient is obtained, and the spin splitting Nernst effect is verified. We systematically study the parameter dependence of the spin splitting Nernst effect while also performing symmetry analysis. The spin splitting Nernst effect can be easily regulated by Fermi surface energy, temperature, transport direction, and system size. Furthermore, in altermagnets, the $xy$-response and $yx$-response spin splitting Nernst coefficients are equal with $N_{s,xy}=N_{s,yx}$, different from the conventional spin Nernst effect where they are opposite. Meanwhile, the spin splitting Nernst effect requires neither spin-orbit coupling nor net magnetism.

For quantum cryptography and quantum computing, an isolated two-state system is required. A spin-split state in a sulfur vacancy in $\mathrm{Mo}{\mathrm{S}}_2$ may be suitable for this purpose. We show that an electron can be trapped for many seconds in such a vacancy, affecting the current along a nearby path, which exhibits random switching between two current states. The coupling to the vacancy can be varied using a magnetic field, implying that this could eventually be controlled by a gate, to load and then isolate the system.