We provide a framework for optimizing energy conversion processes in coherent quantum conductors fed by nonthermal resources. Such nonthermal resources, which cannot be characterized by temperatures or electrochemical potentials, occur in small-scale systems that are smaller than their thermalization length. Using scattering theory in combination with a Lagrange multiplier method, we optimize the device's performance based on the efficiency, precision, or a trade-off between the two at a given output current. The transmission properties leading to this optimal performance are identified. We showcase our findings with the example of a refrigerator exploiting experimentally relevant nonthermal resources, which could result from competing environments or from light irradiation. We show that the performance is improved compared to a device exploiting a thermal resource. Our results can serve as guidelines for the design of energy-conversion processes in future nanoelectronic devices.

Recently, applying a uniaxial stress $\sigma$ of only 40 MPa along the $a$ axis to a single domain structure of MnP has been found to modify the fractional coordinates of each ion irreversibly with respect to $\sigma$, leading to the formation of crystal domains rotated by $\pm 123.1^{\circ }$ around the $b$ axis [Kozawa et al., Sci. Rep. 13, 13750 (2023)]. To reveal the process of this unusual domain formation, we measure the time evolution of magnetization due to the crystal domain formation and perform neutron diffraction measurements under $\sigma$. Threshold stress causing domain formation increases as temperature $\left(T\right)$ decreases, and magnetization along the $a$ axis $\left(M_a\right)$ increases over time on the order of hours with a $T$-dependent relaxation time. These results suggest that this domain formation by $\sigma$ is thermally activated. Based on these results, we achieve controlling the crystal domain formation by regulating $\sigma$ and $T$. Moreover, although $M_a$ increases on the order of hours, spatial disorder is not observed during the change in the fractional coordinates of each ion in the neutron diffraction measurement. This work paves the way for a crystal domain engineering method by using $\sigma$, affecting both fundamental material science and the industrial utilization of materials.

We propose that the existence of vortices in ${\mathrm{FeSe}}_{1-x}{\mathrm{Te}}_x$ with and without Majorana zero modes (MZMs) can be explained by a heterogeneous mixture of strong topological and trivial superconducting domains, with only vortices in the former exhibiting MZMs. We identify the spectroscopic signatures of topological and trivial vortices and show that they are necessarily separated by a domain wall harboring Majorana edge modes. We demonstrate that when a vortex is moved from a trivial to a topological domain in real time, a domain wall Majorana edge mode is transferred to the vortex as an MZM.

Temporal interfaces enable dynamic wave control but face a fundamental bottleneck: temporal reflection and refraction amplitudes depend on incident momentum because the projection coefficients between pre and postquench eigenstates—defined by biorthogonal overlaps in the non-Hermitian case—are generically momentum dependent, which distorts broadband wave packets. We develop a projection-operator framework for temporal scattering and show that when a $\mathcal{PT}$-symmetry phase transition occurs across the interface, the final eigenbasis satisfies a phase-transition-induced orthogonality condition, which renders the overlap magnitudes momentum independent and thus yields broadband-stable temporal splitting. Experiments in an electrically reconfigurable acoustic-cavity lattice confirm momentum-robust scattering over a finite bandwidth, and our analysis further reveals nonorthogonality-induced amplification/attenuation and a null-excitation criterion for stable temporal boundary states. These results position geometric projection as a unifying mechanism for non-Hermitian temporal physics and a practical route to versatile time-domain devices.

The absence of odd-order Shapiro steps is a predicted signature of topological superconductors. Experimentally, the missing first-order Shapiro step has been reported in both putative topological superconducting systems and topologically trivial superconductor-semiconductor Josephson junctions. Here, we revisit this phenomenon in topologically trivial Al-InSb nanosheet Josephson junctions under microwave irradiation. The missing first Shapiro step coincides with a sharp voltage jump during superconducting switching, yet reappears when the jump is lowered and softened by increasing microwave power, temperature, or magnetic field. It also reappears at higher microwave frequencies, consistent with qualitative results from an RSJ model incorporating the sharp jump. These observations indicate that the absence of the first Shapiro step, associated with the sharp switching jump, simply results from their location within the measurement blind region. This work identifies a common but overlooked mechanism underlying the missing first Shapiro step, offering new insights into fractional Josephson effect experiments.

We present a $GW$ space-time algorithm for periodic systems in a Gaussian basis including spin-orbit coupling. We employ lattice summation to compute the irreducible density response and the self-energy, while we employ $k$-point sampling for computing the screened Coulomb interaction. Our algorithm enables accurate and computationally efficient quasiparticle band structure calculations for atomically thin transition-metal dichalcogenides. For monolayer ${\mathrm{MoS}}_{\text{2}}, {\mathrm{MoSe}}_{\text{2}}, {\mathrm{WS}}_{\text{2}}$, and ${\mathrm{WSe}}_{\text{2}}$, computed $GW$ band gaps agree on average within 50 meV with plane-wave-based reference calculations. $G_0{W}_0$ band structures are obtained in less than two days on a laptop (Intel i5, 192 GB RAM) or in less than 30 minutes using 1024 cores. Overall, our work provides an efficient and scalable framework for $GW$ calculations on atomically thin materials.

Motivated by recent experiments, we investigate the spin-$\frac{1}{2}$ XXZ model on the triangular lattice with strong Ising anisotropy, combining large-scale numerical simulations and analytical methods to uncover unconventional spin dynamics at $T=0$. First, we compute the dynamical spin structure factor using density matrix renormalization group (DMRG) simulations and find excellent agreement with inelastic neutron scattering data on the layered compound ${\text{K}}_2\text{Co}{\left({\text{SeO}}_3\right)}_2$. The low-energy spectrum reveals a rotonlike minimum at the $M$ point, absent in linear spin-wave theory, accompanied by peak intensity and a broad continuum above it. Near the $\mathrm{\Gamma }$ point, we observe an approximately linear dispersion with vanishing spectral weight. Second, we compare two analytical frameworks that reproduce the observed features. The first is a hard-core boson approach, which includes (i) an effective staggered boson model at zero magnetic field, (ii) perturbation theory applied to the one-third magnetization plateau, and (iii) a self-consistent mean-field Schwinger boson theory (SBT). The second framework is based on a variational supersolid quantum dimer model (QDM) ansatz, combined with a single-mode approximation. The SBT captures the broad continuum, the $M$-point minimum, and linear dispersion at $\mathrm{\Gamma }$, whereas the QDM reproduces the roton minimum and linear dispersion at finite momentum near $\mathrm{\Gamma }$. Remarkably, both the QDM wave function and the DMRG ground state exhibit nearly identical structure factors with pronounced transverse photonlike excitations. Together, our comprehensive theoretical and numerical analysis elucidates the microscopic origin of supersolid excitations in the XXZ triangular-lattice model and their proximity to a spin-liquid phase observed experimentally.

Multiterminal superconducting junctions have revitalized the investigation of the Josephson effect. One of the most interesting aspects of these hybrid systems is the occurrence of multi-Cooper pair tunneling processes that have no analog in two-terminal devices. Such correlated tunneling events are also intimately connected to the Andreev bound states (ABSs) supported by these structures. Josephson junctions with four superconducting terminals have attracted special attention because they are predicted to support ABSs with nontrivial topological properties. Here, we present a theoretical study of sextets, which are correlated tunneling processes involving three Cooper pairs and four different superconducting terminals. We investigate how sextets can be identified from the analysis of the current-phase relation, show how sextets are connected to the hybridization of ABSs, and discuss their existence in recent experiments on four-terminal devices realized in hybrid Al/InAs heterostructures.

We propose helically twisted homotrilayer transition metal dichalcogenides as a platform for realizing correlated topological phases of matter with higher and tunable Chern numbers. We show that a clear separation of scales emerges for small twist angles, allowing us to derive a low-energy continuum model that captures the physics within moiré-scale domains. We identify regimes of twist angle and displacement field for which the highest-lying hole band is isolated from other bands and is topological with $K$-valley Chern number $C=-2$. We demonstrate that varying the displacement field can induce a transition from $C=-2$ to $-1$, as well as from a topologically trivial band to a $C=-1$ band. We derive an effective tight-binding description for a high-symmetry stacking domain which is valid for a wide range of twist angles, and we show that the $C=-2$ band can remain stable at filling fraction $\nu =-1$ in the presence of interactions in Hartree-Fock calculations.

The ground state of the Kitaev quantum spin liquid on a honeycomb lattice is an intriguing many-body state characterized by its topological order and massive entanglement. One of the significant issues is to prepare and manipulate the ground state as well as excited states in a quantum simulator. Here, we provide a protocol to manipulate the Kitaev quantum spin liquid via digital quantum simulation. A series of unitary gates for the protocol is explicitly constructed, showing its circuit depth is an order of $O\left(N\right)$ with the number of qubits, $N$. We demonstrate the efficiency of our protocol on the IBM Heron r2 processor for $N=8$ and 12. We further validate our theoretical framework through numerical simulations, confirming high-fidelity quantum state control for system sizes up to $N=450$, and discuss the possible implications of these results.

A major question in the field of femtosecond laser-induced demagnetization is whereto the angular momentum lost by the electrons is transferred. Recent ultrafast electron diffraction measurements [Tauchert et al., Nature (London) 602, 73 (2022)] suggest that this angular momentum is transferred to the rotational motion of atoms on a sub-picosecond timescale, but a theory confirmation of this proposition has yet to be given. Here, we investigate the coupled electron-nuclear dynamics during ultrafast demagnetization of $\mathrm{L}{1}_0$ FePt, using Ehrenfest nuclear dynamics simulations combined with the time-dependent density functional theory (TDDFT) framework. We demonstrate that atomic rotations appear, i.e., the generation of phonons carrying finite angular momentum following ultrafast demagnetization. We further show that both ultrafast demagnetization and the generation of phonons with angular momentum arise from symmetry constraints imposed by the spin-orbit coupling, thus providing insight in spin-phonon interaction at ultrafast timescales.

Flat bands correspond to the spatial localization of a quantum particle moving in a field with discrete or continuous translational invariance. The canonical example is the flat Landau levels in a homogeneous magnetic field. Several significant problems—including flat bands in moiré structures—are related to the problem of a particle moving in an inhomogeneous magnetic field with zero total flux. We demonstrate that while perfectly flat bands in such cases are impossible, the introduction of a “non-Abelian component”—a spin field with zero total curvature—can lead to perfect localization. Several exactly solvable models are constructed: (i) a half-space up/down field with a sharp one-dimensional boundary; (ii) an alternating up/down field periodic in one direction on a cylinder; and (iii) a doubly periodic alternating field on a torus. The exact solution on the torus is expressed in terms of elliptic functions. It is shown that flat bands are only possible for certain magic values of the field corresponding to a quantized flux through an individual tile. These exact solutions clarify the simple structure underlying flat bands in moiré materials and provide a springboard for constructing a novel class of fractional quantum Hall states.

Excitons are charge neutral and thus weakly responsive to conventional gating, making magnetic fields a practical external control. Within an effective-mass framework that incorporates momentum-dependent sheet screening $\epsilon \left(q\right)$ and field-induced center-of-mass/relative-motion couplings that is benchmarked against an analytic, constant-${\epsilon }_{\mathrm{eff}}$ hydrogenic estimator, we compute dispersions and binding energies of intra- and interlayer excitons. Intralayer spectra are highly sensitive to screening yet display only weak quadratic diamagnetic shifts with negligible effective-mass renormalization. By contrast, interlayer spectra, which are less sensitive to modeling details, exhibit pronounced linear-in-$B$ energy shifts, enhanced binding, and substantial effective-mass increases. The finite spacer $D$ suppresses short-range screening, which smooths the interaction core and extends its long-range tail, thereby amplifying magnetic confinement. Consequently, low-lying interlayer excited states develop tunable roton-like minima for $B\lesssim 30$ T, implying finite-$P$ brightening. The pronounced interlayer-intralayer contrast establishes magnetic fields as a selective knob for exciton-specific control and tunable optoelectronic functionality.

Van der Waals materials with the surface photovoltaic effect (SPV) enable photodetection over a tunable wavelength range with low power consumption, which benefits layer-dependent band gaps. However, sensitive SPV in the infrared region, especially in a quasisteady illumination condition, is still elusive in layered semiconductors. Here, using angle-resolved photoemission spectroscopy, we report a sensitive SPV in quasiequilibrium in ${\text{NbSi}}_{0.5}{\text{Te}}_2$, with photoresponsivity up to $3\times {10}^6\mathrm{V}/\left(\mathrm{W}{\mathrm{cm}}^{-2}\right)$ at low-intensity low-temperature conditions (LILT). The sensitive SPV is further confirmed by observing the Dember effect, where the photogenerated carrier density is high enough and diffusion currents suppress SPV. Temperature-dependent measurements indicate that intrinsic carriers freezing at low temperature leads to the ultrahigh photoresponse, while a small amount of photon-generated carriers in quasiequilibrium dominate the system. Our work not only provides a promising layered semiconductor for infrared optoelectronic devices with strong infrared SPV at LILT, which has application potential in fields such as quantum information and deep-space exploration, but also paves a way to enhance the light-matter interaction effect by freezing bulk carriers.

High magnetic field and low temperature transport measurements are carried out in order to gain insight into the properties of the charge carriers of ${\text{PtSe}}_2$. In particular, the Shubnikov–de Haas oscillations arising at applied magnetic field strengths $\gtrsim 4.5\text{T}$ are found to occur exclusively in plane. An analysis of the oscillations via the Lifshitz-Kosevich formalism allows determining the charge carrier's cyclotron mass, quantum transport time, Berry phase, Fermi surface cross section, and Dingle temperature. The oscillations emerge at a layer thickness of $\approx 18\text{nm}$ and decrease in frequency for thinner ${\text{PtSe}}_2$ flakes. Further, weak antilocalization (WAL) is observed despite the presence of magnetic moments from Pt vacancies, which typically inhibit such effects. An explanation is provided on how WAL and the Kondo effect can be observed within the same material.

We report on a spectroscopic, enantiomer-dependent study of the linear (LPGE) and circular photogalvanic effect (CPGE) in the structurally chiral multifold fermion material PdGa using THz emission. Both bulk and surface responses were measured in right- and left-handed enantiomers over the $0.48–1.1\mathrm{eV}$ incoming photon energy range. The effect of structural handedness was to invert the polarity of the emitted THz transients, yielding spectra roughly equal in magnitude but opposite in sign for all responses measured, with positive (negative) signals generally corresponding to right- (left-) handed samples. All spectra showed evidence of an intraband component and a previously reported interband resonance originating from transitions between the $\mathrm{\Gamma }$ and $\mathrm{R}$ points of the Brillouin zone. The spectra deriving from the helicoidally dispersing surface states closely matched that of the bulk, whereas the direction of the CPGE surface response rotated in opposite directions as a function of driving photon energy for the two enantiomers, revealing their complementary, helicoidally dispersing nature.

Two-dimensional van der Waals semiconductors feature a variety of stable Coulomb-bound electron-hole complexes, which determine the optical response of the materials and serve as primary carriers of energy and spin-valley encoded information. Importantly, transitions between different excitonic states are found in the terahertz spectral range, motivating the use of strong THz radiation for their manipulation on ultrafast timescales. In this work, we apply this technique to efficiently transfer populations within the manifold of excitonic complexes in monolayer ${\mathrm{WSe}}_2$, combining pulsed optical injection with a perturbation induced by a THz free-electron laser source. Monitoring time-resolved photoluminescence, we show conversion between different Coulomb-bound species across biexcitonic and excitonic regimes. Depending on the lattice temperature, these processes involve both short-lived bright and long-lived dark states. Combining experimental findings with theory support, we outline possible dissociation and formation pathways of charged excitons and biexcitons induced by the THz radiation. Finally, we demonstrate access to the formation dynamics of charged biexcitons under controlled conditions of thermalized populations of their constituents, avoiding complications of excess energies that otherwise occur after nonresonant optical excitation.

Weyl metals, characterized by topologically protected band crossings, are promising for investigating Berry-curvature-mediated transport and developing spintronic devices. Through first-principles calculations, we predict that hexagonal ${\mathrm{Fe}}_2\mathrm{MnSn}$ with the $\mathrm{D}{0}_{19}$-II type structure exhibits magnetic Weyl metal behavior. Two symmetry-protected Weyl nodes situated 24.6 meV and 6.5 meV above the Fermi level, whose cooperative Berry curvature generates a large intrinsic anomalous Hall conductivity (AHC) of 881.6 ${\mathrm{\Omega }}^{-1}$ ${\mathrm{cm}}^{-1}$. Experimentally, polycrystalline $\mathrm{D}{0}_{19}$ type ${\mathrm{Fe}}_2\mathrm{MnSn}$ shows a substantial enhancement in AHC from 162  ${\mathrm{\Omega }}^{-1}$ ${\mathrm{cm}}^{-1}$ at 350 K to 303 ${\mathrm{\Omega }}^{-1}$ ${\mathrm{cm}}^{-1}$ at 10 K with the intrinsic component of 281.5 ${\mathrm{\Omega }}^{-1}$ ${\mathrm{cm}}^{-1}$ extracted through Tian-Ye-Jin (TYJ) scaling, constituting 92.7% of the total AHC and directly confirming Berry curvature as the dominant mechanism. The discrepancy between theoretical and experimental intrinsic AHC values is attributed to the coexistence of the competing $\mathrm{D}{0}_{19}$-I type phase induced by Mn disorder, which disrupts the ideal Berry curvature configuration. This disorder-mediated phase competition offers a new perspective for designing magnetic topological metals. Our work suggests ${\mathrm{Fe}}_2\mathrm{MnSn}$ as a promising candidate for exploring Berry-phase-driven transport in magnetic topological systems with multiple atomic occupations.

Inspired by observations of generalized Wigner crystal states in moiré materials, we systematically investigate charge orderings of electrons on a square lattice with long-range interactions $V\left(r\right)=U{r}^{-\alpha }$. Using simulated annealing Monte Carlo simulations in the classical limit without kinetic energy, we obtain the generalized Wigner crystal states for almost all rational fillings $\nu =\frac{p}{q}$ ($q\le 20$) and different $\alpha$. For large $\alpha$, we find the ground states can be obtained by the so-called Farey construction method by compositing different fundamental stripes with $\frac{1}{n}$-filling (except $\frac{1}{7}, \frac{1}{13}, \frac{1}{17}, \frac{1}{19}, ...$), largely consistent with the greedy lattice algorithm for fast-decay interactions. For small $\alpha$, we further identify the $\frac{3}{8}$-filling as a new fundamental state such that the states for $\frac{1}{3}<\nu <\frac{3}{8}$ can be constructed by the Farey construction method. For $\frac{3}{8}<\nu <\frac{1}{2}$, a dual lattice subtraction applies: removing $(1-2\nu )$-filling states from the half-filled checkerboard state. Further incorporating kinetic energy via self-consistent mean-field calculations shows that most of these Wigner crystal states are stable against quantum fluctuations until melting. Our work establishes a complete classical-to-quantum framework to understand the generalized Wigner crystals on the square lattice, which can be generalized to other underlying lattices.

Materials with broken in-plane mirror symmetry can generate spin current with out-of-plane spin polarization (Z spins), enabling field-free spin-orbit torque (SOT) switching. The second harmonic Hall (SHH) technique is widely used to quantify this spin component electrically. However, these materials often exhibit an antisymmetric planar Hall effect (APHE), which is typically neglected in conventional SHH analysis models. Using rutile $\mathrm{Ru}{\mathrm{O}}_2$ (101) as a model system, we demonstrate that APHE introduces a non-negligible artifact in the SHH signal, leading to a torque extraction error of up to 20% in the dampinglike z component. This deviation, captured by an analytical model, scales with the APHE-to-PHE ratio and the amplitude of in-plane spin components (X and Y spins). Our results underscore the importance of accounting for APHE when evaluating out-of-plane SOT components via SHH, particularly in low-symmetry systems.