We theoretically investigate a tunable and suppressible non-Hermitian skin effect (NHSE) in lattice systems governed by non-Abelian SU(2) gauge fields, Zeeman field, and spin-dependent gain and loss. We show that non-Abelian hopping alone can generate a parity-dependent discrepancy between open- and periodic-boundary spectra, even in the absence of the NHSE. A uniform Zeeman field or spin-dependent gain and loss activates a direction-selective NHSEs, whereas their coexistence gives rise to a bipolar NHSE. Strikingly, we find that a spatially nonuniform Zeeman field generically suppresses the NHSE and drives boundary-accumulated skin modes back into the bulk, irrespective of the modulation profile. This suppression originates from the competition between skin-induced boundary accumulation and gradient-induced Wannier–Stark-like localization. Our results reveal versatile and experimentally accessible mechanisms for engineering, tuning, and suppressing non-Hermitian boundary localization, and provide a promising route toward exploring non-Abelian non-Hermitian physics in platforms such as electrical circuits.

Whether an antiferromagnet can host direction-robust spin-polarized transport without a conventional spin-selective band gap remains a central challenge in antiferromagnetic spintronics. Here, we establish a gapless, direction-robust spin-filtering mechanism in a compensated two-dimensional altermagnetic Weyl semimetal that requires neither a spin-selective band gap nor a large velocity contrast between spin projections. Using Janus monolayer ${\mathrm{Ta}}_2\mathrm{TeSeO}$ as a realistic platform, we combine symmetry analysis with first-principles calculations, full-Brillouin-zone Wannier interpolation, and semiclassical transport. Rotating the Néel vector removes a unitary-mirror constraint and shifts one Weyl-cone pair away from its parent high-symmetry line. For an in-plane Néel vector, the residual $C_{2z}\mathcal{T}$ symmetry forbids the independent ${\sigma }_y$ mass that would open a local gap, allowing the reconstructed cones to shift in momentum while remaining gapless. Breaking unitary $C_{2z}$ simultaneously lifts the energy equivalence of the remaining mirror-pinned Weyl cones. The resulting coexistence of a metallic spin-projected manifold and a low-density-of-states (DOS) Weyl-derived manifold produces a predominantly DOS-driven conductance imbalance. At charge neutrality and 20 K, the longitudinal conductivity polarization for $\mathbf{n}\parallel x$ remains positive for every in-plane current direction and ranges from $76.4\%$ to $82.0\%$. The symmetry-related in-plane Néel orientations provide two distinct spin-filtering states. This Néel-vector-driven symmetry mechanism provides a general route to direction-robust gapless spin filtering in compensated altermagnets.

The exploitation of crystal-lattice symmetries to engineer angular momentum transfer between structured light and magnons marks a novel frontier for optomagnonic research. In Brillouin light scattering, when focused light propagates parallel to an external magnetic field and interacts with ferromagnetic uniform magnons, only optical vortex scattering is expected to be permitted. Due to the combined effects of magneto-optical coupling and optical spin-orbit interaction, the transfer of magnon spin angular momentum to photon orbital angular momentum allows for this distinctive scattering phenomenon. Here, we experimentally demonstrate that, for a specific ferromagnetic crystal orientation, Gaussian beam scattering coexists with the optical vortex scattering, contrary to conventional expectations based on angular momentum conservation between magnons and photons. We show that the crystal lattice, via the rotational umklapp process, provides the missing angular momentum required for the Gaussian beam scattering. Furthermore, our theoretical model predicts a focus-dependent efficiency crossover between Gaussian beam and optical vortex scattering as the numerical aperture increases.

We present a simplified formalism for predicting infrared optical constants from first-principles calculations by considering resonant interaction between infrared photons and the crystal lattice. Addressing limitations of the widely used four-parameter semiquantum Lorentz model, the proposed approach bridges the gap between the harmonic three-parameter model and the rigorous many-body Green's-function-based approaches. By incorporating essential anharmonic effects including four-phonon scattering and phonon renormalization, the model provides an efficient and accurate alternative while maintaining low computational cost. The frequency-dependent refractive indices of MgO and rutile ${\mathrm{TiO}}_2$ are computed and compared with experimental data, demonstrating good quantitative agreement. The framework offers a practical approach for predicting optical properties of materials across a wide range of materials.

Ab initio calculations and angle-resolved photoemission experiments demonstrate that the bulk and surface electronic structure of Weyl semimetal candidate ${\mathrm{MoTe}}_2$ changes significantly by tuning the chemical potential by less than 0.4 eV. Calculations indicate that several Lifshitz transitions can occur among multiple electron and hole Fermi pockets of differing orbital character. Experiments show that 18% Nb-Mo substitution reduces the occupation of bulk and (001) surface bands, effectively producing a quasirigid band shift of $\approx 0.2\mathrm{eV}$. Orbital character and dimensionality of the bulk bands is examined by soft-x-ray angle-resolved photoemission with control of the excitation light polarization. Deposition of alkali-metal atoms on the surface produces electron binding energy shifts consistent with increased band filling. The results indicate that multiple regimes of electronic properties can be easily accessed in this versatile, layered material.

We investigate the dynamics of the Hubbard–Holstein model after a sudden switch-on of the electron–phonon interaction within nonequilibrium dynamical mean-field theory (DMFT). Using the self-consistent Migdal approximation for the electron–phonon coupling together with self-consistent second-order perturbation theory for the electron–electron interaction, we show that the relaxation dynamics exhibits a crossover between electron-dominated and phonon-dominated regimes, extending to finite Hubbard interaction the scenario previously identified in the Holstein model. To investigate the emergence of a self-consistent thermalization of the electron–phonon system, we analyze the DMFT dynamics by enforcing the self-consistency after each global time-evolution, rather than at every time step. This allows us to follow the build-up of a self-consistent thermal bath. In the plane of real time and DMFT iteration number, thermalization is marked by a sharp propagating front. This front appears in electronic observables already for weak quenches within the simulated time window, whereas the phononic sector exhibits a visible front only at sufficiently strong coupling. Thus, at weak coupling the local dispersionless phonons show a delayed onset of front formation, while near and beyond the crossover the front develops on comparable timescales in both the electronic and phononic sectors. Whenever both fronts are resolved, they propagate with the same velocity, showing that thermalization spreads coherently through the coupled electron–phonon system.

A recent study showed that, in spin-1 chiral fermion systems composed of two linearly dispersing bands and one trivial band, impurity scattering produces an asymmetric cusp in the spectral conductivity $\sigma \left(\epsilon \right)$. We demonstrate that this asymmetric cusp markedly enhances the electronic thermoelectric response. Using linear-response theory within the self-consistent Born approximation, we find low-temperature enhancements in both the Seebeck coefficient and the electronic figure of merit. Increasing the curvature of the trivial band further strengthens this cusp-induced enhancement, even though the corresponding density of states becomes smoother. To clarify this mechanism, we introduce a minimal cusp model for $\sigma \left(\epsilon \right)$ and show that the enhancement is most pronounced when the cusp is sharp and strongly asymmetric and when the spectral conductivity at the cusp energy is small.

We consider possible encodings of a qubit within the space spanned by the $p$-orbital manifold of an anisotropic silicon quantum dot, including the effects of alloy disorder. We find two types of avoided crossing in this manifold: one due to alloy disorder and one due to an out-of-plane magnetic field. Defining a qubit at such an avoided crossing offers prolonged coherence time and complete single-qubit control using baseband electrical control of the dot anisotropy. Using a phenomenological two-level fluctuator dipole noise model, we estimate an average dephasing time of $T_2^{*}\approx 10\mu \text{s}$ and a quality factor of $Q\sim {10}^4$. At the avoided crossing due to magnetic field, the qubit is a minor adaptation of the previously proposed $pO$ qubit, spanned by the ground and excited $p$ orbitals in the ground valley. However, at the avoided crossing due to alloy disorder, the qubit is qualitatively different, spanning the ground $p$ orbital in the excited valley and the excited $p$ orbital in the ground valley, and we dub it the $pOv$ qubit. While the charge noise robustness is similar for $pO$ and $pOv$ qubits, we find that $pOv$ qubits have desirable interaction properties. Namely, in contrast to the always-on transverse Coulomb coupling of $pO$ qubits, we show that transverse coupling between $pOv$ qubits is negligible, leaving only a longitudinal two-qubit interaction that can be tuned by modulating the orientation of adjacent elliptical dots.

The magnetic toroidal monopole, a time-reversal-odd scalar, has attracted attention through its characteristic responses, such as electric-field-induced nonreciprocal directional dichroism observed in ${\mathrm{Co}}_2{\mathrm{SiO}}_4$. However, its evaluation in crystalline solids remains unresolved, as it cannot be defined within conventional multipole expansions or thermodynamic formulations. In this paper, we propose a theoretical framework to evaluate the magnetic toroidal monopole in periodic crystals based on the response of relativistic electric polarization to a magnetic field gradient. By incorporating the magnetic-field-gradient correction to the relativistic polarization, we derive an explicit expression for the magnetic toroidal monopole beyond symmetry arguments. The resulting expression is formulated in terms of geometric quantities such as Berry curvatures and orbital magnetic moment defined in an extended parameter space spanning momentum, magnetic field, and electric field. We further perform model calculations for an antiferromagnetic system hosting a magnetic toroidal monopole and confirm that the proposed quantity is finite. These results provide a practical route to characterize magnetic toroidal monopoles in crystalline solids and clarify their quantum geometric nature.

Solid-state high-harmonic generation (s-HHG) is intrinsically sensitive to the phase of interband wave packets, yet in conventional midinfrared (MIR)-driven schemes, carrier injection, acceleration, and emission occur within a single optical cycle. Here we introduce a resonant attosecond injection scheme in which a weak, finite-bandwidth attosecond pulse prepares a phase-defined interband coherence over a finite distribution of crystal momenta at a controlled time within the MIR waveform. We show that resonant attosecond injection reshapes the harmonic spectrum in the weak-field regime, enhancing the first plateau and activating a higher-energy multiband channel. The injected coherence also produces momentum-resolved population fringes and corresponding structures in the $k$-resolved s-HHG current source. For the weak MIR field considered here, the dominant Fourier branches remain close to the field-free interband energy separations, while weaker parallel branches arise from MIR-induced modulation. These results demonstrate that resonant attosecond injection provides a controlled way to prepare and probe band-gap-sensitive multiband dynamics in s-HHG.

The outcomes of projective measurements on a quantum many-body system in a chosen basis are inherently probabilistic. The Shannon entropy of this probability distribution (the “diagonal entropy”) often reveals universal features, such as the existence of a quantum phase transition. A brute-force tomographic approach to estimating this entropy scales exponentially with the system size. Here, we explore using the Lempel-Ziv lossless image compression algorithm as an efficient, scalable alternative, readily implementable in a quantum gas microscope or programmable quantum devices. We test this approach on several examples: one-dimensional quantum Ising model, and two-dimensional states that display conventional symmetry breaking due to quantum fluctuations, or strong-to-weak symmetry-breaking due to local decoherence. We also employ the diagonal mixed state to put constraints on the phase boundaries of our models. In all examples, the compression method accurately recovers the entropy density while requiring at most polynomially many images. We also analyze the singular part of the diagonal entropy density using renormalization group on a replicated action. In the $1+1\mathrm{D}$ quantum Ising model, we find that it scales as $\left|t\right|{log}_2\left|t\right|$, where $t$ is the deviation from the critical point, while in a $2+1\mathrm{D}$ state with amplitudes proportional to the Boltzmann weight of the two-dimensional Ising model, it follows a $t^2{log}_2\left|t\right|$ scaling.

The geometric analogs of Bloch oscillations studied so far have relied on Berry curvature. We show that a weakly inhomogeneous electric field adds a distinct quantum-metric term to semiclassical wavepacket dynamics, generating an oscillatory real-space contribution even when the Berry curvature vanishes. The associated transport response comprises an intrinsic and a scattering-time-dependent part. In the regime studied, the latter can dominate and approach finite saturation at high field when the relative field inhomogeneity is held fixed. A tilted Dirac model illustrates the mechanism. Realistic platforms will likely require synthetically engineered superlattices, with a finite quantum metric and an adequate band gap.

Two-dimensional (2D) Janus WSSe has attracted considerable attention for optoelectronic device applications due to its unique structural asymmetry and exceptional electronic and optical properties. However, intrinsic defects inevitably introduced during experimental growth can significantly modulate its material properties and device performance. In this work, first-principles calculations were performed to systematically investigate the impacts of vacancies, interstitials, and antisite defects on the geometric structure and electronic properties of a Janus WSSe monolayer. Furthermore, the roles of sulfur vacancies (${\mathrm{V}}_{\mathrm{S}}$) and selenium vacancies (${\mathrm{V}}_{\mathrm{Se}}$) in modulating the electronic and optical properties of the 2D ZnO/WSSe van der Waals heterostructure were explored. In the isolated two-dimensional 2H-WSSe monolayer, although ${\mathrm{V}}_{\mathrm{S}}$ and ${\mathrm{V}}_{\mathrm{Se}}$ defects are identified as deep-level defects, the calculated carrier capture coefficients and capture cross sections reveal that they do not act as effective nonradiative recombination centers. Regarding the ZnO/WSSe heterostructure, the introduction of ${\mathrm{V}}_{\mathrm{S}}$ and ${\mathrm{V}}_{\mathrm{Se}}$ narrows the band gap, enhances low-energy light absorption, and modulates interfacial charge transfer without disrupting the heterostructure stability. This work provides a solid theoretical foundation for defect engineering in WSSe-based materials and the design of high-performance ZnO/WSSe heterostructure optoelectronic devices.

Hard-x-ray C $1s$ photoemission from monolayer graphene probes a regime in which nuclear recoil and intrinsic electronic asymmetry contribute on comparable energy scales to the observed spectral line shape. Here we combine experiment and modeling over the photon-energy range $0.8–8\mathrm{keV}$ to resolve this interplay quantitatively. A graphene-specific implementation of the Fujikawa-Takata cumulant formalism, based on an anisotropic vibrational density of states constrained by first-principles phonon calculations, captures the expected recoil scaling with photon energy and emission geometry but fails to reproduce the pronounced asymmetric tails of the measured spectra. To overcome this limitation, we introduce an explicit electronic convolution model in which a photon-energy-independent reference response, dominated by the electronic line shape and extracted from the low-recoil $0.8\mathrm{keV}$ data through a recoil-inclusive fit, is convolved with a phonon recoil kernel carrying the full dependence on photon energy and emission angle. This approach reproduces both the measured line-shape evolution and the observed peak shifts across the explored energy range without refitting the spectra at higher photon energies. The results show that recoil in graphene cannot be described by a baseline treatment in which the phonon recoil kernel is combined only with symmetric lifetime broadening, but must be treated together with the intrinsic many-body electronic response of the C $1s$ line.

Materials containing unreactive elements are attracting increasing attention for their unexpected characteristics such as pressure-driven superconductivity. However, the known helium-incorporating superconductors (HISCs) are constrained by extreme compression, and thus achieving high-temperature superconductivity in helium-based compounds under moderate pressure is a key challenge. Here, we conducted a comprehensive study of the ${\mathrm{Na}}_2\mathrm{He}$-B system, leveraging a first-principles-assisted configuration prediction method, and presented two previously unknown stable phases, encompassing $P{6}_3/mmc {\mathrm{Na}}_2{\mathrm{HeB}}_2$ and Immm ${\mathrm{Na}}_2{\mathrm{HeB}}_7$. In particular, ${\mathrm{Na}}_2{\mathrm{HeB}}_2$ manifests a prototype hexagonal layered structure featuring interlayer sodium-helium co-insertion and a honeycomb-shaped covalent boron grid. Remarkably, calculations of electron–phonon coupling (EPC) uncover that, among HISCs, ${\mathrm{Na}}_2{\mathrm{HeB}}_2$ holds the highest superconducting transition temperature ($T_c$) at a low pressure of 20 GPa, reaching 38 K, which is primarily attributed to the coupling between in-plane B $2p$ electronic states at the Fermi level and Na- and He-governed low-frequency phonon modes. In contrast, the strategy of enhancing the EPC strength through electronic doping ($-0.04e$/cell) enabled ${\mathrm{Na}}_2{\mathrm{HeB}}_2$ to exhibit high-$T_c$ behavior at 42 K. These findings provide important implications for the discovery of additional superconductors composed of inert elements.

We study a finite Floquet chain in which a uniform nearest-neighbor hopping coexists with a periodically rotating, SU(2)-dictated spin-assisted hopping profile. The resulting coupling is spatially inhomogeneous—weakest at the chain boundaries and strongest in the bulk—and produces a frequency-dependent Floquet-Sambe bottleneck. In the closed system, the mean inverse participation ratio of the Floquet eigenstates exhibits a striking nonmonotonic dependence on the driving frequency $\omega$: the states remain extended at both low and high frequencies, but become maximally localized at an intermediate frequency. We demonstrate that this localization maximum occurs at ${\omega }_{\mathrm{peak}}\sim {\mu }_{-s}=\sqrt{2s}$, a scale controlled by the first boundary bottleneck. To connect these spectral properties to measurable transport, we construct an open-system Floquet-Sambe Green's-function inverse participation ratio from the spatial density of the injected scattering state. This open-system diagnostic recovers the same nonmonotonic localization trend as its closed-system counterpart, with the peak shifted to higher frequencies by the static bandwidth and the lead self-energy. These findings establish the driven synthetic spin chain as a directly realizable, frequency-tunable platform for coherent information storage and retrieval, rooted in the interplay of Floquet-Sambe virtual channels, boundary-controlled localization, and frequency-selective transport in emerging multilevel superconducting circuit architectures.

Motivated by intriguing properties of geometrically frustrated systems, in the present work, another member of the triple perovskite family, ${\mathrm{Ca}}_3{\mathrm{CoSb}}_2{\mathrm{O}}_9$, with a ${\text{Co}}^{2+}$ triangular motif, has been synthesized, and its structural, magnetic, and thermal transport properties were studied in detail. The triple perovskite crystallizes in the monoclinic phase with a $P{2}_1/c1$ symmetry. A cusp in the dc magnetic susceptibility, accompanied by a $\lambda$-like feature in the ac susceptibility and specific heat, indicates a transition to an antiferromagnetic state below $T_N\sim 3.8\text{K}$. Magnetic susceptibility measurements confirm the existence of the ${\mathrm{Co}}^{2+}$ moments with $S=1/2$ spin state, a large Curie-Weiss temperature of ${\theta }_{\text{CW}}=-76.70\text{K}$, and a significant degree of magnetic frustration ($f=|{\theta }_{\text{CW}}/T_N|\approx 20$). The temperature-dependent ac magnetization reveal a prominent peak at $T_N$ that exhibits characteristic magnitude suppression and a subtle shift (3.8 to 4.1 K) with increasing frequency from 0.21 to 631 Hz. Additionally, a nondispersive kink at $T\sim 7.0\text{K}$ was observed, indicative of persistent short-range magnetic correlation above $T_N$. Moreover, the absence of a spin-flop transition or a $M_s/3$ magnetization plateau in field-dependent studies up to $16\text{T}$, suggests that the structural distortions in ${\text{Ca}}_3{\text{CoSb}}_2{\text{O}}_9$ stabilize a noncollinear ${120}^{\circ }$ spin structure against field-induced quantum phase transitions.

In this work we study the stabilization of the orthorhombic phases in small $\mathrm{H}{\mathrm{f}}_{0.5}\mathrm{Z}{\mathrm{r}}_{0.5}{\mathrm{O}}_2$ nanoparticles (average size ∼7 nm) annealed under different oxygen partial pressures. Concentration of the oxygen vacancies, which is determined by annealing conditions, was estimated from the electron paramagnetic resonance spectra and x-ray photoelectron spectroscopy. The fraction of the orthorhombic phases, that is determined by the x-ray diffraction and nuclear magnetic resonance, depends on the concentration of oxygen vacancies. Phenomenological calculations based on Landau-Ginzburg-Devonshire theory considering trilinear coupling between nonpolar, antipolar, and polar phonon modes, indicate that chemical strain induced by oxygen vacancies can stabilize the orthorhombic o-III phase with the ferroelectric long-range ordering in small $\mathrm{H}{\mathrm{f}}_{0.5}\mathrm{Z}{\mathrm{r}}_{0.5}{\mathrm{O}}_2$ nanoparticles. The theory confirms the stability of ferroelectric polarization in the vacancy-enriched $\mathrm{H}{\mathrm{f}}_{0.5}\mathrm{Z}{\mathrm{r}}_{0.5}{\mathrm{O}}_2$ nanoparticles. The increase in the intensity of the dielectric permittivity maximum observed near 350–380 K in a PVDF matrix embedded with $\mathrm{H}{\mathrm{f}}_{0.5}\mathrm{Z}{\mathrm{r}}_{0.5}{\mathrm{O}}_2$ nanoparticles annealed in the $\mathrm{CO}+{\mathrm{CO}}_2$ atmosphere is clearly associated with an increase in oxygen vacancy concentration. The vacancies lead to defect-induced elastic dipole formation and an increase in ionic conductivity, which decreases the depolarization field and may induce the ferroelectric-like phase transition in the vacancy-enriched $\mathrm{H}{\mathrm{f}}_{0.5}\mathrm{Z}{\mathrm{r}}_{0.5}{\mathrm{O}}_2$ nanoparticles. Due to the interfacial effects, the negative capacitance states may be realized in weakly screened and spatially isolated $\mathrm{H}{\mathrm{f}}_{0.5}\mathrm{Z}{\mathrm{r}}_{0.5}{\mathrm{O}}_2$ nanoparticles embedded in the PVDF matrix. The present approach based on oxygen-vacancy-induced elastic and screening effects may provide a route for engineering ferroelectric-like states in other nanoscale ferroic oxides.

We study the entanglement entropy (EE) of the one-dimensional transverse-field quantum Ising chain (QIC) and the XX (isotropic XY) chain under various boundary conditions (BCs). We numerically calculate the EE for a system of size $L$ and a subsystem of size $l$ at the critical point. Five BCs are considered: periodic, free-free, fixed-fixed $(+,+)$ and $(+,-)$, and fixed-free. We also employ exact solutions and conformal field theory (CFT) predictions, which yield results highly consistent with our numerical data. In our numerical approach, we apply the Jordan-Wigner transformation to map the spin chain to a system of spinless fermions and compute their correlation functions, from which the EE is subsequently derived. The EE is calculated for 19 different subsystem fractions, fixing $l/L$ at values of $1/20,2/20,\cdots ,19/20$ for each case. All numerical computations are performed using quadruple precision to ensure accuracy. We observe even-odd oscillations in the EE of the XX chain under free-free, fixed-fixed $(+,+)$, fixed-fixed $(+,-)$, and fixed-free BCs. We then fit the calculated EE using finite-size scaling expansions in terms of $L^{-n}$ and $L^{-n}lnL$ for each corresponding case. The fitted parameters for the leading $lnL$ term and the constant term are found to coincide with CFT predictions to very high accuracy. For periodic BCs, the parameter for the $L^{-2}$ correction term as a function of $l/L$ is consistent with the conjecture by Calabrese et al. Furthermore, we conjecture the form of the $L^{-4}$ correction and analytically calculate its leading term using random matrix theory. For the XX chain with free-free BCs, we verify the relationship between the coefficient of the $L^{-1}$ term and $l/L$ extracted from the formula conjectured by M. Fagotti et al., [J. Stat. Mech. (2011) P01017] and we obtain conjectured closed-form expressions for the coefficients of the $L^{-2}, L^{-3}$, and $L^{-4}$ terms, which are supported by high-precision numerical fitting and partial analytical arguments. Utilizing the relationship between free-free and $(+,+)$ BCs, we determine the form of the coefficients for the $L^{-2}$ and $L^{-4}$ terms in the XX chain with $(+,+)$ BCs. Consequently, we obtain first four parts of the alternating term in the EE for the XX chain under free-free and $(+,+)$ BCs. For the EE of the first excited state in the QIC with free-free BCs, we conjecture the exact form of the $L^{-1}$ correction term, which coincides perfectly with our numerical results. For the QIC with fixed-free BCs, we calculate the perturbation expansion around $l/L=0$ and 1 for the correction term stemming from the Ising CFT. Finally, inspired by the resonating valence bond (RVB) picture introduced by N. Laflorencie et al., [Phys. Rev. Lett. 96, 100603 (2006)] we discuss the EE oscillations in the XX chain under the four aforementioned BCs qualitatively.

Altermagnets combine compensated collinear magnetic order with momentum-dependent spin splitting. A key question is how such spin splitting can arise from electronic interactions in a spin-degenerate Dirac semimetal and what spin-resolved transport signatures it produces. We address this issue using a staggered $\pi$-flux Hubbard model. Within a homogeneous, collinear, two-sublattice self-consistent Hartree-Fock ansatz, we show that the Hubbard interaction drives the Dirac semimetal into an altermagnetic phase with an even-parity, $d_{xy}$-wave spin splitting protected by mirror-spin symmetry $\left[C_2\right|\left|M_y\right]$. The interaction-generated order gaps the Dirac cones at half filling and gives rise to an altermagnetic metal upon doping. In the spin-orbit-free limit, we compute the second-order electric and thermoelectric responses and identify a clear channel dependence. The nonlinear charge Hall and Nernst responses are already permitted in the spin-degenerate semimetal and are further reshaped by the interaction-driven Fermi-surface reconstruction, making them nonunique indicators of altermagnetic order. By contrast, the nonlinear spin Hall and spin Nernst responses vanish identically in the identical-spin-block parent and become finite in the pure-spin $yxx$ channel of the ordered state, accompanied by a characteristic sign reversal across half filling. The mirror-spin symmetry produces an orthogonal pure-charge $xyy$ channel and opposite domain parities. These results establish a symmetry-resolved two-channel nonlinear transport diagnostic based on the parent-state null and directional charge-spin separation.