Altermagnets combine compensated collinear magnetic order with momentum-dependent spin splitting in the electronic band structure. Here, we show that rolling a two-dimensional (2D) d-wave altermagnet into a nanotube converts this momentum dependence into chiral-angle-controlled one-dimensional (1D) spin splitting through dimensional projection. A minimal tight-binding model reveals a characteristic nodal–antinodal dependence on the chiral angle θ, with the central circumferential subband exhibiting a cos(2θ) scaling and the projected spin splitting vanishing for the nodal orientation and reversing sign between orthogonal antinodal orientations. First-principles calculations for V_2O and representative symmetric and Janus systems demonstrate that this nodal–antinodal selection rule persists despite curvature-induced structural asymmetry and magnetic moment imbalance. We further show that the projected electronic structure produces chiral-angle-controlled spin-polarized transport: antinodal nanotubes exhibit spin-polarized transmission, whereas the nodal nanotube remains conducting with identical spin-channel transmission. These results demonstrate how dimensional projection can translate the momentum-space spin splitting of a 2D altermagnet into geometrically controlled electronic and transport properties in nanotubes.

Helical spin textures represent the minimal realization of p-wave magnetism which is characterized by momentum-odd spin polarization. Independently, structurally chiral crystals exhibit momentum-odd orbital polarization arising from broken inversion symmetry. Here, we demonstrate that spin-orbit coupling couples these two independent microscopic chirality degrees of freedom, allowing the orbital polarization of a chiral crystal to generate an additional contribution to the p-wave spin splitting. The resulting spin-orbital state is naturally classified by the relative chirality η=χ_cχ_m, giving rise to two symmetry-distinct p-wave phases corresponding to homochiral and heterochiral configurations which can be directly probed by the longitudinal conductivity. These phases exhibit distinct transport signatures, establishing relative chirality as an experimentally accessible symmetry degree of freedom in chiral magnetic systems.

We present an ab initio investigation of magnetic exchange interactions using the spin-spiral method as implemented in the VASP code, comparing fully self-consistent (SC) total-energy calculations with non-selfconsistent (NSC) band-energy evaluations within the same computational framework. Using representative 3d ferromagnets (Fe, Co, Ni) and Mn-based full Heusler compounds, we compute magnon dispersion relations and extract real-space Heisenberg exchange parameters from the Fourier transformation of spin-spiral energies. Curie temperatures are subsequently estimated within the mean-field and random-phase approximations. The SC approach yields exchange parameters and magnon spectra in excellent agreement with experimental and previous theoretical data, confirming its quantitative reliability across different classes of magnetic systems. In contrast, the NSC approach based on a frozen-potential approximation exhibits systematic quantitative deviations: it overestimates spin-spiral energies and exchange couplings in high-moment systems (bcc Fe and Mn-based Heuslers) while underestimating them in low-moment fcc Ni. The magnitude of these discrepancies increases with the magnetic moment size and can exceed several hundred percent in high-moment compounds. Our results demonstrate that while NSC evaluations are computationally efficient, fully SC spin-spiral calculations are essential for obtaining quantitatively reliable exchange interactions within the projector augmented-wave framework.

Lateral 2D tunnel diodes that reproduce metal-insulator-metal (MIM)-diode-like rectification without using dissimilar contacts are attractive for scalable nanoelectronics. MoS2 can exist in both the semiconducting 1H phase and the metallic 1T phase, enabling phase-engineered homojunctions within a single material. First-principles electronic structure and quantum transport calculations show that phase-engineered 1T/1H/1T-MoS2 homojunctions exhibit pronounced MIM-diode-like rectification originating from interfacial charge transfer at asymmetric 1T/1H interfaces. The charge transfer establishes interface dipole steps that impose a built-in potential drop across the 1H barrier, thereby generating a trapezoidal tunnel barrier at zero bias. In contrast, symmetric 1T/1H interfaces do not form an interface dipoles and show no rectification. To clarify the microscopic origin, a lateral graphene/hexagonal-boron-nitride/graphene junction is analyzed as a minimal MIM diode analogue with a simple interface and well-defined barrier, confirming that interface-induced dipoles, rather than work-function difference, enable the effect. The mechanism operates entirely within a single monolayer material system and does not rely on out-of-plane stacking, highlighting compatibility with phase patterning in 2D semiconductors. These results establish lateral 1T/1H/1TMoS2 as a fully 2D, single-material platform for MIM-diode-like rectification and identify the interface-dipole engineering as a general strategy for designing ultrathin lateral tunnel diodes that can serve as building blocks for high-frequency detectors and energy-harvesting devices.

Broken inversion symmetry at the surfaces of centrosymmetric collinear antiferromagnets lifts combined inversion and time-reversal symmetry (PT) and can, in principle, enable nonrelativistic d-wave spin splitting, termed surface altermagnetism. Combining symmetry analysis with first-principles calculations, we show that surface inversion breaking, while necessary, is not sufficient for this effect. Surface altermagnetism emerges only when no antiunitary symmetry survives at the surface that exchanges the two antiferromagnetically coupled surface sublattices and enforces spin degeneracy. We demonstrate this mechanism explicitly for the centrosymmetric G-type antiferromagnets V_3Al and BaMn_2Sb_2, and contrast it with MnPt, where a sublattice-exchanging symmetry survives at the surface in the form of translation-time-reversal symmetry (tT), thereby preserving spin degeneracy despite broken inversion symmetry. The mechanism is shown to apply across multiple classes of centrosymmetric antiferromagnets and remains robust against spin-orbit coupling, although relativistic spin mixing in heavier-element compounds may reduce the observable spin polarization. These results establish a symmetry-based route toward realizing robust nonrelativistic momentum-dependent spin polarization at antiferromagnetic surfaces and interfaces.

There were some errors in the original publication [...]

Altermagnets are a novel class of magnetic materials that bridge the gap between ferromagnets (FMs) and antiferromagnets (AFMs). A key feature is the non-degeneracy of magnon modes where spin splitting occurs, leading to chirality and direction-dependent magnon dispersions governed by symmetry. We explore this in metallic g-wave altermagnets (TPn, where T= V, Cr; Pn= As, Sb, Bi) using density functional and many-body perturbation theories. We analyze the influence of pnictogen substitution on spin splitting and magnon behavior. We uncover anisotropic magnon band splitting aligned with electronic structure, and wavevector- and chirality-dependent damping due to Stoner excitations. We identify regions in the Brillouin zone where the chiral magnon splitting overcomes the damping. These findings suggest altermagnets are promising for spintronic and magnonic technologies, where direction-dependent magnon lifetimes and nonreciprocal magno transport may enable chiral magnon propagation, while wavevector-selective damping could be harnessed for fast and controllable magnetization switching.

Spin-gapless semiconductors (SGSs) are emerging as a promising class of materials for spintronic applications, offering unique opportunities to realize functionalities beyond conventional electronics. In this work, we propose a concept of multifunctional spintronic field-effect transistors (FETs) using SGSs and/or spin-gapped metals (SGMs) as source and drain electrodes. These devices operate similarly to metal-semiconductor Schottky-barrier FETs, where a potential barrier forms between the SGS (or SGM) electrode and the intrinsic semiconducting channel; however, unlike conventional Schottky-barrier FETs, our proposed devices exploit the distinctive spin-dependent transport properties of SGS and SGM electrodes to achieve sub-60-mV/dec switching, significantly surpassing the 60 mV/dec subthreshold swing (SS) limit in traditional MOSFETs, thereby enabling low-voltage operation. Additionally, the proposed FETs exhibit a nonlocal giant magnetoresistance (GMR) effect, enhancing functionality by enabling nonvolatile memory capabilities. The incorporation of SGMs also introduces a negative differential resistance effect with an ultrahigh peak-to-valley current ratio, further expanding the device's multifunctionality. Two-dimensional (2D) nanomaterials provide a promising platform for realizing these advanced FETs. We perform a comprehensive screening of the computational 2D materials database to identify suitable SGS and SGM candidates. Among the materials identified, several exhibit Curie temperatures significantly above room temperature, ensuring robust ferromagnetic properties for practical applications. For device simulations, we select VS2 as the SGS material and, as a proof of concept, employ a nonequilibrium Green's function method combined with density functional theory to simulate the transfer (ID-VG) and output (ID-VD) characteristics of a vertical VS2/Ga2O2 heterojunction FET. Our calculations predict a remarkably low SS of 20 mV/dec, a high on-off ratio of 108, and a significant nonlocal GMR effect, demonstrating the potential of these devices for low-power, high-performance logic and memory applications.

Cold metals, characterized by their distinctive band structures, hold promise for innovative electronic devices such as tunnel diodes with negative differential resistance (NDR) effect and field-effect transistors (FETs) with sub-60 mV/dec subthreshold swing (SS). In this study, we employ the GW approximation and HSE06 hybrid functional to investigate the correlation effects on the electronic band structure of two-dimensional cold metallic materials, specifically focusing on MX2 and MA2Z4 (M = Nb, Ta; X = S, Se, Te; A = Si, Ge; Z = N, P) compounds in 1H structure. These materials exhibit a unique band structure with an isolated metallic band around the Fermi energy, denoted as Wm, as well as two energy gaps: the internal gap EgI below the Fermi level and the external gap EgE above the Fermi level. These three electronic structure parameters play a decisive role in determining the current-voltage (I-V ) characteristics of tunnel diodes, the nature of the NDR effect, and the transfer characteristics and SS value of FETs. Our calculations reveal that both GW and HSE06 methods yield consistent electronic structure properties for all studied compounds. We observed a consistent increase in both internal and external band gaps, as well as metallic bandwidths, across all pn-type cold metal systems. Notably, the internal band gap EgI exhibits the most substantial enhancement, highlighting the sensitivity of these materials to correlation effects. In contrast, the changes in the metallic bandwidth Wm and external band gap EgE are relatively modest. These findings offer valuable insights for designing and optimizing cold metal-based devices. Materials like NbSi2N4, NbGe2N4, and TaSi2N4 show particular promise for high-performance NDR tunnel diodes and sub-60 mV/dec SS FETs.

Gapped metals, a recently proposed class of materials, possess a band gap slightly above or below the Fermi level, behaving as intrinsic p- or n-type semiconductors without requiring external doping. Inspired by this concept, we propose a novel material class: ”spin gapped metals”. These materials exhibit intrinsic p- or n-type character independently for each spin channel, similar to dilute magnetic semiconductors but without the need for transition metal doping. A key advantage of spin gapped metals lies in the absence of band tails that exist within the band gap of conventional p- and n-type semiconductors. Band tails degrade the performance of devices like tunnel field-effect transistors (causing high subthreshold slopes) and negative differential resistance tunnel diodes (resulting in low peak-to-valley current ratios). Here, we demonstrate the viability of spin gapped metals using first-principles electronic band structure calculations on half-Heusler compounds. Our analysis reveals compounds displaying both gapped metal and spin gapped metal behavior, paving the way for next-generation multifunctional devices in spintronics and nanoelectronics.

We present an ab initio investigation of magnetic exchange interactions using the spin-spiral method implemented in the VASP code, with a comparative analysis of the self-consistent (SC) and magnetic force theorem (MFT) approaches. Using representative 3d ferromagnets (Fe, Co, Ni) and Mn-based full Heusler compounds, we compute magnon dispersion relations directly from spin-spiral total energies and extract real-space Heisenberg exchange parameters via Fourier transformation. Curie temperatures are subsequently estimated within both the mean-field and random-phase approximations. The SC spin-spiral calculations yield exchange parameters and magnon spectra in excellent agreement with previous theoretical data, confirming their quantitative reliability across different classes of magnetic systems. In contrast, the MFT approach exhibits systematic quantitative deviations: it overestimates spin-spiral energies and exchange couplings in high-moment systems such as bcc Fe and the Mn-based Heuslers, while underestimating them in low-moment fcc Ni. The magnitude of these discrepancies increases strongly with magnetic moment size, exceeding several hundred percent in the high-moment compounds. These findings underscore the decisive role of self-consistency in accurately determining magnetic exchange parameters and provide practical guidance for future first-principles studies of spin interactions and excitations using the spin-spiral technique.

Cold metals have recently gained attention as a promising platform for innovative devices, such as tunnel diodes with negative differential resistance (NDR) and field-effect transistors with subthreshold swings below the thermionic limit. Recently discovered two-dimensional (2D) MA 2 Z 4 ( M = Ti, Zr, Hf, Nb, Ta; A = Si, Ge; Z = N, P) compounds exhibit both cold -metallic and semiconducting behavior. In this work, we present a computational study of lateral heterojunction tunnel diodes based on 2D NbSi 2 N 4 and HfSi 2 N 4 compounds. Employing density -functional theory combined with a nonequilibrium Greenfunction method, we investigate the current -voltage ( I - V ) characteristics of lateral tunnel diodes with varying barrier thicknesses in both zigzag and armchair orientations. We find that tunnel diodes in the zigzag orientation exhibit significantly higher peak current densities, while those in the armchair orientation display larger peak -to -valley current ratios (PVCRs) compared to the zigzag orientation. Our findings suggest that MA 2 Z 4 materials are promising candidates for realizing NDR tunnel diodes with ultrahigh PVCR values, which could have potential applications in memory, logic circuits, and other electronic devices.

Experimental observations of large exciton binding energies and non-hydrogenic Rydberg series in 2D semiconducting TMDs, along with deviations in plasmon dispersion in 2D metallic TMDs, suggest the presence of a nonconventional screening of the Coulomb interaction. The experimentally observed Mott insulating state in the charge density wave (CDW) reconstructed lattice of TMDs containing 4d and 5d elements further confirms the presence of strong Coulomb interactions in these systems. In this study, we use first-principles electronic structure calculations and constrained random-phase approximation to calculate the Coulomb interaction parameters (partially screened U and fully screened W) between localized $d$ electrons in 2D TMDs. We specifically explore materials represented by the formula MX2 (M=Nb, Ta, Mo, W, and X=S, Se, Te) and consider three different phases (1H, 1T, and 1T'). Our results show that the short-range interactions are strongly screened in all three phases, whereas the long-range interactions remain significant even in metallic systems. This nonconventional screening provides a compelling explanation for the deviations observed in the usual hydrogenic Rydberg series and conventional plasmon dispersion in 2D semiconducting and metallic TMDs, respectively. Our calculations yield on-site Coulomb interaction parameters U within the ranges of 0.8-2.5 eV, 0.8-1.9 eV, and 0.9-2.4 eV for the 1H, 1T, and 1T' structures, respectively. Furthermore, our findings indicate a substantially high ratio of on-site effective Coulomb interaction to bandwidth (U_eff/W_b >> 1) in CDW TMDs, providing robust evidence for the experimentally observed strongly correlated Mott phase.

All-d metallic Heusler compounds are promising materials for nanoelectronic applications. Such materials combining 3d, 4d, and 5d atoms have not yet been studied. In this respect, we perform ab initio electronic structure calculations and focus on Co2MnZ, Rh2MnZ, and Ru2MnZ compounds, where Z represents transition metal atoms from groups 3B, 4B, 5B, and 6B of the periodic table. Our results demonstrate that most of these compounds exhibit a distinctive region of very low minority-spin state density at the Fermi level when crystallized in the L21 lattice structure. The Co-based compounds follow a Slater–Pauling behavior for their total spin magnetic moments, while the Ru-based compounds consistently deviate from the predicted Slater–Pauling values. Rh-based compounds show similarities to Co-based compounds for lighter Z atoms and to Ru-based compounds for heavier Z atoms. We find that the choice of the Z element within the same periodic table column has only a minor effect on the results, except for the Rh2Mn(Cr, Mo, W) compounds. Our findings suggest that these compounds hold significant promise for applications in spintronics and magnetoelectronics.

The negative difl'erential resistance (NDR) tunnel diodes are promising alternative devices for beyond-CMOS (complementary metal oxide semiconductor) computing because they ofl'er several potential applications when integrated with transistors. We propose a semiconductor-free NDR tunnel diode concept that exhibits an ultrahigh peak-to-valley current ratio (PVCR) value. Our proposed NDR diode consists of two cold metal electrodes separated by a thin insulating tunnel barrier. The NDR efl'ect stems from the unique electronic band structure of the cold metal electrodes; i.e., the width of the isolated metallic bands around the Fermi level as well as the energy gaps separating higher-and lower-lying bands determine the current-voltage (I-V) characteristics and the PVCR value of the tunnel diode. By proper choice of the cold metal electrode materials, either a conventional N-type or Lambda-type NDR efl'ect can be obtained . Two-dimensional (2D) nanomaterials ofl'er a unique platform for the realization of proposed NDR tunnel diodes. To demonstrate the proof of concept, we employ the nonequilibr i u m Green function method combined with density functional theory to calculate the I-V characteristic of the lateral (AlI2/MgI2/AlI2) and vertical (NbS2/h-BN/NbS2) heterojunction tunnel diodes based on 2D cold metals. For the lateral tunnel diode, we obtain a Lambda-type NDR efl'ect with an ultrahigh PVCR value of 1016 at room temperature, w h i l e the vertical tunnel diode exhibits a conventional N-type NDR efl'ect with a smaller PVCR value of about 104. The proposed concept provides a semiconductor-free solution for NDR devices to achieve the desired I-V characteristics with ultrahigh PVCR values for memory and logic applications.

The choice of exchange functional is a critical factor in determining the energy bandgap of semiconductors. Ab initio calculations using different exchange functionals, including the conventional generalized-gradient approximation (GGA) functionals, meta-GGA functionals, and hybrid functionals, show significant differences in the calculated energy bandgap for semiconducting half-Heusler compounds. These compounds, which have 18 valence electrons per unit cell, are of great interest due to their thermoelectric properties, making them suitable for energy conversion applications. In addition, accounting for electronic correlations using the GW method also affects the calculated energy bandgaps compared to standard GGA calculations. The variations in calculated energy bandgaps are specific to each material when using different functionals. Hence, a detailed investigation of the electronic properties of each compound is necessary to determine the most appropriate functional for an accurate description of the electronic properties. Our results indicate that no general rules can be established and a comparison with experimental results is required to determine the most appropriate functional.