The quantum geometric tensor unifies the Berry curvature (its imaginary part) and the quantum metric (its real part), yet Raman studies of chiral phonons have so far accessed only the former. We perform circularly polarized Raman spectroscopy on the quantum magnet K_{2}Co(SeO_{3})_{2}, where the field-odd chiral splitting Δω and the field-even center shift δω_{c} collapse onto a single curve across temperature and magnetic field, revealing a common microscopic origin for both observables. Since Δω reflects the Berry curvature, the concomitant even component δω_{c}, arising from the same microscopic origin, captures the field-induced change of the quantum metric-the diagonal Born-Oppenheimer correction. Across two resolvable E_{g} modes, the unified data are well captured by a simple empirical relation, δω_{c}=γ(Δω)^{2}. These results establish Raman spectroscopy as a direct probe of the quantum metric and an operational decomposition of quantum geometry within a single measurement.

Due to its unique electronic properties, boron tends to form various multicenter bonds, enabling the construction of diverse two-dimensional borophene structures through modulation of the number and distribution of boron vacancies within a triangular lattice. In this study, we investigate a large-hole borophene model on heated Ni(111) substrates via molecular beam epitaxy under ultra-high-vacuum conditions. The complex atomic arrangement and electronic structures were investigated by scanning tunneling microscopy, low-energy electron diffraction, angle-resolved photoemission spectroscopy, and density functional theory calculations. Our results suggest that boron atoms are initially incorporated into the Ni surface and preferentially nucleated at step edges. The favorable geometric matching between the proposed structure and the Ni step-edge configuration contributes to the stabilization of the structure and facilitates its formation under the present growth conditions. These findings broaden the structural diversity of 2D borophene sheets and offer insights into the controlled synthesis of complex borophene architectures on metallic substrates.

Honeycomb bismuthene structures on Ag(111) were investigated using low-energy electron diffraction (LEED) and density functional theory. LEED I(V) analysis revealed that 0.5 monolayer (ML) of Bi forms an ultraflat honeycomb lattice with negligible buckling at '120 K, which transforms into other structures upon warming to room temperature. A similar flat bismuthene structure also forms in Mn/Bi/Ag(111), which remains stable even at room temperature. Mn deposition on (p x 3)-rect Bi/Ag(111) induces Bi surface segregation, as confirmed by x-ray photoelectron spectroscopy, resulting in a p(2 x 2) honeycomb bismuthene. The detailed structural investigation provides fundamental basis for characterizing the two-dimensional topological properties of bismuthene grown on Ag(111).

Abstract Altermagnet-based heterojunctions have demonstrated magnetoresistive effects in experiments, however, a predictive theoretical model for non-ferromagnetic structures has remained elusive. In this work, we develop a tunneling-based spin-transport theory that explicitly incorporates the transverse-wavevector (k ∥)-dependent spin polarization of an altermagnet’s transport channels, enabling the prediction of giant tunneling magnetoresistance (TMR). Based on the theory, we predict that the altermagnet KV2Se2O can reach the extreme limit of magnetoresistance. By performing first-principles transport calculations, we verify that magnetic tunnel junctions using the metallic KV2Se2O as the electrodes and few-layer MgO as the spacer exhibit zero-bias magnetoresistance larger than 7.57 × 107%, which is robust against the bias and thickness of the spacer. Our research provides a quantitative design principle for next-generation spin-electronic devices and establishes KV2Se2O/MgO/KV2Se2O as a leading candidate material system for room-temperature ultra-high-density non-volatile memory.

Half metals, which are amenable to perfect spin filtering, can be utilized for high-magnetoresistive devices. However, available half metals are very limited. Here, we demonstrate that materials with intrinsic spin-valley-mismatched (SVM) states can be used to block charge transport, resembling half metals and leading to giant tunneling magnetoresistance. As an example, by using first-principles transport calculations, we show that ferromagnetic 1T-VSe2, 1T-VS2, and 2H-VS2 are such spin-valley-mismatched metals, and giant pessimistic magnetoresistance of more than 99% can be realized in spin-valve van der Waals (vdW) junctions using these metals as electrodes. Another example is the altermagnet KV2Se2O. We show that magnetic tunnel junctions using the metallic KV2Se2O as the electrodes and few-layer MgO as the spacer exhibit zero-bias magnetoresistance larger than 99%, which is robust against the bias and thickness of the spacer. Owing to the intrinsic mismatch of spin states, the central-layer materials for the vdW junctions can be arbitrary nonmagnetic materials, in principle. Our research provides clear physical insights into the mechanism for high magnetoresistance and opens new avenues for the search and design of high-magnetoresistance devices.

The advancement of antiferromagnetic spintronics depends on quantum materials with target symmetry-dictated functionalities, however, their systematic discovery is hindered by the immense configurational complexity of the available material space. Here, we introduce a symmetry-guided, AI-accelerated framework incorporating graph neural networks with high generalization ability to overcome this bottleneck. Based on fully intercalated transition metal dichalcogenides (iTMDs) and using only 200 relaxed partially intercalated structures for transfer learning, our model effectively explores more than 100,000 partially intercalated configurations and identifies 35 altermagnetic and 20 Tτ-antiferromagnetic ground-state candidates. Interestingly, we show that tuning spin-group symmetry through intercalant arrangement or magnetic ordering realizes a series of d-wave altermagnets in these hexagonal systems with high spin-charge conversion efficiency. Furthermore, we reveal plentiful Tτ-antiferromagnets enabling efficient Néel spin-orbit torque switching, driven by giant T-odd spin Edelstein susceptibilities. These results establish iTMDs as a versatile platform for spintronics and provide a general strategy for the accelerated design of symmetry-enforced quantum materials.

Anderson localization, arising from wave interference in disordered systems, profoundly hinders energy transport, yet its impact on radiative heat flux in many-body thermophotonic systems remains unclear. Here, we demonstrate a three-order-of-magnitude suppression of radiative heat transfer, resulting in ultralow radiative heat transfer, in a one-dimensional quasiperiodic chain of plasmonic nanoparticles. This suppression in radiative heat transfer is directly correlated with mode localization, as revealed by the mode decomposition of the transmission coefficient, which serves as evidence of Anderson localization. Furthermore, we elucidate the dependence of radiative thermal conductance reduction on interparticle spacing and material damping rates, uncovering the interplay between intrinsic Ohmic losses, mode localization, and long-range many-body interactions. Our findings advance the understanding of wave-mediated thermal transport in disordered photonic structures and suggest strategies for tailoring nanoscale heat management via engineered disorder. Manipulating thermal transport in nanoscale systems is challenging, particularly in disordered media. Here, the authors show that disorder can cause a significant suppression of radiative heat transfer in nanoparticle chains, a phenomenon identified as a direct signature of Anderson localization.

Due to its unique electronic properties, boron tends to form various multicenter bonds, enabling the construction of diverse two-dimensional borophene structures through modulation of the number and distribution of boron vacancies within a triangular lattice. In this study, we investigate a large-hole borophene model on heated Ni(111) substrates via molecular beam epitaxy under ultra-high-vacuum conditions. The complex atomic arrangement and electronic structures were investigated by scanning tunneling microscopy, low-energy electron diffraction, angle-resolved photoemission spectroscopy, and density functional theory calculations. Our results suggest that boron atoms are initially incorporated into the Ni surface and preferentially nucleated at step edges. The favorable geometric matching between the proposed structure and the Ni step-edge configuration contributes to the stabilization of the structure and facilitates its formation under the present growth conditions. These findings broaden the structural diversity of 2D borophene sheets and offer insights into the controlled synthesis of complex borophene architectures on metallic substrates.

Half metals, which are amenable to perfect spin filtering, can be utilized for high-magnetoresistive devices. However, available half metals are very limited. Here, we demonstrate that materials with intrinsic spin-valley-mismatched (SVM) states can be used to block charge transport, resembling half metals and leading to giant tunneling magnetoresistance. As an example, by using first-principles transport calculations, we show that ferromagnetic 1T-VSe_{2}, 1T-VS_{2}, and 2H-VS_{2} are such spin-valley-mismatched metals, and giant magnetoresistance of more than 99% can be realized in spin-valve van der Waals (vdW) junctions using these metals as electrodes. Owing to the intrinsic mismatch of spin states, the central-layer materials for the vdW junctions can be arbitrary nonmagnetic materials, in principle. Our research provides clear physical insights into the mechanism for high magnetoresistance and opens new avenues for the search and design of high-magnetoresistance devices.

Mobility edges, which demarcate the boundary between extended and localized states, are fundamental to understanding the physics of localization in condensed matter systems. Systems exhibiting exact mobility edges are rare, and the localization properties of phonons have received limited prior investigation. In this work, we reveal analytical mobility edges in one-dimensional quasiperiodic-modulated spring-mass chains. The mobility edges are exactly solved and numerically validated through the eigenfrequency spectra, inverse/normalized participation ratios, and lattice wave dynamics. Our research demonstrates the Anderson localization transition in phonon systems, paving the way for experimental observations of phonon localization.

Van der Waals antiferromagnetic semiconductors are promising platforms for energy-efficient two-dimensional spintronics. However, their intrinsic spin degeneracy and the difficulty of achieving electrical spin control pose major challenges for practical device implementation. Here, we present a distinct spintronic platform based on an antiferromagnetic semiconductor CrSBr, in which carrier doping induced by gate-controlled intercalation drives a reversible, zero-field antiferromagnetic to ferromagnetic phase transition, enabling direct and full electrical control of both magnetic order and spin polarization. Exploiting this transition, we engineer CrSBr/graphene heterostructures that leverage interfacial charge transfer to spatially pattern magnetic phases, resulting in lateral spin valves with gate-controlled spin polarization reversal, all without ferromagnetic contacts. Crucially, this mechanism also enables electrical switching of magnetic order via spin-transfer torque at ultralow current densities (<103 A/cm2), demonstrating its efficiency and device compatibility. These findings open a new paradigm for reconfigurable, all-electrical spintronic systems based on van der Waals antiferromagnetic semiconductors. Electrical doping and charge transfer in 2D antiferromagnet CrSBr reversibly switch its magnetic state, enabling gate-tunable spin valves and ultralow-power spin control without ferromagnetic contacts, advancing fully electrical 2D spintronics.

Two-dimensional semiconductors are set to form the foundation of next-generation electronic and optoelectronic devices such as field-effect transistors, solar cells, and light-emitting devices. carrier mobility is one of the key properties that determines the device performance, such as the switching frequency, the photoelectric efficiency, and so on. The correct evaluation of carrier mobility requires accurate modeling of both the electronic and vibrational properties of a material, and thus it is an intrinsically difficult problem as one cannot focus on only one of the two sets of properties. In this review, we will cover some of the basic aspects of the theoretical calculation of carrier mobility. We will progress from some fundamental models of condensed matter physics to then introduce more advanced and state-of-the-art tools nowadays used to evaluate carrier mobility for a variety of systems. We will also discuss the recent progress of carrier mobility simulations based on first principles for 2D materials with different crystal lattice structures and the effective modulation strategies for charge transport. This strategy is tailored towards layered materials but it is routinely applied to bulk devices.

Smearing methods have been used to compute temperature-dependent phonon dispersions and predict critical temperatures of charge density waves, but usually lead to a much higher result because of its ambiguous mechanism for modeling temperature effects. Here, a three-temperature model was developed to describe the energy transfer process between electrons, soft-mode and non-soft-mode phonons. In particular, mode-selective smearing induced soft-mode phonons were assigned a temperature to analyze its contributions to the relaxation between electrons and phonons. A relative standard was established to screen soft-mode phonons quantitatively for different materials. In addition, three smearing methods (Fermi–Dirac, Gaussian, and Methfessel–Paxton) and eight materials (monolayer or bulk TX2, T = Ti, Nb, Ta and X = Se, S) were tested. Critical temperatures corrected by the three-temperature model were in great agreement with experimental results. This work provides new insights into correctly predicting critical temperatures of charge density waves, addressing the relaxation process of electrons and phonons using smearing method and determining phase transitions by phonon softening.

Honeycomb bismuthene structures on Ag(111) were investigated using low-energy electron diffraction (LEED) and density functional theory. LEED I(V) analysis revealed that 0.5 monolayer (ML) of Bi forms an ultraflat honeycomb lattice with negligible buckling at 120 K, which transforms into other structures upon warming to room temperature. A similar flat bismuthene structure also forms in Mn/Bi/Ag(111), which remains stable even at room temperature. Mn deposition on (p×√(3))-rect Bi/Ag(111) induces Bi surface segregation, as confirmed by X-ray photoelectron spectroscopy, resulting in a p(2×2) honeycomb bismuthene. The detailed structural investigation provides fundamental insights into the characterization of two-dimensional topological properties of bismuthene grown on Ag(111).

In our study, we conduct magnetization and heat capacity measurements to investigate field-induced magnetic phase transitions within the newly synthesized compound K 2 Ni 2 (SeO 3 ) 3 , a spin-1 dimer system arranged on a triangular lattice. From our first-principles simulations, we determine that the spin system in K 2 Ni 2 (SeO 3 ) 3 can be represented as a two-dimensional triangular-lattice spin-1 dimer model, including an intra-dimer exchange of J 1 = 0 . 32 meV, an inter-dimer exchange of J 2 = 0 . 79 meV, and an easy-axis anisotropy of D = 0 . 14 meV. The presence of easy-axis magnetic anisotropy explains the distinct magnetic phase diagrams observed under c-axis directional and in-plane magnetic fields. Notably, our investigation unveils a two-step phase transition with the magnetic field aligned with the c direction. Our findings yield valuable insights into the magnetic phase transitions inherent to geometrically frustrated magnetic systems featuring dimer structures.

Anderson localization has been widely studied in low-dimensional aperiodic electronic, photonic, and acoustic systems. However, the disorder effect in the plasmonic system, where retardation and long-range couplings interact in complex ways, remains an open question. In this work, we investigate the localization properties of one-dimensional quasiperiodic plasmonic chains using the coupled dipole method and linearized Green's function. Our models, which incorporate nearest-neighbor or long-range dipole interactions, reveal localization transitions, mobility edges, and intermediate phases. It is found that long-range dipole interactions and non-Hermiticity due to retardation both play crucial roles in Anderson localization, yielding the emergence of intermediate phases with varying widths. A link between non-Hermiticity and Anderson transition is established by the mean phase rigidity, revealing strong non-Hermiticity along the phase boundary. The plasmonic model involving long-range interplay and retarded effect presents richer localization phenomena than the electronic counterpart that usually includes only nearest-neighbor coupling, laying a foundation for experimental observations of Anderson localization on plasmonic platforms.

Unlike electrons, phonons do not have the charge and spin degrees of freedom. Consequently, it is a big challenge for the control of phonon currents and the design of quantum phonon devices due to the lack of versatile degrees of freedom. In this work, we show that phonon bands of mirror-symmetric materials can be labeled by parities, which can act as a pseudospin of phonons. As a proof-of-concept, we show that perfect pseudospin filtering can be realized using mirror-symmetric graphene-nanoribbon heterojunctions. In addition, we show that the filtering takes place within a remarkably short length scale of just 3 nanometers. Our work reveals an intriguing new facet of phonon behavior and also underscores the immense potential of utilizing phonons as information carriers.

Atomic structures of Sn on Mo(110) are investigated using low-energy electron diffraction (LEED) and density functional theory (DFT) calculation. Sn atoms occupy substitutional sites at elevated temperatures in (3 x 1) structure, corresponding to a coverage of 0.33 ML. The substitutional model agrees with previous LEED, workfunction, and STM results. For (1 x 3) structure at 0.67 ML, Sn atoms adsorb in the nearest three-fold hollow sites. With increasing Sn coverage, the (1 x 4) structure at 0.75 ML, Sn atoms start to fill four-fold hollow sites. On both overlayer phases, Sn structures are flat without significant buckling. Compared with a two-dimensional tin, stanene, which is a stacking of alpha-Sn(111), Sn overlayer on Mo(110) is not related to alpha-Sn(111) but to beta-Sn (100), which is normal metallic

AbstractThe classical problem of best thermoelectrics, which was believed originally solved by Mahan and Sofo [Proc. Natl. Acad. Sci. USA 93, 7436 (1996)], is revisited and discussed in the quantum limit. We express the thermoelectric figure of merit (zT) as a functional of electronic transmission probability $${{{\mathcal{T}}}}$$ T by the Landauer–Büttiker formalism, which is able to deal with thermoelectric transport ranging from ballistic to diffusive regimes. We also propose to apply the calculus of variations to search for the optimal $${{{\mathcal{T}}}}$$ T giving the maximal zT. Our study reveals that the optimal transmission probability $${{{\mathcal{T}}}}$$ T is a boxcar function instead of a delta function proposed by Mahan and Sofo, leading to zT exceeding the well-known Mahan–Sofo limit. Furthermore, we suggest realizing the optimal $${{{\mathcal{T}}}}$$ T in topological material systems. Our work defines the theoretical upper limit for quantum thermoelectrics, which is of fundamental significance to the future development of thermoelectrics.

Research on topological physics of phonons has attracted enormous interest but demands appropriate model materials. Our ab initio calculations identify silicon as an ideal candidate material containing extraordinarily rich topological phonon states. In silicon, we identify various topological nodal lines characterized by quantized Berry phase π, which gives drumhead surface states observable from any surface orientations. Remarkably, a novel type of topological nexus phonon is discovered which is featured by double Fermi-arc-like surface states but requires neither inversion nor time-reversal symmetry breaking. Versatile topological states can be created from the nexus phonons, such as Hopf nodal links by strain. Furthermore, we generalize the symmetry analysis to other centrosymmetric systems and find numerous candidate materials, demonstrating the ubiquitous existence of topological phonons in solids. These findings open up new opportunities for studying topological phonons in realistic materials and their influence on surface physics.