arXiv subjects

Weikang Wu

Publications and source records attributed to Weikang Wu.

At least 19 recordsLinked to original sources

arXiv2026

Symmetry-protected triplet Weyl complexes

The Nielsen-Ninomiya theorem dictates that Weyl nodes must appear in pairs of opposite chirality to preserve global charge neutrality. However, in crystals, specific crystalline symmetries can stabilize multi-Weyl nodes, circumventing this pairwise constraint and enabling compensated Weyl complexes with mixed chiral charges. The minimal configuration of this type is a triplet Weyl complex (TWC), comprising exactly three Weyl nodes. Here, we systematically investigate the symmetry conditions required to realize TWCs. By screening all 1651 magnetic space groups (MSGs) in both spinless and spinful systems, we establish that: (i) Only TWCs with charge magnitudes of $\{1,1,2\}$ and $\{1,2,3\}$ are permitted; (ii) the $\{1,1,2\}$ configuration can be realized in 166 spinless MSGs and 70 spinful MSGs; and (iii) the $\{1,2,3\}$-TWCs, which has not been reported before, can occur in 10 MSGs for both spinless and spinful cases. We explicitly demonstrate the existence of $\{1,2,3\}$-TWC in a tight-binding model. Furthermore, we present the first electronic realization of $\{1,1,2\}$-TWC topological semimetal state in the chiral carbon allotrope DZQH-C$_{36}$, in which the three Weyl nodes form a collinear configuration, leading to a characteristic ``S''-shaped surface Fermi arc pattern. Our findings uncover novel topological states featuring mixed chiral charges and provide guidance for exploring their physics in concrete material systems.

cond-mat.mtrl-sci↗

arXiv2026

Engineering Molecular Rectification: Mechanisms, Modulation Strategies, and Device Integration

Molecular rectifiers, as prototypical components of molecular electronics, present unique opportunities for pushing device miniaturization to its ultimate limits. Nevertheless, challenges including limited rectification ratios (RR), insufficient robustness, and poor reproducibility impede their practical deployment. To make molecular rectifiers competitive with silicon-based devices, it is important to fully understand the design principles and fabrication methods from both mechanistic and experimental perspectives. By holistically considering the transport mechanisms, modulation strategies, fabrication, characterization techniques, and theoretical simulations, this review provides a comprehensive overview of molecular rectifiers. Representative examples of conceptually significant and high-performance molecular rectifier systems are highlighted to illustrate the relationships between rectification mechanisms, molecular design strategies, and device realization. Building on these discussions, we present an outlook for current bottlenecks and future directions to guide the development of molecular rectifiers. This review aims to serve as both a conceptual framework and a technical reference for researchers working at the intersection of molecular electronics and nanoscale device engineering in the post-CMOS era.

cond-mat.mtrl-sci↗

arXiv2026

Selective Fermi-Level Pinning: A Design Strategy for Giant Rectification in Molecular Junctions

Molecular rectifiers are key functional components of molecular-scale integrated circuits, yet achieving high rectification ratios remains a longstanding challenge due to the intrinsic symmetry of resonant tunneling and the complexity of interfacial energy-level alignment. Here, we propose a rectifier design strategy based on selective Fermi-level pinning that breaks transport symmetry via pinning interactions between molecular frontier orbitals and electrodes. This framework enforces tunneling transport to be predominantly governed by unoccupied molecular orbitals, while substantially suppressing contributions from occupied states, thereby establishing a simplified and highly controllable rectification mechanism. The resulting cyclo[n]carbon-based molecular junctions exhibit giant rectification ratios exceeding 103, while retaining exceptional structural robustness against variations in both donor chain length and carbon ring size. This work reveals the critical role of selective Fermi-level pinning in molecular junctions and provides a general design principle for engineering functional single-molecule electronic devices.

cond-mat.mes-hall↗

arXiv2026

Termination-Preserved Ultra-high Tunneling Magnetoresistance in Altermagnetic KV2Se2O

Altermagnets exhibit nonrelativistic spin splitting without net magnetization, establishing a new platform for next-generation spintronic devices. Although altermagnetic tunnel junctions (AMTJs) represent the most promising realizations, their practical applications are hindered by low tunnel magnetoresistance (TMR) ratios and strong sensitivity to interfacial configurations. Here, we systematically explore the transport properties and microscopic mechanisms of AMTJs based on the recently discovered d-wave altermagnet KV2Se2O. Using first-principles calculations and orbital-resolved analysis, we demonstrate that the synergy between compressed nodal-point like spin-degenerate channels and coplanar interfacial magnetic order yields an ultra-high intrinsic TMR above 105% for all interfacial terminations. More importantly, K-termination effectively preserves bulk spin polarization through its unique passivation characteristics, leading to an ultra-high TMR up to 1012%. These results identify the coupling between momentum-space topology and interfacial passivation provides a reliable strategy for realizing giant magnetoresistive responses in altermagnetic spintronic devices.

cond-mat.mtrl-sci↗

arXiv2026

Flat Topological Nodal Lines in Heavy-Fermion Compound CeCoGe$_3$

The interplay between strong electronic correlations, unconventional superconductivity, and symmetry-protected topology provides a fertile ground for discovering exotic quantum states. In this work, we investigate the correlated electronic structure and topological properties of the heavy fermion material CeCoGe$_3$ using density functional theory combined with dynamical mean-field theory calculations. Our results reveal a crossover from high temperature incoherent states to low temperature coherent heavy quasiparticles, accompanied by a mass enhancement of $m^*/m_{\text{DFT}}\sim 52.6$ at $T=25$ K. The interplay between electronic correlation, spin-orbit coupling and the noncentrosymmetric $I4mm$ crystal symmetry stabilize flat topological nodal lines within 10 meV of the Fermi level, which could contribute a significant density of states. The proximity of topological nodal lines to the Fermi surface suggests a potential role in mediating pressure induced unconventional superconductivity. Our work establishes CeCoGe$_3$ as a prototype topological nodal line Kondo semimetal. The coexistence of strong correlation, non-trivial band topology and superconductivity indicate CeCoGe$_3$ as a potential candidate for realizing topological superconductivity.

cond-mat.str-el↗

arXiv2026

Orbital-Selective Spin-Orbit Mott Insulator in Fractional Valence Iridate La$_3$Ir$_3$O$_{11}$

The combination of strong spin-orbit coupling and Coulomb interactions makes the $5d$ iridates a unique platform for realizing novel correlated electronic states. Here, utilizing infrared spectroscopy, we demonstrate that a robust Mott insulating state persists in the $1/3$-hole self-doped system La$_3$Ir$_3$O$_{11}$, evidenced by the collapse of the Drude response and the emergence of sharp excitations across the Mott gap. Our theoretical calculations reveal that the insulating behavior arises from the cooperative interplay of structural distortions, spin-orbit coupling, and Coulomb interactions. Specifically, octahedral distortion and Ir-Ir dimerization split the $t_{2g}$ orbitals, driving the $J_{\mathrm{eff}} = 1/2$ bands toward half-filling while keeping the $J_{\mathrm{eff}} = 3/2$ bands away from it. Consequently, electron correlations induce an orbital-selective Mott transition in the $J_{\mathrm{eff}} = 1/2$ bands, whereas a band-insulating gap develops in the $J_{\mathrm{eff}} = 3/2$ bands, thereby stabilizing the unconventional insulating state in La$_3$Ir$_3$O$_{11}$. These findings provide new insights into the design and understanding of the insulating ground state of spin-orbit-coupled iridates.

cond-mat.str-el↗

arXiv2025

Discovery of nodal-line superconductivity in chiral crystals

Chiral crystals, whose key feature is the structural handedness, host exotic quantum phenomena driven by the interplay of band topology, spin-orbit coupling (SOC), and electronic correlations. Due to the limited availability of suitable chiral-crystal materials, their unconventional superconductivity (SC) remains largely unexplored. Here, we report the discovery of unconventional SC in the La(Rh,Ir)Si family of materials by combining muon-spin spectroscopy, band-structure calculations, and perturbation theory. This family, characterized by a double-helix chiral structure, hosts exotic multifold fermions that are absent in other topological chiral crystals. While LaRhSi behaves as a fully-gapped superconductor, the substitution of 4$d$-Rh by 5$d$-Ir significantly enhances the SOC and leads to the emergence of topological nodal-line SC in LaIrSi. The developed model shows that the nodal-line SC arises from an isotropic SOC with a specific strength. Such an exotic mechanism expands our conventional understanding of material candidates for unconventional SC, which typically rely on a significantly anisotropic SOC to promote the triplet pairing. Our work establishes a new type of phase diagram, which provides a comprehensive roadmap for identifying and engineering unconventional SC in chiral crystals. Furthermore, it calls for renewed investigations of unconventional SC in other widely studied superconductors with a chiral structure.

cond-mat.supr-con↗

arXiv2025

Type-II Antiferroelectricity

Antiferroelectricity (AFE) is a fundamental concept in physics and materials science. Conventional AFEs have the picture of alternating local electric dipoles defined in real space. Here, we discover a new class of AFEs, termed type-II AFEs, which possess opposite polarizations defined in momentum space across a pair of symmetry decoupled subspaces. Unlike conventional AFEs, the order parameter of type-II AFEs is rigorously formulated through Berry-phase theory and can be quantitatively extracted from the electronic band structure. Focusing on a subclass of type-II AFEs that preserve spin-rotation symmetry, we establish the relevant symmetry constraints and identify all compatible spin point groups. Remarkably, we find that type-II AFE order intrinsically coexists with antiferromagnetism, revealing a robust form of magnetoelectric coupling. We construct an altermagnetic model and identify several concrete antiferromagnetic/altermagnetic materials, such as FeS, Cr2O3, MgMnO3, monolayer MoICl2 and bilayer CrI3, that exhibit this novel ordering. Furthermore, we uncover unique physical phenomena associated with type-II spin-AFE systems, including spin current generation upon AFE switching and localized spin polarization at boundaries and domain walls. Our findings reveal a previously hidden class of quantum materials with intertwined ferroic orders, offering exciting opportunities for both fundamental exploration and technological applications.

cond-mat.mtrl-sci↗

arXiv2025

Nonlinear N\'eel Spin-Orbit Torque in Centrosymmetric Antiferromagnets

Electric control of N\'eel vector is a central task of antiferromagnetic (AFM) spintronics. The major scheme so far relies on the linear N\'eel torque, which however is restricted to AFMs with broken inversion symmetry. Here, we propose a nonlinear N\'eel spin-orbit torque, uniquely enabling electric control in the vast class of centrosymmetric AFMs, where the existing scheme fails. Importantly, its intrinsic component, rooted in sublattice-resolved band quantum geometry, offers two additional advantages: It operates also in $\mathcal{PT}$-symmetric AFM insulators, where linear torque is forbidden; and it has anti-damping character, making it more efficient in driving magnetic dynamics. Combined with first-principles calculations, we predict large effect in MnRh and MnBi$_{2}$Te$_{4}$, which can be readily detected in experiment. Our work unveils a new fundamental effect, offers a new strategy of electric control in AFM systems beyond the existing paradigm, and opens the door to the field of nonlinear AFM spintronics.

cond-mat.mtrl-sci↗

arXiv2025

Ideal Weyl fermions and double Kagome bands in a series of distorted armchair-type all-$\emph{sp}^{2}$ carbon networks

The study of the Weyl fermions and Kagome bands has recently attracted significant attention in condensed matter physics. However, realizing of perfect Weyl semimetals and double Kagome bands remains challenging. Here, we report a new class of distorted armchair-type fully sp2-hybridized carbon networks, termed DACN-n. The DACN-n family is characterized by only six pairs of Weyl points on the $k_z=0$ plane near the Fermi level. We calculated the chirality of these Weyl points and found that each carries a topological charge of $\pm$1. Notably, DACN-5 exhibits a double Kagome band, where the Weyl points arise from the intersection between Dirac-type bands in the two sets of Kagome bands. The structural stability of DACN-n is confirmed by phonon spectra, ab initio molecular dynamics simulations, and elastic constant calculations. Additionally, we investigated the surface states of the (001) surface and found that its nontrivial topological properties are attributed to the Fermi arcs connecting a pair of Weyl points with opposite chirality. We also simulated x-ray diffraction patterns to guide experimental synthesis. Our findings not only present a new family of three-dimensional carbon allotropes, but also provide a unique opportunity for exploring ideal Weyl fermions and double Kagome bands.

cond-mat.mtrl-sci↗

arXiv2025

Essentially degenerate hidden nodal lines in two-dimensional magnetic layer groups

According to the theory of group representations, the types of band degeneracy can be divided into accidental degeneracy and essential degeneracy. The essentially degenerate nodal lines (NLs) are typically resided on the high-symmetry lines of the Brillouin zone. Here, we propose a type of NL in two dimension that is essentially degenerate but is hidden within the high-symmetry planes, making it less observable, dubbed a hidden-essential nodal line (HENL). The existence of HENL is guaranteed as long as the system hosts a horizontal glide-mirror symmetry, hence such NLs can be widely found in both non-magnetic and magnetic systems. We perform an exhaustive search over all 528 magnetic layer groups (MLGs) for HENL that can be enforced by glide-mirror symmetry with both spinless and spinfull systems. We find that 122 candidate MLGs host spinless HENL, while 63 candidate MLGs demonstrate spinful HENL. In addition, we reveal that horizontal mirror and time-reversal symmetry in type-II and type-IV MLGs with spin-orbital coupling can enforce HENL formed. The 15 corresponding candidate MLGs have also been presented. Furthemore, we derive a few typical lattice models to characterize the existence for the HENL. For specific electronic fillings in real materials, namely 4$N$+2 in spinless systems (and 2$N$+1 in spinful systems), the presence of the HENLs in candidate MLGs is required regardless of the details of the systems. Using \emph{ab-initio} calculations, we further identify possible material candidates that realize spinless and spinful HENL. Moreover, spinful HENLs exhibit a novel persistent spin texture wih the characteristic of momentum-independent spin configuration. Our findings uncover a new type of topological semimetal state and offer an ideal platform to study the related physics of HENLs.

cond-mat.mtrl-sci↗

arXiv2024

Highly anisotropic Drude-weight-reduction and enhanced linear-dichroism in van der Waals Weyl semimetal Td-MoTe2 with coherent interlayer electronic transport

Weyl semimetal (WSM) states can be achieved by breaking spatial-inversion symmetry or time reversal symmetry. However, the anisotropy of the energy reduction contributing to the emergence of WSM states has seldom been investigated by experiments. A van der Waals metal MoTe2 exhibits a type-II WSM phase below the monoclinic-to-orthorhombic-phase-transition temperature Tc ~ 250 K. Here, we report a combined linearly-polarized optical-spectroscopy and electrical-transport study of MoTe2 at different temperatures. The Drude components in the a-axis, b-axis and c-axis optical conductivity spectra, together with the metallic out-of-plane and in-plane electrical resistivities, indicate the coherent inter-layer and in-plane charge transports. Moreover, the Drude weight in {\sigma}1a({\omega}), rather than the Drude weights in {\sigma}1b({\omega}) and {\sigma}1c({\omega}), decreases dramatically below Tc, which exhibits a highly anisotropic decrease in its Drude weight and thus suggests a strongly anisotropic reduction of the electronic kinetic energy in the WSM phase. Furthermore, below Tc, due to the in-plane anisotropic spectral-weight transfer from Drude component to high-energy region, the in-plane inter-band-absorption anisotropy increases remarkably around 770 meV, and has the largest value (~ 0.68) of normalized linear dichroism among the reported type-II WSMs. Our work sheds light on seeking new WSMs and developing novel photonic devices based on WSMs.

cond-mat.mtrl-sci↗

arXiv2024

Intrinsic Nonlinear Spin Hall Effect and Manipulation of Perpendicular Magnetization

We propose an intrinsic nonlinear spin Hall effect, which enables the generation of collinearly-polarized spin current in a large class of nonmagnetic materials with the corresponding linear response being symmetry-forbidden. This opens a new avenue for field-free switching of perpendicular magnetization, which is required for the next-generation information storage technology. We develop the microscopic theory of this effect, and clarify its quantum origin in band geometric quantities which can be enhanced by topological nodal features. Combined with first-principles calculations, we predict pronounced effects at room temperature in topological metals $\mathrm{PbTaSe_{2}}$ and PdGa. Our work establishes a fundamental nonlinear response in spin transport, and opens the door to exploring spintronic applications based on nonlinear spin Hall effect.

cond-mat.mes-hall↗

arXiv2024

Quantum Metric Nonlinear Spin-Orbit Torque Enhanced by Topological Bands

Effects manifesting quantum geometry have been a focus of physics research. Here, we reveal that quantum metric plays a crucial role in nonlinear electric spin response, leading to a quantum metric spin-orbit torque. We argue that enhanced quantum metric can occur at band (anti)crossings, so the nonlinear torque could be amplified in topological metals with nodal features close to Fermi level. By applying our theory to magnetic Kane-Mele model and monolayer CrSBr, which feature nodal lines and Weyl points, we demonstrate that the quantum metric torque dominates the response, and its magnitude is significantly enhanced by topological band structures, which even surpasses the previously reported linear torques and is sufficient to drive magnetic switching by itself.

cond-mat.mes-hall↗

arXiv2023

Magnetic eight-fold nodal-point and nodal-network fermions in MnB2

Realizing topological semimetal states with novel emergent fermions in magnetic materials is a focus of current research. Based on first-principle calculations and symmetry analysis, we reveal interesting magnetic emergent fermions in an existing material MnB2. In the temperature range from 157 K to 760 K, MnB2 is a collinear antiferromagnet. We find the coexistence of eightfold nodal points and nodal net close to the Fermi level, which are protected by the spin group in the absence of spin-orbit coupling. Depending on the Neel vector orientation, consideration of spin-orbit coupling will either open small gaps at these nodal features, or transform them into magnetic linear and quadratic Dirac points and nodal rings. Below 157 K, MnB2 acquires weak ferromagnetism due to spin tilting. We predict that this transition is accompanied by a drastic change in anomalous Hall response, from zero above 157 K to 200 $\Omega\cdot \text{cm}^{-1}$ below 157 K.

cond-mat.mtrl-sci↗

arXiv2023

Quadratic nodal point in a two-dimensional noncollinear antiferromagnet

Quadratic nodal point (QNP) in two dimensions has so far been reported only in nonmagnetic materials and in the absence of spin-orbit coupling. Here, by first-principles calculations and symmetry analysis, we predict stable QNP near Fermi level in a two-dimensional kagome metal-organic framework material, Cr$_3$(HAB)$_2$, which features noncollinear antiferromagnetic ordering and sizable spin-orbit coupling. Effective kp and lattice models are constructed to capture such magnetic QNPs. Besides QNP, we find Cr$_3$(HAB)$_2$ also hosts six magnetic linear nodal points protected by mirror as well as $C_{2z}T$ symmetry. Properties associated to these nodal points, such as topological edge states and quantized optical absorbance, are discussed.

cond-mat.mes-hall↗

arXiv2023

Realization of multiple topological states and topological phase transitions in (4,0) carbon nanotube derivatives

Exploring various topological states (TS) and topological phase transitions (TPT) has attracted great attention in condensed matter physics. However, so far, there is rarely a typical material system that can be used as a platform to study the TS and TPT as the system transforms from one-dimensional (1D) nanoribbons to two-dimensional (2D) sheet then to three-dimensional (3D) bulk. Here, we first propose that some typical TS in 1D, 2D, and 3D systems can be realized in a tight-binding (TB) model. Following the TB model and further based on first-principles electronic structure calculations, we demonstrate that the structurally stable (4,0) carbon nanotube derivatives are an ideal platform to explore the semiconductor/nodal-point semimetal states in 1D nanoribbons [1D-(4,0)-C16H4 and 1D-(4,0)-C32H4], nodal-ring semimetal state in 2D sheet [2D-(4,0)-C16], and nodal-cage semimetal state in 3D bulk [3D-(4,0)-C16]. Furthermore, we calculate the characteristic band structures and the edge/surface states of 2D-(4,0)-C16 and 3D-(4,0)-C16 to confirm their nontrivial topological properties. Our work not only provides new excellent 2D and 3D members for the topological carbon material family, but also serves as an ideal template for the study of TS and TPT with the change of system dimension.

cond-mat.mtrl-sci↗

arXiv2023

Phonon chirality manipulation mechanism in TMD interlayer-sliding ferroelectrics

As an ideal platform, both the theoretical prediction and first experimental verification of chiral phonons are based on transition-metal dichalcogenide materials. The manipulation of phonon chirality in these materials will have a profound impact on the study of chiral phonons. In this work, we utilize the sliding ferroelectric mechanism to study the phonon chirality manipulation mechanism in transition-metal dichalcogenide materials. Based on first-principles calculations, we study the different effects of interlayer sliding on the phonon properties in bilayer and four-layer MoS$_2$ sliding ferroelectrics. We find that sliding can regulate phonon chirality and Berry curvature, which further affects the phonon angular momentum and magnetization under a temperature gradient and the phonon Hall effect under a magnetic field. Our work connects two emerging fields and opens up a new route to manipulate phonon chirality in transition-metal dichalcogenide materials through the sliding ferroelectric mechanism.

cond-mat.mtrl-sci↗