arXiv subjects

Yu-Hao Wan

Publications and source records attributed to Yu-Hao Wan.

16 recordsLinked to original sources

arXiv2026

Anti-higher-order topological insulators

Duality is a fundamental concept in physics that connects complementary opposites like particles and holes. Similarly, while topological states in topological insulators localize at boundaries, the existence and nature of their dual counterparts remain unexplored. Here, we introduce anti-topological states as the dual of topological states, exemplified by anti-higher-order topological insulators. Unlike higher-order topological insulators, where states localize at corners, anti-higher-order topological insulators host states along edges but absent at corners, realizing an inverted distribution of states. We demonstrate this phenomenon in a bilayer Chern insulator with opposite Chern numbers, where the band inversion surfaces enclose distinct high-symmetry points. The topological invariant distinguishing these phases is given by the topological charges enclosed by band inversion surfaces. This work establishes anti-topology as a new paradigm, opening a chapter in topological research.

cond-mat.mes-hall↗

arXiv2026

Anti-higher-order Weyl semimetal

Higher-order topology extends the bulk-boundary correspondence by enabling corner or hinge localized states. Here we identify an anti-higher-order Weyl semimetal, a three dimensional topological phase in which the conventional boundary hierarchy is reversed. Unlike conventional higher-order Weyl semimetals where bulk topology enforces hinge Fermi arcs, this phase hosts anti-hinge states, meaning the bulk topology forces states to vanish at specific hinge orientations. Using a minimal two-band model, we show how Weyl points separate the Brillouin zone into quantum anomalous Hall and anti-higher-order topological insulating regions, with the latter characterized by a band-inversion surface enclosing two distinct high-symmetry points carrying opposite topological charges. Analytical solutions for Weyl points, Berry curvature monopoles, and slice Chern numbers are derived, with numerical simulations confirming the resulting anti-hinge behavior. Our work establishes anti-higher-order topology as a dual counterpart to conventional higher-order phenomena, further extending the exploration of topological phases.

cond-mat.mes-hall↗

arXiv2026

Quantum anomalous Hall effect in chiral semimetals

The quantum anomalous Hall (QAH) effect is conventionally understood to exist only in Chern insulators, while a recent study has shown that ferromagnetic metals can also host the QAH effect. Between insulators and metals, we demonstrate that QAH can persist even in a chiral semimetal, where conduction and valence bands touch at zero energy. Transport calculations demonstrate that the Hall conductivity of such a system can be quantized in the presence of dephasing. Interestingly, its longitudinal conductivity remains finite and exhibits semimetallic behavior, in contrast to Chern insulators. This unusual transport behavior originates from the quantization of the Berry curvature integral over occupied states and the semimetallic band structure. This chiral semimetal can transition into a Chern insulator, accompanied by the vanishing of longitudinal conductivity and a reduction of the intrinsic length scale of the Hall response. Our results extend the concept of QAH and uncover the semimetallic QAH transport signatures.

cond-mat.mes-hall↗

arXiv2026

Robust quantized thermal conductance of Majorana floating edge bands in d-wave superconductors

We propose and characterize a new class of Majorana boundary states, i.e., floating Majorana edge bands (FMEBs), which emerge in two-dimensional (2D) superconductors that break time-reversal symmetry yet host helical-like transport. In contrast to conventional chiral or helical edge modes, FMEBs form isolated, momentum-separated counterpropagating Majorana modes detached from the bulk continuum. We identify a minimal mechanism for their emergence via anisotropic Wilson masses in a two-band Bogoliubov-de Gennes (BdG) model, and demonstrate their microscopic realization in a quantum anomalous Hall (QAH) insulator proximitized by a $d$-wave superconductor. Using nonequilibrium Green's function (NEGF) simulations, we uncover clear transport fingerprints: a quantized total thermal conductance in two-terminal devices, and a robust half-quantized plateau in four-terminal geometries that cleanly distinguishes FMEBs from chiral $\mathcal{N}= \pm 2$ QAH phases. This thermal response remains remarkably stable under finite temperature, moderate long-range disorder, and finite chemical potential. Our findings establish FMEBs as an experimentally accessible route toward helical-like Majorana transport in systems without time-reversal symmetry, with direct implications for topological quantum computation.

cond-mat.mes-hall↗

arXiv2026

The emergence of net chirality in two-dimensional Dirac fermions system with altermagnetic mass

In two-dimensional lattice systems, massless Dirac fermions undergo doubling, leading to the cancellation of net chirality. We demonstrate that the recently discovered altermagnetism can induce a unique mass term, the altermagnetic mass term, which gaps out Dirac cones with one chirality while maintaining the other gapless, leading to the emergence of net chirality. The surviving gapless Dirac cones retain identical winding numbers and exhibit the quantum anomalous Hall effect in the presence of the trivial constant mass term. When subjected to an external magnetic field, the altermagnetic mass induces Landau level asymmetry in Dirac fermions, resulting in fully valley-polarized quantum Hall edge states. Our findings reveal that Dirac fermions with the altermagnetic mass harbor rich physical phenomena warranting further exploration.

cond-mat.mes-hall↗

arXiv2025

Helical Fermi Arc in Altermagnetic Weyl Semimetal

We investigate the topological properties of modified Dirac Hamiltonians with an altermagnetic mass term and reveal a novel mechanism for realizing altermagnetic Weyl semimetals. Unlike the conventional Wilson mass, the altermagnetic mass drives direct transitions between nontrivial Chern phases of opposite sign and fundamentally reshapes the band inversion surface. By extending this framework to three dimensions, we construct a minimal lattice model that hosts pairs of Weyl nodes as well as coexisting helical Fermi arcs with opposite chirality on the same surface, which is a phenomenon not found in conventional magnetic Weyl semimetals. We further propose a practical scheme to realize these phases in multilayer structures of 2-dimensional Rashba metal with engineered $d$-wave altermagnetic order. Our results deepen the theoretical understanding of mass terms in Dirac systems and provide concrete guidelines for the experimental detection and realization of altermagnetic Weyl semimetals.

cond-mat.mes-hall↗

arXiv2025

Quantum Anomalous Hall Effect in Ferromagnetic Metals

The quantum anomalous Hall (QAH) effect holds fundamental importance in topological physics and technological promise for electronics. It is generally believed that the QAH effect can only be realized in insulators. In this Letter, we theoretically demonstrate that the QAH effect can also be realized in metallic systems, representing a phase distinct from the conventional QAH phase in insulators. This phase is characterized by the coexistence of chiral edge channels and isotropic bulk conduction channels without a bulk energy gap. Notably, in a six-terminal Hall bar, our calculations show that, the quantized Hall conductivity and nonzero longitudinal conductivity can emerge due to dephasing, despite the Hall resistivity itself never becoming quantized. Furthermore, the quantized Hall conductivity exhibits remarkable robustness against disorder. Our findings not only extend the range of materials capable of hosting the QAH effect from insulators to metals, but also provide insights that may pave the way for the experimental realization of the QAH effect at elevated temperatures.

cond-mat.mes-hall↗

arXiv2025

Altermagnetism-Induced Parity Anomaly in Weak Topological Insulators

We demonstrate that introducing altermagnetism on the surface of a weak topological insulator (TI) results in the emergence of a single massless Dirac fermion, exhibiting a parity anomaly. To explore the transport properties induced by this parity anomaly, we propose an effective two-dimensional (2D) lattice model to describe the weak TI surface. This model captures both the energy spectrum and spin texture of the weak TI surface while reducing computational complexity. We show that the weak TI surface hosts a half-integer chiral edge current under the influence of altermagnetism. Additionally, in the presence of decoherence, the Hall conductance attains a half-quantized value. Layer-resolved calculations from a 3D slab model further confirm that surface altermagnetism drives the surface Hall conductance to transition to $e^{2}/2h$, aligning with calculation from the 2D effective lattice model. Our findings establish a link between altermagnetism and quantum anomalies, positioning weak TIs as a potential platform for investigating the parity anomaly without a net magnetic moment.

cond-mat.mes-hall↗

arXiv2025

Interplay of Altermagnetic Order and Wilson Mass in the Dirac Equation: Helical Edge States without Time-Reversal Symmetry

We investigate topological phases in three-dimensional topological insulator (3DTI) thin films interfaced with altermagnetic (AM) orders. Starting from a modified Dirac equation, we elucidate the interplay between the Wilson mass, arising from lattice regularization, and the altermagnetic mass, and show how this interplay fundamentally alters the band topology and boundary modes. In particular, we demonstrate that coupling a 3DTI thin film to AM order induces a topological phase transition: although the total Chern number remains zero across the transition, topological helical edge states emerge after the transition. These helical edge states arise from opposite Chern numbers at different high-symmetry points, and are distinct from both the chiral edge states of the quantum anomalous Hall phase and the helical edge states of the conventional quantum spin Hall states. The quantum transport simulations reveal robust, quantized nonlocal resistance plateaus associated with these helical edge states, which persist even under strong potential and magnetic disorder. Our results establish 3DTI/AM heterostructures as a feasible material platform for engineering and detecting helical topological edge transport without time-reversal symmetry, thus expanding the landscape of topological matter and providing new opportunities for quantum devices.

cond-mat.mes-hall↗

arXiv2025

Tunable Majorana corner states driven by superconducting phase bias in a vertical Josephson junction

The realization and manipulation of Majorana zero modes is a key step in achieving topological quantum computation. In this paper, we demonstrate the existence of Majorana corner states in a superconductor-insulators-superconductor vertical Josephson junction. The position of these Majorana corner states can be precisely and easily controlled by the superconducting phase bias, which be confirmed through both numerical and edge state theoretical analysis. In addition, we propose a protocol for achieving topological braiding of the Majorana corner states in a system of three circular vertical Josephson junctions. Our findings advance the field of topological quantum computation by providing new insights into the efficient and precise manipulation of Majorana corner states.

cond-mat.supr-con↗

arXiv2024

Engineering topologically protected zero-dimensional interface end states in antiferromagnetic heterojunction graphene nanoflakes

We investigate the energy band structure and energy levels of a heterojunction composed of two antiferromagnetic graphene nanoflakes with opposite in-plane antiferromagnetic orderings, in which the modified Kane-Mele model is employed. Before forming an antiferromagnetic graphene heterojunction, the energy gap of helical edge states in each isolated graphene nanoflake are opened by the antiferromagnetic ordering and there is no the in-gap corner state. We find that when two opposite antiferromagnetic graphenes are coupled to form a heterojunction nanoflake, topologically protected zero-dimensional in-gap states can be induced. In addition, we demonstrate that the in-gap states locate at the end of the interface and are robust against magnetic disorder, Anderson disorder, and interfacial magnetic defects. The position and number of the in-gap interface end states in the heterojunction sample can be precise quantum controlled.

cond-mat.mes-hall↗

arXiv2024

Magnetization-Induced Phase Transitions on the surface of 3D Topological Insulators

From the low-energy model, the topological field theory indicates that the surface magnetization can open a surface gap in 3D topological insulators (TIs), resulting in a half-quantized Hall conductance. Here by employing the realistic lattice model, we show the occurrence of { the surface phase transitions}, accompanied with the sharp changes of the surface Chern number from $\frac{1}{2}$ to $-\frac{3}{2}$ finally to $-\frac{1}{2}$, in 3D TIs induced by surface magnetization. These surface phase transitions lead to the sudden jumps in the magneto-electric coefficient and the quantum Hall conductance, which are experimentally observable. Furthermore, we present the phase diagram that elucidates the behavior of the 3D TI surface Chern numbers under surface magnetization for different $Z_{4}$ topological numbers. Our study highlights the presence of the new phases with broken bulk-boundary correspondence and enriches understandings of the properties of TIs.

cond-mat.mes-hall↗

arXiv2024

Quarter-quantized thermal Hall effect with parity anomaly

We show that in the proximity of s-wave superconductors, the magnetic topological surface states can transform into Majorana surface state, featuring a single gapless Majorana cone with parity anomaly when the superconducting pairing gap matches the surface magnetization gap. The emergence of $N=1/2$ Majorana chiral edge current is observed at the boundaries between the gap region and the gapless region. Additionally, in systems with a single gapless Majorana cone, a quarter-quantized thermal Hall conductance appears under the dephasing. By mapping the system to a conductor-network model, we identify the appearance of 1/4 chiral heat channels as the cause of the quarter-quantized Hall thermal conductance. We observe the stability of this quarter-quantized thermal conductance under temperature variations, serving as a distinctive feature indicating the presence of a single gapless Majorana cone in the system. Our models can be experimentally realized using magnetic topological insulators or iron-based superconductors.

cond-mat.mes-hall↗

arXiv2024

Universal theory of tunable second-order topological corner states induced by interlayer coupling in twist bilayer Chern insulators

We propose a universal theory for tunable second-order topological corner states induced by interlayer coupling in bilayer Chern insulators with opposite Chern numbers. We demonstrate that the existence of the topological corner state is determined by the relationship between the twist angle of the bilayer Chern insulators and the normal angles of the two sides of the corner. In addition, the position of these corner states can be sensitively controlled by the twist angle, as confirmed by a rigorous analysis of edge state theory. Our findings serve as a universal theory, opening avenues for the design and realization of higher-order topological materials.

cond-mat.mes-hall↗

arXiv2024

Classification of Chern Numbers Based on High-Symmetry Points

The Chern number is a crucial topological invariant for distinguishing the phases of Chern insulators. Here we find that for Chern insulators with inversion symmetry, the Chern number alone is insufficient to fully characterize their topology. Specifically, distinct topological phases can be differentiated based on skyrmions at different high-symmetry points. Interfaces between these topological phases exhibit gapless helical states, which provide counter-propagating transport channels and robust quantized transport. Additionally, we identify topological transitions that do not involve changes in the Chern number but can be characterized by transitions of skyrmions between high-symmetry points. These transitions arise due to the toroidal structure of the two-dimensional Brillouin zone, which is generally applicable to two-dimensional periodic lattice system. Our research introduces new degrees of freedom for controlling topological optical transport and deepens the understanding of Chern insulators with inversion symmetry.

cond-mat.mes-hall↗

arXiv2024

The General Principle behind Magnetization-induced Second-Order Topological Corner States in the Kane-Mele Model

We propose a general principle for realizing second-order topological corner states in the modified Kane-Mele model with magnetization. It is demonstrated that the sign of the edge Dirac mass depends on the magnetization of the edge sublattice termination. By adjusting the directions of magnetization according to the type of sublattice at the termination of two edges, a mass domain wall can be induced in the presence of topological corner states at an arbitrary position. All previous work on introducing magnetization in the Kane-Mele model to realize second-order topological corner states can be explained by the presence of the Dirac mass domain wall with opposite signs. Applying this principle, we design square-shaped and armchair-type hexagon-shaped graphene nanoflakes with edge magnetization, allowing for the emergence of second-order topological corner states. Our findings serve as a general theory, demonstrating that the realization of second-order topological corner states is not limited by boundary type or nanoflake shape.

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