arXiv subjects

Linghao Huang

Publications and source records attributed to Linghao Huang.

7 recordsLinked to original sources

arXiv2026

Vortex-Number-Controlled Josephson Diode Polarity in Corbino Junctions

We demonstrate that the polarity of the Josephson diode effect in Corbino Josephson junctions can be deterministically controlled by the Josephson-vortex number, which arises as a generic consequence of structured spatial inhomogeneity. By solving the continuum Andreev spectral problem, we identify a mechanism in which the vortex number selectively filters specific spatial Fourier harmonics of the local inhomogeneity. This harmonic selection reshapes the amplitudes and relative phases of higher-order Josephson current harmonics, ultimately reversing the critical-current asymmetry. Numerical simulations of both an effective one-dimensional edge model and full two-dimensional lattice models confirm the robustness of this mechanism. Crucially, our results show that a vortex-parity-dependent reversal of diode polarity is not an exclusive signature of Majorana physics, but can emerge generically from geometric and structural inhomogeneities in Corbino junctions.

cond-mat.supr-con↗

arXiv2026

Revisiting quadratic band crossing: from interaction-driven instability to intrinsic topology

The realization of robust quantum anomalous Hall (QAH) phases at elevated temperatures remains a central challenge in condensed matter physics. While quadratic band crossing points (QBCP) provide a promising route towards QAH states, existing proposals are largely confined to idealized models or hindered by interaction-driven competing orders. Here, we demonstrate that these limitations are not intrinsic to QBCP but arise from their specific implementation. We propose a general mechanism where band inversion between a symmetry-protected orbital doublet (e.g. $d_{xz},d_{yz}$) and an isolated orbital (e.g. $d_{z^2}$)-generically generates a QBCP with opposite curvature. This crossing is directly gapped at the single-particle level by intrinsic atomic spin-orbit coupling, while the underlying band inversion naturally shields the resulting topological gap against other interaction-driven instabilities. We further suggest monolayer compounds $MNX_2$ ($M$= Ni, Pd, Pt; $N$= Nb, Ta; $X$= S, Se, Te) as a realistic material class that intrinsically realizes this mechanism. These findings provide a concrete pathway toward robust QAH phases in correlated materials.

cond-mat.mes-hall↗

arXiv2026

Moir\'e Ferroelectricity-Driven Band Engineering in Twisted Square Bilayers

We develop the moir\'e band theory for M-valley twisted square homobilayers with layer groups $P$-$42m$ and $P$-$4m2$, and propose candidate material realizations. We show that moir\'e ferroelectricity-originating from sliding ferroelectricity in the untwisted bilayers-provides an independent control knob for miniband engineering in addition to interlayer tunneling. The competition between these two effects enables controlled switching between layer-resolved bilayer minibands and an effective single isolated miniband. Remarkably, these systems exhibit an emergent momentum-space nonsymmorphic symmetry in the absence of external magnetic fields. Large-scale \emph{ab initio} calculations identify Cu$_2$WS$_4$ and GeCl$_2$ as representative materials realizing the ferroelectricity- and tunneling-dominated regimes, respectively. Our results establish twisted square homobilayers as a promising platform for correlated band engineering beyond moir\'e hexagonal systems.

cond-mat.mes-hall↗

arXiv2025

Revealing Superconducting Chiral Edge Modes via Resistance Distributions

Inducing superconducting correlations in quantum anomalous Hall (QAH) states offers a promising route to realize topological superconductivity with chiral Majorana edge modes. However, the definitive identification of these modes is challenging. Here we propose detecting superconducting chiral edge modes via the probability distribution of the resistance, or equivalently the charge transmission of QAH-superconductor heterojunctions. Remarkably, the distribution for coherent edge exhibits distinct characteristics for different topological superconducting phases in sufficiently long junctions, and this difference remains robust against weak decoherence. These findings provide insights into transport phenomena beyond the clean limit and highlight the resistance distribution as a compelling signature for distinguishing topological superconducting phases.

cond-mat.mes-hall↗

arXiv2024

Edge optical effect as a probe of chiral topological superconductors

We study the optical effect of chiral topological superconductors in two dimensions. The linear optical response from chiral Bogoliubov edge modes in clean superconductors has in-gap resonances, which is originated from the transitions within the edge particle-hole pair bands. Interestingly, the number of resonance peaks is determined by the Bogoliubov-de Gennes Chern number of topological superconductors. Such a sharply distinctive feature in optical absorption offers a simple way to distinguish topological superconductors with different Chern numbers. We further demonstrate that linear optical effect could probe different topological phases in quantum anomalous Hall insulator-superconductor junction devices. This finding provides an applicable method to detect chiral Bogoliubov edge states and is distinguishable from collective modes in superconductors and possible trivial explanations.

cond-mat.mes-hall↗

arXiv2023

Second-order optical response of superconductors induced by supercurrent injection

We develop a theory of the nonlinear optical responses in superconducting systems in the presence of a dc supercurrent. The optical transitions between particle-hole pair bands across the superconducting gap are allowed in clean superconductors as the inversion symmetry breaking by supercurrent. Vertex correction is included in optical conductivity to maintain the $U(1)$ gauge symmetry in the mean-field formalism, which contains the contributions from collective modes. We show two pronounced current-dependent peaks in the second-harmonic generalization $σ^{(2)}(2ω,ω,ω)$ at the gap edge $2\hbarω=2Δ$ and $\hbarω=2Δ$ and one in the photocurrent effect $σ^{(2)}(0,ω,-ω)$ at $\hbarω=2Δ$, all of which diverge in the clean limit. We demonstrate this in the models of a single-band superconductor with $s$-wave and $d$-wave pairings, and Dirac fermion systems with $s$-wave pairing. Our theory predicts that the current-induced peak in $\text{Im}[σ^{(2)}(ω)]$ is proportional to the square of the supercurrent density in the $s$-wave single-band model, with the same order of magnitude as the recent experimental observation of second-harmonic generation in NbN by Nakamura et al. [Phys. Rev. Lett. 125, 097004 (2020)]. Supercurrent induced nonlinear optical spectroscopy provides a valuable toolbox to explore novel superconductors.

cond-mat.supr-con↗

arXiv2023

Josephson Diode Effect in Topological Superconductor

We investigate the Josephson diode effect (JDE) in topological Josephson junctions. By both analytic and numerical calculations, we find that while a Josephson junction in the topological phase may exhibit higher diode efficiency compared to that in the trivial phase, this behavior is not universal. The presence of Majorana bound states is not a sufficient condition for a large diode effect. Furthermore, the diode efficiency undergoes substantial changes only in specific regions along the topological phase transition boundary, and a significant diode effect does coincide with the topological phases. Thereby our paper suggests the utilization of topological superconductivity for enhanced JDE, and also the Josephson diode effect may serve as an indicator for topological superconductor phase. These results suggest a nuanced relationship between the topological aspects of Josephson junctions and Josephson diode effect.

cond-mat.supr-con↗