arXiv subjects

Junkang Huang

Publications and source records attributed to Junkang Huang.

12 recordsLinked to original sources

arXiv2026

Sequential Topological Superconductivity in a Square Lattice with Chiral Charge Density Waves

The interplay between charge order and superconductivity offers a fertile ground for emergent quantum phases. Here we theoretically investigate a square-lattice superconductor coexisting with a composite charge density wave (CDW) consisting of a real bond modulation (charge bond order, CBO) and an imaginary hopping modulation (chiral flux phase, CFP) that breaks time-reversal symmetry. We uncover that, while CFP alone does not induce topology in square lattices, its coexistence with CBO drives the system into two topologically nontrivial superconducting phases with Chern numbers $C=+2$ and $C=-2$. The low-temperature thermal Hall conductivity $\kappa_{xy}$ exhibits quantized plateaus proportional to the Chern number, providing a clear experimental fingerprint. Our results establish the square lattice as a pristine platform for engineering topological superconductivity through the synergy of real and imaginary bond modulations.

cond-mat.supr-con↗

arXiv2026

Direction-selective triplet pairing and spin-edge locking in altermagnetic metals

We investigate self-consistent unconventional superconductivity in a two-dimensional $d$-wave altermagnetic metal. We find that momentum-dependent altermagnetic spin splitting suppresses opposite-spin singlet pairing and stabilizes highly anisotropic equal-spin triplet order. In the spin-conserving limit, this directional triplet pairing gives rise to nearly dispersionless Majorana boundary states associated with effective one-dimensional topological channels. Rashba spin-orbit coupling mixes spin sectors, activates additional pairing components, and drives the system into a mixed-parity superconducting state with dispersive Majorana boundary states. The spin-resolved boundary spectra further reveal a characteristic locking between boundary orientation and spin polarization, reflecting the underlying altermagnetic symmetry. These results identify altermagnetic spin splitting as an intrinsic mechanism for selecting unconventional pairing and generating spin-resolved Majorana boundary states without external magnetic fields.

cond-mat.supr-con↗

arXiv2025

Central Charges and Vacuum Moduli of 2d $\mathcal{N}=(0,4)$ Theories from Class $\mathcal{S}$

We investigate 2d $\mathcal{N}=(0,4)$ supersymmetric theories obtained from a topologically-twisted reduction of 4d $\mathcal{N}=2$ class $\mathcal{S}$ theories on a Riemann surface. This study addresses subtle aspects of central charges, unbroken gauge groups, and emergent superconformal R-symmetries of these theories. Focusing on infrared vacuum structures, we propose conjectural formulas for the central charges. For theories with the gauge group $SU(2)$, we use a Lagrangian description to analyze the vacuum moduli spaces. In particular, we examine two distinct branches -- the special Higgs branch and the twisted Higgs branch -- by computing their Hilbert series, and find agreement with the proposed central charge formulas.

hep-th↗

arXiv2025

Higher-order topological superconductivity in type-II time-reversal-symmetric Weyl semimetals with a hybrid pairing

We employed the self-consistent method on a two-orbital type-II time-reversal-symmetric Weyl semimetal, revealing a hybrid pairing of singlet $s$-wave and triplet $p$-wave. We present a detailed analysis of the normal-state electronic structure and the self-consistent results. Our findings indicate that the selection of hybrid pairings is governed by distinct surface Fermi-arc configurations: specifically, $s$-wave pairing dominates on the bottom surface, while $p$-wave pairing prevails on the top. Furthermore, the emergent superconducting state is a second-order topological superconductors with hinge states in the system. Our results identify type-II time-reversal-invariant Weyl semimetals as a promising intrinsic platform for realizing unconventional and topological superconductivity.

cond-mat.supr-con↗

arXiv2025

Effective perpendicular electric field as a probe for interlayer pairing in ambient-pressure superconducting La$_{2.85}$Pr$_{0.15}$Ni$_{2}$O$_{7}$ thin films

Recent angle-resolved photoemission spectroscopy (ARPES) experiments on La$_{2.85}$Pr$_{0.15}$Ni$_2$O$_7$ thin films have revealed a superconducting gap near the diagonal direction for the $d_{x^2-y^2}$ orbital, confined to a narrow momentum region. Our numerical calculations indicate that interlayer pairing is dominant, resulting in an $s_\pm$-wave symmetry. We propose employing perpendicular electric fields, a practical method in thin film systems, to verify the pairing symmetry. Our calculations predict that such fields will induce Fermi arcs or nodal points and significantly modulate the gap near the diagonal, with the modulated region overlapping the area probed by ARPES. This approach provides an effective tool for probing pairing symmetry in bilayer nickelate thin films, especially given current limitations in experimental techniques.

cond-mat.supr-con↗

arXiv2025

Probing Sign-Changing Order Parameters via Impurity States in unconventional superconductors: Implications for La$_3$Ni$_2$O$_7$ Superconductors with interlayer pairing

Motivated by the desire to investigate the fundamental relationship between impurity-induced states and the sign change of the superconducting order parameter, as well as to explore the impurity effects in Ruddlesden-Popper nickelate superconductors with interlayer pairing, we employ the $T$-matrix approach to study single impurity scattering in unconventional superconductors. Our work focuses on two distinct pairing scenarios: intralayer $d$-wave pairing and interlayer $s$-wave pairing. For systems with intralayer $d$-wave pairing, we establish an intrinsic connection between the $d$-wave pairing symmetry and the emergence of mid-gap resonant states. Through a combination of analytical derivations and numerical simulations, we demonstrate that the appearance of in-gap states is directly linked to the sign reversal of the order parameter along the Fermi surface. In interlayer pairing systems, our results reveal the presence of pronounced resonant peaks, which can also be attributed to the sign-changing nature of the order parameter. We further extend our analysis to the bilayer nickelate superconductor La$_3$Ni$_2$O$_7$, providing a theoretical investigative of impurity effects in this material. Our findings not only elucidate the complex interplay between pairing symmetries and impurity-induced states in unconventional superconductors but also offer a powerful tool for probing the pairing mechanisms in nickelate-based high-temperature superconductors. This work lays the groundwork for future experimental and theoretical investigations into the unique electronic properties of these emerging materials.

cond-mat.supr-con↗

arXiv2024

Branes and Representations of DAHA $C^\vee C_1$: affine braid group action on category

We study the representation theory of the spherical double affine Hecke algebra (DAHA) of $C^\vee C_1$, using brane quantization. By showing a one-to-one correspondence between Lagrangian $A$-branes with compact support and finite-dimensional representations of the spherical DAHA, we provide evidence of derived equivalence between the $A$-brane category of $\mathrm{SL}(2,\mathbb{C})$-character variety of a four-punctured sphere and the representation category of DAHA of $C^\vee C_1$. The $D_4$ root system plays an essential role in understanding both the geometry and representation theory. In particular, this $A$-model approach reveals the action of an affine braid group of type $D_4$ on the category. As a by-product, our geometric investigation offers detailed information about the low-energy effective dynamics of the SU(2) $N_f=4$ Seiberg-Witten theory.

hep-th↗

arXiv2024

Constraints on the orbital flux phase in $A$V$_3$Sb$_5$ from polar Kerr effect

The $A$V$_3$Sb$_5$ ($A=$ K, Rb, Cs) family of Kagome metals hosts unconventional charge density wave order whose nature is still an open puzzle. Accumulated evidences point to a time-reversal symmetry breaking orbital flux phase that carries loop currents. Such an order may support anomalous Hall effect. However, the polar Kerr effect measurements that probe the a.c. anomalous Hall conductivity seems to have yielded contradictory results. We first argue on symmetry grounds that some previously proposed orbital flux order, most notably the one with Star-of-David distortion, shall not give rise to anomalous Hall or polar Kerr effects. We further take the tri-hexagonal orbital flux phase as an exemplary Kagome flux order that does exhibit anomalous Hall response, and show that the Kerr rotation angle at two relevant experimental optical frequencies generally reaches microradians to sub-milliradians levels. A particularly sharp resonance enhancement is observed at around $\hbar \omega =1$ eV, suggesting exceedingly large Kerr rotation at the corresponding probing frequencies not yet accessed by previous experiments. Our study can help to interpret the Kerr measurements on $A$V$_3$Sb$_5$ and to eventually resolve the nature of their CDW order.

cond-mat.mes-hall↗

arXiv2024

Impact of Charge Density Waves on Superconductivity and Topological Properties in AV$_3$Sb$_5$ Kagome Superconductors

We investigates the electronic structure and superconducting gaps in the charge density wave (CDW) states of vanadium-based Kagome superconductors AV$_3$Sb$_5$, focusing on the concurrent presence of CDW and superconducting orders. Two predominant CDW configurations are explored: the trihexagonal (TrH) and star-of-David (SoD) patterns, involving charge bond order (CBO) and chiral flux phase (CFP), corresponding to real and imaginary bond orders. In the isotropic $s$-wave superconducting state, the presence of CBO alone maintains an isotropic superconducting gap, whereas the introduction of CFP induces anisotropy in the gap, manifesting time-reversal symmetry breaking due to the CFP. Our analysis extends to the topological properties of these states, revealing a marked topological phase transition in the TrH configuration from a trivial to a non-trivial state with increasing CFP intensity. This transition suggests that the introduction of CFP could catalyze the emergence of topological superconductivity, potentially leading to the presence of Majorana excitations. The results contribute significantly to understanding the complex interplay between various CDW patterns and superconductivity in Kagome superconductors. They provide a theoretical framework for the diverse experimental observations of energy gaps and open new avenues for research into topological superconductivity and its potential applications. This study underscores the necessity for further experimental and theoretical exploration to unveil novel interwinded quantum states and functionalities in these intriguing materials.

cond-mat.supr-con↗

arXiv2024

Interlayer Pairing Induced Partially Gapped Fermi Surface in Trilayer La$_4$Ni$_3$O$_{10}$ Superconductors

We explore the superconducting pairing mechanisms in the trilayer $\mathrm{La}_4\mathrm{Ni}_3\mathrm{O}_{10}$ material through self-consistent mean-field calculations. Our findings demonstrate that intralayer pairings are substantially weaker compared to interlayer ones. Remarkably, in the state characterized by interlayer pairing, we detect the presence of partially gapped Fermi surfaces, a fascinating occurrence attributable to the disparity between the inner and outer conducting layers of $\mathrm{La}_4\mathrm{Ni}_3\mathrm{O}_{10}$. Moreover, this study provides valuable insights into the lower superconducting transition temperatures observed in $\mathrm{La}_4\mathrm{Ni}_3\mathrm{O}_{10}$ compounds. This contributes to a deeper understanding of its distinct superconducting attributes.

cond-mat.supr-con↗

arXiv2024

Exotic Topological Phenomena in Chiral Superconducting States on Doped Quantum Spin Hall Insulators with Honeycomb Lattices

We have conducted a theoretical investigation of the topological phenomena associated with chiral superconducting pairing states induced in a doped Kane-Mele model on a honeycomb lattice. Through numerical analysis, we have obtained exotic phase diagrams for both the $d+id$ and $p+ip$ superconducting states. In the case of the $d+id$ pairing state, higher Chern number states with $\left| C \right| = \pm 4$ emerge. The Chern number decreases as the spin-orbit coupling is introduced. For the $p+ip$ pairing state, additional phase transition lines are present in the overdoped region near the Van Hove singularity point, leading to the emergence of higher Chern number phases with $\left| C \right| = \pm 6$. These higher Chern number phases are further verified through the bulk-edge correspondence. To understand the origin of the exotic topological phase diagrams in the chiral superconducting state, we have examined the electronic structure at the phase transition lines. This investigation provides insight into the complex interplay between chiral superconductivity and topological properties, potentially paving the way for the discovery of new materials with unique topological properties.

cond-mat.supr-con↗

arXiv2023

Impurity and vortex States in the bilayer high-temperature superconductor $\mathrm{La}_3\mathrm{Ni}_2\mathrm{O}_7$

We perform a theoretical examination of the local electronic structure in the recently discovered bilayer high-temperature superconductor ${\mathrm{La}_3\mathrm{Ni}_2\mathrm{O}_7}$. Our method begins with a bilayer two-orbital tight-binding model, incorporating various pairing interaction channels. We determine superconducting order parameters by self-consistently solving the real-space Bogoliubov-de Gennes (BdG) equations, revealing a robust and stable extended s-wave pairing symmetry. We investigate the single impurity effect using both self-consistent BdG equations and non-self-consistent T-matrix methods, uncovering low-energy in-gap states that can be explained with the T-matrix approach. Additionally, we analyze magnetic vortex states using a self-consistent BdG technique, which shows a peak-hump structure in the local density of states at the vortex center. Our results provide identifiable features that can be used to determine the pairing symmetry of the superconducting ${\mathrm{La}_3\mathrm{Ni}_2\mathrm{O}_7}$ material.

cond-mat.supr-con↗