arXiv subjects

Yu-Xuan Li

Publications and source records attributed to Yu-Xuan Li.

11 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

Dynamical Steering and Unambiguous Signature of Majorana Corner Modes in Altermagnetic Josephson Junctions

Dynamical manipulation of Majorana zero modes and their unambiguous distinction from topologically trivial states remain paramount challenges in topological quantum computation. Here, we propose a phase-biased altermagnetic Josephson junction as a versatile platform for generating and controlling Majorana corner configurations. Moving beyond conventional global parameter tuning that merely toggles the topological phase in situ, our platform utilizes the macroscopic superconducting phase difference and the N\'eel-vector orientation as independent control knobs to dynamically reshape the boundary mass. This synergistically enables the deterministic spatial relocation of Majorana corner modes (MCMs) among selected corners of a fixed device geometry. Crucially, this spatial reconfiguration yields a definitive experimental fingerprint: a control-correlated conductance switching. As the MCMs are relocated, the quantized zero-bias peak perfectly emerges at the target corner while simultaneously vanishing at the initial one. This macroscopically phase-locked spatial correlation effectively eliminates false positives from trivial Andreev bound states, establishing a control-correlated diagnostic and a promising route toward future Majorana braiding architectures.

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↗

arXiv2026

Beyond Kasner Epochs: Ordered Oscillations and Spike Dynamics Inside Black Holes with Higher-Derivative Corrections

Building upon the long-standing paradigm that dynamics near a spacelike singularity are governed by a sequence of Kasner epochs, we demonstrate that this picture is fundamentally altered when higher-curvature or quantum gravitational corrections are included. By incorporating such terms alongside a minimally coupled scalar field, we discover three distinct dynamical phases near the singularity: modified Kasner eons, persistent periodic oscillations, and oscillatory spike dynamics with growing amplitude. In particular, the Kasner-like geometry persisting only in highly constrained situations. The latter two regimes represent a clean departure from classical Kasner phenomenology, revealing a richer and more ordered landscape of behaviors in the deep interior of black holes beyond Einstein gravity. This work establishes a comprehensive approach for understanding the gravitational nonlinearity in the most extreme gravitational environment.

gr-qc↗

arXiv2025

Tunable Topological Superconductivity by Fully Compensated Ferrimagnets

We propose a platform based on a fully compensated ferrimagnet (fFIM) for realizing and controlling topological superconductivity with Majorana bound states across multiple dimensions. Through symmetry analysis and microscopic modeling, we demonstrate that fFIM-based heterostructures host (i) Majorana zero modes localized at the ends of one-dimensional nanowires, (ii) chiral Majorana edge states along two-dimensional boundaries, and (iii) tunable Majorana corner modes in higher-order topological phases. The unique properties of fFIMs enable an electric field to drive topological superconductivity phase transitions and N\'eel vector orientation to control the spatial distribution of Majorana modes, without external magnetic fields. Crucially, the absence of net magnetization in fFIM-based heterostructures preserves superconductivity, circumventing the usual trade-off between tunability and superconducting coherence in magnetized systems. Our results establish fFIM-based heterostructures as a versatile platform for tunable topological superconductivity.

cond-mat.supr-con↗

arXiv2024

Creation and Manipulation of Higher-Order Topological States by Altermagnets

We propose to implement tunable higher-order topological states in a heterojunction consisting of a two-dimensional (2D) topological insulator and the recently discovered altermagnets, whose unique spin-polarization in both real and reciprocal space and null magnetization are in contrast to conventional ferromagnets and antiferromagnets. Based on symmetry analysis and effective edge theory, we show that the special spin splitting in altermagnets with different symmetries, such as $d$-wave, can introduce Dirac mass terms with opposite signs on the adjacent boundaries of the topological insulator, resulting in the higher-order topological state with mass-domain bound corner states. Moreover, by adjusting the direction of the N\'{e}el vector, we can manipulate such topological corner states by moving their positions. By first-principles calculations, taking a 2D topological insulator bismuthene with a square lattice on an altermagnet MnF$_2$ as an example, we demonstrate the feasibility of creating and manipulating the higher-order topological states through altermagnets. Finally, we discuss the experimental implementation and detection of the tunable topological corner states, as well as the potential non-Abelian braiding of the Dirac corner fermions.

cond-mat.mes-hall↗

arXiv2023

Majorana corner modes and tunable patterns in an altermagnet heterostructure

The mutual competition and synergy of magnetism and superconductivity provide us with a very valuable opportunity to access topological superconductivity and Majorana Fermions. Here, we devise a heterostructure consisting of an $s$-wave superconductor, a 2D topological insulator and an altermagnet, which is classified as the third magnet and featured by zero magnetization but spin polarization in both real and reciprocal spaces. We find that the altermagnet can induce mass terms at the edges that compete with electron pairing, and mass domains are formed at the corners of sample, resulting in zero-energy Majorana corner modes (MCMs). The presence or absence of MCMs can be engineered by only changing the direction of the Néel vector. Moreover, uniaxial strain can effectively manipulate the patterns of the MCMs, such as moving and interchanging MCMs. Experimental realization, remarkable advantages of our proposal and possible braiding are discussed.

cond-mat.supr-con↗

arXiv2023

High-temperature Majorana corner modes in a $d+id'$ superconductor heterostructure: Application to twisted bilayer cuprate superconductors

The realization of Majorana corner modes generally requires unconventional superconducting pairing or $s$-wave pairing. However, the bulk nodes in unconventional superconductors and the low $T_c$ of $s$-wave superconductors are not conducive to the experimental observation of Majorana corner modes. Here we show the emergence of a Majorana corner mode at each corner of a two-dimensional topological insulator in proximity to a $d+id'$ pairing superconductor, such as heavily doped graphene or especially a twisted bilayer of a cuprate superconductor, e.g., Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$, which has recently been proposed as a fully gapped chiral $d_{x^2-y^2}+id_{xy}$ superconductor with $T_c$ close to its native 90 K, and an in-plane magnetic field. By numerical calculation and intuitive edge theory, we find that the interplay of the proximity-induced pairing and Zeeman field can introduce opposite Dirac masses on adjacent edges of the topological insulator, which creates one zero-energy Majorana mode at each corner. Our scheme offers a feasible route to achieve and explore Majorana corner modes in a high-temperature platform without bulk superconductor nodes.

cond-mat.supr-con↗

arXiv2022

Higher order topological state induced by $d$-wave competing orders in high-T$_c$ superconductor based heterostructure

We introduce a two-dimensional Chern insulator in proximity to a $d$-wave pseudogap state of the high-T$_c$ superconducting material as an effective platform to realize the higher order topological system. The proximity-induced $d$-density-wave (DDW) order in the Chern insulator layer serves as an effective mass. The edge states will be fully gapped by this DDW order. In the real space, the sign of the DDW order parameter changes at the system corners due to the $d$-wave factor, leading to the gapless corner states, indicating that this system may be in a higher order topological state. The higher order topology in this coupled system is confirmed based on the calculation of the edge polarization and the quadrupole moment. In the superconducting state where the superconducting order and the DDW order coexist, the Majorana corner states emerge.

cond-mat.supr-con↗

arXiv2020

Rotational symmetry breaking and partial Majorana corner states in a high-Tc superconductor based heterostructure

Applying a microscopic model, we study theoretically the quasiparticle excitation of a twodimensional topological insulator (TI) being in proximity to a high-Tc superconductor. In the momentum space, the proximity induced pairing term in the TI layer includes both the singlet channel and triplet channel, leading to the C4 rotational symmetry breaking of the energy bands and the quasiparticle spectra. For a cylinder geometry, the zero energy edge states may appear but they are localized at the upper boundary. For the finite-size system with open boundaries, the zero energy states at the upper boundary disappear and the Majorana bound states emerge at the two lower corners. All of the results can be understood well through exploring the pairing order parameter and the anomalous Green's function.

cond-mat.supr-con↗

arXiv2019

Thick-Net: Parallel Network Structure for Sequential Modeling

Recurrent neural networks have been widely used in sequence learning tasks. In previous studies, the performance of the model has always been improved by either wider or deeper structures. However, the former becomes more prone to overfitting, while the latter is difficult to optimize. In this paper, we propose a simple new model named Thick-Net, by expanding the network from another dimension: thickness. Multiple parallel values are obtained via more sets of parameters in each hidden state, and the maximum value is selected as the final output among parallel intermediate outputs. Notably, Thick-Net can efficiently avoid overfitting, and is easier to optimize than the vanilla structures due to the large dropout affiliated with it. Our model is evaluated on four sequential tasks including adding problem, permuted sequential MNIST, text classification and language modeling. The results of these tasks demonstrate that our model can not only improve accuracy with faster convergence but also facilitate a better generalization ability.

cs.LG↗