arXiv subjects

Yanmei Cai

Publications and source records attributed to Yanmei Cai.

3 recordsLinked to original sources

arXiv2026

Tuning superconducting pairing symmetry via a staggered potential in the doped honeycomb Hubbard model

The ability to control superconducting pairing symmetry is crucial for designing unconventional and topological superconductors, yet practical tuning parameters beyond chemical doping remain limited. In this study, we investigate the effect of a tunable sublattice staggered potential on the pairing symmetry in the doped honeycomb Hubbard model. Determinant quantum Monte Carlo at finite temperature and constrained-path quantum Monte Carlo at zero temperature are employed to compute spin susceptibilities and pairing correlations in different channels. We find that increasing the staggered potential suppresses antiferromagnetic fluctuations and, at low doping, induces a transition in the dominant pairing tendency from $d+id$-wave to $f_n$-wave, with consistent results from both quantum Monte Carlo methods. In contrast, at higher doping levels, the system remains dominated by $d+id$-wave pairing even under an enhanced staggered potential. Moreover, strengthening the on-site interaction $U$ enhances the dominant pairing channel, underscoring the essential role of electronic correlations. Our results establish the staggered potential as a practical band-engineering tool for selecting unconventional pairing symmetries without varying the doping concentration, providing inspiration for designing graphene-based artificial superconductors and related doped band insulators such as Li${}_x$MNCl.

cond-mat.str-el↗

arXiv2026

Magnetic correlations and superconducting pairing near higher-order Van Hove singularities

Higher-order Van Hove singularities in strongly correlated electron systems provide a fertile ground for emergent electronic orders and superconductivity. This study investigates the interplay between magnetic fluctuations and superconducting pairing near higher-order Van Hove singularities on the honeycomb lattice, a paradigmatic platform relevant to graphene. By incorporating third-nearest-neighbor hopping $t''$, we uncover a universal crossover: ferromagnetic fluctuations dominate below the higher-order Van Hove filling, while antiferromagnetic fluctuations take over toward half filling. A key finding is that the already dominant $f_n$-wave pairing is enhanced in the critical region of this magnetic crossover by the higher-order Van Hove. This enhancement is driven by the synergistic effect of the higher-order Van Hove singularities-induced divergent density of states and the competing magnetic fluctuations. Although increased hopping parameters generally suppress superconducting correlation, we identify a critical $t''$ that anomalously enhances pairing via the higher-order Van Hove renormalization. Furthermore, the nearest-neighbor Coulomb interaction suppresses the pairing correlation function in a sign-independent manner. Our results clarify the competitive mechanisms between magnetic fluctuations and unconventional superconductivity in higher-order Van Hove singularities systems, offering a theoretical basis for tailoring quantum phases in graphene-based materials via band engineering.

cond-mat.str-el↗

arXiv2025

Pairing Symmetry Crossover from $d$-wave to $s_{\pm}$-wave in a Bilayer Nickelate Driven by Hund's Coupling and Crystal Field Splitting

The pairing symmetry of the recently discovered bilayer nickelate superconductor La$_3$Ni$_2$O$_7$ is a subject of intense debate in condensed matter physics, with the two leading theoretical candidates being a sign-reversing $s_{\pm}$-wave and a $d$-wave state. To investigate its ground-state properties in the intermediate coupling regime which is critical for real materials, we construct a two-orbital bilayer Hubbard model and employ the constrained-path quantum Monte Carlo method for large-scale simulations. By systematically calculating ground-state pairing correlation functions across parameter spaces, we map its pairing symmetry phase diagram. We find that an increasing Hund's coupling selectively enhances the interlayer $s_{\pm}$-wave pairing while suppressing the intralayer $d$-wave pairing. Similarly, a larger crystal field splitting drives a transition from $d$-wave- to $s_{\pm}$-wave-dominant states. Further analysis reveals that the strength of the intralayer $d$-wave pairing is strongly correlated with the $(π, π)$ antiferromagnetic spin fluctuations, which are in turn effectively suppressed by a large crystal field splitting, thereby weakening the $d$-wave pairing channel. Additionally, the dominant pairing symmetry transition region roughly overlaps with the inversion of orbital occupancy response to Hubbard $U$, suggesting an intrinsic link between pairing competition and orbital physics. Our results indicate that, within the parameter regime relevant to the actual material, the $s_{\pm}$-wave is the most probable pairing symmetry.

cond-mat.str-el↗