arXiv subjects

Chenye Qin

Publications and source records attributed to Chenye Qin.

5 recordsLinked to original sources

arXiv2026

Optically locked low-noise photonic microwave oscillator

The next-generation sensing and communication applications rely on high-frequency microwave generation with low-noise. The microwave photonic technology is promising by the practical application is limited by its complex architecture so far. Here, we demonstrate an optically locked low-noise photonic microwave oscillator, so that all the optical components are packaged within a small module of 166 mL, and low noise microwave generation is achieved at 10.4 GHz with single-sideband phase noise of -54 dBc/Hz at 10 Hz, -141 dBc/Hz at 10 kHz, and -162 dBc/Hz at 10 MHz offset. Above performance arises from a dual-laser self-injection-locking scheme to a single Fabry-Perot cavity with high Q exceeding 10^8, with over 20 dB common-mode noise suppression. The low-noise nature of such reference is coherently transferred to the X-band through a high-performance TFLN electro-optic comb chip, thereby overcoming long-standing barriers in photonic microwave integration to enable truly field-deployable low-noise microwave generation.

physics.optics↗

arXiv2025

Intertwined charge and spin instability of La$_3$Ni$_2$O$_7$

Research on nickel-based superconductors has progressed from infinite-layer LaNiO$_2$ to finite-layer La$_{6}$Ni$_{5}$O$_{12}$, and most recently to the Ruddlesden-Popper phase La$_3$Ni$_2$O$_7$, which was found to exhibits onset of superconductivity at $\sim$80\,K under a pressure of $\sim$16\,GPa. Unlike the superconductivity mainly driven by the $d_{x^2-y^2}$ orbital in infinite-layer nickelates, the Ni-$d_{z^2}$ and O-2$p$ orbitals contribute significantly to the low energy states and potentially to the superconducting electron pairing mechanism of La$_3$Ni$_2$O$_7$. Employing density functional calculations and multi-orbital multi-atom cluster exact diagonalization including local exchange and Coulomb interactions, here we analyze the pressure dependent low-energy electronic states of the Ni$_2$O$_9$ cluster, relevant for the bilayer phase of La$_3$Ni$_2$O$_7$. The various possible spin states and the exchange and superexchange mechanisms of the Ni$_2$O$_9$ cluster are quantified via the involvement of the Ni-$3d_{3z^2-r^2}$ orbitals and the atomic Hund's rule exchange, the apical bridging O-$2p_z$ orbitals, and the orbitals involved in the formation of local Zhang-Rice singlet like states. We find that the leading configurations contributiong to the cluster ground-states both for nominal valence and also with local charge fluctuations, do not involve occupation of the apical oxygen, instead they favor formation of in-plane Zhang-Rice singlet like states between an O ligand hole and the Ni $3d_{z^2-y^2}$ orbital. We also highlight two possible charge and spin ordered states suggested by our cluster results, that are nearly degenerate at all relevant pressures within our modelling.

cond-mat.supr-con↗

arXiv2023

Effects of different concentrations of topotactic hydrogen impurities on the electronic structure of nickelate superconductors

Infinite-layer nickelate superconductors have recently been discovered to share both similarities and differences with cuprate superconductors. Notably, the incorporation of hydrogen (H) through topotactic reduction has been found to play a critical role in their electronic structure and, consequently, their superconductivity. In this study, we utilized a theoretical approach combining density-functional theory and impurity approximation to design three characteristic multi-orbital Hubbard models representing low, moderate, and high concentrations of topotactic-hydrogen. Consistent with experimental findings, our simulations revealed that both low and high concentrations of topotactic-hydrogen induce high-spin states ($S$=1) that are composed by holes at $d_{x^2-y^2}$ and $d_{z^2}$ orbitals and consequently the emergent inter-site hopping between $d_{z^2}$ to $d_{x^2-y^2}$ is unfavorable for superconductivity. Conversely, an optimal concentration of 25\% H aligns with the single Ni-$d_{x^2-y^2}$ band picture of superconductivity in infinite-layer nickelates, demonstrating its beneficial effect on promoting superconducting behavior.

cond-mat.supr-con↗

arXiv2023

Inversion symmetry breaking in bilayer multi-orbital Hubbard model with impurity approximation

We investigated the Cu/Ni-O$_2$ bilayer multi-orbital Hubbard model with Cu/Ni impurity approximation embedded in the O lattice by incorporating the 3d$^{8}$ multiplet structure coupled to a full O-2p band. For this simplified model of describing the local electronic structure of hole doped homo-bilayer Cu(Ni)O$_2$-Cu(Ni)O$_2$ and hetero-bilayer CuO$_2$-NiO$_2$, we demonstrate that the homo-bilayer system hosts rich phase diagram with inversion symmetry breaking between two layers at strong enough interlayer hybridization, especially the coexistence of two-hole singlet and triplet states in opposite layers. Besides, we show that the interlayer hybridization in hetero-bilayer systems destabilizes the Zhang-Rice singlets or 3d$^{8}$ triplets within each layer via charge transfer between layers. The relevance of these electronic redistribution to the bilayer or interface systems of cuprates and/or nickelates are discussed.

cond-mat.str-el↗

arXiv2021

Electrically Tunable Four-Wave-Mixing in Graphene Heterogeneous Fiber for Individual Gas Molecule Detection

Detection of individual molecules is the ultimate goal of any chemical sensor. In the case of gas detection, such resolution has been achieved in advanced nanoscale electronic solid-state sensors, but it has not been possible so far in integrated photonic devices, where the weak light-molecule interaction is typically hidden by noise. Here, we demonstrate a scheme to generate ultrasensitive down-conversion four-wave-mixing (FWM) in a graphene bipolar-junction-transistor heterogeneous D-shaped fiber. In the communication band, the FWM conversion efficiency can change steeply when the graphene Fermi level approaches 0.4 eV. In this condition, we exploit our unique two-step optoelectronic heterodyne detection scheme, and we achieve real-time individual gas molecule detection in vacuum. Such combination of graphene strong nonlinearities, electrical tunability, and all-fiber integration paves the way toward the design of versatile high-performance graphene photonic devices.

cond-mat.mes-hall↗