arXiv subjects

Chengcheng Xiao

Publications and source records attributed to Chengcheng Xiao.

7 recordsLinked to original sources

arXiv2026

Self-Synchronized Terahertz and X-Ray Free-Electron Lasers from a Single Pre-Bunched Electron Beam

Ultrafast pump-probe spectroscopy combining intense terahertz (THz) and X-ray pulses is a critical tool for investigating complex structural and electronic dynamics in materials. However, current setups combining THz sources and X-ray free-electron lasers (FELs) often suffer from high system complexity, inherent timing jitter, or limited THz pulse properties. Here, we experimentally demonstrate the generation of intrinsically synchronized, strong-field, narrow-band THz and X-ray FELs from a single pre-bunched electron beam. Sequentially passing the beam through X-ray and THz amplifiers reveals a highly synergistic process: the initial periodic THz density modulation notably boosts the X-ray FEL pulse energy, while robustly surviving the intense X-ray emission to drive high-power, narrow-band THz radiation. Originating from the same electron bunch, the two pulses inherently maintain a precise, constant time delay. This jitter-free scheme establishes a highly reliable platform tailored for both X-ray-pump/THz-probe and THz-pump/X-ray-probe experiments.

physics.acc-ph↗

arXiv2026

Theory and Discovery of Electrides

Electrides are materials with electrons localized at interstitial regions of the crystal lattice and have been identified as promising candidates for a variety of applications, including catalysis, electron emission, and superconductivity. We present a theoretical framework for the origin of interstitial electrons in electrides. We demonstrate that this theory can explain electride-like behavior in prototypical electrides, and we use it to develop descriptors for the high-throughput discovery of new inorganic electride candidates from first principles. We also show that the same concepts can explain electride-like behavior in other classes of material, including high-pressure electrides and organic electrides and, more broadly, provide an alternative understanding of F-center defects and solvated electrons.

cond-mat.mtrl-sci↗

arXiv2026

Demonstration of High-Gain Harmonic Lasing in a Terahertz Free-Electron Laser

Compact Free-Electron Lasers (FELs) offering broad, continuous spectral tunability are traditionally constrained by fixed-parameter magnetic structures and the necessity for high-energy electron beams. High-gain Harmonic Lasing (HL) has long been proposed as a solution to overcome these limitations; however, a robust experimental verification of this principle has remained absent. Here, we report the first experimental demonstration of high-gain HL. By employing a frequency-tunable electron beam density modulation to dominate the fundamental instability, we achieved sustained FEL amplification at the 3rd and 5th harmonics of the wiggler. The HL mode generated output power comparable to conventional fundamental operation with enhanced stability and narrower spectral bandwidth. Notably, we demonstrate that HL extends the spectral coverage by a factor of two under fixed facility constraints, achieving pulse energies up to 540 {\mu}J. These results establish high-gain HL as a versatile mechanism for advancing compact, wavelength-flexible FEL facilities.

physics.acc-ph↗

arXiv2025

Hot-carrier generation in bimetallic Janus nanoparticles

Energetic electrons and holes generated from the decay of localized surface plasmons in metallic nanoparticles can be harnessed in nanoscale devices for photocatalysis, photovoltaics or sensing. In this work, we study the generation of such hot carriers in bimetallic Janus nanoparticles composed of Au, Ag and Cu using a recently developed atomistic modelling approach that combines a solution of the macroscopic Maxwell equation with large-scale quantum-mechanical tight-binding models. We first analyze spherical Janus nanoparticles whose unique hot-carrier spectrum can be associated with the spectra of the two hemispheres and the interface coupling and find that under solar illumination the Ag-Au system exhibits the highest hot-carrier generation rate. For dumbbell-shaped Janus nanoparticles, we observe a significant increase in hot-carrier generation with increasing neck size. This is caused by a dramatic enhancement of the electric field in the neck region. We also study the dependence of hot-carrier generation on the light polarization and find that the largest generation rates are obtained when the electric field is perpendicular to the interface between the two metals due to the maximal dipole coupling with the electric field. The insights from our study will guide the experimental design of efficient hot-carrier devices based on bimetallic Janus nanoparticles.

physics.optics↗

arXiv2020

Origin and Electronic Behavior of Improper Ferroelectricity in AB2 (A=Cr, Mo, W; B=S, Se, Te) Transition Metal Dichalcogenides

Persistent electrical polarized states are fundamentally important to the electric industry as they can be used in the non-volatile memory, the artificial neuromorphic network, and negative capacitors, making ultralow energy consumption electronic devises possible. With the recent development in low dimensional ferroelectric materials, emerging 2D out-of-plane ferroelectric materials like MoTe2 have great potential for future development. Despite previous phenomenological studies, the underlying microscopic origin of ferroelectricity is still missing. Here, using density functional theory and Wannier function methods, we reveal that the origin of ferroelectricity of these transition metal dichalcogenides comes from the Jahn taller effect and followed by a covalent bonding between transition metal atoms. Moreover, the atypical electronic behavior of these monolayer AB2 (A=Cr, Mo, W; B=S, Se, Te) TMDs compare to traditional improper ferroelectrics hints a strong electronic origin of the polarization, suitable for future industrial applications.

cond-mat.mes-hall↗

arXiv2019

Superconducting phase diagram and nontrivial band topology of structurally modulated Sn$_{1-x}$Sb$_{x}$

We report the discovery of superconductivity in binary alloy Sn$_{1-x}$Sb$_{x}$ with $x$ in the range of 0.43 to 0.6, which possesses a modulated rhombohedral structure due to the incommensurate ordering of Sn and Sb layers along the $c$-axis. The specific heat measurements indicate a weakly coupled, fully gapped superconducting state in this homogeneity range with a maximum bulk $T_{\rm c}$ of 1.58 K at $x$ = 0.46, though the electronic specific heat and Hall coefficients remain nearly $x$-independent. The nonmonotonic dependence of the bulk $T_{\rm c}$ is discussed in relation to the effects of Sb-layer intercalation between the [Sn$_{4}$Sb$_{3}$] seven-layer lamellae that are the essential building block for superconductivity. On the other hand, a zero-resistivity transition is found to take place well above the bulk superconducting transition, and the corresponding $T_{\rm c}$ increases monotonically with $x$ from 2.06 K to 3.29 K. This contrast, together with the uniform elements distribution revealed by energy dispersive x-ray mapping, implies that the resistive transition is due to the strain effect at the grain boundary rather than the compositional inhomogeneity. The first-principles calculations on the representative composition Sn$_{4}$Sb$_{3}$ ($x$ = 0.43) indicate that it is topologically nontrivial similar to Sb, but with different Z$_{2}$ invariants (0;111). Our results not only identify a new superconducting region in the Sn-Sb phase diagram, but also provide a viable platform to study the interplay between structural modulation, nontrivial band topology and superconductivity.

cond-mat.supr-con↗

arXiv2017

Ferroelectricity and Antiferroelectricity in Elemental Group-V Monolayer Materials

Ferroelectricity is usually found in compound materials composed by different elements. Here, based on first-principles calculations, we reveal the first example of spontaneous electrical polarization and ferroelectricity in stable two-dimensional elemental materials: elemental Group-V (As, Sb, and Bi) monolayers. The polarization is due to the spontaneous lattice distortion with atomic layer buckling. Interestingly, for Bi monolayer, apart from the ferroelectric phase, we find that it can also host an antiferroelectric phase. The Curie temperatures of these elemental materials can be higher than room temperature, making them promising for realizing ultrathin ferroelectric devices of broad interest.

cond-mat.mtrl-sci↗