arXiv subjects

Zhiyu Tao

Publications and source records attributed to Zhiyu Tao.

6 recordsLinked to original sources

arXiv2026

Dimensionality-Dependent Exciton Dispersion in a Single-Band Mott Insulator

Excitonic band structure is critical for investigating exciton dynamics. Theoretically, quantum effects from exchange scattering between electron-hole pairs significantly modulate exciton dispersion. Here, we report the direct observation of dimensionality-dependent exciton dispersion in a single-band Mott insulator Nb3Cl8 through high-resolution electron energy loss spectroscopy. In the high-temperature phase, the exciton in Nb3Cl8 hosts an exceptionally large binding energy, and exhibits clear quasi-two-dimensional massless linear dispersion. In contrast, in the low-temperature phase, the exciton splits into two bands, both displaying three-dimensional parabolic dispersion. These dramatic changes in the exciton dispersion stem from the dimensional mutation driven by a substantial enhancement of interlayer coupling across the phase transition. This Letter provides a clear and typical example of how exciton behavior evolves with dimensionality.

cond-mat.str-el↗

arXiv2026

Plasmonic polaron in self-intercalated 1T-TiS2

Electron-boson coupling is central to a comprehensive understanding of the diverse physical phenomena emerging from many-body interactions. Yet less attention has been paid to how plasmons, collective bosonic modes of electron density oscillation, interact with conduction electrons and how external parameters can tune this interaction. Here, we present a clear display of composite quasiparticles stemming from electron-plasmon coupling, known as the plasmonic polaron, in self-intercalated 1T-TiS2, by using angle-resolved photoemission spectroscopy (ARPES), high-resolution electron energy loss spectroscopy (HR-EELS) and first-principles calculations. The single particle spectral function exhibits a distinctive plasmon-loss satellite with the same characteristic energy scale determined by HR-EELS measurements. The bosonic energy scale of plasmonic polaron is tunable by controlling charge carrier density and temperature, distinguishing itself from conventional polarons arising from electron-phonon interactions. Furthermore, we find that the dielectric screening strongly affects the formation of the plasmonic polaron states. Our findings provide direct spectroscopic evidence of plasmonic polarons and establish self-intercalated layered materials as a promising platform for studying, controlling, and harnessing plasmonic interactions in quantum materials.

cond-mat.mtrl-sci↗

arXiv2025

Observation of Topological Nodal-Ring Phonons in Monolayer Hexagonal Boron Nitride

Topological physics has evolved from its initial focus on fermionic systems to the exploration of bosonic systems, particularly phononic excitations in crystalline materials. Two-dimensional (2D) topological phonons emerge as promising candidates for future technological applications. Currently, experimental verification of 2D topological phonons has remained exclusively limited to graphene, a constraint that hinders their applications in phononic devices. Here, we report experimental evidence of topological phonons in monolayer hexagonal boron nitride using advanced high-resolution electron energy loss spectroscopy. Our high-precision measurements explicitly demonstrate two topological nodal rings in monolayer hexagonal boron nitride, protected by mirror symmetry, expanding the paradigm of 2D topological phonons beyond graphene. This research not only deepens fundamental understanding of 2D topological phonons, but also establishes a phononic device platform based on wide-bandgap insulators, crucial for advancements in electronics and photonics applications.

cond-mat.mtrl-sci↗

arXiv2024

Energy-efficient Hybrid Model Predictive Trajectory Planning for Autonomous Electric Vehicles

To tackle the twin challenges of limited battery life and lengthy charging durations in electric vehicles (EVs), this paper introduces an Energy-efficient Hybrid Model Predictive Planner (EHMPP), which employs an energy-saving optimization strategy. EHMPP focuses on refining the design of the motion planner to be seamlessly integrated with the existing automatic driving algorithms, without additional hardware. It has been validated through simulation experiments on the Prescan, CarSim, and Matlab platforms, demonstrating that it can increase passive recovery energy by 11.74\% and effectively track motor speed and acceleration at optimal power. To sum up, EHMPP not only aids in trajectory planning but also significantly boosts energy efficiency in autonomous EVs.

cs.RO↗

arXiv2023

Observation of the Breakdown of Optical Phonon Splitting in a Two-dimensional Polar Monolayer

Phonon splitting of the longitudinal optical and transverse optical modes (LO-TO splitting), a ubiquitous phenomenon in three-dimensional (3D) polar materials, is essential for the formation of the 3D phonon polaritons. Theories predict that the LO-TO splitting will break down in two-dimensional (2D) polar systems, but direct experimental verification is still missing. Here, using monolayer hexagonal boron nitride (h-BN) as a prototypical example, we report the direct observation of the breakdown of LO-TO splitting and the finite slope of the LO phonons at the center of the Brillouin zone in 2D polar materials by inelastic electron scattering spectroscopy. Interestingly, the slope of the LO phonon in our measurements is lower than the theoretically predicted value for a freestanding monolayer due to the screening of the Cu foil substrate. This enables the phonon polaritons (PhPs) in monolayer h-BN/Cu foil to exhibit ultra-slow group velocity (~ 5 x 10^-6 c, c is the speed of light) and ultra-high confinement (~ 4000 times smaller wavelength than that of light). Our work reveals the universal law of the LO phonons in 2D polar materials and lays a physical foundation for future research on 2D PhPs.

cond-mat.mtrl-sci↗

arXiv2022

Geometric Effect of High-Resolution Electron Energy Loss Spectroscopy on the Identification of Plasmons: An Example of Graphene

High-resolution electron energy loss spectroscopy (HREELS) is one of the most powerful methods to detect the dispersion of plasmons. However, we find that in the HREELS measurement, the scattering geometric configuration will seriously affect the identification of plasmons. Here, taking graphene as an example, using the HREELS capable of two-dimensional energy-momentum mapping combined with the intensity distribution calculations, we visually display the intensity distribution of the scattering geometric factor. We demonstrate that the energy loss peaks from the scattering geometric effect may be misinterpreted as the features of an acoustic plasmon. In any HREELS measurement, it is necessary to evaluate the effect of the scattering geometry quantitatively to identify the intrinsic surface excitations.

cond-mat.mes-hall↗