arXiv subjects

Fangliang Wu

Publications and source records attributed to Fangliang Wu.

4 recordsLinked to original sources

arXiv2026

Observation of cooperative strong coupling between optical phonon and crystal-field excitations in a pseudo Jahn-Teller system

Cooperative interactions between localized electronic excitations and crystal lattice are central to the emergence of complex structural phases in materials. However, the scaling relations governing these collective behaviors remain largely unexplored. Here, using magneto-Raman spectroscopy, we report the direct observation of the strongly coupled optical phonon and non-degenerate crystal-field excitations (CFEs) in ErFeO3. By independently tuning the effective population of Jahn-Teller-active erbium ions through temperature and chemical dilution with Jahn-Teller-inactive yttrium ions, we identify the coupling strength varies linearly with the square root of electronic excitations population. Notably, Y-doping reveals the hybridization gap reduces significantly faster than predicted by density scaling alone, indicating phonon coherence is essential for establishing this cooperative interaction. Our findings highlight the role of optical phonons in mediating short-range interactions that drive cooperative Jahn-Teller effect, evidencing the pathway for tailoring electronic and vibrational properties of Jahn-Teller materials through population control.

cond-mat.mtrl-sci↗

arXiv2025

Magnetic switching of phonon angular momentum in a ferrimagnetic insulator

Circularly polarized phonons offer a new route for mediating angular momentum in solids. However, controlling phonon angular momentum without altering the material's structure or composition remains challenging. Here, we demonstrate the non-volatile switching of angular momentum-carrying phonons by leveraging intrinsic ferrimagnetism in an insulator. We find a pair of chiral phonons with giant energy splitting reaching 20% of the phonon frequency, due to spontaneously broken time-reversal symmetry. With a moderate magnetic field, the phonon angular momentum of the two chiral phonon branches can be switched along with the magnetization. Notably, near the critical temperature, the effective phonon magnetic moment is enhanced, reaching 2.62 Bohr magneton, exceeding the moment of a magnon. A microscopic model based on phonon-magnon coupling accounts for the observations. Furthermore, we identify two types of phononic domains with opposite phonon Zeeman splitting and propose the existence of topologically protected phononic edge modes at domain boundaries. These results demonstrate effective manipulation of chiral phonons with magnetism, and pave the way for engineering chiral phononic domains on the micrometer scale.

cond-mat.mtrl-sci↗

arXiv2023

Chirality selective magnon-phonon hybridization and magnon-induced chiral phonons in a layered zigzag antiferromagnet

Two-dimensional (2D) magnetic systems possess versatile magnetic order and can host tunable magnons carrying spin angular momenta. Recent advances show angular momentum can also be carried by lattice vibrations in the form of chiral phonons. However, the interplay between magnons and chiral phonons as well as the details of chiral phonon formation in a magnetic system are yet to be explored. Here, we report the observation of magnon-induced chiral phonons and chirality selective magnon-phonon hybridization in a layered zigzag antiferromagnet (AFM) FePSe$_3$. With a combination of magneto-infrared and magneto-Raman spectroscopy, we observe chiral magnon polarons (chiMP), the new hybridized quasiparticles, at zero magnetic field. The hybridization gap reaches 0.25~meV and survives down to the quadrilayer limit. Via first principle calculations, we uncover a coherent coupling between AFM magnons and chiral phonons with parallel angular momenta, which arises from the underlying phonon and space group symmetries. This coupling lifts the chiral phonon degeneracy and gives rise to an unusual Raman circular polarization of the chiMP branches. The observation of coherent chiral spin-lattice excitations at zero magnetic field paves the way for angular momentum-based hybrid phononic and magnonic devices.

cond-mat.mtrl-sci↗

arXiv2021

Coherent strong-coupling of terahertz magnons and phonons in a Van der Waals antiferromagnetic insulator

Emergent cooperative motions of individual degrees of freedom, i.e. collective excitations, govern the low-energy response of system ground states under external stimulations and play essential roles for understanding many-body phenomena in low-dimensional materials. The hybridization of distinct collective modes provides a route towards coherent manipulation of coupled degrees of freedom and quantum phases. In magnets, strong coupling between collective spin and lattice excitations, i.e., magnons and phonons, can lead to coherent quasi-particle magnon polarons. Here, we report the direct observation of a series of terahertz magnon polarons in a layered zigzag antiferromagnet FePS3 via far-infrared (FIR) transmission measurements. The characteristic avoided-crossing behavior is clearly seen as the magnon-phonon detuning is continuously changed via Zeeman shift of the magnon mode. The coupling strength g is giant, achieving 120 GHz (0.5 meV), the largest value reported so far. Such a strong coupling leads to a large ratio of g to the resonance frequency (g/ω) of 4.5%, and a value of 29 in cooperativity (g^2/γ_{ph}γ_{mag}). Experimental results are well reproduced by first-principle calculations, where the strong coupling is identified to arise from phonon-modulated anisotropic magnetic interactions due to spin-orbit coupling. These findings establish FePS3 as an ideal testbed for exploring hybridization-induced topological magnonics in two dimensions and the coherent control of spin and lattice degrees of freedom in the terahertz regime.

cond-mat.mtrl-sci↗