Chiral Vibration Research Articles

Three-stage ultrafast demagnetization dynamics in a monolayer ferromagnet

Intense laser pulses can be used to demagnetize a magnetic material on an extremely short timescale. While this ultrafast demagnetization offers the potential for new magneto-optical devices, it poses challenges in capturing coupled spin-electron and spin-lattice dynamics. In this article, we study the photoinduced ultrafast demagnetization of a prototype monolayer ferromagnet Fe3GeTe2 and resolve the three-stage demagnetization process characterized by an ultrafast and substantial demagnetization on a timescale of 100 fs, followed by light-induced coherent A1g phonon dynamics which is strongly coupled to the spin dynamics in the next 200–800 fs. In the third stage, chiral lattice vibrations driven by nonlinear phonon couplings, both in-plane and out-of-plane are produced, resulting in significant spin precession. Nonadiabatic effects are found to introduce considerable phonon hardening and suppress the spin-lattice couplings during demagnetization. Our results advance our understanding of dynamic charge-spin-lattice couplings in the ultrafast demagnetization and evidence angular momentum transfer between the phonon and spin degrees of freedom.

Superatomic‐based chirality: Asymmetric structures constructed by superatoms

AbstractChirality is one of the fundamental properties of molecules traditionally constructed from atoms. Here, we report for the first time the successful construction of asymmetric chiral structures utilizing highly symmetric endohedral metallofullerene superatoms based on their own bonding properties. Specifically, stable mirror‐symmetric sinister and rectus structures are obtained by selecting a superatom capable of forming four chemical bonds as the chiral center. Further analysis shows that the chiral vibration frequency of superatomic assemblies can be as low as a few wavenumbers, which greatly expands the range of chiral spectra compared to atom‐based molecules. We term this type of chirality based on superatoms as “superatomic‐based chirality”. It is anticipated that this work will significantly expand the variety of chiral structures at the atomic level.

Nuclear chiral rotation within Relativistic Configuration-interaction Density functional theory

The Relativistic Configuration-interaction Density functional (ReCD) theory that combines the advantages of large-scale configuration-interaction shell model and relativistic density functional theory is extended to study nuclear chiral rotation. The energy spectra and transition probabilities of the chiral doublet bands are reproduced satisfactorily without any free parameters. By analyzing the probability amplitudes of the wavefunctions, the significant roles of configuration mixing and four quasiparticle states to the chiral doublets are revealed. The evolution from chiral vibration to static chirality is clearly illustrated by the K plot and azimuthal plot. The present investigation provides both microscopic and quantal descriptions for nuclear chirality for the first time and demonstrates the robustness of chiral geometry against the configuration mixing as well as the four quasiparticle states.

From chiral vibration to tilted-axis wobbling within broken chiral symmetry

The effect of non-axial rigid alignment of the quasiparticle spins on the behaviour of the chiral partner bands is investigated within a semiclassical treatment of a particle-rotor Hamiltonian. A valence h11/2 proton particle and a h11/2 neutron hole are used to calculate the energy spectrum of the chiral partner bands as a function of the angles defining the rigid alignments of the quasiparticle spins. Distinct dynamical characteristics are identified in specific angular momentum ranges and tilting angles. It is found that the high spin static chirality regime transforms into a wobbling tilted axis rotation at sufficiently high deviations of the quasiparticle spins from the principal intrinsic axes. The experimental realization of the model is exemplified for the chiral bands of 132Pr and 138Pm.

Interpretation of chiral symmetry breaking and octupole correlations in Cs124 by the reflection-asymmetric triaxial particle rotor model

The positive-parity doublet bands with configuration $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ and negative-parity bands with $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}({g}_{7/2}{d}_{5/2})$ observed in $^{124}\mathrm{Cs}$, and the possibility of multiple chiral doublets ($\mathrm{M}\ensuremath{\chi}\mathrm{D}$) with octupole correlations are investigated using the reflection-asymmetric triaxial particle rotor model. The calculated excitation energies, energy staggering parameters, and the electromagnetic transitional probabilities are in good agreement with the data available and satisfy the expected features of chiral doublet bands. The angular momentum geometry and its evolution with spin are studied with the angular momentum components and the azimuthal plot. In comparison with a typical chiral vibration pattern for the positive-parity doublet bands, a transient static chirality around $I=12\ensuremath{\hbar}$ is shown for the calculated negative-parity doublet bands.

Plasmon-phonon coupling between mid-infrared chiral metasurfaces and molecular vibrations.

Plasmon-phonon coupling between metamaterials and molecular vibrations provides a new path for studying mid-infrared light-matter interactions and molecular detection. So far, the coupling between the plasmonic resonances of metamaterials and the phonon vibrational modes of molecules has been realized under linearly polarized light. Here, mid-infrared chiral plasmonic metasurfaces with high circular dichroism (CD) in absorption over 0.65 in the frequency range of 50 to 60 THz are demonstrated to strongly interact with the phonon vibrational resonance of polymethyl methacrylate (PMMA) molecules at 52 THz, under both left-handed and right-handed circularly polarized (LCP and RCP) light. The mode splitting features in the absorption spectra of the coupled metasurface-PMMA systems under both circular polarizations are studied in PMMA layers with different thicknesses. The relation between the mode splitting gap and the PMMA thickness is also revealed. The demonstrated results can be applied in areas of chiral molecular sensing, thermal emission, and thermal energy harvesting.

Static quadrupole moments of nuclear chiral doublet bands

The static quadrupole moments (SQMs) of nuclear chiral doublet bands are investigated for the first time taking the particle-hole configuration π(1h11/2)⊗ν(1h11/2)−1 with triaxial deformation parameters in the range 260∘≤γ≤270∘ as examples. The behavior of the SQM as a function of spin I is illustrated and analyzed. It is found that in the region of chiral vibrations the SQMs of doublet bands are strongly varying with I, whereas in the region of static chirality the SQMs of doublet bands are almost constant. Hence, the measurement of SQMs provides a new criterion for distinguishing the modes of nuclear chirality. Moreover, in the high-spin region the SQMs can be approximated by an analytic formula with a proportionality to cos⁡γ for both doublet bands. This provides a way to extract experimentally the triaxial deformation parameter γ for chiral bands from the measured SQMs.

Role of triaxiality in the structure of chiral partner bands

The spectrum and wave-functions of chiral partner band states are obtained by treating semiclassically a particle-rotor Hamiltonian with rigid quasiparticle alignments and arbitrary triaxial deformation. The results for valence h11/2 proton particle and h11/2 neutron hole alignments are investigated as a function of total angular momentum and the magnitude of the triaxial deformation. It is shown that the chiral vibration persists in more angular momentum states with decreasing triaxial deformation. At sufficiently small triaxial deformation, the emergence of static chirality is observed even for low spin states which compete with the chiral vibration component.

Behavior of the collective rotor in nuclear chiral motion

The behavior of the collective rotor in the chiral motion of triaxially deformed nuclei is investigated using the particle rotor model by transforming the wave functions from the $K$-representation to the $R$-representation. After examining the energy spectra of the doublet bands and their energy differences as functions of the triaxial deformation, the angular momentum components of the rotor, proton, neutron, and the total system are investigated. Moreover, the probability distributions of the rotor angular momentum ($R$-plots) and their projections onto the three principal axes ($K_R$-plots) are analyzed. The evolution of the chiral mode from a chiral vibration at the low spins to a chiral rotation at high spins is illustrated at triaxial deformations $\gamma=20^\circ$ and $30^\circ$.

Multichiral facets in symmetry restored states: Five chiral doublet candidates in the even-even nucleus Nd136

A triaxial projected shell model including configurations with more than four quasiparticles in the configuration space is developed and applied to investigate the recently reported five chiral doublets candidates in a single even-even nucleus $^{136}\mathrm{Nd}$. The energy spectra and transition probability ratios $B(M1)/B(E2)$ are reproduced satisfactorily. The configuration mixing along the rotational bands is studied by analyzing the intrinsic composition of the eigenfunctions. The chiral geometry of these nearly degenerate bands is examined by the K plot and the azimuthal plot, and the evolution from the chiral vibration to the static chirality with spin is clearly demonstrated for four pairs of partner bands. For bands D3 and D3-C, due to strong configuration mixing, their azimuthal plots show features of planar rotation and it is difficult to interpret them as chiral partners.

Entanglement of single-photons and chiral phonons in atomically thin WSe2

Quantum entanglement is a fundamental phenomenon that, on the one hand, reveals deep connections between quantum mechanics, gravity and spacetime1,2, and on the other hand, has practical applications as a key resource in quantum information processing3. Although it is routinely achieved in photon–atom ensembles4, entanglement involving solid-state5–7 or macroscopic objects8 remains challenging albeit promising for both fundamental physics and technological applications. Here, we report entanglement between collective, chiral vibrations in a two-dimensional WSe2 host—chiral phonons (CPs)—and single-photons emitted from quantum dots9–13 (QDs) present in it. CPs that carry angular momentum were recently observed in WSe2 and are a distinguishing feature of the underlying honeycomb lattice14,15. The entanglement results from a ‘which-way’ scattering process, involving an optical excitation in a QD and doubly-degenerate CPs, which takes place via two indistinguishable paths. Our unveiling of entanglement involving a macroscopic, collective excitation together with strong interactions between CPs and QDs in two-dimensional materials opens up ways for phonon-driven entanglement of QDs and engineering chiral or non-reciprocal interactions at the single-photon level. A ‘which-way’ scattering process can generate entanglement between single photons and collective chiral vibrations in two-dimensional tungsten diselenide. The result opens up ways for engineering non-reciprocal interactions at the quantum level.

Lifetime measurements in the chiral-candidate doublet bands of La130

The lifetimes of the excited states belonging to the chiral-candidate doublet bands built on the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}^{\ensuremath{-}1}$ configuration in $^{130}\mathrm{La}$ have been measured by applying the Doppler-shift attenuation method and the in-beam fast timing technique. Excited states were populated in the $^{121}\mathrm{Sb}(^{12}\mathrm{C},3n)$ reaction at a bombarding energy of 54 MeV. The ${7}^{+}$ bandhead of the yrast band was identified as an isomeric state with a lifetime of $\ensuremath{\tau}({7}^{+})=0.38(7)\phantom{\rule{0.16em}{0ex}}\mathrm{ns}$. Similar reduced transition probabilities $B(M1)$ and $B(E2)$ were found for the states with the same spin in the partner bands. The results revealed an even-odd spin dependence in the $B(E2)$ values, whereas the $B(M1)$ values vary nearly monotonically with increasing spin. The experimental properties of the doublet bands in $^{130}\mathrm{La}$ are compared with theoretical calculations done in the frame of the two-quasiparticles-plus-triaxial-rotor model. The static chirality is not supported by the obtained data; however, chiral vibrations cannot be excluded.

Two-dimensional collective Hamiltonian for chiral and wobbling modes

A two-dimensional collective Hamiltonian (2DCH) on both azimuth and polar motions in triaxial nuclei is proposed to investigate the chiral and wobbling modes. In the 2DCH, the collective potential and the mass parameters are determined from three-dimensional tilted axis cranking (TAC) calculations. The broken chiral and signature symmetries in the TAC solutions are restored by the 2DCH. The validity of the 2DCH is illustrated with a triaxial rotor ($\gamma=-30^\circ$) coupling to one $h_{11/2}$ proton particle and one $h_{11/2}$ neutron hole. By diagonalizing the 2DCH, the angular momenta and energy spectra are obtained. These results agree with the exact solutions of the particle rotor model (PRM) at high rotational frequencies. However, at low frequencies, the energies given by the 2DCH are larger than those by the PRM due to the underestimation of the mass parameters. In addition, with increasing angular momentum, the transitions from the chiral vibration to chiral rotation and further to longitudinal wobbling motion have been presented in the 2DCH.

Chirality in atomic nuclei: 2013

Progresses of the chirality in atomic nuclei are reviewed, in particular, the recently proposed collective Hamiltonian based on tilted axis cranking approach to describe chiral vibration and rotation modes, and the experimental achievements for chirality and multiple chiral doublets, i.e., in 106 Ag , 133 Ce and 103 Rh . The first experimental evidences of multiple chiral doublet bands with distinct and identical configuration found in 133 Ce and 103 Rh are discussed in detail.

Chiral vibrations in theA=135region

Chiral vibrations in the $A=135$ region are studied in the framework of a RPA plus self-consistent tilted axis cranking formalism. In this model chiral vibrations appear as a precursor toward the static chiral regime. The properties of the RPA phonons are discussed and compared to experimental data. We discuss the limits of the chiral region and the transition to the nonharmonic regime.

Chirality in odd-ARh isotopes within the triaxial particle rotor model

Adopting the fully quantal triaxial particle rotor model, the candidate chiral doublet bands in odd-$A$ nuclei $^{103}$Rh and $^{105}$Rh with $\pi g_{9/2}^{-1}\otimes\nu h^{2}_{11/2}$ configuration are studied. For the doublet bands in both nuclei, agreement is excellent for the observed energies over entire spin range and $B(M1)/B(E2)$ at higher spin range. The evolution of the chiral geometry with angular momentum is discussed in detail by the angular momentum components and their probability distributions. Chirality is found to change from chiral vibration to nearly static chirality at spin $I=37/2$ and back to another type of chiral vibration at higher spin. The influence of the triaxial deformation $\gamma$ is also studied.

New aspects of chiral symmetry breaking in atomic nucleus

The significant progresses of the chirality in atomic nuclei are briefly reviewed for both experimental and theoretical sides. A particle rotor model is developed which couples several valence protons and neutrons to a rigid triaxial rotor core and applied to investigating the chirality in odd-A nucleus 135Nd. Static chirality has been shown to be a transient phenomenon surrounding by chiral vibrations. It is found that the B(M1) staggering is associated strongly with the characters of nuclear chirality, i.e., the staggering is weak in chiral vibration region while strong in the static chirality region.

Chirality in odd-A nucleus 135Nd in particle rotor model

A particle rotor model is developed which couples several valence protons and neutrons to a rigid triaxial rotor core. It is applied to investigating the chirality in odd-A nucleus 135Nd with πh11/22⊗νh11/2−1 configuration for the first time in a fully quantal approach. For the two chiral sister bands, the observed energies and the B(M1) and B(E2) values for the in-band as well as interband transitions are reproduced excellently. Root mean square values of the angular momentum components and their probability distributions are used for discussing in detail the chiral geometry of the aplanar rotation and its evolution with angular momentum. Chirality is found to change from a soft chiral vibration to nearly static chirality at spin I=39/2 and back to another type of chiral vibration at higher spin.

Evolution of chirality from γ soft 108Ru to triaxial 110,112Ru

Rotational bands in 108,110,112Ru have been investigated by means of γ–γ–γ and γ–γ(θ) coincidences of prompt γ rays emitted in the spontaneous fission of 252Cf. The positive parity bands are described by different versions of IBA, where 108Ru is best described as a γ-soft nucleus whereas 110,112Ru are more like rigid triaxial rotors. New ΔI=1 negative parity doublet bands are found. In case of 110,112Ru, these are interpreted as soft chiral vibrations. Many of the experimental findings can be explained by microscopic calculations that combine the TAC mean-field with random phase approximation but a simple geometrical explanation is not apparent.

From chiral vibration to static chirality in Nd135

From chiral vibration to static chirality in Nd135