Abstract Spin and orbital angular-momentum transfer between lattice vibrations and electrons has become an important focus beyond traditional electron-phonon coupling. Recent studies of spin-rotation coupling have shown that the rotational motion of lattice elastic vibrations can directly interact with the electron spin. Here we develop a microscopic description of the electron-phonon angular momentum coupling beyond spin-rotation coupling, which includes both the electron spin and orbital angular momentum from the relative motion of atoms in a local co-rotating lattice. We relate the lattice angular velocity to the atom-relative angular momentum through the inertia tensor, so that the lattice angular momentum, coupled to total electron angular momentum, contains both phonon spin and orbital angular momentum. The microscopic construction connects with continuum rotation descriptions, extends to non-rigid motion, and reveals discrete-lattice effects beyond the long-wavelength limit. These results provide a microscopic framework of electron-phonon coupling with spin and orbital angular momentum transfer, enabling both studies of phonon-driven electron spin and orbital dynamics and electron-driven phonon spin and orbital dynamics.
Abstract UTe 2 , a strong candidate for spin-triplet superconductivity, hosts novel step-edge states and Yin-Yang vortices on its (011) surface, both of which are intimately connected to topological surface states. However, the interaction between these two types of states remains unexplored. Here, we use scanning tunneling microscopy/spectroscopy (STM/STS) to investigate the coupling between step-edge states and Yin-Yang vortex states in UTe 2 . We uncover pronounced edge-vortex interactions, and find that the resulting in-gap spectral reconstruction is spatially asymmetric and depends sensitively on the position of the step edge relative to the vortex. Most strikingly, when the Yang vortex directly coincides with the step edge, the zero-energy conductance peak, a candidate Majorana mode signal, is locally suppressed. Our findings reveal an unexplored interplay between topological boundary states and vortex bound states in a spin-triplet superconductor, and establish step edges as a local tuning factor for vortex zero modes, providing possibilities for spatially selective manipulation of candidate Majorana modes through engineered boundary geometries.
Abstract Piezoelectric materials typically exhibit opposite longitudinal and transverse mechanical responses under an electric field, reflecting the electromechanical analogue of a positive Poisson’s ratio. Auxetic piezoelectricity, in which longitudinal and transverse coefficients share the same sign, has recently emerged as an unconventional electromechanical response; yet its intrinsic realization and electrical tunability in relaxor ferroelectrics with complex domain structures remain elusive. Here, we demonstrate intrinsic and electrically switchable auxetic piezoelectricity in rhombohedral relaxor ferroelectric Pb(Mg 1 / 3 Nb 2 / 3 )O 3 -PbTiO 3 by combining first-principles calculations and quantitative piezoelectric measurements. Density functional perturbation theory reveals that a positive transverse piezoelectric response is symmetry-allowed in the rhombohedral phase and primarily originates from internal-strain contributions associated with cooperative Pb–O displacements. Experiments on single-domain (111) pc -oriented crystals confirm the existence of an intrinsic auxetic state. Beyond the single-domain limit, in situ bias-dependent measurements reveal continuous and reversible electric-field-driven switching between auxetic and conventional piezoelectric states within the same crystal. A tensor-rotation-based multi-domain model quantitatively reproduces the bias-dependent response and identifies domain redistribution, enabled by the large shear piezoelectric coefficient, as the microscopic origin of the switching behavior. These findings establish auxetic piezoelectricity as an intrinsic and electrically programmable response in rhombohedral relaxor ferroelectrics, providing a general route toward reconfigurable electromechanical functionalities.
Abstract Laser cooling of semiconductors requires a high external quantum efficiency for phonon-assisted upconversion while suppressing heat generated by background absorption and non-radiative relaxation. Nanophotonic resonances can strengthen the upconversion channel, but in a single-mode structure may also enhance parasitic pump heating. We introduce a two-cavity non-Hermitian architecture that separates preparation of a lower reservoir state from extraction of the phonon-promoted radiative state. A passive exceptional point, containing no optical gain, is placed in the output branch, where it reshapes the projected final-state optical response; all anti-Hermitian diagonal terms describe radiative leakage, internal absorption, or material decay. For a CdS parameter set, the four-mode calculation gives a 1.23 × 10 3 enhancement of upconverted photoluminescence (UCPL) relative to a single-mode control, while the pump-induced heat load rises by only 2.8×10 -3 %. The gain consists of a factor of 3.45×10 2 from the independent output resonance and a further factor of 3.56 from exceptional-point tuning.
Abstract Light carrying spin angular momentum (SAM) can exert optical torque and drive particles into rotational motion. Although optical torque reversal has been achieved by tailoring particle properties or incident field parameters, the respective roles of the electric and magnetic components of transverse SAM in governing the torque on an isotropic particle remain unresolved. Here, reversible control of the out of plane optical torque on an absorbing isotropic Mie sphere is demonstrated in interference fields formed by two or three plane waves. Two orthogonal linear polarization states selectively activate torque pathways mediated by the electric and magnetic components of the transverse SAM, while intermediate polarization states allow both pathways to coexist. Notably, polarization controls the optical torque by tuning the relative weights of electric and magnetic multipolar contributions. Once higher order Mie channels become appreciable, competition among these contributions can reverse the total torque and switch the particle rotation between clockwise and counterclockwise directions. These results reveal distinct mechanical roles of the electric and magnetic components of transverse SAM and establish spin channel selection as a mechanism for polarization controlled optical torque reversal.
