Physical review letters最新文献

Hexagonal MnTe is an altermagnetic semiconductor with g-wave symmetry of spin polarization in momentum space. In the nonrelativistic limit, this symmetry mandates that electric current flowing in any crystallographic direction is unpolarized. However, here I show that elastic strain is effective in inducing the spin splitting effect in MnTe. For this analysis, a spin-orbit-coupled k·p Hamiltonian for the valence band maximum at the A point is derived and fitted to eigenvalues calculated from first principles. The spin splitting angle is calculated using the Boltzmann approach in the relaxation-time approximation. The spin splitting gauge factor exceeds 30 near the valence band maximum. Thus, with suitable substrate engineering, MnTe can be used as an efficient source and detector of spin current in spintronic devices. Proper inclusion of the Rashba-Dresselhaus spin-orbit coupling is crucial for the correct description of the transport properties of MnTe.

Intrinsic breakdown strength (F_{bd}), as the theoretical upper limit of electric field strength that a material can sustain, plays important roles in determining dielectric and safety performance. The well accepted concept is that a larger band gap (E_{g}) often leads to a larger intrinsic breakdown strength. In this work, we analytically derive a simplified model of F_{bd}, showing a linear relationship between F_{bd} and the maximum electron density of states (DOS_{max}) within the energy range spanning from the conduction band minimum (CBM) to CBM+E_{g}. Using the Wannier interpolation technique to reduce the cost of calculating the F_{bd} for various three- and two-dimensional materials, we find that the calculated F_{bd} did not show any simple relationship with band gap, but it behaves linearly with the DOS_{max}, consistent with our theoretical derivation. Our work shows that the DOS_{max} is more fundamental than the band gap value in determining the F_{bd}, thus providing useful physical insights into the intrinsic dielectric breakdown strength and opening directions for improving high-power devices. The dimensional effects on F_{bd} has also been revealed that monolayers tend to have larger F_{bd} due to reduced screening effects.

The low-energy enhancement (LEE) in γ-ray strength functions has been experimentally identified in a large number of nuclei during the past two decades; however, the origin of the enhancement is not fully understood. Building on previous theoretical work, we investigate the LEE and its relation to the scissors mode (SM) with an independent theoretical approach. We apply a novel angular-momentum-projected shell-model method that explicitly endows degrees of freedom to describe the scissors motion. Taking the recently measured γ-ray strength functions in Neodymium isotopes as examples, we find that the LEE arises from a quasi-free scissors motion appearing only in weakly-deformed nuclei, which can be viewed as an approximate free-rotation of neutrons with respect to protons. This leads us to propose a new type of collective motion, scissors rotation, to contrast the scissors vibration widely known in well-deformed nuclei. The observed LEE is naturally interpreted as the first evidence for this collective excitation mode.

Genuine multipartite nonlocality and nonlocality arising in networks composed of several independent sources have been investigated separately. While some genuinely entangled states cannot be verified by violating a single Bell-type inequality, a quantum network consisting of different sources enables the certification of the nonclassicality of all sources. In this Letter, we propose the first method to verify both types of nonlocality simultaneously in a single experiment. We consider a quantum network comprising a bipartite source and a tripartite source. We demonstrate that there are quantum correlations that cannot be simulated if the tripartite source distributes biseparable systems while the bipartite source distributes even stronger-than-quantum systems. These correlations can be used to verify both the genuine multipartite nonlocality of generalized Greenberger-Horne-Zeilinger states and the full network nonlocality that is stronger than all the existing results. Experimentally, we observe both types of nonlocality in a high-fidelity photonic quantum network by violating a single network Bell inequality.

Realizing deterministic, high-fidelity entangling interactions-of the kind that can be utilized for efficient quantum information processing-between photons remains an elusive goal. Here, we address this long-standing issue by devising a protocol for creating and manipulating highly entangled superpositions of well-controlled states of light by using an on-chip photonic system that has recently been shown to implement three-dimensional, non-Abelian quantum holonomy. Our calculations indicate that a subset of such entangled superpositions are maximally entangled, "volume-law" states, and that the underlying entanglement can be distilled and purified for applications in quantum science. Crucially, we generalize this approach to demonstrate the potentiality of deterministically entangling two arbitrarily high, N-dimensional quantum systems, by formally establishing a deep connection between the matrix representations of the unitary quantum holonomy-within energy-degenerate subspaces in which the total excitation number is conserved-and the (2j+1)-dimensional irreducible representations of the rotation operator, where j=(N-1)/2 and N≥2. Specifically, our protocol deterministically entangles spatially localized modes that are not only distinguishable but are also individually accessible and amenable to state preparation and measurement, and therefore, we envisage that this entangling mechanism could be utilized for deterministic quantum information processing with light.

The field of active nematics has traditionally employed descriptions based on dipolar activity. However, it is theoretically predicted that interactions with a substrate, prevalent in most biological systems, lead to novel forms of activity, such as quadrupolar activity, that are governed by hydrodynamic screening. Here, combining experiments and numerical simulations, we show that upon light-induced solidification of the underlying medium, microtubule-kinesin mixtures undergo a transformation that leads to a biphasic active suspension. Using an active lyotropic model, we prove that the transition is governed by screening effects that alter the dominant form of active stress. Specifically, the combined effect of friction and quadrupolar activity leads to a hierarchical folding that follows the intrinsic bend instability of the active nematic layer. Our results demonstrate the dynamics of the collapse of orientational order in active nematics and present a new route for controlling active matter by modifying the activity through changing the surrounding environment.

In order to overcome the challenge of lacking polarization encoding in integrated quantum photonic circuits, we propose a scheme to realize arbitrary polarization manipulation of a single photon by integrating a single quantum emitter in a photonic waveguide. In our scheme, one transition path of the three-level emitter is designed to simultaneously couple with two orthogonal polarization degenerate modes in the waveguide with adjustable coupling strengths, and the other transition path of the three-level emitter is driven by an external coherent field. The proposed polarization converter has several advantages, including arbitrary polarization conversion for any input polarization, tunable working frequency, excellent antidissipation ability with high-conversion efficiency, and atomic-scale size. Our Letter provides an effective solution to enable the polarization encoding of photons that can be applied in the integrated quantum photonic circuits, and will boost quantum photonic chips.

We report on the charge dynamics of kagome FeGe, an antiferromagnet with a charge density wave (CDW) transition at T_{CDW}≃105  K, using polarized infrared spectroscopy and band structure calculations. We reveal pronounced optical anisotropy along the a and c axis, as well as an unusual response associated with three-dimensional CDW order. Above T_{CDW}, there is a notable transfer of spectral weight (SW) from high to low energies, promoted by the magnetic splitting-induced shift in bands. Across the CDW transition, we observe a sudden SW transfer from low to high energies over a broad range, along with the emergence of new excitations around 1200  cm^{-1}. These results contrast with observations from other kagome metals like CsV_{3}Sb_{5}, where the nesting of VHSs leads to a clear CDW gap feature. Instead, our findings can be accounted for by a 2×2×2 CDW ground state driven by a first-order structural transition involving large partial Ge1 dimerization. Our Letter thus unveils a complex interplay among structure, magnetism, and charge order, offering valuable insights for a comprehensive understanding of CDW order in FeGe.

We present the first measurement of the missing energy due to nuclear effects in monoenergetic, muon neutrino charged-current interactions on carbon, originating from K^{+}→μ^{+}ν_{μ} decay at rest (E_{ν_{μ}}=235.5  MeV), performed with the J-PARC Sterile Neutrino Search at the J-PARC Spallation Neutron Source liquid scintillator based experiment. Toward characterizing the neutrino interaction, ostensibly ν_{μ}n→μ^{-}p or ν_{μ}^{12}C→μ^{-}^{12}N, we define the missing energy as the energy transferred to the nucleus (ω) minus the kinetic energy of the outgoing proton(s), E_{m}≡ω-∑T_{p}, and relate this to visible energy in the detector, E_{m}=E_{ν_{μ}}(235.5  MeV)-m_{μ}(105.7  MeV)+[m_{n}-m_{p}(1.3  MeV)]-E_{vis}. The missing energy, which is naively expected to be zero in the absence of nuclear effects (e.g., nucleon separation energy, Fermi momenta, and final-state interactions), is uniquely sensitive to many aspects of the interaction, and has previously been inaccessible with neutrinos. The shape-only, differential cross section measurement reported, based on a (77±3)% pure double-coincidence kaon decay-at-rest signal (621 total events), provides detailed insight into neutrino-nucleus interactions, allowing even the nuclear orbital shell of the struck nucleon to be inferred. The measurement provides an important benchmark for models and event generators at hundreds of MeV neutrino energies, characterized by the difficult-to-model transition region between neutrino-nucleus and neutrino-nucleon scattering, and relevant for applications in nuclear physics, neutrino oscillation measurements, and Type-II supernova studies.