Science China Physics, Mechanics & Astronomy最新文献

Magnetic skyrmions, topologically protected spin textures, are promising for both fundamental studies of topological magnetism and spintronic applications in data storage, logic processing, true random number generators, and neuromorphic computing. Yet, their energy dissipation, a key metric for evaluating manipulation efficiency and dynamics, remains elusive. Here, magnetotropic dissipation in B20 MnSi is characterized by dynamic cantilever magnetometry (DCM). Magnetotropic dissipation in the skyrmion phase is about one order of magnitude smaller than in topologically trivial helical and conical states, which is attributed to the topological characteristic that preserves spin configurations and minimizes energy loss to the electron/ phonon heat bath, as confirmed by micromagnetic simulations. A magnetotropic dissipation phase diagram is further constructed, revealing little temperature dependence of skyrmion magnetotropic dissipation, indicative of negligible magnonic contributions to the magnetotropic dissipation process. Our results reveal the low magnetotropic dissipation characteristic and underlying mechanisms of skyrmions, and demonstrate that DCM can resolve dissipation down to 7×10⁻¹⁴ kg/s, enabling detailed investigations of magnetic materials at microscale dimensions.

Quasi-one-dimensional RbMn₆Bi₅, the first pressure-induced ternary Mn-based superconductor, exhibits a phase diagram analogous to those of cuprate and iron-based superconductors, with superconductivity neighboring antiferromagnetic order. Here, we use ⁵⁵Mn and ⁸⁷Rb nuclear magnetic resonance (NMR) to unravel its magnetic structure and fluctuations. Above the Néel temperature (T_N), strong antiferromagnetic fluctuations dominate, characteristic of a paramagnetic state with pronounced spin-lattice relaxation rate enhancement. Below T_N, a first-order phase transition establishes a commensurate antiferromagnetic order, where Mn atoms at the pentagon corners exhibit distinct magnetic moments with different orientations, while the central Mn atom carries no magnetic moment. The complex magnetic architecture, revealed by zero-field and high-magnetic-field NMR spectra, contrasts with earlier neutron diffraction models proposing uniform spin density waves, instead supporting localized moment ordering with charge rearrangement. The proximity of robust antiferromagnetic fluctuations to the high-pressure superconducting phase suggests a potential role for magnetic excitations in mediating unconventional Cooper pairing, akin to paradigmatic high-T_c systems. These findings provide critical insights into the interplay between geometric frustration, magnetic order, and superconductivity in manganese-based materials.

Confined gas and ionic hydrates play vital roles in energy storage, carbon capture, and water desalination. Yet, the fundamental interactions between water films and hydrophobic molecules remain poorly understood. Here, we investigated nanoconfined monolayer methane hydrates encapsulated within graphene capillaries, exploring their phase behavior through crystal structure prediction combined with a machine-learning force field. We identified a thermodynamically stable two-dimensional tetragonal compound CH₄(H₂O)₄ under moderate pressures. Its hydrogen bonding network markedly differs from that of 2D pure or porous ice, giving rise to multiple plastic phases in which methane and water molecules rotate. Remarkably, 2D CH₄(H₂O)₄ transitions into a superionic state featuring proton diffusion at pressures as low as ∼3 GPa, substantially lower than that required for 2D ice. The calculated phase diagram further reveals that CH₄ molecule incorporation elevates the melting temperatures above 350 K while reducing the onset pressure for superionicity. These findings provide fundamental insight into hydrophobic gas hydrate under nanoscale confinement and open new avenues for applications in energy storage and hydrocarbon capture.

We introduce a mock galaxy catalog built for the China Space Survey Telescope (CSST) extragalactic surveys using the primary runs of the Jiutian N-body simulation suites. The catalogs are built by coupling the galaxy evolution and assembly (gaea) semi-analytical model of galaxy formation with merger trees extracted from the simulations using the hierarchical bound-tracing (hbt+) algorithm. The spectral energy distributions (SEDs) and broadband magnitudes are computed using the neural-network-based stellar population synthesizer StarDuster, which is trained on radiative transfer simulations to account for detailed galaxy geometry in modeling dust obscuration. Galaxy light-cones up to z = 5 are subsequently generated with the Blic light-cone builder, which interpolates the properties of galaxies over time using an optimized interpolation scheme. The resulting catalogs exhibit good convergence in many statistical properties of the galaxy population produced from two different resolution simulations. The catalogs reproduce a number of observed galaxy properties across a range of galaxy mass and redshift, including the stellar mass functions, the luminosity function, gas mass fraction, galaxy size-mass relation, and galaxy clustering. We also present the photometric and redshift distributions of galaxies expected to be observed in the CSST surveys.

Recent studies of moiré physics have unveiled a wealth of opportunities for significantly advancing the field of quantum phase transitions. However, properties of reentrant phase transitions driven by moiré strength are poorly understood. Here, we investigate the reentrant sequence of phase transitions and the invariant of the universality class in moiré-modulated extended Su-Schrieffer-Heeger (SSH) model. For the simplified case with intercell hopping w = 0, we analytically derive renormalisation relations of Hamiltonian parameters to explain the reentrant phenomenon. For the general case, numerical phase boundaries are calculated in the thermodynamic limit. The bulk boundary correspondence between zero-energy edge modes and the entanglement spectrum is revealed from the degeneracy of both quantities. We also address the correspondence between the central charge obtained from entanglement entropy and the change in winding number during the phase transition. Our results shed light on the understanding of universal characteristics and bulk-boundary correspondence for moiré induced reentrant phase transitions in 1D condensed-matter systems.

Converting magnetization spin to orbital current often relies on strong spin-orbit interaction that may cause additional angular momentum dissipation. We report that coherent magnetization dynamics in magnetic nanostructures can evanescently pump an orbital current into adjacent semiconductors due to the coupling between their stray electromagnetic field and electron orbitals without relying on spin-orbit coupling. The underlying photonic spin of the electromagnetic field governs the orbital polarization that flows along the gradient of the driven field. Due to the joint effect of the electric and magnetic fields, the orbital Hall current that flows perpendicularly to the gradient of the time-varying field is also generated and does not suffer from the orbital torque. These findings extend the paradigm of orbital pumping to include photonic angular momentum and pave the way for developing low-dissipation orbitronic devices.

In this article, we propose that superradiant echoes can be achieved at room temperature by applying a laser illumination and a microwave Hahn echo sequence to a diamond with a high concentration of nitrogen-vacancy (NV) centers placed in a dielectric microwave cavity. We identify that the combined action of two microwave driving pulses and a free evolution imprints a frequency grating among NV spin sub-ensembles, and the multiple re-phasing of the grated spin sub-ensembles leads to multiple superradiant echoes through a collective coupling with the cavity. Furthermore, we show that the superradiant echoes can be actively tailored through the microwave pulses and the laser illumination by adjusting the grating parameters, and the multiple re-phasing dynamics is analogous to the one leading to superradiant beats in atomic optical clock systems. In the future, the spin sub-ensembles grating and the resulting echoes can be further optimized with dynamical decoupling, which might pave the way for applications in quantum sensing.

The preservation of quantum coherence is besieged by a fundamental dogma: its revival necessitates non-Markovian memory effects from structured environments. This paradigm has constrained quantum control strategies and obscured simpler paths to coherence protection. Here, we shatter this belief by demonstrating unambiguous coherence revival even in strictly Markovian regimes, achieved solely through basis engineering in the σ_x/σ_y bases. We establish a comprehensive analytical framework for predictive coherence control, delivering three universal design principles. First, we derive a minimum critical noise based frequency, (omega_{0}^{c} approx {pi over {t_{rm max}}}) serving as a universal criterion for engineering non-Markovian dynamics over any interval [0, t_max]. Crucially, we show that Markovian environments (ω₀ < ω ^c₀ ) can exhibit coherence revival when the Zeeman energy satisfies ω_k > π/(2t_max), establishing basis engineering as an independent control dimension that separates revival dynamics from environmental memory. Furthermore, for non-Markovian environments, we provide exact conditions for periodic and complete revival: setting ω₀ = n · 6.285/t_max guarantees revival in the σ_z basis, while combining it with ω_k = πω₀/6.285 ensures perfect revival in the σ_x/σ_y bases. Our results, validated by rigorous quantum simulations, provide a predictive toolkit for coherence control, offering immediate strategies for enhancing quantum memory, sensing, and error mitigation.

In quantum information processing, the development of fast and robust control schemes remains a central challenge. Although quantum adiabatic evolution is inherently robust against control errors, it typically demands long evolution times. In this work, we propose to achieve rapid adiabatic evolution, in which nonadiabatic transitions induced by fast changes in the system Hamiltonian are mitigated by flipping the nonadiabatic transition matrix using π pulses. This enables a faster realization of adiabatic evolution while preserving its robustness. We demonstrate the effectiveness of our scheme in both two-level and three-level systems. Numerical simulations show that, for the same evolution duration, our scheme achieves higher fidelity and significantly suppresses nonadiabatic transitions compared to the traditional STIRAP protocol.