Science China Physics, Mechanics & Astronomy最新文献

The nontrivial band topology of Chern insulator can enrich the content of its Hofstadter butterfly spectra, which is closely related to recent experiments in twisted bilayer graphene and cold atom systems. We investigate the Hofstadter spectrum for various models of Chern insulators under a rational flux ({phi_{0}}over{q}), here (phi_{0}={hover{e}}) and q being an integer. We find the number of splitting subbands is ∣q − C∣ with C denoting the Chern number of parent band. Importantly, anomalous open-orbital subbands with Chern numbers q − 1 and −q − 1 emerge unexpectedly, which are beyond the parameter window (−q/2, q/2) of the Diophantine equation studied by Thouless-Kohmoto-Nightingale-den Nijs [Phys. Rev. Lett. 49, 405 (1982)]. The emergence of anomalous open orbits can be traced by analyzing the evolution of the Hofstadter spectrum, identifying as a new type of topological phase transition. These novel findings not only pinpoint the peculiar Hofstadter spectrum of Chern insulator, but also provide routes to study exotic characteristics beyond the Landau level physics.

Non-Hermitian dynamics exhibits a wealth of surprising and potentially useful phenomena. However, it is typically realized by coupling a system with thermal reservoirs, which makes the system suffer from thermal fluctuations associated with the dissipation. Here, we propose a dissipation-free approach to realize non-Hermitian dynamics using a superconducting circuit composed of two resonators and a superconducting qutrit. The non-Hermiticity arises in the dynamical matrix for the evolution of the two resonators in the Heisenberg picture, via a photon-number non-conserved dynamics. The energy spectrum of the non-Hermitian dynamical matrix can be retrieved by measuring the state of the two resonators, and a phase transition of the energy spectrum can be observed by varying the control parameters. In the realization of the non-Hermitian dynamics, the dissipation of the system and the post-selection are not required. Thus, the approach is implemented in a deterministic way, and the reservoir-induced noise is suppressed. Numerical simulations indicate that the energy spectrum of the non-Hermitian dynamical matrix obtained via the measurement of the resonators is in accordance with the theoretical prediction. Moreover, we demonstrate the parity discrimination for the state of two four-level qudits as an application, exhibiting the potential of the non-Hermitian dynamics in the field of quantum measurement. This work opens a new avenue for the realization of non-Hermitian dynamics and may have a significant implication in exploring the non-Hermitian phenomena.

Motivated by experimental measurements, we investigate the p-Ω correlation functions and interactions on the basis of a quark model. By solving the inverse scattering problem with channel coupling, we renormalize the coupling to other channels into an effective single-channel p-Ω potentials. The effects of Coulomb interaction and spin-averaging are also discussed. According to our results, the depletion of the p-Ω correlation functions, which is attributed to the J^P = 2⁺ bound state not observed in the ALICE Collaboration’s measurements (Nature 588, 232 (2020)), can be explained by the contribution of the attractive J^P = 1⁺ component in spin-averaging. So far, we have provided a consistent description of the p-Ω system from the perspective of the quark model, including the energy spectrum, scattering phase shifts, and correlation functions. The existence of the p-Ω bound state has been supported by all three aspects. Additionally, a sign of the p-Ω correlation function’s subtle sub-unity part can be seen in experimental measurements, which warrants more precise verification in the future.

The recent transport measurements of La₃Ni₂O₇ uncovered a “right-triangle” shape of the superconducting dome in the pressure-temperature (P-T) phase diagram. Motivated by this, we perform theoretical first-principles studies of La₃Ni₂O₇ with the pressure ranging from 0 to 100 GPa. Notably, we reveal a pressure dependence of the (text{Ni-}d_{,z^{2}}) electron density at the Fermi energy ((n_{z}^{E_{rm{F}}})) that highly coincides with such shape. On this basis, we further explore the electronic structure under uniaxial stress. By tracking the stress response of (n_{z}^{E_{rm{F}}}), we propose that superconductivity can be achieved by applying only ⋃2 GPa of compression along the c axis. The idea is further exemplified from the perspectives of lattice distortion, band structure, Fermi surface and superconducting phase coherence. We also discuss the possible charge modulation under the stress and provide an insight into the relation between (n_{z}^{E_{rm{F}}}) and the superconducting T_c in La₃Ni₂O₇ system. Our study provides new routes to the search of high-T_c superconductors in future experiments.

Liquid-liquid transition in metallic melts is an intriguing phenomenon often confused with liquid-liquid separation, oxidation or precipitation. Here, we employ a state-of-the-art ultrafast chip-based differential scanning calorimeter to investigate the thermal behavior of six metallic melts, ranging from unary to quinary systems, at temperatures above their liquidus. Calorimetric signals of liquid-liquid transition vary across systems: Sn melts showed no direct endothermic or exothermic events, though liquid-liquid transition influenced solidification and melting temperatures, while Yb-Zn melts exhibited an exothermic peak during cooling, indicating liquid-liquid transition. Thermal signals in other systems including Li, Pd-Ni-P, Yb-Mg-Zn-Cu and Au-Ag-Pd-Cu-Si, are primarily driven by compositional changes. Our in-situ analysis provides new insights into the structural and compositional evolution of metallic melts, offering significant implications for the design and processing of novel materials.

Acoustic orbital angular momentum (OAM) provides an infinite set of orthogonal bases in Hilbert space and significantly boosts the link capacity and data transmission rate. High-capacity and low-crosstalk OAM detection within compact physical space is highly desired to effectively harness this spatial dimension of sound wave, but the existing mechanisms generally either operate only for finite OAMs with predetermined mode orders or rely on complicated active devices. Here, we propose a phase saddle point (PSP) transformation mechanism for distinguishing and demultiplexing acoustic OAM modes in a passive, mode-adaptive, high-efficiency, and high-accuracy paradigm. The phase mask characterized by a PSP in the specific area is created through the single-pass log-polar transformation without prior information of incident modes, whose interaction with incident vortex beams of different OAM modes will yield the translation of the stationary phase point and thereby generate the corresponding focused line spots at distinct lateral positions. We theoretically elucidate the mode-adaptive response of PSP transformation by deriving the quantitative relationship between the OAM order and line spot offset. This mode adaptability enables our mechanism to detect OAM of arbitrary mode orders and mode numbers with the inter-mode crosstalk being effectively suppressed, beyond attainable with the existing methods. The effectiveness of our proposed mechanism is validated by demonstrating several distinct examples of single-mode OAM sorting and multi-mode synthesized vortex beam demultiplexing. We anticipate this mode-adaptive methodology, designed for compact dimensions and featuring with low crosstalk and uniform efficiency, will find important applications in OAM information processing.