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The body–boundary correspondence refers to the relationship between the body and boundary states of topological insulators (TIs). In TIs, the presence of boundary states is connected to the bulk topological properties of the material. The topology can be identified by studying the energy of the topological modes within the bulk bandgap. However, not all topological materials exhibit boundary states within the insulating energy gap. In many cases, the presence of boundary states can be hidden or masked by the bulk energy bands, making it difficult to measure TIs. Recent experiments have shown that defects, which are commonly found in crystalline materials, can be used as probes to explore higher-order topologies that have been recently realized on various platforms. These defects can generate fractional charges and stable bound states in the dispersion region, allowing us to observe the clear body–disclination correspondence. We have performed simulations using a coupled acoustic cavity system with C3 and C5 symmetries to investigate the body–disclination correspondence in topological crystal insulators (TCIs) in the field of acoustics. Simulation and theoretical results have demonstrated that defects such as disclinations can be used to probe higher-order topologies that were previously unobservable in three-dimensional structures. This approach allows us to detect fractional mode charges and stable bound states, which are crucial for understanding the topological nature of TCIs. Our work demonstrates the potential of using disclination defects to study the intricate relationship between the body and boundary states in topological materials, particularly in the context of acoustics. [ABSTRACT FROM AUTHOR]

The measurement of topological insulators is usually achieved by measuring spectra, which is inadequate in higher-order topological insulators because the separation of bandgaps may be blurred, such as body boundaries and corner state hybridization, and the above measurement requires that the energy of the topological mode must be located in the bulk bandgap to be measured. Recent experiments have shown a strong relationship between the fractional mode charge and the location of the Wannier center in the crystal body. The fractional quantization of the corner charge originates from the filling anomaly, and the fractional mode charge can be calculated from experimental measurements of the local density of states to describe the topological state of the system, which has been demonstrated in optical systems. We have achieved a similar effect in acoustics by utilizing a coupled acoustic-cavity system featuring C3, C4, and C6 symmetries for simulation. Furthermore, we extended our study to 3D third-order topological crystalline insulators to validate the fractional-corner charge approach. The simulation and theoretical results demonstrate that the fractional mode charge can clearly identify the high-order topology, even without gap states. [ABSTRACT FROM AUTHOR]

An attractive avenue for a memory device is offered by thermally induced magnetization switching (TIMS), which is expected to increase the storage density. As an essential step in TIMS, the transient ferromagnetic-like state (TFLS) has attracted much attention. Here, our research analyzes the TFLS from the perspective of magnetization rate based on extensive atomic spin simulations in a parameter space necessary for the formation of TIMS. The results demonstrate that the evolution of the magnetization rate for both Fe and Gd sublattices has two peaks at different timescales, and the two peaks are driven by the Langevin field and the exchange field, respectively. By modulating the pulse fluence, the initial temperature, the pulse duration, the electron–phonon coupling factor, and the damping constant, we find that the first peak of the magnetization rate depends not only on the electron thermal bath and temperature of the phonon but also on the energy transfer rate between the electronic system and the spin system. Moreover, we elucidate the role played by the Langevin field and the exchange field in TFLS formation when modulating the pulse fluence, initial temperature, and pulse duration. The simulation results show that the enhancement of the Langevin field prolongs the duration of TFLS. The enhancement of the exchange field at a long pulse duration before the electron system cools down leads to the shortening of the TFLS duration. However, the time required for Gd demagnetization after the electron system cools down to the Curie temperature changes only slightly when modulating these simulated parameters. [ABSTRACT FROM AUTHOR]