CyberSec Research

In antiferromagnetic spintronics, accessing the spin degree of freedom is essential for generating spin currents and manipulating magnetic order, which generally requires lifting spin degeneracy. This is typically achieved through relativistic spin-orbit coupling or non-relativistic spin splitting in altermagnets. Here, we propose an alternative approach: a dynamical spin splitting induced by an optical field in antiferromagnets. By coupling the driven system to a thermal bath, we demonstrate the emergence of steady-state pure spin currents, as well as linear-response longitudinal and transverse spin currents. Crucially, thermal bath engineering allows the generation of a net spin accumulation without relying on spin-orbit coupling. Our results provide a broadly applicable and experimentally tunable route to control spins in antiferromagnets, offering new opportunities for spin generation and manipulation in antiferromagnetic spintronics.

While the landscape of free-fermion phases has drastically been expanded in the last decades, recently novel multi-gap topological phases were proposed where groups of bands can acquire new invariants such as Euler class. As in conventional single-gap topologies, obstruction plays an inherent role that so far has only been incidentally addressed. We here systematically investigate the nuances of the relation between the non-Bravais lattice configurations and the Brillouin zone boundary conditions (BZBCs) for any number of dimensions. Clarifying the nomenclature, we provide a general periodictization recipe to obtain a gauge with an almost Brillouin-zone-periodic Bloch Hamiltonian both generally and upon imposing a reality condition on Hamiltonians for Euler class. Focusing on three-band $\mathcal{C}_2$ symmetric Euler systems in two dimensions as a guiding example, we present a procedure to enumerate the possible lattice configurations, and thus the unique BZBCs possibilities. We establish a comprehensive classification for the identified BZBC patterns according to the parity constraints they impose on the Euler invariant, highlighting how it extends to more bands and higher dimensions. Moreover, by building upon previous work utilizing Hopf maps, we illustrate physical consequences of non-trivial BZBCs in the quench dynamics of non-Bravais lattice Euler systems, reflecting the parity of the Euler invariant. We numerically confirm our results and corresponding observable signatures, and discuss possible experimental implementations. Our work presents a general framework to study the role of non-trivial boundary conditions and obstructions on multi-gap topology that can be employed for arbitrary number bands or in higher dimensions.

Strain engineering is an effective tool for tailoring the properties of two-dimensional (2D) materials, especially for tuning quantum phenomena. Among the limited methods available for strain engineering under cryogenic conditions, thermal mismatch with polymeric substrates provides a simple and affordable strategy to induce biaxial compressive strain upon cooling. In this work, we demonstrate the transfer of unprecedentedly large levels of uniform biaxial compressive strain to single-layer WS$_2$ by employing a pre-straining approach prior to cryogenic cooling. Using a hot-dry-transfer method, single-layer WS$_2$ samples were deposited onto thermally expanded polymeric substrates at 100 $^\circ$C. As the substrate cools to room temperature, it contracts, inducing biaxial compressive strain (up to ~0.5%) in the WS$_2$ layer. This pre-strain results in a measurable blueshift in excitonic energies compared to samples transferred at room temperature, which serve as control (not pre-strained) samples. Subsequent cooling of the pre-strained samples from room temperature down to 5 K leads to a remarkable total blueshift of ~200 meV in the exciton energies of single-layer WS$_2$. This energy shift surpasses previously reported values, indicating superior levels of biaxial compressive strain induced by the accumulated substrate contraction of ~1.7%. Moreover, our findings reveal a pronounced temperature dependence in strain transfer efficiency, with gauge factors approaching theoretical limits for ideal strain transfer at 5 K. We attribute this enhanced efficiency to the increased Young's modulus of the polymeric substrate at cryogenic temperatures.

We show that Yb(trensal) molecular nanomagnet, embedding an electronic spin qubit coupled to a nuclear spin qudit, provides an ideal platform to probe entanglement in a qubit-qudit system.This is demonstrated by developing an optimized pulse sequence to show violation of generalized Bell inequalities and by performing realistic numerical simulations including experimentally measured decoherence. We find that the inequalities are safely violated in a wide range of parameters, proving the robustness of entanglement in the investigated system. Furthermore, we propose a scheme to study qudit-qudit entanglement on a molecular spin trimer, in which two spins 3/2 are linked via an interposed switch to turn on and off their mutual interaction.

Remote excitation using guided optical modes -- such as waveguides, fibers, or surface waves -- offers a promising alternative to direct optical excitation for surface-enhanced Raman scattering (SERS), particularly in applications requiring reduced heating, minimal invasiveness, and on-chip integration. However, despite its widespread use, systematic comparisons between remote and direct excitation remain limited. Here, we quantitatively benchmark both schemes by measuring power-dependent SERS responses from individual plasmonic nanogaps. We statistically analyze the maximum achievable SERS intensity before structural degradation, extract local temperatures, and evaluate signal-to-noise ratios (SNR). Our findings reveal that both remote and direct SERS share a common electric-field limit, despite exhibiting different levels of heating. This suggests that spectral evolution is primarily governed by the local electric field, which drives nanoscale atomic migration rather than excessive heating. Nonetheless, the lower heating associated with remote excitation enhances the Raman SNR by approximately 30%, improving measurement quality without compromising signal strength. This study establishes a quantitative framework for evaluating excitation strategies in plasmonic sensing, and challenges common assumptions about the role of heating in nanostructural stability under strong optical excitation.

To date, inorganic halide perovskite nanocrystals show promising contributions in emerging luminescent materials due to their high tolerance to defects. In particular, the development of cesium lead iodide (CsPbI3) has shown its efficiency for light-harvesting properties. However, further implementation is hindered due to the toxicity of the lead content. Therefore, in this study, we introduced Cu atoms to partially substitute Pb atoms (5% Cu) in the CsPbI3 lattice as a solution to reduce Pb toxicity. A partial lead material is substituted using Cu displays a larger Stokes shift (-67 nm) compared to the pristine, and resulted doped CsPbI3 not undergo the undesired self absorption. An outcome is focused on the champion of fast-component (tau_1) decay time ~0.6 ns. Temperature-dependent radioluminescence outlines an incremental change in the emission intensity is marginally centered at 713 +- 16 nm, which indicates Cu-doped CsPbI3 is not greatly affected by temperature. In addition, we report that the light yield (LY) pristine CsPbI3 after doping is increased to 3.0 +- 0.8 photons/keV. Our work provides physical insights into a tunable scintillation property using transition metal doping toward lead-free based scintillating perovskites.

Exploring topological matters with exotic quantum states can update the understanding of topological phases and broaden the classification of topological materials. Here, we report a class of unconventional hybrid-order topological insulators (HyOTIs), which simultaneously host various different higher-order topological states in a single $d$-dimensional ($d$D) system. Such topological states exhibit a unique bulk-boundary correspondence that is different from first-order topological states, higher-order topological states, and the coexistence of both. Remarkably, we develop a generic surface theory to precisely capture them and firstly discover a $3$D unconventional HyOTI protected by inversion symmetry, which renders both second-order (helical) and third-order (corner) topological states in one band gap and exhibits a novel bulk-edge-corner correspondence. By adjusting the parameters of the system, we also observe the nontrivial phase transitions between the inversion-symmetric HyOTI and other conventional phases. We further propose a circuit-based experimental scheme to detect these interesting results. Particularly, we demonstrate that a modified tight-binding model of bismuth can support the unconventional HyOTI, suggesting a possible route for its material realization. This work shall significantly advance the research of hybrid topological states in both theory and experiment.

Advances in circuit quantum electrodynamics have enabled the generation of arbitrary nonclassical microwave states and paved the way for addressing novel physics questions. Here, we present a theoretical study of the electrical current in a Josephson tunnel junction interacting with a nonclassical electromagnetic environment. This allows us to generalize classical transport phenomena like photon-assisted tunneling and Shapiro steps to the quantum regime. We predict that the analysis of the supercurrent in such a setup enables the complete reconstruction of quantum states of the electromagnetic environment, something that is not possible with normal tunnel junctions.