Color centers in hexagonal boron nitride have emerged as promising candidates for quantum information applications due to their efficient and bright single-photon emission. Despite the challenges in directly characterizing these emitters, the interaction of defects with external fields, such as the Stark shift, offers valuable insights into their local geometric configurations. In this study, we focus on clarifying the possible origin of the distinct Stark shift characteristics observed experimentally, particularly in the emission energy around 2 eV. We find that the local symmetry of the defects plays a crucial role in determining the nature of the Stark shift, which can be either linear or quadratic. Additionally, the local dielectric environment significantly influences the Stark shift response. Our calculations not only enhance the understanding of the microstructure of these hitherto unknown emitters, but they also pave the way for their more effective utilization as single-photon sources and qubits in quantum technologies.

Hall effect, resistivity, magnetoresistivity, and magnetic susceptibility measurements were performed on phosphorus (P)-doped ZnTe and ${\mathrm{Zn}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ single crystals with free-hole concentrations near the Mott critical density, $N_c=7.7\times {10}^{18}{\mathrm{cm}}^{-3}$ for ZnTe. The results reveal a temperature-driven metal-insulator transition (MIT) at a characteristic temperature $T_m$, accompanied by a paramagnetic-to-spin-glass phase transition. Above $T_m$, in the paramagnetic phase, electrical conductivity is dominated by nearest-neighbor hopping of holes within the impurity band. Below $T_m$, in the insulating spin-glass phase, the magnetic susceptibility increases and exhibits a positive Curie-Weiss temperature, $T_{\mathrm{CW}}=2.1\mathrm{K}$. In this regime, charge transport is governed by the hopping of small magnetic polarons within the Mn subsystem, leading to colossal negative magnetoresistance and pronounced magnetoresistive memory effects. These phenomena are interpreted in terms of charge-transfer coupling between ${\mathrm{Mn}}^{2+}$ ions and holes bound to ionized P acceptors, leading to the formation of ${\mathrm{Mn}}^{3+}$ ions and the electrical compensation of the acceptors. The coexistence of ${\mathrm{Mn}}^{2+}$ and ${\mathrm{Mn}}^{3+}$ gives rise to a ferromagnetic double-exchange interaction between ${\mathrm{Mn}}^{2+}\text{−}{\mathrm{Mn}}^{3+}$ pairs, which competes with the intrinsic antiferromagnetic superexchange between ${\mathrm{Mn}}^{2+}$ ions. This competition underlies the observed spin-glass behavior. These results provide insights into the interplay between hole transport and magnetic properties in diluted magnetic semiconductors near the MIT.

We theoretically reveal that the enhanced electric-field concentration in the conventional plasmonic dimers arise from charge redistribution. The redistribution is governed by the quasistatic Coulomb interactions, where the self-interaction energy of collective charges within a monomer plays an irreplaceable role. This finding is further confirmed by the additional red shifts of hybridized modes in plasmonic nanorod dimers at short distances. Conversely, the situation in a composite cavity consisting of a plasmonic nanorod and a dielectric disk is quite different, where the charges of the nanorod are merely amplified while maintaining the same distribution pattern as an individual nanorod, resulting in near-field concentration remaining at the level of an individual nanorod. Inspired by the charge interaction characteristics in dimers, we further constructed a plasmonic dimer cavity modified with molecules attached to the gap-facing surfaces. By leveraging the Coulomb interactions between small molecules and the collective charges of the metal, one can obtain enhanced charge concentration around the gap-facing surfaces. The corresponding coupling strength between the molecules-modified cavity and a single quantum emitter can be enhanced by several times or more compared to the unmodified case, with the enhancement factor dependent on parameters such as molecular number, transition dipole moment, and molecule-cavity distance.

The non-Hermitian skin effect is a topological phenomenon, resulting in the condensation of bulk modes near the boundaries. Due to the localization of bulk modes at the edges, boundary effects remain significant even in the thermodynamic limit. This renders conventional Bloch band theory inapplicable and hinders the accurate computation of the spectrum. The amoeba formulation addresses this problem by determining the potential from which the spectrum can be derived using the generalized Szegö's limit theorem, reducing the problem to an optimization of the Ronkin function. While this theory provides insights into non-Hermitian physics, challenges arise from the multiband nature and symmetry-protected degeneracies, even in one-dimensional cases. In this work, we investigate one-dimensional two-band class ${\mathrm{AII}}^{†}$ systems, where Kramers pairs invalidate the conventional amoeba formalism. We find that these challenges can be overcome by optimizing the symmetry-decomposed Ronkin functions, which is achieved by extrapolating the total Ronkin function. Finally, we propose a generalized Szegö's limit theorem for class ${\mathrm{AII}}^{†}$ and numerically demonstrate that our approach correctly computes the potential and localization length.

We investigate the eigenstates, that is, the wave functions of Rydberg excitons in cuprous oxide quantum wells and derive expressions relating them to the oscillator strengths of different exciton states. Using the B-spline expansion, we compute the wave functions in coordinate space and estimate the oscillator strengths. The symmetry properties of the states and the nonseparability of the wave functions are illustrated. Wave functions associated with resonances above the scattering threshold, particularly those of bound states in the continuum as well as their partner states, are also given.

Using a microscopic model, we show that the large-momentum scattering of electrons in flat bands deviates significantly from that of the Coulomb scattering. In particular, we find that large-momentum scattering is enhanced at $\theta \lesssim 4^{\circ }$, with a nonmonotonic momentum dependence appearing near the magic angle. For $\theta \gtrsim 1.2^{\circ }$, the enhanced large-momentum scattering can be attributed to the compact Wannier function. On the other hand, for $\theta \lesssim 1.2^{\circ }$, the nonmonotonic momentum dependence of the interaction matrix cannot be explained by a simple Wannier orbital, indicating a nontrivial modification of the electron-electron scattering. Notably, the range of angles $\theta$ where the large-momentum scattering is enhanced differs from the magic angles at which nearly flat bands emerge, suggesting that the angle dependence of material properties provides information about the effect of the interaction. The results highlight unusual features of the interaction in moiré graphene.

Angle-resolved photoemission spectroscopy is employed to study the electronic structure of bulk ${\mathrm{TiSe}}_2$ before and after doping with potassium impurities. A splitting in the conduction band into two branches is observed after room-temperature deposition. The splitting energy increases to approximately 130 meV when the sample is cooled to 40 K. One branch exhibits a nondispersive two-dimensional feature, while the other shows the characteristics of three-dimensional bulk band dispersion. Core-level spectroscopy suggests that the K impurities predominantly occupy the intercalated sites within the van der Waals gap. The results indicate the formation of a quasi-freestanding ${\mathrm{TiSe}}_2$ layer. Additionally, doping completely suppresses the periodic lattice distortion in the surface region. These findings are further supported by density functional theory calculations, which compare the band structure of monolayer and bulk ${\mathrm{TiSe}}_2$ with experimental data. Thus, the dimensional and intrinsic electronic properties of $1T\text{−}{\mathrm{TiSe}}_2$ can be controlled through the intercalation procedure used in this work.

We investigated the effect of hydrostatic pressure on the quasi-one-dimensional superconductor ${\mathrm{TaSe}}_3$, using Raman spectroscopy, synchrotron x-ray diffraction, and first-principles calculations. Our studies reveal the weak topological nature of ${\mathrm{TaSe}}_3$ under ambient conditions. The application of hydrostatic pressure to the material shows a series of topological quantum phase transitions. Specifically, we observe a transition from weak to strong topological phase at 3 GPa followed by another transition to a weak topological phase at 8 GPa. The topologically dark surfaces in the initial and final weak topological phases are different, as indicated by the weak indices (101) and (100), respectively. The surface spectrum of ${\mathrm{TaSe}}_3$ in the strong phase indicates a Dirac point at the center of the Brillouin zone with spin helicity. We also observe the existence of Rashba-like spin splitting of the electronic states on the surfaces, owing to the discontinuous nature of the potential at the surface and the presence of spin-orbit coupling. Our study reveals the extremely rich properties that emerge in ${\mathrm{TaSe}}_3$ with the application of pressure, shedding light on its importance in next-generation quantum devices.

We study the electronic structure of the chiral semimetal PdGa by means of the de Haas–van Alphen and Shubnikov–de Haas effect. We find that the Fermi surface of PdGa comprises multiple pockets split by spin-orbit coupling. We compare our experimental findings with the band structure calculated ab initio. We demonstrate that the quantum oscillation spectra can be fully understood by considering topological nodal plane degeneracies at the Brillouin zone boundary and magnetic breakdown between individual Fermi-surface pockets. Expanding traditional analysis methods, we explicitly calculate magnetic breakdown frequencies and cyclotron masses while taking into account that extremal breakdown trajectories may reside away from the planes of the single-band orbits. We further analyze high-frequency contributions arising from breakdown trajectories involving multiple revolutions around the Fermi surface which are distinct from conventional harmonic frequencies. Our results highlight the existence of gaps induced by spin-orbit coupling throughout the band structure of PdGa, the relevance of nodal planes on the Brillouin zone boundary, and the necessity for a comprehensive analysis of magnetic breakdown.

The van der Waals semiconductor SnSe has exceptional thermoelectric properties with a high figure of merit ($ZT$) of 2.6. Extensive research has investigated its “camel's back” valence-band structure, which is commonly regarded as an indicator for high thermoelectric performance. However, its interband excitonic properties are not fully understood. Here, we report near-infrared magnetotransmission spectroscopy measurements on SnSe thin films in pulsed magnetic fields $B$ of up to 60 T. They reveal two indirect excitonic absorption processes (in momentum space), associated with the two maxima in the camel's back valence-band structure. The magneto-optical data indicate the presence of interband transitions to the excited $2p$ excitonic states rather than the $1s$ ground state. This observation is consistent with previous first-principles calculation of the electronic structure based on angular momentum and parity-conservation selection rules.

We report on an investigation of the structural and ferroelectric properties of ${\mathrm{Al}}_{1\text{–}x}{\mathrm{Sc}}_x\mathrm{N}$, ${\mathrm{Sc}}_y{\mathrm{Ga}}_x\mathrm{N}$ $(x+y=1)$, and quaternary ${\mathrm{Al}}_{1\text{–}x\text{–}y}{\mathrm{Sc}}_y{\mathrm{Ga}}_x\mathrm{N}$ alloys using density functional theory (DFT) calculations. The calculated spontaneous polarization $\left(P_{\mathrm{sp}}\right)$ and coercive field $\left(E_c\right)$ values for the ${\mathrm{Al}}_{1\text{–}x}{\mathrm{Sc}}_x\mathrm{N}$ and ${\mathrm{Sc}}_y{\mathrm{Ga}}_x\mathrm{N}$ $(x+y=1)$ ternary systems are in good agreement with experimental data, validating the computational approach. We find that the composition-induced structural transformation to the ferroelectric wurtzite phase in ${\mathrm{Al}}_{1\text{–}x}{\mathrm{Sc}}_x\mathrm{N}$ is strongly correlated with changes in the out-of-plane lattice parameter, while in ${\mathrm{Sc}}_y{\mathrm{Ga}}_x\mathrm{N}$ $(x+y=1)$, the transformation involves structural changes in both in-plane and out-of-plane lattice parameters. van der Waals interactions play a crucial role in accurately predicting the out-of-plane lattice parameters and, consequently, $P_{\mathrm{sp}}$. Our study of the quaternary alloys reveals regions in compositional space with reduced $E_c$, offering insights into the design of improved ferroelectric materials for next-generation electronic devices.

Self-assembled optically active quantum dot molecules (QDMs) allow the creation of protected qubits via singlet-triplet spin states. The qubit energy splitting of these states is defined by the tunnel coupling strength and is, therefore, determined by the potential landscape and is fixed during growth. Applying an in-plane magnetic field increases the confinement of the hybridized wave functions within the quantum dots, leading to a decrease of the tunnel coupling strength. We achieve a tuning of the coupling strength by $53.4\%\pm 1.7\%$. The ability to fine-tune this coupling is essential for quantum network and computing applications that require quantum systems with near identical performance.

The heavy-fermion superconductor (SC) ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ ($T_{\text{c}}$ = 0.35 K) shows two SC phases SC1 and SC2 when a magnetic field is applied parallel to the $c$ axis of the tetragonal unit cell. All experiments to date have indicated that the change in SC order parameter detected at ${\mu }_{\text{0}}{H}^{*}\approx 4\mathrm{T}$ is due to strong Rashba spin-orbit coupling at the Ce sites caused by the locally noncentrosymmetric environments of the otherwise globally centrosymmetric crystalline structure. Another phase (phase I) exists in this material below $T_{\text{0}}$ = 0.54 K. In a previous specific heat study [K. Semeniuk et al., Phys. Rev. B 107, L220504 (2023)], we have shown that phase I persists up to a field ${\mu }_{\text{0}}{H}_{\text{0}}\approx 6\mathrm{T}$, larger than $H^{*}$. From thermodynamic arguments, we expected the phase-I boundary line to cross phase SC2 at a tetracritical point. However, we could not find any signature of the phase-I line inside the SC2 phase and speculated that this was because the $T_0\left(H\right)$ line is almost perpendicular to the $H$ axis and therefore invisible to $T$-dependent measurements. This would imply a weak competition between the two order parameters. Here, we report magnetic-field-dependent measurements of the magnetostriction and ac susceptibility on high-quality single crystals. We see clear evidence of the singularity at $H_0$ inside the SC2 phase and confirm our previous prediction. Furthermore, we observe the transition across the $T^{*}\left(H\right)$ line in $T$-dependent specific heat measurements, which show that the $T^{*}\left(H\right)$ line is not perpendicular to the field axis but has a positive slope. Our findings support recent muon spin resonance results which suggest coexistence of phase I with SC.

${\mathrm{CuBiSCl}}_2$ exhibits strongly contrasting anisotropies in charge and phonon transport, showing superior electron mobility (138 ${\mathrm{cm}}^2/\mathrm{V}\mathrm{s}$) yet ultralow lattice thermal conductivity (0.40 W/mK) along the $a$ axis at 300 K. This exceptional combination arises from the anisotropic bonding hierarchy where ${\left[{\mathrm{BiSCl}}_2\right]}_n$ ribbons facilitate efficient charge conduction through delocalized Bi-$6p$/S-$3p$ networks, while soft Cu-dominated vibrations strongly scatter heat-carrying phonons in the same direction. The resulting high-power factor (1.71 mW/${\mathrm{mK}}^2$ at 700 K) and peak $ZT$ of 1.57 establish ${\mathrm{CuBiSCl}}_2$ as a paradigm for realizing the “phonon glass-electron crystal” concept through crystallographic engineering.

Momentum-dependent nonrelativistic spin splitting in altermagnets is determined by crystal symmetry and thus it is difficult to tune spin splitting for a specific material. The discovery and design of antiferromagnets with tunable ferromagnetic-like nonrelativistic spin splitting is of great significance for both basic science and practical applications. In this work, we propose the multiple-state polarized antiferromagnets (PAFMs), which couple multiple polarization states and antiferromagnetic order and thus realize tunable ferromagnetic-like spin splitting. For realizing multiple polarization states, we propose a symmetry design concept by considering two factors: broken spatial inversion symmetry for ferroelectricity, and low interface symmetry for multiple potential wells. Based on these two considerations, we choose the displacement-type ferroelectric monolayer with the out-of-plane polarization and different atomic arrangements on the upper and lower surfaces. As an example, in the displacement-type antiferroelectric ${\mathrm{Nb}}_3{\mathrm{I}}_8$ bilayers, two opposite sliding ferroelectric states induce opposite spin splitting. Furthermore, in displacement-type ferroelectric bilayers, the displacement-type ferroelectricity and sliding ferroelectricity can coexist. Due to the spontaneous broken spatial inversion symmetry and low interface symmetry, multiple polarization states with a suitable transition barrier in between are obtained. Considering the coupling between the displacement-type ferroelectricity and sliding ferroelectricity, there exist six polarization states corresponding to different spin splitting, which can be controlled by an external electric field. Therefore, the nonvolatile electric-field controllable ferromagnetic-like spin splitting over the whole Brillouin zone can be achieved in PAFMs, providing strong theoretical support for future multistate information storage and multifunctional spintronic devices based on multiple polarization states and tunable spin polarization.

Frustrated magnetism in face-centered-cubic (fcc) magnetic sublattices remains underexplored but holds considerable potential for exotic magnetic behavior. Here we report on the crystal structure and the magnetic and thermodynamic properties of the $A$-site-vacant hydroxide double perovskite ${\mathrm{MnSn}\left(\mathrm{OH}\right)}_{\text{6}}$. Despite dominant antiferromagnetic interactions among ${\text{Mn}}^{2+}$ moments, evidenced by a negative Curie-Weiss temperature, the lack of a sharp thermodynamic transition down to 350 mK implies the absence of long-range magnetic order. However, a broad hump in the specific heat at 1.6 K suggests short-range correlations. Neutron diffraction at low temperatures confirms the presence of three-dimensional antiferromagnetic correlations, manifested as diffuse magnetic scattering with a correlation length $\xi =24.66\AA$ and magnetic propagation vectors $\mathbf{k}=\left(\frac{1}{2}\frac{1}{2}\frac{1}{2}\right)$ and $\left(00.6250\right)$ at 20 mK.