We investigate bipartite entanglement between two distant parties, $A$ and $B$, comprising local magnetic impurities (or qudits) induced by the quench through $sd$ exchange in a field-effect transistor geometry. A wave-function-based time-dependent formalism is employed by including non-dissipative responses that allow for the control of entanglement via gate voltages. Our study focuses on the birth (or origin) and early growth of entanglement, by introducing environment support states that render site- and layer-resolved logarithmic negativity (LN) and mutual information (MI). In the minimal set, where party $A$ ($B$) consists of a qubit, we identify entanglement sudden deaths (ESDs), which are explained by a visualization picture analyzing the density matrix. Vibrating electron currents facilitate the birth of entanglement, while they are not required for its growth and subsistence. The LN emerges near the edge layers in $A$ and $B$, while MI shows up outside these two parties within the spacing layer. The MI is born earlier than the LN. When a gate voltage large enough to disjoint part of the system is applied within the spacing region, it partially suppresses the entanglement, quantified by the LN. This suppression does not appear immediately after the presence of the disjoint voltage. Applying this disjoint voltage to the site(s) hosting the qubit(s) helps prevent the site- and layer-resolved LN from encountering ESDs. The local impurities in parties $A$ and $B$ are initially of opposite spin directions in an unentangled state, as can be prepared by two of our proposed protocols. However, the features described above do not depend on the chosen protocols.

Using the Landau-Ginzburg-Devonshire approach, we study light-induced phase transitions, evolution of polar state, and domain morphology in photoferroelectric nanoparticles (NPs). Light exposure increases the free-carrier density near the NP surface and may in turn induce phase transitions from the nonpolar paraelectric to the polar ferroelectric phase. Using the uniaxial photoferroelectric ${\mathrm{Sn}}_2{\mathrm{P}}_2{\mathrm{S}}_6$ as an example, we show that visible light exposure induces the appearance and vanishing of striped, labyrinthine, or curled domains and changes in the polarization-switching hysteresis loop shape from paraelectric curves to double, pinched, and single loops, as well as the shifting in the position of the tricritical point. Furthermore, we demonstrate that an ensemble of noninteracting photoferroelectric NPs may exhibit superparaelectric-like features at the tricritical point, such as strongly frequency-dependent giant piezoelectric and dielectric responses, which can potentially be exploited for piezoelectric applications.

Using first-principles techniques, we study the structural, magnetic, and electronic properties of (111)-oriented ${\left({\mathrm{LaMnO}}_3\right)}_{2n}|{\left({\mathrm{SrMnO}}_3\right)}_n$ superlattices of varying thickness ($n=2,4,6$). We find that the properties of the thinnest superlattice ($n=2$) are similar to the celebrated half-metallic ferromagnetic alloy ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_3$, with quenched Jahn-Teller distortions. At intermediate thickness ($n=4$), the $a^{-}{a}^{-}{a}^{-}$ tilting pattern transitions to the $a^{-}{a}^{-}{c}^{+}$ tilting pattern, driven by the lattice degrees of freedom in the ${\mathrm{LaMnO}}_3$ region. The emergence of the Jahn-Teller modes and the spatial extent needed for their development play a key role in this structural transition. For the largest thickness considered ($n=6$), we unveil an emergent separation of Jahn-Teller and volume-breathing orders in the ground-state structure with the $a^{-}{a}^{-}{c}^{+}$ tilting pattern, whereas it vanishes in the antiferromagnetic configurations. The ground state of all superlattices is half-metallic ferromagnetic, not affected by the underlying series of structural transitions. Overall, these results outline a thickness-induced crossover between the physical properties of bulk ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_3$ and bulk ${\mathrm{LaMnO}}_3$.

Using first-principles calculations combined with the Löwdin partitioning method, we investigate the layer-resolved topological properties of the Ising superconductor $\mathrm{Nb}{\mathrm{Se}}_2$ proximity coupled with a two-dimensional metallic ferromagnet ${\mathrm{Fe}}_3\mathrm{Ge}{\mathrm{Te}}_2$ (FGT). We first reveal that the top $\mathrm{Nb}{\mathrm{Se}}_2$ monolayer develops a nontrivial band topology under the lateral compression caused by the FGT overlayer, while the remaining $\mathrm{Nb}{\mathrm{Se}}_2$ layers maintain their band triviality. More significantly, the top $\mathrm{Nb}{\mathrm{Se}}_2$ monolayer exhibits distinctly different band topology when the FGT magnetization is switched off or on, characterized by a topological invariant $Z_2=1$ or Chern number $C=1$, respectively. We further confirm that the Ising pairing nature in the top $\mathrm{Nb}{\mathrm{Se}}_2$ monolayer is well preserved in the heterostructure. This study not only provides an appealing candidate system for realizing topological Ising superconductivity, but also presents a generic first-principles based approach for describing topological superconductivity beyond prevailing empirical phenomenological modeling.

The presentation of magnetic moment in a long period of time is the key ingredient for the surface supported single atom magnets (SAMs) in potential usages of ultrahigh density magnetic storage and possible realizations of quantum devices. It requires magnetic adatom not only to have the appropriate degenerate magnetic ground states to match with a specific point symmetry of local environment but also to suffer a compatible crystal field (CF) action, prohibiting the quantum tunneling of magnetization (QTM) and maximizing the effective reversal energy barrier ($U_{\mathrm{rev}}$). We employed the density function theory (DFT) and multiplet simulations as well as the CF Hamiltonian calculations to explore the deposition stability, magnetic moment, and magnetic relaxation of lanthanide adatom (Dy) on an insulating graphene oxide (GO) on Cu(111) substrate. Our DFT calculations revealed that Dy-$sd$ electrons primarily contribute to strong adsorption and the number of $4f$ electrons in the Dy adatom remains the same as that in the isolated Dy atom, labeled as $+\mathrm{II}$ state within $4f^{10}$ configuration, which are basically unaffected by Cu(111) substrate. In combination of the simulated x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism spectra (XMCD), and the energy spectrum of magnetic quantum levels, we identified that Dy adatom presents a stable magnetic moment in a long relaxation time and shows a predominant out-of-plane magnetization orientation. The degenerate ground states $|J=8,m_j\approx \pm 8\rangle$ of Dy adatom are protected from the QTM by $C_{3v}$ symmetry provided by the substrate CF, while there appears the QTM between the degenerate second-excited states $|J=8,m_j=\pm 6\rangle$. The spin-flip excitations from $|J=8,m_j\approx \pm 8\rangle$ states to $|J=8,m_j\approx \pm 7\rangle$ states and subsequently the de-excitations to $|J=8,m_j\approx \mp 8\rangle$ states reduce the magnetization reversal barrier from 24.57 to 10.52 meV. We estimated a long magnetic lifetime of 2715 s at 4.5 K, indicating that the stabilized magnetic moments and thus the hysteresis of Dy adatom could be experimentally measured in a liquid helium environment.

We study electron-electron and electron-phonon mediated pairing in the Holstein extended Hubbard model on the kagome lattice near the van Hove fillings, and we investigate their combined effects on electron pairing states. We find that their combination can promote exotic pairings in a crossover region, where the filling is close to a van Hove singularity. In particular, at the $p$-type van Hove filling, the $E_{1u}$ ($p$-wave) and $B_{2u}$ ($f_{y^3-3y{x}^2}$-wave) pairings become leading, and at the $m$-type van Hove filling, the $E_{1u}$ and $A_{2g}$ ($i$-wave) pairings get promoted. Moreover, we show that the electron-phonon interaction acquires a significant momentum dependence, due to the sublattice texture of the Fermi surfaces, which can promote non-$s$-wave pairing. We present a detailed analysis of these pairing propensities, and we discuss implications for the vanadium-based kagome superconductors ${A\text{V}}_3{\mathrm{Sb}}_5$.

The quantization of conductance in the presence of nonmagnetic point defects is a consequence of topological protection and the spin-momentum locking of helical edge states in two-dimensional topological insulators. This protection ensures the absence of backscattering of helical edge modes in the quantum Hall phase of the system. However, in this paper, we focus on exploring an approach to spoil such conductance quantization. We propose that a linear arrangement of (nonmagnetic) on-site impurities can effectively cause deviations from the conductance quantization of the edge states in the Kane-Mele model. To investigate this phenomenon, we consider an armchair ribbon containing a line defect spanning its width. Utilizing the tight-binding model and nonequilibrium Green's function method, we calculate the transmission coefficient of the system. Our results reveal a suppression of conductance at energies near the lower edge of the bulk gap for positive on-site potentials. To further comprehend this behavior, we perform analytical calculations and discuss the formation of an impurity channel. This channel arises due to the overlap of in-gap bound states, linking the bottom edge of the ribbon to its top edge, consequently facilitating backscattering. Our explanation is supported by the analysis of the local density of states at sites near the position of impurities.

We use theory and first-principles calculations to explore mechanisms for control of the translational and point group symmetries of crystals in ultrafast optical experiments. We focus, in particular, on mechanisms that exploit anharmonic (biquadratic) lattice couplings between a driven infrared-active phonon mode and other modes at arbitrary wave vector, which are always allowed by symmetry in any space group. We use Floquet theory to develop a general phase diagram depicting the various dynamical regimes accessible to materials, with simulated dynamics to illustrate how the biquadratic coupling changes materials structures depending on both extrinsic factors (light pulse characteristics) and intrinsic materials parameters (phonon frequencies and phonon coupling strengths). We use our phase diagram, in conjunction with density functional theory calculations, both to suggest experiments to reveal hidden structural order in perovskite ${\mathrm{KTaO}}_3$ and to provide additional insights into recently reported experiments on ${\mathrm{SrTiO}}_3$ and ${\mathrm{LiNbO}}_3$.

A stationary inflection point (SIP) in the Bloch dispersion relation of a periodic waveguide is an exceptional point degeneracy where three Bloch eigenmodes coalesce, forming the so-called frozen mode with a divergent amplitude and vanishing group velocity of its propagating component. We have developed a theoretical framework to study the time evolution of wavepackets centered at an SIP. Analysis of the evolution of the statistical moment distribution of linear pulses shows a strong deviation from the conventional ballistic wavepacket dynamics in dispersive media. The presence of nonlinear interactions dramatically changes the situation, resulting in a mostly ballistic propagation of nonlinear wavepackets with the speed and even the direction of propagation essentially dependent on the wavepacket amplitude. Such a behavior is unique to nonlinear wavepackets centered at an SIP and can be used for the realization of a novel family of beam power routers for classical waves.

We investigate the signature of magnetic surface anisotropy in nanoparticles in their spin-flip neutron scattering cross section. Taking into account the isotropic exchange interaction, an external magnetic field, a uniaxial or cubic magnetic anisotropy for the particle's core, and several models for the surface anisotropy (Néel, conventional, random), we compute the spin-flip small-angle neutron scattering (SANS) cross section from the equilibrium spin structures obtained using the Landau-Lifshitz equation. The sign of the surface anisotropy constant, which is related to the appearance of tangential- or radial-like spin textures, can be distinguished from the momentum-transfer dependence of the spin-flip signal. The data cannot be described by the well-known and often-used analytical expressions for uniformly magnetized spherical or core-shell particles, in particular at remanence or at the coercive field. Based on a second-order polynomial expansion for the magnetization vector field, we develop a novel minimal model for the azimuthally averaged magnetic SANS cross section. The theoretical expression considers a general magnetization inhomogeneity and is not restricted to the presence of surface anisotropy. It is shown that the model describes very well our simulation data as well as more complex spin patterns such as vortexlike structures. Only seven expansion coefficients and some basis functions are sufficient to describe the scattering behavior of a very large number of atomic spins.

We construct a complete numerically exact solution of a mean-field quantum spin glass model—the transverse field Sherrington-Kirkpatrick model—by implementing a continuous-time quantum Monte Carlo method in the presence of full replica symmetry breaking. We extract the full numerically exact phase diagram, displaying a glassy phase with continuous replica symmetry breaking at small transverse fields and low temperatures. A paramagnetic phase emerges once thermal and quantum fluctuations melt the spin glass. We characterize both phases by extracting the order parameter as well as the static and dynamical local spin susceptibilities. The static susceptibility shows a plateau in the glassy phase, but it remains smooth across the phase boundary. For the imaginary part of the dynamical susceptibility, we find an Ohmic, i.e., linear in $\omega$, scaling for small frequencies $\omega$, with a slope independent of the transverse field. These results compare qualitatively well with ac susceptibility measurements on a dipole-coupled three-dimensional Ising magnet—the ${\mathrm{LiHo}}_x{\mathrm{Y}}_{1-x}{\mathrm{F}}_4$ compound—in a transverse magnetic field. Our work provides a general framework for the exact numerical solution of mean-field quantum glass models, and it constitutes an important step towards understanding glassiness in realistic systems.

Phosphorus donor nuclear spins in silicon couple weakly to the environment, making them promising candidates for high-fidelity qubits. The state of a donor nuclear spin qubit can be manipulated and read out using its hyperfine interaction with the electron confined by the donor potential. Here we use a master-equation-based approach to investigate how the backaction from this electron-mediated measurement affects the lifetimes of single and multidonor qubits. We analyze this process as a function of electric and magnetic fields and hyperfine interaction strength. Apart from single nuclear spin flips, we identify an additional measurement-related mechanism, the nuclear spin flip-flop, which is specific to multidonor qubits. Although this flip-flop mechanism reduces qubit lifetimes, we show that it can be effectively suppressed by the hyperfine Stark shift. We show that using atomic precision donor placement and engineered Stark shift, we can minimize the measurement backaction in multidonor qubits, achieving larger nuclear spin lifetimes than single donor qubits.

Metal-insulator transitions (MITs) are ubiquitous in strongly correlated electron systems. However, there is an unexplored area of study: the artificially confined systems of strained quantum wells that are comprehensively studied in semiconductors for practical device applications. Here we have systematically studied quantum wells of ${\mathrm{Sr}}_{1–x}{\mathrm{La}}_x\mathrm{V}{\mathrm{O}}_3$, a compound that evolves from a $3d^1$ metal ($\mathrm{SrV}{\mathrm{O}}_3$) to a $3d^2$ Mott insulator ($\mathrm{LaV}{\mathrm{O}}_3$). The two-dimensional confinement is shown to enhance the stability of the insulating phase, shifting the critical MIT value of $x$ from $x=0$.82 for the bulk to around $x=0.50$ at a thickness of 4 unit cells (u.c.); below 3 u.c. the insulating state merges with the newly emerging $d^1$ Mott insulator state ($x=0$). The Mott insulator states are further stabilized by a tensile epitaxial strain, presumably due to the enhanced correlation in selectively occupied $d_{xy}$ orbitals. These findings pave the way for exploring Mott physics in an artificially confined system of a strongly correlated electron system.

We investigate the superconducting properties of inversion-symmetric twisted trilayer graphene by considering different parent states, including spin-singlet, triplet, and SO(4) degenerate states, with or without nodal points. By placing transition metal dichalcogenide layers above and below twisted trilayer graphene, spin-orbit coupling is induced in TTLG and, due to inversion symmetry, the spin-orbit coupling does not spin split the bands. The application of a displacement field $\left(D_0\right)$ breaks the inversion symmetry and creates spin splitting. We analyze the evolution of the superconducting order parameters in response to the combined spin-orbit coupling and $D_0$-induced spin splitting. Utilizing symmetry analysis combined with both a direct numerical evaluation and a complementary analytical study of the gap equation, we provide a comprehensive understanding of the influence of spin-orbit coupling and $D_0$ on superconductivity. These results contribute to a better understanding of the superconducting order in twisted trilayer graphene.