Motivated by the recent findings on the $T$-linear electronic scattering rate in the two-dimensional Hubbard model, we have investigated the three-orbital Emery model and its temperature-dependent electronic and quasiparticle scattering rates by adopting dynamical cluster quantum Monte Carlo simulations. By focusing on two characteristic site energies ${\epsilon }_p$ of $\mathrm{O-2}p$ orbital relevant to cuprates and nickelates separately, our exploration discovered that, for ${\epsilon }_p=3.24$ relevant to cuprates, the scattering rate can exhibit a linear-$T$ dependence at low temperature for a range of intermediate densities. In contrast, for larger ${\epsilon }_p=6.0$ presumably relevant to nickelates, a wide range of densities support a downturn of the scattering rate below the temperature scale $T\sim 0.1$ with possibly two consecutive nearly linear-$T$ regimes connected via a smooth crossover around $T\sim 0.1$. Furthermore, the temperature-dependent quasiparticle scattering rate generically departs from the unity slope as predicted by the Planckian dissipation theory. Our presented work provides valuable insights on the extensively studied three-orbital Emery model, particularly on the quantitative examination of non-Fermi-liquid features of scattering rates.

Global hybrid exchange-correlation energy functionals within generalized Kohn-Sham density functional theory have long been established as part of the standard repertoire for electronic structure calculations. Accurate electronic band structures of solids are indispensable for a wide variety of applications and should provide a sound prediction of phonon-induced band gap renormalization at finite temperatures. We employ our previously introduced formalism of general hybrid functionals within the approximate density functional tight-binding (DFTB) method to present insights into the accuracy of temperature dependent band gaps obtained by a dielectric dependent global hybrid functional. The work targets the prototypical group-IV semiconductors diamond and silicon. Following [Zacharias et al. Phys. Rev. Lett. 115, 177401 (2015)], we sample the nuclear wave function by stochastic Monte Carlo integration as well as the deterministic one-shot procedure [M. Zacharias and F. Giustino, Phys. Rev. B 94, 075125 (2016)] derived from it. The computational efficiency of DFTB enables us to further compare these approaches, which fully take nuclear quantum effects into account, with classical Born-Oppenheimer molecular dynamic (BOMD) simulations. While the quantum mechanical treatments of Zacharias et al. yield band gaps that are in good agreement with experiment, calculations based on BOMD snapshots inadequately describe the renormalization effect at low temperatures. We demonstrate the importance of properly incorporating nuclear quantum effects by adapting the stochastic approach to normal amplitudes that arise from the classical equipartition principle. For low temperatures, the results thus obtained closely resemble the BOMD predictions, while anharmonic effects become important beyond 500 K. Comparisons between DFTB parametrized from semilocal DFT, and global hybrid DFTB, suggest that Fock-type exchange systematically yields a slightly more pronounced electron-phonon interaction, and hence stronger gap renormalization and zero-point corrections.

Topologically protected edge states of phonons are commonly believed to be immune to backscattering according to previous theoretical works. However, the scattering behavior of the numerous topological phonon (TP) states discovered in natural crystalline materials in recent years has not been concretely examined. In the present work, our analysis of the spring model device shows that the topologically protected phonon edge mode will also be scattered if a suitable backscattering channel is constructed. Based on atomistic S-matrix method, we extend phonon band unfolding technique and explore the robustness of TP transport in zigzag graphene nanoribbon (ZGNR) device through first-principles calculation. Our results show that TP edge states in ZGNR experience strong scattering because the bulk phonon modes provide backscattering channels for TPs in the local band gaps. These computational results indicate that topological phonon edge states located within local band gaps, in ZGNRs or even in other nanomaterials, may not exhibit the robustness as expected. Exploring TP states within natural full band gaps of crystalline materials may present a more effective strategy for mitigating backscattering challenges.

We realize the initialization, manipulation, and readout of qubits in triangular triple quantum dots (TTQDs) with theoretical and numerical simulation calculations. In the initialization, the degenerate ground states can be split by adding a vertical magnetic flux or a bias voltage at the initial time. This is consistent with the magnetoelectric equivalence proposed in previous work, and both cause chiral state splitting. In the manipulation, we add an inhomogeneous Zeeman field to the TTQDs. Based on the Heisenberg model of the two-level system, it is obtained that the applied Zeeman field gradient will cause Rabi oscillation of the two chiral states' occupation probability, which also corresponds to the manipulation of chiral qubits on the Bloch sphere. The Rabi cycle and amplitude vary with the gradient of the Zeeman field and the internal chiral term, and numerical simulation is consistent with the theoretical results. Finally, we give a possible readout method to use for the topological blockage of chiral and conduction current. This method provides an alternative idea for qubits, which can realize quantum coding by using the smallest chiral topological structure.

We find the recently developed strongly constrained and appropriately normed (SCAN) functional, now widely used in calculations of many materials, is not able to reliably describe the properties of deep defects and small polarons in a set of wide-bandgap semiconductors and insulators $(\mathrm{ZnO}, \mathrm{ZnSe}, \mathrm{GaN}, {\mathrm{Ga}}_2{\mathrm{O}}_3, \text{and} \mathrm{NaF})$. By comparing first-principles calculations using the SCAN functional against established experimental information and first-principles calculations using a hybrid functional, we find that the SCAN functional systematically underestimates the magnitude of the structural distortions at deep defects and tends to delocalize the charge density of these defect states.

It is shown that semiconductor nanoscale resonators with extreme dielectric confinement accelerate the diffusion of electron-hole pairs excited by nonlinear absorption. The response function of the effective carrier density is computed by an efficient eigenmode expansion technique. A few eigenmodes of the diffusion equation effectively capture the long-timescale carrier decay rate, which is advantageous compared to time-domain simulations. Notably, the eigenmode approach elucidates the contribution to carrier diffusion of the in-plane and out-of-plane cavity geometry. These results and insights may be used to optimize the design of various photonic devices, e.g., for applications in all-optical signal processing.

We set up and parametrize a Hubbard model for interacting quantum dots in bilayer graphene and study double dots as the smallest multidot system. We demonstrate the tunability of the spin and valley multiplets, Hubbard parameters, and effective exchange interaction by electrostatic gate potentials and the magnetic field. Considering both the long- and short-range Coulomb interactions, we map out the various spin and valley multiplets and calculate their energy gaps for different dot sizes and interdot separations. For half-filling and large valley splittings, we derive and parametrize an effective Heisenberg model for the quantum dot spins.

Chiral symmetry plays an indispensable role in topological classifications as well as in the understanding of the origin of bulk or boundary flat bands. The conventional definition of chiral symmetry refers to the existence of a constant unitary matrix anticommuting with the Hamiltonian. Since a constant unitary matrix has constant eigenvectors, boundary flat bands enforced by chiral symmetry, which share the same eigenvectors with the chiral symmetry operator, are dictated to carry fixed (pseudo)spin polarizations and be featureless in quantum geometry. In this paper, we generalize the chiral symmetry and introduce a concept termed subchiral symmetry. Unlike the conventional chiral symmetry operator defined as constant matrix, the subchiral symmetry operator depends on partial components of the momentum vector, as do its eigenvectors. We show that topological gapped or gapless systems without chiral symmetry, but with subchiral symmetry, can support boundary flat bands, which exhibit topological spin textures and quantized Berry phases. We expect that such intriguing boundary flat bands could give rise to a variety of exotic physics in the presence of interactions or disorders.

We study a system composed of graphene decorated with an array of islands with $C_{3v}$ symmetry that induce quantum dot (IQD) regions via proximity effects and give rise to several spin-orbit couplings (SOCs). We evaluate transport properties for an array of IQDs and analyze the conditions for realizing isolated valley conductances and valley-state localization. The resulting transmission shows a square-type behavior with wide gaps that can be tuned by adjusting the strength of the staggered intrinsic SOCs. Realistic proximity effects are characterized by weak SOC strengths, and the analysis of our results in this regime shows that the Rashba coupling is the important interaction controlling valley properties. As a consequence, a top gate voltage can be used to tune the valley polarization and switch the valley scattering for positive or negative incident energies. A proper choice of SOC strengths leads to higher localization of valley states around the linear array of IQDs. These systems can be implemented in heterostructures composed of graphene and semiconducting transition-metal dichalcogenides (TMDs) such as ${\mathrm{MoSe}}_2$, ${\mathrm{WSe}}_2$, ${\mathrm{MoS}}_2$, or ${\mathrm{WS}}_2$. In these setups, the magnitudes of induced SOCs depend on the twist angle, and due to broken valley degeneracy, valley-polarized currents at the edges can be generated in a controllable manner as well as localized valley states. Our findings suggest an alternative approach for producing valley-polarized currents and propose a corresponding mechanism for valley-dependent electron optics and optoelectronic devices.

All-optical spin switching (AOS) is a new phenomenon found in a small group of magnetic media, where a single laser pulse can switch spins from one direction to another, without assistance of a magnetic field, on a time scale much shorter than existing magnetic technology. However, despite intensive efforts over a decade, its underlying working principle remains elusive. Here through manganese-based Heusler ferrimagnets, we show that a group of flat bands around the Fermi level act as gateway states to form efficient channels for spin switching, where their noncentrosymmetry allows us to correlate the spin dynamics to the second-order optical response. To quantify their efficacy, we introduce the third-rank Pancharatnam-Berry tensor (PB tensor), ${\mathit{\eta }}^{\left(3\right)}=\langle i\left|\mathbf{p}\right|m\rangle \langle m\left|\mathbf{p}\right|f\rangle \langle f\left|\mathbf{p}\right|i\rangle ,$ where $|i\rangle$, $|m\rangle$ and $|f\rangle$ are initial, intermediate and final band states, respectively, and $\mathbf{p}$ is the momentum operator. A picture emerges: Those which show AOS, such as the recently discovered ${\mathrm{Mn}}_2\mathrm{RuGa}$, always have a large PB tensor element but have a small sublattice spin moment ratio, consistent with the prior experimental small remanence criterion. This does not only reveal that the delicate balance between the large PB tensor element and the small sublattice spin ratio plays a decisive role in AOS, but also, conceptually, connects the $n\mathrm{th}$-order nonlinear optics to $(n+1)\mathrm{th}$-rank PB tensors in general.

The one-dimensional Su-Schrieffer-Heeger (SSH) model is central to band topology in condensed matter physics, which allows us to understand and design distinct topological states. In this work we find another mechanism to analogize the SSH model in a spinful system, realizing an obstructed atomic insulator by introducing intrinsic spin-orbit coupling and in-plane Zeeman field. In our model the midgap states originate from a quantized hidden polarization with invariant index ${\mathbb{Z}}_2$ (0; 01) due to the local inversion symmetry breaking. When the global inversion symmetry is broken, a charge pumping is designed by tuning the polarization. Moreover, by introducing the $p+ip$ superconductor pairing potential, a topological phase dubbed obstructed superconductor (OSC) is identified. This new state is characterized by invariant index ${\mathbb{Z}}_2$ (0; 01) and nonchiral midgap states. More interestingly, these nonchiral edge states result in a chiral-like nonlocal conductance, which is different from the traditional chiral topological superconductor. Our findings not only find another strategy to achieve a spinful SSH model but also predict the existence of OSC, providing a promising avenue for further exploration of its transport properties.

Motivated by the observation of partial magnetic order in kagome-based magnets, we study the classical kagome Ising antiferromagnet, known as kagome spin ice, including further-neighbor interactions at zero and finite temperature. While the nearest-neighbor model displays an extensive ground-state degeneracy, various symmetry-breaking states can appear upon including additional couplings. Among these, peculiar partially ordered states have been proposed. We present results from large-scale Monte Carlo simulations, establishing that such partial order is stabilized by third-neighbor couplings along the hexagon diagonals. We show that these states arise due to the emergence of one-dimensional chains in an entirely frustrated environment, and that they are stable with respect to further couplings. We discuss their finite-temperature properties in detail, highlight the magnetic states' peculiarities depending on the diagonal couplings' sign, and suggest observing these states using thermodynamic probes.

The low-energy excitation spectrum of a metal-free phthalocyanine molecule on Ag(111) is probed in scanning tunneling spectroscopy experiments. The use of functionalized $p$-orbital and $s$-orbital tips leads to markedly different results. While CO-terminated $p$-wave tips probe the zero-energy Abrikosov-Suhl resonance induced by the molecular Kondo effect, Ag-coated $s$-wave tips—in strong contrast—feign the absence of the Kondo effect due to a missing Abrikosov-Suhl resonance. Reducing the vertical distance between the $s$-orbital tip and the molecule progressively unveils the resonance, compatible with findings for the $p$-orbital tip in the far tunneling range. A mechanism based on orbital overlap is suggested as the tentative origin of the observations. The CO-functionalized tip is then used to explore the altered Kondo effect of the tautomerized phthalocyanine.

In this work, we study the statistics of a generic noninteracting many-body fermionic system whose single-particle counterpart has a single-particle mobility edge (SPME). We first prove that the spectrum and the extensive conserved quantities follow the multivariate normal distribution with a vanishing standard deviation $\sim O(1/\sqrt{L})$ in the thermodynamic limit, regardless of SPME. Consequently, the theorem rules out an infinite-temperature or high-temperature many-body mobility edge (MBME) for generic noninteracting fermionic systems in any dimension. Further, we also prove that the spectrum of a one-dimensional fermionic many-body system with short-range interactions is qualitatively similar to that of a noninteracting many-body system up to the third-order moment. These results partially explain why neither short-range [Phys. Rev. B 107, 035129 (2023)] nor long-range interacting systems exhibit an infinite-temperature MBME in a one-dimensional system.

Liquid-liquid phase separation (LLPS) is a prevalent phenomenon in silicate liquids. The ionic potential of the cations is widely recognized as a pivotal factor controlling the immiscibility extent of silicates; nonetheless, the intricate relationship between the two has yet to be fully understood. Here, using ab initio molecular dynamics simulations, we study the static and dynamic structural evolutions in a prototypical LLPS system ($\mathrm{Ti}{\mathrm{O}}_2\text{−}\mathrm{Si}{\mathrm{O}}_2$), aiming to decode the structural origin of the nonmonotonic dependence of ionic potential on immiscibility extent. The simulations reproduce the initial stage of phase separation as represented by formation of microscale aggregative Ti-Ti clusters upon cooling. Such microphase separation primarily arises from the Coulombic repulsion between $\mathrm{T}{\mathrm{i}}^{4+}$ cations and adjacent $\mathrm{S}{\mathrm{i}}^{4+}$ nodes, rather than the previously believed repulsion between poorly shielded $\mathrm{T}{\mathrm{i}}^{4+}$ cations. Analysis of dynamics reveals that the transport of $\mathrm{T}{\mathrm{i}}^{4+}$ cations across the Si-O-Si network is more sluggish than that of alkali (alkaline)-earth cations. Slow dynamics of $\mathrm{T}{\mathrm{i}}^{4+}$ cations are decoupled from their local coordination structure, but instead, it highly depends on the topological rigidity of these nearest-neighbor Ti–O bonds. As such, the high ionic potential of $\mathrm{T}{\mathrm{i}}^{4+}$ cations drives them away from nearby-network $\mathrm{S}{\mathrm{i}}^{4+}$ nodes, promoting immiscibility. On the other hand, this same potential causes strong topological rigidity, and hence, suppresses immiscibility by hindering the $\mathrm{T}{\mathrm{i}}^{4+}$ migration. This dual effect of the ionic potential questions the classical structural model in LLPS and provides insights into the association between immiscibility extent and ionic potential.

The dynamics described by the non-Hermitian Hamiltonian typically capture the short-term behavior of open quantum systems before quantum jumps occur. In contrast, the long-term dynamics, characterized by the Lindblad master equation, drive the system towards a nonequilibrium steady state (NESS), which is an eigenstate with zero energy of the Liouvillian superoperator, denoted as $\mathcal{L}$. Conventionally, these two types of evolutions exhibit distinct dynamical behaviors. However, in this study we challenge this common belief and demonstrate that the effective non-Hermitian Hamiltonian can accurately represent the long-term dynamics of a critical two-level open quantum system. The criticality of the system arises from the exceptional point of the effective non-Hermitian Hamiltonian. Additionally, the NESS is identical to the coalescent state of the effective non-Hermitian Hamiltonian. We apply this finding to a series of critical open quantum systems and show that a local dissipation channel can induce collective alignment of all spins in the same direction. This direction can be well controlled by modulating the quantum jump operator. The corresponding NESS is a product state and maintains long-time coherence, facilitating quantum control in open many-body systems. This discovery paves the way for a better understanding of the long-term dynamics of critical open quantum systems.

The dispersive propagation and absorption in the domain of a Drude-Lorentz dielectric modified by a magnetic current are classically investigated, taking as the starting point the Drude electric permittivity, in connection with the chiral magnetic effect. Using standard electromagnetic methods, the dispersion relations and refractive indices are evaluated and discussed, as well as the group and the energy velocities. We consider three configurations for the magnetic conductivity tensor: isotropic, antisymmetric, and symmetric. In all these cases, we carry out the group velocity and the energy velocity, for investigating the properties of signal propagation. We observe that the isotropic magnetic conductivity enhances the signal propagation at low and intermediary frequencies, while the symmetric and antisymmetric conductivities severely constrain the wave propagation in these frequency windows.

We predict a coherent nonlocal coupling of ferromagnetic and antiferromagnetic magnetization dynamics via transverse phonon momentum current in a nonmagnetic insulator spacer. This coupling requires perpendicular alignment of magnetic moments to the phonon propagation direction. Our results bridge the divide between ferromagnetic and antiferromagnetic spintronics, offering pathways for integrating diverse magnetic elements into spintronic devices.

The enantiomorphous (chiral) crystal class of Sohncke-type Pb(TiO)$\mathrm{C}{\mathrm{u}}_4{\left(\mathrm{P}{\mathrm{O}}_4\right)}_4$ permits the rotation of the plane of polarization of light (optical activity). Copper ions participate in noncollinear antiferromagnetic order below a temperature ≈ 7 K, with magnetoelectric and piezomagnetic effects permitted. Crystal and magnetic symmetries of Pb(TiO)$\mathrm{C}{\mathrm{u}}_4{\left(\mathrm{P}{\mathrm{O}}_4\right)}_4$ are fully incorporated in calculated resonant x-ray Bragg diffraction patterns that are successfully compared with existing limited experimental data [Misawa et al., Phys. Rev. B 103, 174409 (2021)]. Specifically, there is additional intensity of a Bragg spot (a chiral signature) from circular polarization (helicity) in the primary beam of x rays. The chiral signature is shown to arise from Cu axial magnetic dipoles, with the prospect of future experiments revealing interference between magnetic dipoles and (Templeton-Templeton) chargelike quadrupoles. An expression for the additional intensity used by Misawa et al. does not respect magnetic symmetry, and our symmetry-informed answer overturns their principal conclusions about chirality and magnetic order. Dirac quadrupoles and octupoles are potentially strong sources of diffraction when the reflection vector is parallel to the unique direction in the tetragonal lattice. Notably, a Dirac quadrupole is a parity- and time-odd atomic multipole unlike a multisite spin entity previously mentioned in the context of Pb(TiO)$\mathrm{C}{\mathrm{u}}_4{\left(\mathrm{P}{\mathrm{O}}_4\right)}_4$ [Kimura et al., Phys. Rev. B 97, 134418 (2018)].