Marrying the predictive power of ab initio calculations with many-body effects remains a challenging task in two-dimensional (2D) materials, where efficient carrier-carrier interaction challenges established approximation schemes. In particular, understanding exciton-phonon interaction from first principles is a field of growing interest. Here, we present a many-body theory for coupled free-carrier, exciton, phonon and photon dynamics based on carrier-carrier and carrier-phonon interaction matrix elements obtained via projection on Wannier orbitals. The framework is applied to study the impact of carrier-phonon correlations on optical spectra and coupled nonequilibrium carrier-phonon kinetics in monolayer ${\mathrm{MoSe}}_2$. We find that non-Markovian effects and dynamical buildup of quasiparticles are only properly described if correlations at least on the two-phonon level are included. Our studies open a perspective to advance the material-realistic many-body description of nonequilibrium physics in 2D nanostructures.

The exploration of electrides holds great promise for advancing both fundamental physics and chemistry, owing to their unique characteristics arising from loosely bound interstitial anionic electrons. Here we report a class of cross-chain electrides, distinguished by two distinct anionic electron subchannels forming alternating chains in real space. Through structural symmetry analysis and first-principles calculations, we identify two-dimensional $M_2\mathrm{N}$ $(M=\mathrm{Ti},\mathrm{Zr},\mathrm{Hf})$ materials as prototypical systems exhibiting these unique features. The anionic electron channels on the upper and lower surfaces of these materials display a vertically alternating pattern, with their projected bands revealing momentum-dependent splitting behavior in the reciprocal space, protected by a crystal symmetry operation $\mathcal{O}$. Notably, the cross-chain electride characteristic in the $M_2\mathrm{N}$ monolayers is independent of the layer number and remains robust on the upper and lower surfaces of layered structures, presenting pronounced and robust surface interstitial electronic states. Additionally, we have explored the superconductivity of these systems, and found that both ${\mathrm{Ti}}_2\mathrm{N}$ and ${\mathrm{Zr}}_2\mathrm{N}$ are intrinsic superconductors with superconducting transition temperatures below 1.0 K. Further results show that appropriate hole doping can significantly enhance their superconducting transition temperatures and can induce the ${\mathrm{Hf}}_2\mathrm{N}$ monolayer to exhibit superconductivity. Our findings provide valuable insights into the design and tuning of electrides with enhanced superconducting properties, offering another pathway for deeply understanding the interplay between electride behavior and superconductivity in materials.

The non-Hermitian skin effect (NHSE) is a phenomenon that emerges in non-Hermitian systems. Non-Hermitian systems can be flexibly realized by introducing non-Hermitian terms in circuits. In topolectrical circuits, nonreciprocal hopping is realized by scaling linear elements, which introduces non-Hermitian terms. In this work, we report the experimental realization of the NHSE in such nonreciprocal circuits. By introducing a quasiperiodic potential, the experimental realization of the interconversion between the NHSE and Anderson localization (AL) is observed in a nonreciprocal quasiperiodic circuit based on the nonreciprocal Aubry-André (AA) model, which undergoes a skin-effect–localization phase transition depending on the strength of the quasiperiodic potential. In addition, we design and fabricate a dedicated circuit board with preset component slots, enabling continuous tuning of circuit parameters without the need for multiple circuit boards. This flexible platform allows us to experimentally identify the phase-transition point between the NHSE and AL. Our results fill an important gap in previous studies, where this transition point had not been precisely characterized. Our circuit system also provides a simpler platform to explore localization phenomena in nonreciprocal systems.

We investigate some thermodynamic and magnetic properties of the Hubbard model on two three-dimensional extensions of the Lieb lattice: the perovskite Lieb lattice (PLL) and the layered Lieb lattice (LLL). Using determinant quantum Monte Carlo (DQMC) simulations alongside Hartree-Fock and cluster mean-field theory approaches, we analyze how flat-band degeneracy, connectivity, and lattice anisotropy influence the emergence of magnetic order. Our results show that both geometries support finite-temperature magnetic transitions, namely, ferromagnetic (FM) on the PLL and antiferromagnetic (AFM) on the LLL. Further, we have established that the critical temperature $T_c$, as a function of the uniform onsite coupling $U$, displays a maximum, which is larger in the AFM case than in the FM one, despite the absence of flat bands in the LLL. We also provide numerical evidence to show that flat bands in the PLL rapidly generate magnetic moments, but a small interorbital coordination suppresses the increase of $T_c$ at large interaction strength $U/t$. By contrast, the LLL benefits from higher connectivity, favoring magnetic order even in the absence of flat bands. The possibilities of anisotropic interlayer hoppings and inhomogeneous onsite interactions were separately explored. We have found that magnetism in the PLL is hardly affected by hopping anisotropy since the main driving mechanism is the preserved flat band; for the LLL, by contrast, spectral weight is removed from $d$ sites, which increases $T_c$ more significantly. At mean-field level, we have obtained that setting $U=0$ on $p$ sites and $U=U_d\ne 0$ on $d$ sites leads to a quantum critical point at some $U_d$; this behavior was not confirmed by our DQMC simulations.

We use a slave-boson approach to study the band renormalization and pair susceptibility in the normal state of iron-based superconductors in presence of strong Coulomb repulsion and Hund's interaction. Our results show orbital selectivity toward localization of $xy$ orbitals and its interplay with superconductivity. We also compare the recently proposed triplet resonating valence bond (tRVB) theory of superconductivity in iron-based superconductors with the more conventional $s_{\pm }$ pairing. We show that both favor a superconductivity when the $xy$ orbital is delocalized, but the tRVB superconductivity supports a second weaker dome when $xy$ orbital is localized.

It is well established that at zero magnetic field $h=0$, the spin diffusion constant of the spin-$\frac{1}{2}$ XXZ chain is for anisotropy $\mathrm{\Delta }>1$ finite for both low and high temperatures, implying that the type of spin transport is normal diffusive. Although it is expected that this holds for all finite temperatures $T>0$, the calculation of the spin diffusion constant for all $T$ is typically intractable. Here we consider a class of energy eigenstates that exist both for anisotropies $\mathrm{\Delta }=1$ and $\mathrm{\Delta }>1$. We show that at the isotropic point their contributions are behind the diffusion constant being infinite, spin transport being anomalous superdiffusive for $T>0$. That for $\mathrm{\Delta }>1$ such states do not contribute to the diffusion constant is shown to imply it is finite, spin transport being normal diffusive for $T>0$. By combining the connection through a Jordan-Wigner transformation of the spin-$\frac{1}{2}$ XXZ chain to the one-dimensional (1D) lattice spinless fermion model at zero chemical potential $\mu =0$, for $V/J\ge 1$ with its Bethe-ansatz solution, where $V$ is the nearest-neighbor Coulomb repulsion and $J=2t$ is twice the hopping integral $t$, in this paper we also address the issue of the $T>0$ charge transport of that model at $\mu =0$. It is found to be anomalous superdiffusive for $V/J=1$ and normal diffusive for $V/J>1$. Our results thus open the door to a key advance in the understanding for all finite temperatures $T>0$ of the spin transport in the spin-$\frac{1}{2}$ XXZ chain at $h=0$ for anisotropy $\mathrm{\Delta }\ge 1$ and of the charge transport in the 1D lattice spinless fermion model at $\mu =0$ for $V/J\ge 1$.

We study charge and heat transport from first principles in the topological Weyl semimetal TaAs. Electron-phonon coupling matrix elements are calculated using density-functional perturbation theory and used to derive the thermoelectric transport coefficients, including the electrical conductivity, Seebeck coefficient, electronic thermal conductivity, and the Peltier coefficient. We compare the self-energy and momentum-relaxation-time approximations to the iterative solution of the Boltzmann transport equation, finding that they give similar results for TaAs provided the chemical potential is treated accurately. We derive a second equation in the iterative method to solve for transport under thermal gradients. Interestingly, the Onsager reciprocity between $S$ and $\mathrm{\Pi }$ is no longer imposed, allowing us to treat systems that break time-reversal symmetry, in particular, magnetic materials. We compare our results with available experimental data for TaAs: the agreement is excellent for ${\sigma }_{xx}$, while ${\sigma }_{zz}$ is overestimated, probably caused by differences in experimental carrier concentrations. The Seebeck coefficient is of the same order of magnitude in theory and in experiments, and we find that its low-$T$ behavior also strongly depends on the doping level.

Geometric frustration in quantum spin systems can lead to exotic ground states. In this study, we investigate the $\mathrm{SU}\left(3\right)$ spin model on the checkerboard lattice to explore the effects of frustration arising from its point-connected $(N+1)$-site local structure. We employ the density matrix renormalization group (DMRG) and exact diagonalization (ED) techniques to determine the ground state properties. Our results reveal the absence of both three-sublattice antiferromagnetic order and valence cluster solid order. Instead, we identify ground states with bond stripe patterns sensitive to boundary conditions and system size, comprising staggered singlet arrays and uniform flat stripes. Notably, these stripes are relatively decoupled, and similar patterns can be reconstructed in quasi-one-dimensional ladders. These findings suggest that geometric frustration drives the system toward a mixed phase, combining characteristics of spin-liquid and valence cluster solid states, providing new insights into the behavior of frustrated quantum spin systems.

Here we investigate the topological properties of moiré bands in twisted bilayer ${\mathrm{WSe}}_2$ $\left(\mathrm{t}{\mathrm{WSe}}_2\right)$ by means of quantum oscillation experiments. Magnetoresistance measurements manifest clear Shubnikov–de Haas (SdH) oscillations in $\mathrm{t}{\mathrm{WSe}}_2$ under moderate displacement fields. Landau-level fan diagram unveils a Berry phase of $\pi$ at half filling. Temperature-dependent measurements indicate a hole effective mass $m^{*}\sim 0.17m_e$, which is much smaller than that of monolayer and bilayer ${\mathrm{WSe}}_2$. Increasing the hole density away from half-filling state leads to an increased $m^{*}$ accompanied with a trivial Berry phase. These observations can be well understood by considering a Dirac-like band crossing at low-energy scales induced by a nonzero displacement field in $\mathrm{t}{\mathrm{WSe}}_2$. Our work reveals the modulation of band topology by a perpendicular displacement field, offering avenues to engineer moiré bands for gate-tunable twist transistors.

We show that chiral edge states in graphene under quantum Hall effect conditions can be selectively probed and excited by terahertz or infrared radiation with single-quasiparticle sensitivity without affecting bulk states. Moreover, valley-selective excitation of edge states is possible with high fidelity. The underlying physical mechanism is the inevitable violation of adiabaticity and inversion symmetry breaking for electron states near the edge. This leads to the formation of Landau-level-specific and valley-specific absorbance spectral peaks that are spectrally well separated from each other and from absorption by the bulk states, and have different polarization selection rules. Furthermore, inversion symmetry breaking enables coherent driving of chiral edge photocurrents due to second-order nonlinear optical rectification which becomes allowed in the electric-dipole approximation.

Kagome materials have attracted enormous research interest recently owing to their diverse topological phases and manifestation of electronic correlation. Here, we present the electronic structure of a distorted ferromagnetic kagome metal, ${\mathrm{NdTi}}_3{\mathrm{Bi}}_4$, exhibiting a transition temperature of 9 K. Our investigation employs a combination of angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory (DFT) calculations. We discover the presence of two “flat” bands which are found to originate from the kagome structure formed by Ti atoms with a major contribution from Ti $d_{xy}$ and Ti $d_{x^2-y^2}$ orbitals. We also observed multiple Van Hove singularities (VHSs) in its electronic structure, with one VHS lying near the Fermi level. The ARPES data reveal the existence of Dirac cone at the $\overline{K}$ point, a finding which is corroborated by our DFT calculations. These findings present a detailed electronic structure capable of hosting correlation-driven phenomenon in this novel ferromagnetic kagome metal.

Static and dynamical magnetic and electronic properties of the kagome metal ${\mathrm{Sc}}_3{\mathrm{Mn}}_3{\mathrm{Al}}_7{\mathrm{Si}}_5$ have been investigated by ${}^{27}\mathrm{Al}$ nuclear magnetic resonance (NMR) measurements. Two distinct ${}^{27}\mathrm{Al}$-NMR signals with two different values of quadrupolar frequencies of ${\nu }_{\mathrm{Q}}$ = 1.55(2) and 1.07(2) MHz are observed, which are assigned to Al(1) and Al(2), respectively. From the detailed NMR spectrum measurements under three different magnetic field directions and the density functional theory calculations, the principal axes of the electric field gradient for each Al site have been determined. The temperature dependence of Knight shift ($K$) shows a similar temperature dependence of the DC magnetic susceptibility $\chi$ except for the low-temperature region below $\sim 50$ K where $K$ is almost constant while $\chi$ keeps increasing, which suggests that the increase in $\chi$ at low temperatures is not intrinsic. ${}^{27}\mathrm{Al}$ spin-lattice relaxation rate divided by temperature ($1/T_{1}T$) is found to be constant, confirming the metallic state of ${\mathrm{Sc}}_3{\mathrm{Mn}}_3{\mathrm{Al}}_7{\mathrm{Si}}_5$ from a microscopic point of view. Based on a Korringa ratio analysis using the $T_1$ and $K$ data, ferromagnetic fluctuations are found to dominate in ${\mathrm{Sc}}_3{\mathrm{Mn}}_3{\mathrm{Al}}_7{\mathrm{Si}}_5$. These fluctuations are suggested to be very slow with frequencies on the order of kilohertz or lower.

Non-Hermiticity naturally breaks down the adiabaticity and thus leads to non-Abelian behaviors in multiband systems. Here, we study how non-Abelian properties emerge in non-Hermitian systems by considering a multiband non-Hermitian model: the nonreciprocal Su-Schrieffer-Heeger (SSH) ladder that is formed by coupling two nonreciprocal SSH chains. Under periodic boundary conditions, we analytically obtain the exact phase diagrams of the geometry of band structure classified by its complex value and gap type, and of the non-Abelian topology based on a newly defined gauge-invariant winding number under the chiral symmetry. Under open boundary conditions, we find that the bulk-boundary correspondence survives in the thermodynamic limit but breaks down for finite sizes along with the emergence of critical non-Hermitian skin effects when the interleg coupling is weak, where the decaying length $\xi$ of the bulk skin modes varies with the system size $L$, satisfying the scale-free power law $\xi \propto L$. Finally, we demonstrate the non-Abelian dynamics of a Bloch state subject to an external constant force in the pseudo-Hermitian symmetric regime in comparison with the non-Hermitian Wilson lines. Our work may stimulate further interests in nontrivial non-Abelian behaviors in non-Hermitian and open quantum systems.

We present a first-principles investigation of phonon thermal transport in monolayer graphene under biaxial tensile strain at room temperature. Surprisingly, when four-phonon (4ph) scattering is included, we observe a remarkable strain-induced enhancement of lattice thermal conductivity ($\kappa$)—nearly doubling at 5% strain—in stark contrast to the strain-insensitive $\kappa$ predicted by three-phonon (3ph) theory. This unexpected enhancement arises from the strain-induced suppression of both 3ph and 4ph scattering, primarily due to the linearization of the flexural acoustic (ZA) phonon branch, which severely restricts the phase space for ZA-involved scattering processes. Our calculations further show that the role of 4ph scattering in reducing $\kappa$ diminishes substantially with strain. Notably, the ZA phonons are found to persist as the primary heat carriers even under large strain, though their relative contribution to $\kappa$ decreases considerably. Additionally, we unveil that tensile strain markedly weakens nonresistive normal processes, thereby suppressing nondiffusive phonon transport. These findings provide fundamental insights into the strain-engineered phonon-phonon interactions and thermal transport in graphene.

In crystals with broken time-reversal symmetry, zone-center phonons can acquire a finite angular momentum via velocity-dependent forces on the nuclei. Despite having the same order of magnitude as the electron spin angular momentum, the phonon angular momentum can be hard to detect because the frequency splitting is small. Here, by developing a theory of lattice magneto-optical effects in reflection and transmission, we show that infrared magnetic circular dichroism is a sensitive probe of zone-center phonon chirality. We evaluate the infrared magneto-optical Faraday, Kerr, and circular-dichroism spectra of ${\mathrm{CrI}}_3$ from time-dependent density-functional theory in the adiabatic local-density approximation. We find sizable circular dichroism from the infrared-active ${\mathrm{E}}_u$ mode at $\approx 214{\mathrm{cm}}^{-1}$, even though the calculated splitting is only 0.22 ${\mathrm{cm}}^{-1}$.

Topological magnon insulators exhibit robust edge modes with chiral properties similar to quantum Hall edge states. However, due to their strong localization at the edges, interactions between these chiral edge magnons can be significant, as we show in a model of coupled magnon-conserving spin chains in an electric field gradient. The chiral edge modes remain edge-localized and do not scatter into the bulk, and we characterize their scattering phase: for strongly localized edge modes, we observe significant deviation from the bare scattering phase. This renormalization of edge scattering can be attributed to bound bulk modes resonating with the chiral edge magnons in the spirit of Feshbach resonances in atomic physics. We argue that the scattering dynamics can be probed experimentally with a real-time measurement protocol using inelastic scanning tunneling spectroscopy. Our results show that interaction among magnons can be encoded in an effective edge model of reduced dimensionality, where the interactions with the bulk renormalize the effective couplings. Our work introduces a systematic way to determine the many-body effective theory for edge states in topological magnon insulators.

In Weyl semimetals, the conduction and valence bands intersect at distinct points on the Brillouin zone (Weyl points), which act as monopoles of Berry curvature in momentum space. This nontrivial band topology, identified from electronic structure calculations, gives rise to various exotic magnetotransport properties. Hybrid functional calculations that incorporate a portion of exact exchange, magnetotransport measurements, and temperature-dependent resistivity confirm nontrivial band topology and half-metallicity in ${\mathrm{CoS}}_2$ of magnetic ordering temperature $T_{\mathrm{C}}\approx 128\mathrm{K}$. However, electronic structure calculations also show that application of small strain transforms this half metallic character to the metallic. Interestingly, the magnetoresistance (MR) of the ${\mathrm{CoS}}_2$ films at low fields and $T\le 60\text{K}$ is suggestive of weak localization. The MR changes signs from negative to positive value as the $T$ goes from $<T_{\mathrm{C}}$ to $>T_{\mathrm{C}}$. Experimental observation of anomalous Hall resistivity and ab initio computed band structure, Berry curvature, and Hall conductivity (${\sigma }_{xy}$) demonstrate that the ${\sigma }_{xy}$ in ${\mathrm{CoS}}_2$ is primarily driven by the intrinsic Karplus-Luttinger contribution, often linked to Berry phase physics.

We report the experimental realization of a spin-1/2 extended diamond chain in a verdazyl-Cu complex, where competing interactions and lattice distortions give rise to exotic quantum phases. The magnetic properties exhibit a zero-field energy gap and 1/2 magnetization plateau, which is explained by a dimer-monomer model. Considering the effective interactions between the monomers, three types of dimer-dimer phases are expected to appear as the ground state, depending on the magnitude of the lattice distortions. By mapping to the nonlinear sigma model, three phases are distinguished topologically, and a symmetry-protected topological phase equivalent to the Haldane phase is identified. Furthermore, a nontrivial magnetization is observed above the 1/2 plateau region, suggesting a gapped dimer phase accompanied by a spontaneous breaking of translational symmetry. The discovery of this rare quantum state has broad implications for strongly correlated systems, topological matter, and quantum information science, where symmetry and topology play crucial roles.

The system with the interplay between superconductivity, nontrivial band topology and strongly correlated electrons is of great interest due to the emergent novel quantum phases, such as topological superconductivity and strongly correlated topological phases. Such system is rarely found in realistic materials, recent examples are moiré graphene, ${\mathrm{FeTe}}_{0.55}{\mathrm{Se}}_{0.45}$ and kagome superconductors. In this work, we report that ${\mathrm{SrSn}}_3$ is a prototype of superconducting alloy with an odd $Z_2$ invariant, which is supported by the existence of topologically nontrivial surface states. Moreover, we find that strong spin-orbit coupling plays a dominant role in the formation of the flat-bands at Fermi level in ${\mathrm{SrSn}}_3$, which result in both considerable electron correlations (identified by a large carrier effective mass $m_C^{*}/m_0\approx 3.06$ and a large Kadowaki-Wood ratio $A/{\gamma }^2\sim 7.94\times {10}^{-4}\mu \mathrm{\Omega }\mathrm{cm}{\mathrm{mJ}}^2{\mathrm{mol}}^2{\mathrm{K}}^2$) and strong-coupling superconductivity ($2\mathrm{\Delta }/k_B{T}_c\sim 4.90$ and $T_c/T_F\sim 2.34\times {10}^{-3}$), that coexist with the topological surface states, characterized by the nontrivial Berry phase of de Hass-van Alphen oscillations (${\varphi }_B\sim \pi$). Remarkably, we observed a surface superconducting state, manifested as an extremely large surface-to-bulk critical field ratio ($H_{c3}/H_{c2}\sim 18.3$) and a linear temperature-dependent critical field. Our findings reveal that ${\mathrm{SrSn}}_3$ is a promising candidate for studying the interplay between nontrivial band topology and correlated electron phenomena induced by strong spin-orbit coupling.