Antiferromagnetic graphene nanoribbons (AFM-GNRs) hold significant potential in spintronics and quantum computing. However, achieving high spin-density AFM-GNRs remains a challenge. Herein, we report two unconventional routes for producing AFM-GNRs from closed-shell rhombene units (RUs), including (i) applying compression on the bonds between RUs to enhance the interunit Coulomb repulsion and (ii) merging the edges of RUs to release the confined spin states. Density functional theory and tight-binding calculations demonstrate the spin distribution and spin generation mechanisms for both routes.

At finite temperature, conserved charges undergo thermal fluctuations in a quantum many-body system in the grand canonical ensemble. The full structure of the fluctuations of the total $\mathrm{U}\left(1\right)$ charge $Q$ can be succinctly captured by the generating function $G\left(\theta \right)=\langle {\mathrm{e}}^{\mathrm{i}\theta Q}\rangle$. For a 1D translation-invariant spin chain in the thermodynamic limit, the magnitude $\left|G\left(\theta \right)\right|$ scales with the system size $L$ as $ln\left|G\left(\theta \right)\right|=-\alpha \left(\theta \right)L+\gamma \left(\theta \right)$, where $\gamma \left(\theta \right)$ is the scale-invariant contribution and may encode universal information about the underlying system. In this work, we investigate the behavior and physical meaning of $\gamma \left(\theta \right)$ when the system is periodic. We find that $\gamma \left(\theta \right)$ only takes nonzero values at isolated points of $\theta$, which is $\theta =\pi$ for all our examples. In two exemplary lattice systems, we show that $\gamma \left(\pi \right)$ takes quantized values when the $\mathrm{U}\left(1\right)$ symmetry exhibits a specific type of 't Hooft anomaly with other symmetries. In other cases, we investigate how $\gamma \left(\theta \right)$ depends on microscopic conditions (such as the filling factor) in field theory and exactly solvable lattice models.

Gapped fracton phases constitute a new class of quantum states of matter, which connects to topological orders but does not fit easily into existing paradigms. They host unconventional features such as sub-extensive and robust ground-state degeneracies as well as sensitivity to lattice geometry. We investigate the anisotropic ${\mathbb{Z}}_N$ Laplacian model [Phys. Rev. B 107, 125121 (2023)], which can describe a family of fracton phases defined on arbitrary graphs. Focusing on representative geometries where the 3D lattices are extensions of 2D square, triangular, honeycomb, and the Kagome lattices into the third dimension, we study their ground-state degeneracies and mobility of excitations, and examine their entanglement renormalization group (ERG) flows. All models show bifurcating behaviors under ERG but have distinct ERG flows sensitive to both $N$ and lattice geometry. In particular, we show that the anisotropic ${\mathbb{Z}}_N$ Laplacian models defined on the extensions of triangular and honeycomb lattices are equivalent when $N$ is coprime to 3. We also point out that, in contrast to previous expectations, the model defined on the extension of Kagome lattice is robust against local perturbations if and only if $N$ is coprime to 6.

The interacting spin-1/2 trimer system hosts a range of exotic quasiparticles, which have been observed through inelastic neutron scattering (INS) and this system has attracted significant attention in recent studies. We theoretically investigate the resonant inelastic x-ray scattering (RIXS) spectra in a frustrated spin-1/2 trimer chain, as realized in ${\mathrm{Na}}_2{\mathrm{Cu}}_3{\mathrm{Ge}}_4{\mathrm{O}}_{12}$, with Cu $d^9$ 1/2 spins. We compute multispin correlations contributing to spin-conserving (SC) and non-spin-conserving (NSC) RIXS cross sections using ultrashort core-hole lifetime expansion within the Kramer-Heisenberg formalism. These excitations involve flipping spins of up to three spin-1/2 trimers and include the INS single spin-flip excitations in the lowest order of the NSC channel. We identify the fractionalization of two coupled frustrated trimers in terms of spinons, doublons, and quartons in the spectra evaluated using exact diagonalization, complementing prior studies single spin-spin flip excitation in inelastic neutron scattering. Specifically, we uncover two new high-energy modes at $\omega \approx 2.4J_1$ and $3.0J_1$ in the NSC and SC channels that are accessible at the Cu $K$-edge and $L$-edge RIXS spectra, which were missing in the INS study. This, therefore, provides pathways to uncover all the possible excitations in coupled trimers. Our work opens new opportunities for understanding the nature of fractionalization and RIXS spectra of frustrated, low-dimensional spin chains.

The ground-state quantum geometry is at the root of several static and adiabatic properties, while genuinely dynamic properties are routinely addressed via Kubo formulas, whose essential entries are the excited states. It is shown here that the ground-state metric-curvature tensor evolves in time by means of a causal unitary operator, which by construction elucidates the geometrical effect of the excited states in compact form. In the condensed-matter case the generalized tensor encompasses the whole conductivity tensor at arbitrary frequencies in both insulators and metals, with the exception of the Drude term in the metallic case; the latter is shown to be eminently nongeometrical.

We study theoretically the neutral and charged excitons in two-dimensional semiconductors with an isotropic dispersion of charge carriers. Such a situation is realized in CrSBr-based van der Waals heterostructures. We calculate the binding energies of excitons and trions and explore their dependence on the mass ratio, dielectric screening, and interlayer distance in bilayer structures. We also address the effects of exciton-light coupling, including the radiative decay and long-range electron-hole exchange interaction, and briefly analyze correlations between the excitons and the Fermi sea of resident electrons. The estimates for CrSBr bilayers are in reasonable agreement with recent experiments.

As a unique transport regime at the nanoscale, superdiffusive thermal transport has demonstrated its significance in nanophysics and potential applications in nanoscale thermal management. However, notable controversies between theoretical and experimental works persist regarding its origin in one-dimensional (1D) systems. Here we investigate the superdiffusive thermal transport behavior in 1D van der Waals $\mathrm{NbS}{\mathrm{e}}_3$ nanowires using molecular dynamics and lattice dynamics simulations combined with a machine learning potential. As a signature of superdiffusive thermal transport, a power-law length-dependent thermal conductivity $\kappa \propto L^{\beta }$ is uncovered at small diameters. The effects of phonon confinement and elastic stiffening on superdiffusive thermal transport are elucidated. We demonstrate that the stiffening of the elastic constant only appears along the nanowires, affecting a subset of phonon modes with minimal impact on thermal transport. The low-frequency phonons, which significantly contribute to thermal transport, are predominantly affected by phonon confinement. Our theoretical analysis reveals that phonon confinement enhances the momentum-conserving scattering events, inducing phonon hydrodynamics and enabling the observed superdiffusive thermal transport. Our results provide valuable insights into nanoscale thermal transport, which are crucial for phonon transport and thermal management at the nanoscale.

Based on a hybrid light-matter unitary transformation for cavity quantum electrodynamics, we investigate the spectral shift of an atom induced by quantum fluctuations in a chiral vacuum cavity. Remarkably, we find an intriguing angular momentum dependent shift in the spectra of bound states. Our approach shows promise in going beyond traditional perturbative methods and demonstrates effectiveness even in the strong-coupling limit, as evidenced by our numerical benchmarks in the case of a two-dimensional quantum harmonic oscillator. In addition, we establish a cavity-interaction picture for calculating the chiral vacuum Rabi oscillation in the strong-coupling limit for a generic central potential. The anomalous spectral shift revealed in this study possesses both fundamental and practical significance and could be readily observed in experiments.

We study theoretically the Meissner effect in non-Hermitian systems of BCS type, i.e., with an electron-electron interaction leading to the mean-field description in a Cooper channel, via superfluid stiffness. We show that depending on the values of the mean fields, chemical potential, and temperature, we obtain a paramagnetic or diamagnetic Meissner effect. Notably, the positive real part of the product of the mean fields guarantees a diamagnetic Meissner effect in an $s$-wave three-dimensional (3D) non-Hermitian superconductor. Once the mean fields are close to being anti-Hermitian, 2D $s$-, $p_x$-, and $d$-wave superconductors exhibit interesting behavior, including negative superfluid stiffness giving the paramagnetic Meissner effect for certain parameters. Negative superfluid stiffness indicates instability of this collective state.

The eigenstates of one-dimensional Hermitian and non-Hermitian (NH) tight-binding systems (in the presence/absence of quasiperiodic potential) and an external electric field undergo complete localization with equally spaced eigenenergies, known as the Wannier-Stark (WS) localization. In this paper, we demonstrate that when the electric field is slowly modulated with time, nontrivial phases with multiple mobility edges emerge in place of the WS localized phase, which persists up to a certain strength of the non-Hermiticity. On the other hand, for a large driving frequency, we retrieve the sharp delocalized to the usual (no WS) localized phase transition, similar to the static NH Aubry-André-Harper type without any electric field. This vanishing of WS localization can be attributed solely to the time-periodic drive and occurs irrespective of the non-Hermiticity. Interestingly, under the open boundary condition, we find that contrary to the undriven systems where an external electric field destroys the skin effect (SE) completely, the SE appears in certain regimes of the parameter space when the electric field is temporally driven. This appearance of SE is closely related to the absence of extended unitarity. In addition, in the presence of the drive, the skin states are found to be multifractal, contrary to its generic nature in such NH systems. An in-depth understanding about the behavior of the states in the driven system is established from the long-time dynamics of an initial excitation.

In this article, we study quantum critical phenomena in surfaces of symmetry-protected topological matter, i.e., surface topological quantum criticality. A generic phase boundary of gapless surfaces in a symmetry-protected state shall be a codimension one manifold in an interaction parameter space of dimension $D_p$ (where $p$ refers to the parameter space) where the value of $D_p$ further depends on bulk topologies. In the context of fermionic topological insulators that we focus on, $D_p$ depends on the number of half-Dirac cones $\mathcal{N}$. We construct such manifolds explicitly for a few interaction parameter spaces with various $D_p$ values. Most importantly, we further illustrate that in cases with $D_p=3$ and 6, there are submanifolds of fixed points that dictate the universalities of surface topological quantum criticality. These infrared stable manifolds are associated with emergent symmetries in the renormalization-group-equation flow naturally appearing in the loop expansion. Unlike in the usual order-disorder quantum critical phenomena, typically governed by an isolated Wilson-Fisher fixed point, we find in the one-loop approximation surface topological quantum criticalities are naturally captured by conformal manifolds where the number of marginal operators uniquely determines their codimensions. Isolated strong-coupling fixed points also appear, usually as the endpoints in the phase boundary of surface topological quantum phases. However, their extreme infrared instabilities along multiple directions suggest that they shall be related to multicritical surface topological quantum critical phenomena rather than generic surface topological quantum criticality. We also discuss and classify higher-loop symmetry-breaking effects, which can either distort the conformal manifolds or further break the conformal manifolds down to a few distinct fixed points.

Recent penetration depth measurement reported the observation of possible unconventional superconductivity in the miassite ${\mathrm{Rh}}_{17}{\mathrm{S}}_{15}$ single crystals, evidenced by the linear-in-temperature penetration depth at low temperatures, thereby suggesting the presence of the lines of node in its superconducting gap structure. Here we measure the thermal conductivity of ${\mathrm{Rh}}_{17}{\mathrm{S}}_{15}$ single crystals down to $\sim 110$ mK and up to a field of 8 T ($\simeq 0.4H_{c2}$). In marked contrast to the penetration depth measurement, we observe a negligible residual linear term ${\kappa }_0/T$ in zero field, in line with the nodeless gap structure. The rapid increase of ${\kappa }_0\left(H\right)/T$ at low field suggests multiple nodeless gaps with significantly different magnitudes. The multigap structure is also supported by the specific heat data, which suggests one of the energy gaps is much smaller than the other. This small superconducting gap may help to reconcile two seemingly conflicting views on the superconducting gap structure, from the penetration depth and the thermal conductivity measurements. Finally, the first-principles calculations show two electronic bands crossing the Fermi level, forming a complex shape of Fermi surfaces. We discuss the implications of our findings for any possible unconventional superconductivity in this strongly correlated $d$-electron system.

Central to the development of next-generation spintronic memories that are high speed, reliable, and offer high storage density, all-electrical manipulation of antiferromagnetic Néel order has emerged as a prominent area of research in recent years. We present an investigation of current-induced Néel order switching in W/IrMn heterostructures, examining the dependence of the magnetoresistance signal on temperature and current density. We found that distinct mechanisms can lead to alterations in the shape and direction of the signal, and by incorporating a supplemented model based on thermal activation, we quantitatively distinguished between magnetic and nonmagnetic contributions within the signal response and provided a detailed explanation referencing the distribution of antiferromagnetic grain volumes. Our findings reveal that within a moderate current range, the switching of the Néel vector dominated the detected Hall signal, while at high currents, pronounced thermal effects including electromigration became predominant. This comprehensive analysis paves the way for further research aimed at achieving full electrical control and harnessing the potential of antiferromagnets in more complex spintronic devices.

Motivated by the recent experiments on van der Waals heterostructures involving metallic and Mott insulating layers, we construct a moiré extension of the Kondo-Heisenberg model and study its phase diagram via Abrikosov fermion mean field theory in one and two dimensions. Our analysis indicates that the stacking dependent Kondo interaction can lead to a variety of phases. In particular, we show that magnetic order and heavy quasiparticles can nucleate at different regions in the moiré unit cell leading to a macroscopic real space phase inhomogeneity. We observe that these factors can lead to a metal to Kondo insulator percolation transition in two dimensions. Our results highlight the rich physics that can arise in moiré superlattices that are composed of inherently strongly correlated layers.

For several decades the low carrier density local moment magnet ${\mathrm{EuB}}_6$ has been considered a candidate material for ferromagnetic polarons. There is, however, no consistent explanation for the host of intriguing observations that have accrued over the years, including a prominently nonmonotonic resistivity near $T_c$, and spatial textures—with a characteristic spatial and energy scale—observed via scanning tunneling spectroscopy. We resolve these features using a Heisenberg-Kondo lattice model for ${\mathrm{EuB}}_6$, using exact-diagonalization-based Langevin dynamics. Over a temperature window $\sim 0.7T_c–1.5T_c$ we observe electronic and magnetic textures with the correct spatial and energy scale, and confirm an associated nonmonotonic resistivity. We predict a distinctly “non-Drude” optical conductivity in the polaronic phase, and propose a field-temperature phase diagram testable through spin-resolved tunneling spectroscopy. Beyond ${\mathrm{EuB}}_6$, we argue that the anomalous properties magnetic polaron materials occur due to a nonmonotonic change in spatial character of “near Fermi level” eigenstates with temperature, and the appearance of a pseudogap near $T_c$.

Due to the dominant Kitaev exchange interactions, the cobaltate, ${\mathrm{Na}}_3{\mathrm{Co}}_2{\mathrm{SbO}}_6$, has been considered to be approximate to the Kitaev quantum spin liquid (QSL). Here, we investigate both magnetic dilution and chemical pressure effects of ${\mathrm{Na}}_3{\mathrm{Co}}_2{\mathrm{SbO}}_6$ by the substitutions of ${\mathrm{Mg}}^{2+}$ for ${\mathrm{Co}}^{2+}$ through the structural, optical, magnetic, and thermodynamic measurements. No structural transition has been observed, and the band gaps remain constant at all doping levels. Combining with the magnetic and thermodynamic measurements, we find that the antiferromagnetic transition temperature is continuously suppressed with increasing Mg doping levels and completely disappears at $x=0.2$. Interestingly, when the doping level $x$ is larger than 0.2, neither long-range magnetic order nor spin glass state has been detected, and the specific heat has a residual linear term at zero field. All features indicate that the ${\mathrm{Na}}_3\left({\mathrm{Co}}_{2-x}{\mathrm{Mg}}_x\right){\mathrm{SbO}}_6$ system enters into a novel spin disorder state.

The recent discovery of the Weyl semimetal CeAlSi with simultaneous breaking of inversion and time-reversal symmetries has opened up new avenues for research into the interaction between light and topologically protected bands. In this work, we present a comprehensive examination of the shift current and injection current responsible for the circular photogalvanic effect in CeAlSi using first-principles calculations. Our investigation identifies a significant injection current of 4 $\mathrm{mA}/{\mathrm{V}}^2$ over a broad range in the near-infrared region of the electromagnetic spectrum, exceeding previously reported findings. In addition, we explored several externally controllable parameters to further enhance the photocurrent. A substantial boost in the injection current is observed when applying uniaxial strain along the $c$ axis of the crystal: a 5% strain results in a remarkable 64% increment. The exceptional photocurrent response in CeAlSi suggests that magnetic noncentrosymmetric Weyl semimetals may provide promising opportunities for novel photogalvanic applications.

Antiperovskite materials are recognized for potentially hosting a variety of topological surfa ce states. Mn-based antiperovskite ${\mathrm{Mn}}_3\mathrm{ZnC}$ is one of the nodal line semimetals that exhibits complex magnetic states with both ferromagnetic and ferrimagnetic order below $\sim 420$ K and $\sim 200$ K, respectively. In this work, we report the contribution of Berry curvature to the anomalous Hall effect (AHE) and anomalous Nernst effect (ANE) in ${\mathrm{Mn}}_3\mathrm{ZnC}$. The value of anomalous Hall conductivity is found to be $\sim 175{\mathrm{\Omega }}^{-1}{\text{cm}}^{-1}$ at 2 K, with an intrinsic contribution of $\sim 57{\mathrm{\Omega }}^{-1}{\text{cm}}^{-1}$. The scaling analysis of the anomalous Hall resistivity suggests that both intrinsic Berry curvature and extrinsic scattering mechanisms contribute to the AHE in the ferrimagnetic state; whereas in the ferromagnetic state, it is governed by the intrinsic Berry curvature mechanism only. In the temperature range $T=2-100\mathrm{K}$, the electrical and thermal transport properties indicate a significant contribution of electron–magnon scattering. We demonstrate that the ANE and AHE are commonly related via the Mott's relation. The peak values of the anomalous Nernst coefficient $S_{xy}^A$ and the anomalous Peltier coefficient ${\alpha }_{xy}^A$ are $\sim 0.45\mu \text{V/K}$ and $\sim 0.31\mathrm{A}/\mathrm{mK}$, respectively, at a temperature of $\sim 150\mathrm{K}$. Our results indicate that the observed ANE arises from contributions of both extrinsic skew scattering and intrinsic Berry curvature mechanisms.

Interlayer (IL) excitons found in some transition metal dichalcogenide semiconductors have unusual properties under an applied electric or magnetic field with potential for device applications. Using magneto-optical Kerr effect spectroscopy, we have measured the Landé $g$ factor (LGF) of excitons in bulk $2H\text{−}{\mathrm{MoSe}}_2$ and $2H\text{−}{\mathrm{MoTe}}_2$ on which there are few reports, with some being contradictory. Presence of the IL exciton was independently verified using laser modulated photoreflectance spectroscopy. In ${\mathrm{MoSe}}_2,$ the measured LGF values for the ground state $A_{1s}$ and IL excitons were $g_{A_{1s}}$ $=-3.5\pm 0.2$ and $g_{\text{IL}}$ $=+3.3\pm 0.4$. In ${\mathrm{MoTe}}_2,$ the LGF values were $g_{A_{1s}}$ $=-2.0\pm 0.3$ and $g_{\text{IL}}$ $=+3.0\pm 1$. The magnitude of $g_{\text{IL}}$ in both materials is more than a factor of 3 lower than in bulk 2H-${\mathrm{MoS}}_2$. Density functional theory based calculations with inclusion of the Coulomb interaction via the $GW+\text{Bethe}$-Salpeter equation enabled exciton identification and LGF estimations. Comparison with an approximate additive model for LGF, which considers contributions arising from spin, orbital, and valley angular momentum, indicates a diminished role of the valley angular momentum in determining the LGF of excitons in bulk $2H\text{−}{\mathrm{MoSe}}_2$ and $2H\text{−}{\mathrm{MoTe}}_2$.