We evaluate theoretically the possibility to realize Majorana zero modes in hybrid devices made from topological-insulator nanowires proximity-coupled to a superconductor. Such systems have been suggested as building blocks of future topological quantum computers, as they have been predicted to realize Majorana zero modes protected by large gaps. A main obstacle is, however, the presence of a relatively large density of charged impurities, $n_{\text{imp}}\approx {10}^{19}{\mathrm{cm}}^{-3}$. Based on extensive numerical simulations, we show that the proximity to the superconductor leads to an efficient screening of the disorder potential. By analyzing the Majorana splitting energy, the size of the Andreev gap and the localization of edge modes, we show that robust Majorana modes can be realized for realistic levels of impurity concentrations and wire radii.

Exceptional points (EPs), as unique spectral singularities in non-Hermitian systems, play a crucial role throughout the study of non-Hermitian physics. Despite extensive investigations on single or isolated EPs, the collective behavior of multiple EPs and their intricate interplay remain largely unexplored, particularly in experiments. Here, we demonstrate a universal non-Abelian conservation rule that governs the collective interactions of multiple EPs. Specifically, we construct a two-dimensional three-band non-Hermitian lattice and experimentally implement it using an acoustic coupled-resonator system in synthetic momentum space. By measuring eigenfrequency braids, we precisely identify the topological charges of EPs and observe distinct braiding consequences for momentum loops enclosing the same EP. More intriguingly, by tracking the transmutations of multi-EP charges, we evidence that two pairwise-created EPs do not annihilate upon collision but instead coalesce into a new higher-order EP. Our findings represent a major advance in exploring non-Hermitian non-Abelian physics, potentially unlocking new avenues for applications.

Fourfold anisotropic magnetoresistance (AMR) has been widely observed in quantum materials, but the underlying mechanisms remain poorly understood. Here, we find, in a variety of three-dimensional Dirac materials that can be unifiedly described by the massive Dirac equation, the intrinsic orbital magnetic moments of electrons vary synchronously with the magnetic field and give rise to a $\pi$ periodic correction to its velocity, further leading to unusual fourfold AMR, dubbed orbital fourfold AMR. Our theory not only explains the observation of fourfold AMR in bismuth but also uncovers the nature of the dominant fourfold AMR in thin films of the antiferromagnetic topological insulator ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$, which arises from the near cancellation of twofold AMR from the surface states and bulk states due to distinct spin-momentum lockings. Our work provides another mechanism for the creation and manipulation of orbital fourfold AMR in both conventional conductors and various topological insulators.

Spatially indirect excitons in semiconductor quantum wells are relevant to basic research and device applications because they exhibit enhanced tunability, delocalized wave functions, and potentially longer lifetimes relative to direct excitons. Here we investigate the properties of indirect excitons and their coupling interactions with direct excitons in asymmetric InGaAs double quantum wells using optical multidimensional coherent spectroscopy and photoluminescence excitation spectroscopy. Analyses of the spectra confirm a strong influence of many-body effects and reveal that excited-state zero-quantum coherences between direct and indirect excitons in the quantum wells dephase faster than the much-higher-energy single-quantum coherences between excitonic excited states and ground states. The results also suggest an important energy-dependent role of continuum states in mediating system dynamics, and they indicate that dephasing mechanisms are associated with uncorrelated or anticorrelated energy-level fluctuations.

Altermagnetism has recently drawn considerable attention in three- and two-dimensional materials. Here we extend this concept to quasi-one-dimensional (Q1D) monolayers assembled from single-atomic magnetic chains. Through systematically examining nine types of structures, two stacking orders, intra- and interchain magnetic couplings, we identify four out of 30 promising structural prototypes for hosting altermagnetism, which yields 192 potential monolayer materials. We further confirm eight thermodynamically stable Q1D monolayers via high-throughput calculations. Using symmetry analysis and first-principles calculations, we find that the existence of altermagnetism is determined by the type of interchain magnetic coupling and predict three intrinsic altermagnets, ${\mathrm{CrBr}}_3$, ${\mathrm{VBr}}_3$, and ${\mathrm{MnBr}}_3$, due to their ferromagnetic interchain couplings and five extrinsic ones, ${\mathrm{CrF}}_3$, ${\mathrm{CrCl}}_3$, ${\mathrm{CrI}}_3$, ${\mathrm{FeCl}}_3$, and ${\mathrm{CoTe}}_3$, ascribed to their neglectable or antiferromagnetic interchain couplings. Moreover, the interchain magnetic coupling here is highly tunable by manipulating the interchain spacing, leading to experimentally feasible transitions between altermagnetic and nodal-line semiconducting states. In addition, applying external electric fields can further modulate the spin splitting. Our findings establish a highly tunable family of Q1D altermagnets, offering fundamental insights into the intricate relationship between geometry, electronic structure, and magnetism. These discoveries hold significant promises for experimental realization and future spintronic applications.

Spin chirality in antiferromagnets offers new opportunities for spintronics. The kagome antiferromagnet ${\mathrm{Mn}}_3\mathrm{Sn}$ is a paradigmatic material in which the antiferromagnetic order parameter can be detected and controlled by electrical means. However, direct investigation of the magnetic texture of ${\mathrm{Mn}}_3\mathrm{Sn}$ has been challenging because of the tiny moment hosted in its magnetic octupole, hindering further clarification of this unique material. Here, we address this issue by observing the stray magnetic field from ${\mathrm{Mn}}_3\mathrm{Sn}$ using a diamond-based quantum scanning microscope. The spatially resolved intrinsic domains and domain walls in a high-quality single-crystalline ${\mathrm{Mn}}_3\mathrm{Sn}$ film quantitatively reveal the polarization angle of the magnetic octupole in the kagome plane, the domain's local magnetization, the domain wall's width and chirality, and the octupole order in domain walls. Our nanoscale investigation of ${\mathrm{Mn}}_3\mathrm{Sn}$, a powerful complement to macroscopic measurements, paves the road for developing chiral antiferromagnetism and its potential for spintronic applications.

Alkali metal intercalated iron selenide superconductors $A_x{\mathrm{Fe}}_{2-y}{\mathrm{Se}}_2$ exhibit unique properties, such as the coexistence of superconductivity and antiferromagnetism, along with an iron-vacancy-order superstructure. However, due to microscopic phase separation, the relationship between these properties and superconductivity remains elusive. In this study, we have employed high-spatial-resolution magnetic force microscopy $\left(\mathrm{MFM}\right)$, Raman spectroscopy, and scanning electron microscopy–energy dispersive x-ray spectroscopy $\left(\mathrm{SEM}\text{−}\mathrm{EDX}\right)$ to identify and characterize the superconducting phase. Below the superconducting critical temperature $T_{\mathrm{c}}$, the striped regions exhibit a pronounced diamagnetic response, while the surrounding areas remain unaffected, providing direct evidence that the striped regions constitute the superconducting phase. $\mathrm{SEM}\text{−}\mathrm{EDX}$ and high-spatial-resolution Raman scattering results reveal a stoichiometry of ${\mathrm{K}}_{0.57}{\mathrm{Fe}}_{1.89}{\mathrm{Se}}_2$ in the striped regions, with a single Raman peak at $173.3{\mathrm{cm}}^{-1}$. Temperature- and polarization-dependent Raman scattering spectra further show that, at low temperatures, this peak shifts to $201{\mathrm{cm}}^{-1}$ in the $B_{1g}$ channel, while a new peak emerges at $165{\mathrm{cm}}^{-1}$ in the $A_{1g}$ channel. The $\mathrm{Fe}:\mathrm{Se}$ ratio in the stripe phase $(1.89:2)$, along with the number, symmetry, and frequencies of the phonon modes, is consistent with the $\mathrm{FeSe}$ layers. These results indicate that the superconducting phase in the striped regions retains an approximately intact $\mathrm{FeSe}$ layer. Our findings underscore the critical role of the intact $\mathrm{FeSe}$ layer in $\mathrm{FeSe}$-based superconductors and provide new insights into the mechanism of high-$T_{\mathrm{c}}$ superconductivity.

Altermagnetic (AM) states have compensated collinear magnetic configurations that are invariant under a combination of real-space rotation and time reversal. While these symmetries forbid a direct bilinear coupling of the AM order parameter with a magnetic field, they generally enable piezomagnetism, manifested as a trilinear coupling with the magnetic field and strain. Here, we show that, as a result of this coupling, in an altermagnet subjected to random strain, the magnetic field triggers an effective random field conjugate to the AM order parameter, providing a rare realization of a tunable random-field Ising model. Specifically, we find two competing effects promoted by an external magnetic field: an increasing random-field disorder, which suppresses long-range AM order, and an enhanced coupling to elastic fluctuations, which favors AM order. By solving the corresponding random-field transverse-field Ising model via a mean-field approach, we obtain the temperature-magnetic field phase diagram of an inhomogeneous AM state for different strengths of random-strain disorder, unveiling the emergence of a field-induced reentrant AM phase. We also discuss the fingerprints of this rich behavior on several experimentally-accessible quantities, such as the shear modulus, the elastocaloric effect coefficient, and the AM order parameter. Our results reveal an unusual but experimentally feasible path to tune AM order with uniform magnetic fields.

Predicting accurate band gaps and optical properties of lower-dimensional materials, including two-dimensional van der Waals (vdW) materials and their heterostructures, remains a challenge within density functional theory (DFT) due to their unique screening compared to their bulk counterparts. Additionally, accurate treatment of the dielectric response is crucial for developing and applying screened-exchange dielectric-dependent range-separated hybrid functionals (SE-DD-RSH) for vdW materials. In this work, we introduce a SE-DD-RSH functional to the 2D vdW materials like ${\mathrm{MoS}}_2$, ${\mathrm{WS}}_2$, $h\mathrm{BN}$, black phosphorus (BP), and $\beta \text{−}\mathrm{InSe}$. By accounting for in-plane and out-of-plane dielectric responses, our method achieves accuracy comparable to advanced many-body techniques like $G_0{W}_0$ and BSE@$G_0{W}_0$ at a lower computational cost. We demonstrate improved band gap predictions and optical absorption spectra for both bulk and layered structures, including some heterostructures like ${\mathrm{MoS}}_2/{\mathrm{WS}}_2$. This approach offers a practical and precise tool for exploring electronic and optical phenomena in 2D materials, paving the way for efficient computational studies of layered systems.

We discovered a new rare-earth-based quantum magnet ${\mathrm{Rb}}_3\mathrm{Yb}{\left({\mathrm{VO}}_4\right)}_2$, in which the ${\mathrm{Yb}}^{3+}$ ions form an equilateral triangular lattice (space group $\mathrm{P}\overline{3}\mathrm{m}$ 1), without detectable antisite disorder. Magnetic susceptibility, magnetization, specific heat, and electron spin resonance were measured. The results reveal weak antiferromagnetic interactions between the ${\mathrm{Yb}}^{3+}$ ions with Curie-Weiss temperature ${\theta }_{\text{CW}}\sim -0.45$ K and the absence of spin glass or long-range magnetic ordering down to 1.8 K. The ground state of the system is well separated from the first excited Kramers doublet by an energy gap of 23.65 meV (274 K), leading to an effective spin-orbit entangled spin of $J_{\text{eff}}=1/2$ below a characteristic temperature of 80 K. The easy-plane type of anisotropy with $g_{ab}=2.68$ ($ab$ plane) and $g_c=2.30$ ($c$ axis) and gapless excitation are also established. These features are further supported by the crystal electric-field calculations and fittings of the magnetic data. Our findings make ${\mathrm{Rb}}_3\mathrm{Yb}{\left({\mathrm{VO}}_4\right)}_2$ a promising candidate for further exploration of spin-orbit entangled nature and potential spin-liquid state in the rare-earth triangular-lattice quantum magnets.

To assess prior mean-field claims that the interacting Kane-Mele model hosts a novel $z\text{−}\mathrm{antiferromagnetic}$ (AFM) Chern insulating phase for a wide range of sublattice potentials, we analyze the Kane-Mele-Hubbard model in the presence of a sublattice potential using nonperturbative determinant quantum Monte Carlo simulations. We find instead that the true low-temperature state is a quantum spin Hall insulator for intermediate values of the sublattice potential ${\lambda }_v$ and large on-site repulsion. Two kinds of magnetic fluctuations are found to compete: $z\text{−}$ and $xy\text{−}\mathrm{AFM}$. The latter dominates at low temperature leading to a stabilization of the quantum spin Hall state as opposed to $\mathrm{a}z\text{−}\mathrm{AFM}$ Chern insulator. Our work is consistent with the robust quantum spin Hall effects which are consistently observed at even-integer fillings over a wide range of parameters in twisted bilayer ${\mathrm{MoTe}}_2$ and ${\mathrm{WSe}}_2$ as well as AB-stacked ${\mathrm{MoTe}}_2/{\mathrm{WSe}}_2$.

We present a novel approach within the functional renormalization group framework for computing critical exponents that characterize the time evolution of out-of-equilibrium many-body systems. Our approach permits access to quantities involved in the renormalization procedure, using an expansion about time-translation invariant problems. This expansion can be upgraded to a fully time-dependent computation by iteration. As a prototypical example, we compute the aging exponent $\theta$ describing the dynamics of model A following a sudden quench to the critical point. Already at leading order, the approach demonstrates remarkable accuracy when compared with MC simulations and resummed perturbative expansions in the range $2<d<4$. This yields results that surpass those of the two-loop $\epsilon$ expansion in accuracy and match analytically known benchmarks at large $N$. These findings contribute to a deeper understanding of out-of-equilibrium universality and open new avenues for nonperturbative studies of critical dynamics, as well as for exploring the critical behavior of systems with spatial boundaries.

We introduce and study interacting topological states that arise in time-reversal symmetric bands with an underlying obstruction to forming localized states. If the $U\left(1\right)$ valley symmetry linked to independent charge conservation in each time-reversal sector is spontaneously broken, the corresponding “excitonic” order parameter is forced to form a topologically nontrivial texture across the Brillouin zone. We show that the resulting phase, which we dub a textured exciton insulator, cannot be given a local-moment description because of a form of delicate topology. Using toy models of bands with Chern or Euler obstructions to localization, we construct explicit examples of the Chern or Euler texture insulators (CTIs or ETIs) they support, and demonstrate that these are generically competitive ground states at intermediate coupling. We construct field theories that capture the response properties of these new states. Finally, we identify the incommensurate Kekulé spiral phase observed in magic-angle bi- and trilayer graphene as a concrete realization of an ETI.

We explore the phase diagrams of moiré materials in search of a class of intervalley-coherent correlated insulating state: the Chern texture insulator (CTI). This phase of matter, proposed in a companion paper [Kwan et al., Phys. Rev. B 112, 035129 (2025).], breaks valley $U\left(1\right)$ symmetry in a nontrivial fashion wherein the valley order parameter is forced to texture in momentum space as a consequence of band topology. Using detailed Hartree-Fock studies, we establish that the CTI emerges as an energetically competitive intermediate-coupling ground state in several moiré systems that lack a twofold rotation symmetry that forbids the single-particle topology essential to the formation of the CTI valley texture.

The role of twist angle (${\theta }_t$) in tailoring the physical properties of heterostructures is emerging as a new paradigm in two-dimensional materials. The influence of flat electronic bands near the magic angle ($\sim 1.1^{\circ }$) on the phononic properties of twisted bilayer graphene (t-BLG) is not well understood. In this work, we systematically investigate the $G$ and $2D$ Raman modes of t-BLG samples with twist angles ranging from $\sim 0.3^{\circ }$ to $\sim 3^{\circ }$ using micro-Raman spectroscopy. A key finding of our work is the splitting of the $G$ mode near the magic angle due to moiré potential induced phonon hybridization. The linewidth of the low-frequency component of the $G$ mode ($G^{-}$), as well as the main component of the $2D$ mode, exhibits enhanced broadening near the magic angle due to increased electron-phonon coupling, driven by the emergence of flat electronic bands. Additionally, temperature-dependent Raman measurements (6–300 K) of a magic-angle twisted bilayer graphene sample (${\theta }_t\sim 1^{\circ }$) reveal an almost tenfold increase in phonon anharmonicity induced temperature variation in both components of the split $G$ mode, as compared to a Bernal-stacked bilayer graphene sample, further emphasizing the role of phonon hybridization in this system. These studies could be important for understanding the thermal properties of the twisted bilayer graphene systems.

The valley degree of freedom in two-dimensional (2D) semiconductors, such as gapped bilayer graphene (BLG) and transition metal dichalcogenides, is a promising carrier of quantum information in the emerging field of valleytronics. While valley dynamics have been extensively studied for moderate band gap 2D semiconductors using optical spectroscopy techniques, very little is known about valley lifetimes in narrow band gap BLG, which is difficult to study using optical techniques. Here, we report single-particle valley relaxation times $T_1$ exceeding several microseconds in electrostatically defined BLG quantum dots using a pulse-gating technique. The observed dependence of $T_1$ on perpendicular magnetic field can be understood qualitatively and quantitatively by a model in which $T_1$ is limited by electron-phonon coupling. We identify the coupling to acoustic phonons via the bond length change and via the deformation potential as the limiting mechanisms.

Density functional theory (DFT) calculations of charged molecules and surfaces are critical to applications in electrocatalysis, energy materials, and related fields of materials science. DFT implementations such as the Vienna ab initio simulation package (vasp) compute the electrostatic potential under three-dimensional (3D) periodic boundary conditions, necessitating charge neutrality. In this work, we implement 0D and 2D periodic boundary conditions to facilitate DFT calculations of charged molecules and surfaces, respectively. We implement these boundary conditions using the Coulomb kernel truncation method. Our implementation computes the potential under 0D and 2D boundary conditions by selectively subtracting unwanted long-range interactions in the potential computed under 3D boundary conditions. By combining the Coulomb kernel truncation method with a computationally efficient padding approach, we remove nonphysical potentials from vacuum in 0D and 2D systems. To illustrate the computational efficiency of our method, we perform large supercell calculations of the formation energy of a charged chlorine defect on a sodium chloride (001) surface and perform long-timescale molecular dynamics simulations on a stepped gold (211) water electrode-electrolyte interface.

The D'yakonov-Perel' (DP) spin-relaxation mechanism has traditionally been associated with either relativistic spin-orbit coupling, which breaks space-inversion symmetry, or inhomogeneous magnetization, which breaks both time-reversal and translational symmetries. Here, we investigate a spin-relaxation mechanism in altermagnetic systems which possess novel magnetic states characterized by sublattices connected through crystal-rotation symmetries and opposite spins with zero overall net magnetization and absence of spin-orbit coupling. We find that altermagnetic states exhibit DP-type spin relaxations in both strong- and weak-scattering regimes, with the spin-relaxation rate decreasing to zero as the temperature approaches the critical temperature of the altermagnetic phase transition. Although the overall scattering strength governs both spin and momentum relaxation, the spin relaxation is controlled by a distinct correlation time that arises from the dephasing of spin precession, which involves a high-order angular factor rather than the backscattering factor. Moreover, using a kinetic approach incorporating rigorous microscopic scattering, we also study the spin Hall current and demonstrate that this signal is highly anisotropic and proportional to the degree of altermagnetic order.

In three dimensions, there is a nontrivial quantum cellular automaton (QCA), which disentangles [Haah, Fidkowski, and Hastings, Commun. Math. Phys. 398, 469 (2023)] the three-fermion Walker-Wang model, a model whose action depends on Stiefel-Whitney classes of the spacetime manifold. Here we present a conjectured generalization to higher dimensions. For an arbitrary symmetry protected topological phase of time reversal whose action depends on Stiefel-Whitney classes, we construct a corresponding QCA that we conjecture disentangles that phase. Some of our QCA are Clifford, and we relate these to a classification theorem of Clifford QCA. We also identify Clifford QCA in $4m+1$ dimensions, for which we find a low-depth circuit description using non-Clifford gates but not with Clifford gates.

Nanoscale self-localized topological spin textures, such as domain walls and skyrmions, are of interest for the fundamental physics of magnets and spintronics applications. Ferrimagnets (FiMs), in the region close to the angular momentum compensation point, are promising materials because of their ultrafast spin dynamics at nonzero magnetization. In this work, we study specific features of the FiM domain wall (DW) dynamics, which are absent in both ferromagnets (FM) and antiferromagnets (AFM). In low-damping FMs and AFMs $(\alpha \ll 1)$, the nonstationary forced motion of DWs is characterized by slow $({\mathit{t}}_{\mathrm{diss}}\propto 1/\alpha )$ changes of the DW's velocity and internal structure for all accepted values of the DW energy $E$ and its linear momentum $P$—a consequence of the stability of DWs for any value of $P$. In contrast, the dispersion law of FiM DWs has specific points, $P=P_{\mathrm{cr}}$ and $E_{\mathrm{cr}}=E\left(P_{\mathrm{cr}}\right)$, such that stable DWs are only present for $P<P_{\mathrm{cr}}$, i.e., $P_{\mathrm{cr}}$ and $E_{\mathrm{cr}}$ act as endpoints in the $E\left(P\right)$ dependence. We show that when a field-like torque driven DW reaches this endpoint, it falls into a highly-nonequilibrium state with the excitation of fast $(t\ll {\mathit{t}}_{\mathrm{diss}})$ and highly-nonlinear intrawall magnetization dynamics, covering a wide frequency range up until the frequencies of propagating spin waves. The domain wall finally throws off an “excessive” energy by a short “burst” of the propagating spin waves and returns to the stationary state; the full picture of the forced motion is a periodic repetition of such “explosive” events.