Transition metal dichalcogenides exhibit remarkable optical properties due to the diverse number of strongly bound excitons, which can be fine-tuned by alloying. Despite a flurry of research activity in characterizing these excitons, a comprehensive and profound understanding of their behavior with temperature is lacking. Here, we report the rich spectrum of excitonic features within bulk van der Waals alloy ${\mathrm{Mo}}_{0.5}{\mathrm{W}}_{0.5}{\mathrm{S}}_2$ and ${\mathrm{Mo}}_{0.5}{\mathrm{W}}_{0.5}{\mathrm{Se}}_2$ single crystals through temperature-dependent reflectance spectroscopy and first-principles calculations. We observed Rydberg excitons and interlayer excitons in both the single crystals. Notably, we provide the first experimental evidence of highly energetic ${\mathrm{A}}^{\prime }$ and ${\mathrm{B}}^{\prime }$ excitons in ${\mathrm{Mo}}_{0.5}{\mathrm{W}}_{0.5}{\mathrm{S}}_2$ at room temperature. The strong carrier-phonon scattering significantly broadens the ${\mathrm{A}}^{\prime }, {\mathrm{B}}^{\prime }$, and interlayer excitons at room temperature in bulk ${\mathrm{Mo}}_{0.5}{\mathrm{W}}_{0.5}{\mathrm{S}}_2$ single crystal compared to its selenide. Our findings, supported by density functional theory and Bethe-Salpeter equation calculations, signify the crucial role of carrier-phonon interactions. These results open pathways for next-generation optoelectronic devices and quantum technologies operating at high temperature.

The properties of 2D materials are strongly influenced by their substrate, leading to a variety of proximity effects like screening, charge transfer, and hybridization. Surprisingly, there is a dearth of theoretical studies on these effects. Particularly, previous theoretical research on the star of David (SOD) structure in $1T\text{−}{\mathrm{NbSe}}_2$ has focused on single-layer configurations or stacking with the same $1T$ phase without any real substrate. Here, we depart from these approaches and explore how these proximity effects shape the electronic and magnetic properties of the $1T\text{−}{\mathrm{NbSe}}_2$ phase when it is grown on the metallic $1H\text{−}{\mathrm{NbSe}}_2$ substrate. Using density functional calculations, we establish a common framework to define the key characteristics of both free-standing $1T\text{−}{\mathrm{NbSe}}_2$ and $1H\text{−}{\mathrm{NbSe}}_2$. We then identify the optimal stacking arrangement for these two layers, revealing a transfer from the $1T$ to the $1H$ phase and a reorganization of charge within each layer. Our findings indicate that the magnetic moment of the SOD structure is still robust; however, it is diminished due to a reduction in the on-site Coulomb interaction of the Hubbard bands. Additionally, the interlayer coupling induces metallicity in the $1T$ phase and increases the decoupling of the lower Hubbard band from the valence band.

Due to photon-assisted transport processes, chiral edge modes induced by periodic driving do not directly mediate quantized transport. Here we show how narrow-bandwidth “energy filters” can restore quantization by suppressing photon-assisted transport through Floquet sidebands. We derive a Floquet-Landauer-type equation to describe transport through such an energy-filtered setup, and show how the filter can be integrated out to yield a sharply energy-dependent renormalized system-lead coupling. We show analytically and through numerical simulations that a nearly quantized conductance can be achieved in both off-resonantly and resonantly induced quasienergy gaps when filters are introduced. The conductance approaches the appropriate quantized value on each plateau with increasing system and filter size. We introduce a “Floquet distribution function” and show both analytically and numerically that it approaches the equilibrium Fermi-Dirac form when narrow-band filters are introduced, highlighting the mechanism that restores quantized transport.

Moiré superlattices provide a striking tool to controllably engineer electronic structures and realize various exotic quantum phenomena in two-dimensional (2D) systems. Surprisingly, moiré potential has recently been reported to extend its influence into three-dimensional (3D) graphitic thin films. Here, using angle-resolved photoemission spectroscopy, we report that 3D electronic states of transition-metal dichalcogenides (TMDs) can be modulated by interfacial moiré potential. The bulk electronic states of $\mathrm{C}{\mathrm{u}}_x\mathrm{TiS}{\mathrm{e}}_2$ unambiguously exhibit moiré clones due to the lattice mismatch with the noble-gas monolayer atop. We demonstrate that the interfacial moiré effect strongly couples with charge ordering with 3D wave vectors, which plays an important role in the formation of the mixed-dimensional moiré effect. We further exclude the final-state diffraction mechanism for the observed replicas. The moiré period can be further in situ tuned by different noble-gas atoms and annealing temperatures. Our results broaden the horizon of the mixed-dimensional moiré family from graphitic systems to TMD-based heterostructures and shed light on constructing functional devices based on versatile 2D-3D mixed-dimensional heterostructures.

Towards the efficient simulation of near-term quantum devices using tensor network states, we introduce an improved real-space parallelizable matrix-product state (MPS) compression method. This method enables efficient compression of all virtual bonds in constant time, irrespective of the system size, with controlled accuracy, while it maintains the stability of the wave-function norm without necessitating sequential renormalization procedures. In addition, we introduce a parallel regauging technique to partially restore the deviated canonical form, thereby improving the accuracy of the simulation in subsequent steps. We further apply this method to simulate unitary quantum dynamics and introduce an improved parallel time-evolving block-decimation (pTEBD) algorithm. We employ the improved pTEBD algorithm for extensive simulations of typical one- and two-dimensional quantum circuits, involving over 1000 qubits. The obtained numerical results unequivocally demonstrate that the improved pTEBD algorithm achieves the same level of simulation precision as the current state-of-the-art MPS algorithm but in polynomially shorter time, exhibiting nearly perfect weak scaling performance on a modern supercomputer.

Dirac nodal sphere (DNS) semimetals possess unique electronic properties beyond the Dirac nodal points and Dirac nodal lines paradigm. However, Dirac nodal sphere semimetals are very rare in real materials as it is very difficult to realize with discrete crystal point group symmetries. In this work, a silicon structure $({\mathrm{I}4}_1/\mathrm{acd}\text{−}{\mathrm{Si}}_{80})$ with pseudo-Dirac nodal sphere (PDNS) is proposed via the high-throughput screening for silicon based on our ${\mathrm{RG}}^2$ code and transferable tight-binding (TB) method from 2573 silicon allotropes. The results show that the pseudo-Dirac nodal sphere is around the $\mathrm{\Gamma }$ point with glide symmetries protected Dirac nodal loops (DNLs) on high-symmetry planes and tiny energy gap $(<1 \mathrm{meV})$ at the general band crossing points. Our calculations of phonon spectrum, $ab$ initio molecular dynamics, elastic constants, and formation energy show that ${\mathrm{I}4}_1/\mathrm{acd}\text{−}{\mathrm{Si}}_{80}$ is a metastable phase of silicon. Furthermore, ${\mathrm{I}4}_1/\mathrm{acd}\text{−}{\mathrm{Si}}_{80}$ exhibits interesting photoelectric properties with photoexcitable high-velocity Dirac fermions and has potential applications in Si-based photoelectric devices.

It is discussed whether like charges can be attracted to each other at a negative permittivity. The possibility of achieving negative permittivity in dielectric-conductor metamaterials due to localized surface plasmon resonance is shown. The possibility of manipulating the resonance frequency in a wide range of frequencies from zero to the plasma frequency by applying a magnetic or electric field is shown. The possibility of breakup of electron-hole pairs (exciton cold dissociation) and formation of electron-electron bound pairs at negative permittivity and nonzero frequency is discussed.

The Landau level mixing is the key in understanding the mysterious $5/2$ fractional quantum Hall effect in GaAs quantum well. Theoretical calculations with and without Landau level mixing show striking differences. However, the way to deal with the considerable strong Landau level mixing in GaAs is still unsatisfactory. We develop a method combining the screening and the perturbation theories to study the nature of the $5/2$ fractional quantum Hall effect in GaAs efficiently. The screening, which has been successful in explaining ZnO systems integrates out the low-energy Landau levels close to the related Landau level, while the other high-energy Landau levels are integrated out by the perturbation theory. We find that the ground states still hold the quasitriplet degeneracy, which implies the Pfaffian nature of the system. Furthermore, the particle-hole symmetry is only weakly violated since the particle-hole parity is close to unity. We propose that the ground state in the finite-size calculations could be approximated as a variational superposition of the Pfaffian and anit-Pfaffian states. In the experimental environment the symmetrized Pfaffian component is dominant, corresponding to a thermal conductance around 2.5 quanta that can be understood consequently.

Two-dimensional materials are a highly tunable platform for studying the momentum space topology of the electronic wavefunctions and real space topology in terms of skyrmions, merons, and vortices of an order parameter. Such textures for electronic polarization can exist in moiré heterostructures. A quantum-mechanical definition of local polarization textures in insulating supercells was recently proposed. Here, we propose a definition for local polarization that is also valid for systems with topologically nontrivial bands. We introduce semilocal hybrid polarizations, which are valid even when the Wannier functions in a system cannot be made exponentially localized in all dimensions. We use this definition to explicitly show that nontrivial real-space polarization textures can exist in topologically nontrivial systems with nonzero Chern number under (1) an external superlattice potential, and (2) under a stacking-induced moiré potential. In the latter, we find that while the magnitude of the local polarization decreases discontinuously across a topological phase transition from trivial to topologically nontrivial, the polarization does not completely vanish. Our findings suggest that band topology and real-space polar topology may coexist in real materials.

It is generally assumed that a high spatial resolution of a microscope requires a large numerical aperture of the imaging lens or detector. In this study, the information limit of 15 pm is achieved in transmission electron microscopy using only the bright-field disk (small numerical aperture) via multislice ptychography. The results indicate that high-frequency information has been encoded in the bright-field disk due to the multiple scattering of electrons in the objects, making it possible to break the diffraction limit of imaging via bright-field ptychography.

We consider the fractional quantum Hall effect (FQHE) at the filling factor $8/17$, where signatures of incompressibility have been observed in the zeroth Landau level of bilayer graphene. We propose an Abelian state described by the “$\overline{(8/3)}\overline{2}{1}^3$” parton wave function, where a parton itself forms an FQHE state. This state is topologically distinct from the $8/17$ Levin-Halperin state, a daughter state of the Moore-Read state. We carry out extensive numerical exact diagonalization of the Coulomb interaction at 8/17 in the zeroth Landau level of bilayer graphene but find that our results cannot conclusively determine the topological order of the underlying ground state. We work out the low-energy effective theory of the $\overline{(8/3)}\overline{2}{1}^3$ edge and make predictions for experimentally measurable properties of the state which can tell it apart from the 8/17 Levin-Halperin state.

The mirror twin boundary (MTB) within semiconducting transition metal dichalcogenides (TMDs) not only provides a versatile platform to explore exotic phenomena of one-dimensional (1D) systems, but also offers an effective building block to introduce novel electronic states in the TMDs. In spite of extensive efforts on introducing the MTBs in the TMDs, creating and manipulating the MTBs with custom-designed sites remains an outstanding challenge in experiment. Here we present a facile method for in situ generation of MTBs in three different TMDs at predetermined positions by scanning tunneling microscope (STM) tip pulses. In $\mathrm{MoT}{\mathrm{e}}_2$, the length and density of the MTBs can be further manipulated using a STM tip. Moreover, we demonstrate the ability to introduce uniform-sized and orderly arranged MTB triangular loops, which generate low-energy flat electronic bands in the $\mathrm{MoT}{\mathrm{e}}_2$. A periodic modulation in the density of states with a $3a$ period ($a$ is the lattice constant) is observed in the MTBs. Unexpectedly, our experiment indicates that the MTBs exhibit length preference with $3\mathit{Na}$ ($N$ is an integer), implying that the mechanism for the periodic modulation in the density of states also plays a role in affecting the formation of the MTBs.

We investigate the entanglement structure and wave function characteristics of continuously monitored free fermions with $\mathrm{U}\left(1\right)$ symmetry in two spatial dimensions. By deriving the exact fermion replica-quantum master equation, we line out two approaches: (i) a nonlinear sigma model analogous to disordered free fermions, resulting in an $\mathrm{SU}\left(R\right)$-symmetric field theory of symmetry class AIII in ($2+1$) space-time dimensions, or (ii) for bipartite lattices, third quantization leading to a non-Hermitian $\mathrm{SU}\left(2R\right)$-symmetric Hubbard model. Using exact numerical simulations, we explore the phenomenology of the entanglement transition in two-dimensional (2D) monitored fermions, examining entanglement entropy and wave function inverse participation ratio. At weak monitoring, we observe characteristic $LlogL$ entanglement growth and multifractal dimension $D_q=2$, resembling a metallic Fermi liquid. Under strong monitoring, wave functions localize and the entanglement saturates towards an area law. Between these regimes, we identify a high-symmetry point exhibiting both entanglement growth indicative of emergent conformal invariance and maximal multifractal behavior. While this multifractal behavior aligns with the nonlinear sigma model of the Anderson transition, the emergent conformal invariance is an unexpected feature not typically associated with Anderson localization. These discoveries add a new dimension to the study of 2D monitored fermions and underscore the need to further explore the connection between nonunitary quantum dynamics in $D$ dimensions and quantum statistical mechanics in $D+1$ dimensions.

The phenomenon of chirality-induced spin selectivity (CISS) refers to the coupling between structural chirality and the spin polarization of conduction electrons. While previous studies of CISS have primarily focused on systems exhibiting charge current flow, our investigation aims to explore CISS within a charge-current-free environment. This approach is intended to overcome the challenges posed by pinholes in chiral molecular films. In this study, we investigated the Gilbert damping of NiFe layers deposited on two-dimensional chiral hybrid lead-iodide perovskites, utilizing the time-resolved magneto-optical Kerr effect. Our results reveal a minor variation in the Gilbert damping constant on the magnetization direction of the NiFe. This subtle change in the damping constant, observed when pure spin current is injected from NiFe to the chiral perovskite via spin pumping, aligns with previous observations of modest CISS-induced magnetoresistance in a multilayer device, contrasting with the significant magnetoresistance detected in spin-polarized conductive atomic force microscopy measurements. Our findings contribute valuable insight into the understandings of CISS-related phenomena, paving the way for further research in this field.

We study the ground-state properties of antiferromagnetic $J_1\text{−}{J}_2$ chains with half-integer spins ranging from $S=\frac{3}{2}$ to $S=\frac{11}{2}$ using the density-matrix renormalization group method. We map out the ground-state phase diagrams as a function of $\frac{J_2}{J_1}$ containing topological phases with alternating $\frac{2S-1}{2}$ and $\frac{2S+1}{2}$ valence bonds. We identify these topological phases and their boundaries by calculating the string order parameter, the dimer order parameter, and the spin gap for those $\mathrm{high}\text{−}S$ systems in the thermodynamic limit (finite-size scaling). We find that these topological regions narrow down inversely with $S$ and converge to a single point at $\frac{J_2}{J_1}=\frac{1}{4}$ in the classical limit—a critical threshold between commensurate and incommensurate orders. In addition, we extend the discussion of the Majumder-Ghosh state, previously noted only for $S=\frac{1}{2}$, and speculate about its possible presence as a ground state in half-integer high-spin systems over a substantial range of $\frac{J_2}{J_1}$ values.

We consider the macroscopic dynamics of systems with charge and spin currents, using the methods of Onsager's irreversible thermodynamics. Applied to systems with spin-orbit interaction (SOI), we derive Onsager relations showing that, if electrical disequilibrium leads to spin currents, magnetic disequilibrium leads to charge currents. We consider three examples of such SOI. Two of these predicted charge currents have not previously appeared. By measuring these charge currents one can infer the corresponding spin currents.

We present muon spin rotation and relaxation (μSR) results for chalcogenide spinels $\mathrm{CuC}{\mathrm{r}}_2{X}_4$ with $X=\mathrm{S}$ and Se. Both compounds are known as ferromagnetic metals with high Curie temperatures. Our μSR and magnetization data show clear signatures for additional magnetic transitions far below the respective Curie temperatures. They can be related to changes in the Cr valence system from the mixed valence between $\mathrm{C}{\mathrm{r}}^{3+}$ and $\mathrm{C}{\mathrm{r}}^{4+}$ at high temperatures with collinear ferromagnetism to a charge-ordered state at low temperatures with a different ferromagnetic structure. Our results demonstrate that the electronic systems and the related spin structures of both compounds are more complex than assumed so far.

Ternary hydrides are considered as the ideal candidates with high critical temperature $\left(T_c\right)$ stabilized at submegabar pressure, evidenced by the recent discoveries in ${\mathrm{LaBeH}}_8$ (110 K at 80 GPa) and ${\mathrm{LaB}}_2{\mathrm{H}}_8$ (106 K at 90 GPa). Here, we investigate the crystal structures and superconductivity of an Ac-B-H system under pressures of 100 and 200 GPa by using an advanced structure method combined with first-principles calculations. As a result, nine stable compounds were identified, where B atoms are bonded with H atoms in the formation with diverse ${\mathrm{BH}}_x$ motifs, e.g., methanelike $\left({\mathrm{BH}}_4\right)$, polythenelike, ${\left({\mathrm{BH}}_2\right)}_n$, and ${\mathrm{BH}}_6$ octahedron. Among them, seven Ac-B-H compounds were found to become superconductive. In particular, ${\mathrm{AcBH}}_7$ was estimated to have a $T_c$ of 122 K at 70 GPa. Our in-depth analysis reveals that the B-H interactions in the ${\mathrm{BH}}_6$ units play a key role in its high superconductivity and stability at submegabar pressure. Our current results provide a guidance for future experiments to synthesize ternary hydride superconductors with high-$T_c$ at moderate pressure.