For the production of transition-metal dichalcogenides by molecular beam epitaxy, an understanding of the interaction between chalcogenide atoms and metal surfaces is of fundamental interest. Here, we describe the occurrence of stable surface telluride phases when reacting submonolayer amounts of tellurium with a Pt(111) surface. We find that when approaching a Te amount of 0.44 monolayers from below, a disordered Te adsorbate phase is converted into a long-range ordered Pt(111)-$(3\times 3)$-4Te surface telluride, which is stable against loss of Te up to 890 K. Adding further Te, heavy domain walls develop that condense into a well-ordered domain structure with $(10\times 10)$ periodicity. It hosts 49 Te atoms per unit cell and is thermally stable up to 770 K. These two phases are the only existing Te-induced surface reconstructions in the submonolayer regime. The atomic structure of the two phases is determined using low-energy electron diffraction intensity analysis, scanning tunneling microscopy, and density functional theory. The resulting complex surface structures are revealed with picometer accuracy and a great agreement between the employed methods. In particular, the analysis of the $(10\times 10)$ structure demonstrates the currently achievable state-of-the-art for low-energy electron diffraction structural analyses in terms of experimental surface preparation and data collection but also of computational methods, and it leads the way to building up a structural database for two-dimensional materials and their interfaces.

We show that electron interaction with the crystal lattice imposes stringent symmetry constraints on the atomic orbital moment propagation. We present examples that elucidate the underlying mechanisms and reveal an additional effect of ultrafast orbital moment oscillations not captured by the semiclassical models. The constraints revealed by our analysis warrant reinterpretation of prior observations and suggest routes for efficient orbitronic device implementation.

The recent discovery of high-$T_c$ superconductivity in bilayer nickelate ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ under high pressure has stimulated great interest concerning its pairing mechanism. We argue that the weak coupling model from the almost fully filled $d_{z^2}$ bonding band cannot give rise to its high $T_c$, and thus propose a strong coupling model based on local interlayer spin singlets of Ni-$d_{z^2}$ electrons due to their strong on-site Coulomb repulsion. This leads to a minimal effective model that contains local pairing of $d_{z^2}$ electrons and a considerable hybridization with near quarter-filled itinerant $d_{x^2-y^2}$ electrons on nearest-neighbor sites. Their strong coupling provides a unique two-component scenario to achieve high-$T_c$ superconductivity. Our theory highlights the importance of the bilayer structure of superconducting ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ and points out a potential route for the exploration of more high-$T_c$ superconductors.

The outcomes of measurements are characterized by an infinite family of generalized uncertainties, or cumulants, which provide information beyond the mean and variance of the observable. Here, we investigate the cumulants of a conserved charge in a subregion with corners. We derive nonperturbative relations for the area law, and more interestingly, the angle dependence, showing how it is determined by geometric moments of the correlation function. These hold for translation invariant systems under great generality, including strongly interacting ones. We test our findings by using two-dimensional topological quantum Hall states of bosons and fermions at both integer and fractional fillings. We find that the odd cumulants' shape dependence differs from the even ones. For instance, the third cumulant shows nearly universal behavior for integer and fractional Laughlin Hall states in the lowest Landau level. Furthermore, we examine the relation between even cumulants and the Rényi entanglement entropy, where we use our results for the fractional state at filling 1/3 to compare these quantities in the strongly interacting regime. We discuss the implications of these findings for other systems, including gapless Dirac fermions, and more general conformal field theories.

The phonon transport mechanisms and ultralow lattice thermal conductivities (${\kappa }_{\mathrm{L}}$) in silver halide $\mathrm{Ag}X$ ($X=\mathrm{Cl},\mathrm{Br},\mathrm{I}$) compounds are not yet well understood. Herein, we study the lattice dynamics and thermal property of $\mathrm{Ag}X$ under the framework of perturbation theory and the two-channel Wigner thermal transport model based on accurate machine learning potentials. We find that an accurate extraction of the third-order atomic force constants from largely displaced configurations is significant for the calculation of the ${\kappa }_{\mathrm{L}}$ of $\mathrm{Ag}X$, and the coherence thermal transport is also non-negligible. In AgI, however, the calculated ${\kappa }_{\mathrm{L}}$ still considerably overestimates the experimental values even including four-phonon scatterings. Molecular dynamics (MD) simulations using machine learning potential suggest an important role of the higher-than-fourth-order lattice anharmonicity in the low-frequency phonon linewidths of AgI at room temperature, which can be related to the simultaneous restrictions of the three- and four-phonon phase spaces. The ${\kappa }_{\mathrm{L}}$ of AgI calculated using MD phonon lifetimes including full-order lattice anharmonicity shows a better agreement with experiments.

In this study, we investigate the finite-temperature properties of the spin-1/2 $J_1-J_2$ Heisenberg model on the kagome lattice using the orthogonalized finite-temperature Lanczos method. Under a zero magnetic field, the specific heat exhibits a double-peak structure, as $|J_2|$ increases. Additionally, at approximately $J_2=0$, the magnetic entropy remains finite, even at low temperatures. The finite-temperature magnetization curve reveals the asymmetric melting behavior of the 1/3 plateau around $J_2=0$. As $|J_2|$ increases, the 1/3 plateau becomes more stable, exhibiting symmetric melting behavior. Specifically, for $J_2>0$, the $\mathbf{Q}=\mathbf{0}$ up-up-down structure is stabilized, whereas for $J_2<0$, the $\sqrt{3}\times \sqrt{3}$ up-up-down structure is stabilized.

The Kitaev honeycomb model, which is exactly solvable by virtue of an extensive number of conserved quantities, supports a gapless quantum spin liquid phase as well as gapped descendants relevant for fault-tolerant quantum computation. We show that the anomalous edge modes of one-dimensional (1D) cluster-state-like symmetry-protected topological (SPT) phases provide natural building blocks for a variant of the Kitaev model that enjoys only a subextensive number of conserved quantities. The symmetry of our variant allows a single additional nearest-neighbor perturbation, corresponding to an anisotropic version of the $\mathrm{\Gamma }$ term studied in the context of Kitaev materials. We determine the phase diagram of the model using exact diagonalization. Additionally, we use the density matrix renormalization group to show that the underlying 1D SPT building blocks can emerge from a ladder Hamiltonian exhibiting only two-spin interactions supplemented by a Zeeman field. Our approach may provide a pathway toward realizing Kitaev honeycomb spin liquids in spin-orbit-coupled Mott insulators.

As the in-plane magnetized counterparts of skyrmions in two dimensions, magnetic bimerons are swirling topological spin textures consisting of two merons. Here we theoretically and numerically investigate the dynamics of a bimeron induced by the monochromatic spin wave in a ferromagnetic thin film. The micromagnetic simulation results reveal that unlike the ferromagnetic skyrmion reported in previous studies, the bimeron can be pushed away from (or pulled towards) the wave source at the low (high) spin wave frequency. These numerical results are in line with the particle collision model formulating the interplay between the spin wave and magnetic bimeron. Our findings provide guidelines for constructing future bimeron-based spintronic devices with ultralow energy consumption.

Inspired by recent advances in the fabrication of surface superlattices, and in particular the triangular lattice made of tin (Sn) atoms on silicon, we study an extended Hubbard model on a triangular lattice. The observations of magnetism in these systems justify the inclusion of a strong on-site repulsion, and the observation of superconductivity suggests including an effective, nearest-neighbor attractive interaction. The attractive interaction mimics the effect of strong on-site repulsion near half filling, which can be seen in strong-coupling vertex calculations such as the Eliashberg method. With this extended Hubbard model on a triangular lattice with its geometrical frustration, we find a rich phase diagram of various magnetic orders and pairing functions, within the framework of self-consistent mean field theory. We uncover the competition between magnetism and unconventional superconductivity, and their coexistence for triplet pairings. We follow the Fermi surface of the system as the system is doped away from half filling and find nesting vectors and a Lifshitz transition, which provide an intuitive understanding of the phase transitions between the many orders we consider.

The lack of superconductivity in the family of materials $A{B}_2{\mathrm{As}}_2$ $(A=\mathrm{Sr},\mathrm{Ba}$ and $B=\mathrm{Cr},\mathrm{Mn})$ under doping or pressure is an intriguing issue, considering the resemblance of these materials to their cousin materials and superconductors $(\mathrm{Ba},\mathrm{Sr}){\mathrm{Fe}}_2{\mathrm{As}}_2$. In this context, the suppression of magnetism together with the presence of electron and hole pockets in the Brillouin zone seem to be fundamental ingredients to explain superconductivity. In this paper, we report a tetragonal to collapsed-tetragonal phase transition in ${\mathrm{SrCr}}_2{\mathrm{As}}_2$ under high pressure with the appearance of hole and electron pockets in the Brillouin zone. In this collapsed-tetragonal phase, a residual local magnetic moment in the Cr-ion site and a finite global magnetic energy are derived. This scenario would suggest why superconductivity is prevented in this compound. Our observations were obtained from the analysis of synchrotron x-ray diffraction measurements of polycrystalline samples of ${\mathrm{SrCr}}_2{\mathrm{As}}_2$, and using first-principles simulations, under pressures $P$ in the range $1.4 \mathrm{GPa}<P<20 \mathrm{GPa}$ at room temperature.

$\mathrm{NaOs}{\mathrm{O}}_3$ exhibits an unusual metal-insulator transition (MIT) that has been touted as Slater type, though there are observations that do not entirely conform to this typing. Consistent with a Slater transition, the cell volume and crystal symmetry show no change on cooling through the transition, but both $a$ and $b$ axes in this $Pbnm$ orthorhombic perovskite show a clear kink, and the splitting between them enlarges slightly. Since atomic positions, determined by fitting the intensity of state-of-the-art neutron diffraction data, exhibit no anomalies within the measurement uncertainty, the origin of the $a\text{−}b$ splitting and the kink in the data have not yet been elucidated. Understanding the origin of these subtle structural changes across the transition temperature may provide understanding about the electronic behavior. In this paper, we connect local structural changes to changes in the lattice parameters through (1) well-established structural modeling and (2) density functional theory (DFT) calculations. This approach successfully reveals a subtle but significant change of the O-Os-O bond angle on cooling through $T_{\mathrm{MIT}}$. A Madelung energy calculation suggests that this bond angle change signals electron localization in the $t_{2g}$ orbital complex, and this is verified by DFT, which shows an electronic transition from itinerant to localized electronic behavior along with the bond angle shift. In this detailed structural study, we add an important though heretofore overlooked element in the microscopic picture of the MIT in $\mathrm{NaOs}{\mathrm{O}}_3$.

The electronic band structure can change with temperature in Mott and Kondo insulators, even without a phase transition. Here, to clarify the underlying mechanism, the spectral function at nonzero temperature is studied. By considering the selection rules, the spin excited states of Mott and Kondo insulators, whose excitation energies are lower than the charge gap, are shown to emerge in the electronic spectral function at nonzero temperature, exhibiting momentum-shifted magnetic dispersion relations from the band edges, as in the case of the doping-driven Mott transition at zero temperature. Based on this characteristic, we interpret the numerical results for the temperature-driven change in the band structure in the one- and two-dimensional Hubbard models, Hubbard ladder, and one-dimensional periodic Anderson model at half-filling obtained using the cluster perturbation theory with the low-temperature Lanczos method. This characteristic also explains why the band structures of Mott and Kondo insulators can change with temperature even in the energy regime far higher than the temperature and why spectral weights emerge in the energy regime within the band gap, where the excitation energies are lower than the lowest electronic excitation energy from the ground state. Furthermore, if the bandwidth of the spin excitation is comparable to the electronic band gap, the emergent electronic modes can cross the Fermi level and gain spectral weight as the temperature increases, which leads to an insulator-metal crossover. These features are primarily caused by the spin excited states that are transparent in electronic measurements at zero temperature, in contrast to the conventional view where thermal effects on electron-added states, electron-removed states, and static spin correlations are considered to mainly affect the band structure. This innovative perspective provides a different understanding from the conventional view on the electronic states at nonzero temperatures.

We study the spin-orbit proximity effects in a hybrid heterostructure built from a one-dimensional (1D) armchair carbon nanotube and two-dimensional (2D) buckled monolayer bismuthene. We show, by performing first-principles calculations, that Dirac electrons in the nanotube exhibit large spin-orbit coupling due to the close vicinity of bismuthene. The calculated low-energy band structure and the spin texture of the proximitized nanotube display a strong dependence on the position of the nanotube on the substrate, similar to the twist-angle dependence found in 2D heterostructures. Based on the first-principles results, we formulate an effective low-energy Hamiltonian of the nanotube, and we identify key interactions governing the proximity spin-orbit coupling. The proximity-induced spin splitting of Dirac cone bands is in the meV range, confirming an efficient transfer of spin-orbit coupling from bismuthene to the nanotube.

In this paper, we report on the thermal conductivity of ${\mathrm{RbV}}_3{\mathrm{Sb}}_5$ and ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ with three-dimensional charge density wave phase transitions from 40 to 500 K measured by pump-probe thermoreflectance techniques. At room temperature, the in-plane (basal plane) thermal conductivities are found to be moderate, with $12\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ of ${\mathrm{RbV}}_3{\mathrm{Sb}}_5$ and $8.8\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$, and ultralow cross-plane (stacking direction) thermal conductivities are observed, with $0.72\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ of ${\mathrm{RbV}}_3{\mathrm{Sb}}_5$ and $0.49\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$. A unique glasslike temperature dependence in the cross-plane thermal conductivity is observed, which decreases monotonically even lower than the Cahill-Pohl limit as the temperature decreases below the phase transition point $T_{\mathrm{CDW}}$. This temperature dependence is found to obey the hopping transport picture. In addition, a peak in cross-plane thermal conductivity is observed at $T_{\mathrm{CDW}}$ as a fingerprint of the modulated structural distortion along the stacking direction.

We study the response of spin and charge order in single crystals of ${\mathrm{La}}_{1.875}{\mathrm{Ba}}_{0.125}{\mathrm{CuO}}_4$ to uniaxial stress through ${}^{139}\mathrm{La}$ nuclear magnetic resonance and ${}^{63}\mathrm{Cu}$ nuclear quadrupole resonance, respectively. In unstressed ${\mathrm{La}}_{1.875}{\mathrm{Ba}}_{0.125}{\mathrm{CuO}}_4$, the low-temperature tetragonal structure sets in below $T_{\text{LTT}}=57\mathrm{K}$, while the charge order and the spin order transition temperatures are $T_{\text{CO}}=54\mathrm{K}$ and $T_{\text{SO}}=37\mathrm{K}$, respectively. We find that uniaxial stress along the [110] lattice direction strongly suppresses $T_{\text{CO}}$ and $T_{\text{SO}}$, but has little effect on $T_{\text{LTT}}$. In other words, under stress along [110] a large splitting ($\approx 21\mathrm{K}$) opens between $T_{\text{CO}}$ and $T_{\text{LTT}}$, showing that these transitions are not tightly linked. On the other hand, stress along [100] causes a slight suppression of $T_{\text{LTT}}$ but has essentially no effect on $T_{\text{CO}}$ and $T_{\text{SO}}$. Magnetic field $H$ along [110] stabilizes the spin order: the suppression of $T_{\text{SO}}$ under stress along [110] is slower under $H\parallel \left[110\right]$ than $H\parallel \left[001\right]$. We develop a Landau free-energy model, and we interpret our findings as an interplay of symmetry-breaking terms driven by the orientation of spins.

Quantum corrals represent an intriguing class of confining nanostructures engineered through tip manipulation of individual adsorbed species at surfaces and have contributed significantly towards our fundamental understanding of several quantum phenomena including quantum mirage and Kondo physics. Despite their maturity and ongoing research interest, the nature of adatom scattering/confining potentials including the question whether they represent potential barriers or wells remains elusive. Here we address this issue utilizing the electron plane-wave expansion and boundary element methods for several adatom-based quantum corrals and superlattices. We show that the experimentally reported modulation in the local density of states (LDOS) at the corral center can be equally well reproduced irrespective of the sign of adatom potential. The knowledge of the sign requires access to LDOS at/nearby adatoms, where bound states, so far undetected experimentally for corrals, should show up solely for negative adatom potential. Next we show that by arranging the adatoms into superlattices, the sign of the scattering potential can be undoubtedly identified without the quest for bound-state measurements. Our results agree with the experimentally fabricated Ce superlattice showing a clear signature of Ce adatoms acting as scattering potential wells. This unambiguous assignment of the potential sign is brought by the distinct band structures developed on coupling which lead into sign-dependent LDOS features. These findings are of fundamental and practical importance for the development of quantum designer artificial superlattices with tailored electronic structures.

The van der Waals layered ferroelectric ${\mathrm{CuInP}}_2{\mathrm{S}}_6$ has been found to exhibit a variety of intriguing properties arising from the fact that the Cu ions are unusually mobile in this system. While the polarization switching mechanism is usually understood to arise from Cu ion motion within the monolayers, a second switching path involving Cu motion across the van der Waals gaps has been suggested. In this work, we perform zero-temperature first-principles calculations on such switching paths, focusing on two types that preserve the periodicity of the primitive unit cell: “cooperative” paths preserving the system's glide mirror symmetry, and “sequential” paths in which the two Cu ions in the unit cell move independently of each other. We find that ${\mathrm{CuInP}}_2{\mathrm{S}}_6$ features a rich and varied energy landscape, and that sequential paths are clearly favored energetically both for cross-gap and through-layer paths. Importantly, these segments can be assembled to comprise a globally insulating cycle with the out-of-plane polarization evolving by a quantum as the Cu ions shift to neighboring layers. In this sense, we argue that ${\mathrm{CuInP}}_2{\mathrm{S}}_6$ embodies the physics of a quantized adiabatic charge pump.