${\mathrm{ScF}}_3$ has attracted much attention because of its simple crystal structure and negative thermal expansion (NTE) over a wide temperature range. No other binary trifluoride has the same crystal structure and exhibits NTE in as wide a temperature range as ${\mathrm{ScF}}_3$. There has hitherto been no sufficient explanation for this fact. Herein, to discuss the phase stability and the NTE behavior of ${\mathrm{ScF}}_3$, the six binary trifluorides $B{\mathrm{F}}_3$ ($B$ = Sc, Y, La, Al, Ga, In) are thoroughly compared by using $abinitio$ molecular-dynamics calculations with the on-the-fly machine-learning technique, first-principles lattice-dynamics calculations, and electronic-structure analyses based on group-representation theory and the band-unfolding method. The present study reveals that (i) the $a^{-}{a}^{-}{a}^{-}$ octahedral rotational distortion (ORD) in ${\mathrm{ScF}}_3$ increases the frequency of the crucial phonons for realizing NTE, leading to a weakening of the NTE behavior under hydrostatic pressure; (ii) the group-representation theory predicts the emergence of ORDs triggered by the second-order Jahn-Teller effect in cubic ${\mathrm{ScF}}_3, {\mathrm{YF}}_3, {\mathrm{AlF}}_3, {\mathrm{GaF}}_3$, and ${\mathrm{InF}}_3$; (iii) cubic ${\mathrm{ScF}}_3$ and ${\mathrm{YF}}_3$ do not possess ORD without pressure due to their slight orbital overlap between the cations and anions; (iv) ${\mathrm{ScF}}_3$ has a delicate balance between the repulsive force term and the energy stabilization term, induced by the octahedral rotational phonon modes; and (v) metastable cubic ${\mathrm{YF}}_3$ and ${\mathrm{LaF}}_3$ exhibit NTE behaviors. Our findings would provide an understanding of a material-design principle for realizing NTE.

We theoretically investigate the tunneling transport in a repulsively interacting ultracold Bose-Fermi mixture. A two-terminal model is applied to such a mixture, and the supersymmetry-like tunneling current through the junction can be induced by the bias of the fermion chemical potential between two reservoirs. The goldstino, which is the Nambu-Goldstone fermionic mode associated with the spontaneous sypersymmetry breaking and appears as a gapped mode in the presence of the explicit supersymmetry breaking in existing Bose-Fermi mixtures, is found to contribute to the tunneling transport as a supercharge exchanging process. Our study provides a potential way to detect the goldstino transport in cold atom experiments.

${\text{La}}_5{\text{Co}}_2{\text{Ge}}_3$ is an itinerant ferromagnet with a Curie temperature $T_C$ of $\sim 3.8\mathrm{K}$ and a remarkably small saturated moment of $0.1{\mu }_B/\text{Co}$. Here we present the growth and characterization of single crystals of the ${\text{La}}_5{\text{(Co}}_{1-x}{\text{Ni}}_x{)}_2{\text{Ge}}_3$ series for 0.00 $\le x\le 0.186$. We measured powder x-ray diffraction, composition as well as anisotropic temperature-dependent resistivity, temperature and field-dependent magnetization along with heat capacity on these single crystals. We also measured muon-spin rotation/relaxation $\left(\mu \text{SR}\right)$ for some Ni substitutions $(x=0.027,0.036,0.074)$ to study the evolution of internal field with Ni substitution. Using the measured data we infer a low temperature, transition temperature-composition phase diagram for ${\text{La}}_5{\text{(Co}}_{1-x}{\text{Ni}}_x{)}_2{\text{Ge}}_3$. We find that $T_C$ is suppressed for low dopings, $x\le 0.014$; whereas for $0.036\le x\le 0.186$, the samples are antiferromagnetic with a Néel temperature $T_N$ that goes through a weak and shallow maximum ($T_N\sim 3.4\mathrm{K}$ for $x\sim 0.07$) and then gradually decreases to 2.4 K by $x=0.186$. For intermediate Ni substitutions, $0.016\le x\le 0.027$, two transition temperatures are inferred with $T_N>T_C$. Whereas the $T\text{–}x$ phase diagram for ${\text{La}}_5{\text{(Co}}_{1-x}{\text{Ni}}_x{)}_2{\text{Ge}}_3$ and the $T\text{–}p$ phase diagram determined for the parent ${\text{La}}_5{\text{Co}}_2{\text{Ge}}_3$ under hydrostatic pressure are grossly similar, changing from a low-doping or low-pressure ferromagnetic (FM) ground state to a high-doped or high-pressure antiferromagnetic (AFM) state, perturbation by Ni substitution enabled us to identify an intermediate doping regime where both FM and AFM transitions occur.

We consider electronic spectra of carbon nanotubes and their perturbation by impurity atoms absorbed at different positions on nanotube surfaces, within the framework of the Anderson hybrid model. Special attention is given to the cases in which Dirac-like 1D modes appear in the nanotube spectrum and their hybridization with localized impurity states produces, at growing impurity concentration $c$, onset of a mobility gap near the impurity level and even opening, at yet higher $c$, of some narrow delocalized range within this mobility gap. Such behaviors are compared with similar effects in the previously studied 2D graphene and armchair-type graphene nanoribbons. Some possible practical applications are discussed.

We systematically investigate the correlations between exciton binding energies and various easily calculated ground-state properties (“predictors”) that have been proposed to correlate with them. We do so for 51 bulk compounds, ranging from simple binary semiconductors to more exotic materials such as noble gas solids, perovskites, and layered systems and show that using only a few easily calculable parameters, a broadly applicable clustering of materials according to their exciton binding energies is possible. While no single one of the proposed parameters satisfactorily predicts the exciton binding energy, a combination of several parameters that enter the Wannier-Mott model or characterize the nature of the valence band and the ionicity of the compound allows a reliable automated clustering of exciton binding energies. The results allow an efficient estimation of the importance of excitonic effects without the need for expensive many-body perturbation theory calculations or other advanced numerically demanding ab initio approaches.

Heterostructures of magnetic topological insulators (MTIs) and superconductors (SCs) in two-dimensional (2D) slab and one-dimensional (1D) nanoribbon geometries have been predicted to host, respectively, chiral Majorana edge states (CMESs) and Majorana bound states (MBSs). We study the topological properties of such MTI/SC heterostructures upon variation of the geometry from wide slabs to quasi-1D nanoribbon systems and as a function of the chemical potential, the magnetic doping, and the induced superconducting pairing potential. To do so, we construct effective symmetry-constrained low-energy Hamiltonians accounting for the real-space confinement. For a nanoribbon geometry with finite width and length, we observe different phases characterized by CMESs, MBSs, as well as coexisting CMESs and MBSs, as the chemical potential, the magnetic doping, and/or the width are varied.

Fractonic matter can undergo unconventional phase transitions driven by the condensation of particles that move along subdimensional manifolds. We propose that this type of quantum critical point can be realized in a bilayer of crossed Rydberg chains. This system exhibits a transition between a disordered phase and a charge-density-wave phase with subextensive ground-state degeneracy. We show that this transition is described by a stack of critical Ising conformal field theories which become decoupled in the low-energy limit. We also analyze the transition using a Majorana mean-field approach for an effective lattice model, which confirms the picture of a fixed point of decoupled critical chains. We discuss the unusual scaling properties and derive anisotropic correlators that provide signatures of subdimensional criticality in this realistic setup.

The interaction between electromagnetic fields and optical phonons in two-dimensional (2D) van der Waals (vdW) materials such as $\alpha \text{−}\mathrm{Mo}{\mathrm{O}}_3$ produces a strong phonon-polariton effect within the midinfrared to terahertz frequency range. This phonon-polariton effect is highly anisotropic in nature because of the in-plane anisotropic lattice vibration of $\alpha \text{−}\mathrm{Mo}{\mathrm{O}}_3$, which needs to be explored. In this paper, we have successfully synthesized cm-scale high-quality $\alpha \text{−}\mathrm{Mo}{\mathrm{O}}_3$ crystals using the physical vapor deposition technique. Using helicity-resolved Raman spectroscopy, we have investigated the chiral phonon modes in $\alpha \text{−}\mathrm{Mo}{\mathrm{O}}_3$ by varying flake thicknesses as well as a fast-hand distinction between the $A_g$ and $B_{1g}$ modes in different flake thicknesses exfoliated from the parent crystal. Our findings indicate the existence of chiral phonons in $\alpha \text{−}\mathrm{Mo}{\mathrm{O}}_3$ and their strong dependency of chirality over the thickness of the flakes. Additionally, our analysis reveals strong in-plane anisotropy in as-grown $\alpha \text{−}\mathrm{Mo}{\mathrm{O}}_3$, which is confirmed through angle-resolved Raman spectroscopy, and the degree of anisotropy is estimated quantitatively with respect to the thickness of the $\alpha \text{−}\mathrm{Mo}{\mathrm{O}}_3$ flake. It is observed that the anisotropy ratio is different for different Raman modes. However, the variation of the anisotropy ratio for a particular mode is strongly dependent on the thickness of $\alpha \text{−}\mathrm{Mo}{\mathrm{O}}_3$. Furthermore, two sets of $A_g$ modes were observed in $\alpha \text{−}\mathrm{Mo}{\mathrm{O}}_3$ through the Raman optical activity measurements. One set of $A_g$ modes is oriented along the $a$ axis and another set along the $b$ axis. In this study of chiral phonon modes and the corresponding anisotropy along the in-plane direction, we provide valuable insights into the design of polarization-sensitive photonic devices.

We theoretically investigate the effect of anisotropy on electron diffraction in two-dimensional (2D) systems. The calculations are performed by means of both analytical semiclassical and microscopic tight-binding approaches, with the anisotropy being introduced by assuming direction-dependent effective masses and hoppings, respectively. Single and double slits with different orientations with respect to the anisotropy axis are considered. Using these models, we obtain analytical expressions for the wave function and numerical results for the probability current density for both investigated cases. In addition, we specify the conditions under which there is constructive or destructive interference in the interference pattern in the double-slit case. The results show that anisotropy can lead to a collimation effect, as well as a steering of the diffracted electronic beam, which may, in turn, allow the control of the charge carriers' propagation to be used in nanoelectronic devices based on anisotropic 2D media systems.

In this work, we employ the quantum perturbation theory to investigate the photoinduced currents in graphene quantum dots (GQDs). We find that under the radiation of circularly polarized light (CPL), two types of currents may exist. One is dynamic and oscillates along the electric field of light; the other is quasisteady, rotating around certain centers in the GQD. The rotational currents can generate a magnetic moment, an effect known as the inverse Faraday effect. We develop a tight-binding-based perturbation theory to describe these intriguing and novel currents in GQDs. We also analytically analyze the oscillation direction of the dynamic currents and the transfer mechanism of angular momentum in this process. We find in some nondegenerate cases the rotational photoinduced currents disappear due to symmetry breaking in the system, and the transferred angular momentum is converted into lattice chiral vibration. This research reveals the current distributions and angular momentum exchange in excited GQD systems and suggests potential applications in ultrafast magnetic memory and photodetector devices.

Surface melting of solidified hydrogen has attracted attention in the field of superfluidity, but the existence of surface melting of solid hydrogen itself is still controversial. In the present study, we developed cryogenic time-of-flight secondary ion mass spectrometry (TOF-SIMS) capable of detecting surface melting by selectively analyzing hydrogen on the outermost surface. Combined with low-energy ion scattering for well-defined film growth, we successfully investigated the surface structural transition of the quenched condensed hydrogen film grown on polycrystalline tungsten substrate below the triple point. It was found that the TOF-SIMS intensity variation of ${\mathrm{H}}^{+}$ ions by increasing the temperature of the solid hydrogen film at a constant ramp rate (temperature-programmed TOF-SIMS) shows two prominent features: the increase accompanied by sublimation, and the decrease due to the elimination of the hydrogen admolecule from the tungsten surface. Both features are well explained by the desorption of hydrogen molecules from the solid surface. We observed no evidence of surface melting.

The prototypical antiferroelectric perovskite ${\mathrm{PbZrO}}_3$ (PZO) has garnered considerable attention in recent years due to its significance in technological applications and fundamental research. Many unresolved issues in PZO are associated with large length- and time-scales, as well as finite temperatures, presenting significant challenges for first-principles density functional theory studies. Here, we introduce a deep-learnining interatomic potential of PZO, enabling investigation of finite-temperature properties through large-scale atomistic simulations. Trained using an elaborately designed dataset, the model successfully reproduces a large number of phases, in particular, the recently discovered 80-atom antiferroelectric $Pnam$ phase and ferrielectric $Ima2$ phase, providing precise predictions for their structural and dynamical properties. Using this model, we investigated phase transitions of multiple phases, including $Pbam\text{/}Pnam, Ima2$, and $R3c$, which show high similarity to the experimental observation. Our simulation results also highlight the crucial role of free energy in determining the low-temperature phase of PZO, reconciling the apparent contradiction: $Pbam$ is the most commonly observed phase in experiments, while theoretical calculations predict other phases exhibiting even lower energy. Furthermore, in the temperature range where the $Pbam$ phase is thermodynamically stable, typical double polarization hysteresis loops for antiferroelectrics were obtained, along with a detailed elucidation of the structural evolution during the electric-field induced transitions between the nonpolar $Pbam$ and polar $R3c$ phases.

The presence of competing interactions arising from geometry leads to frustration in quantum spin models. As a consequence, the ground state of such systems often displays a large degeneracy that can be lifted by thermal or quantum effects. One such example is the antiferromagnetic Ising model on the kagome lattice. It was shown that while the same model on the triangular lattice is ordered at zero temperature for small transverse field as a result of an order by disorder mechanism, the kagome lattice resists any such effects and exhibits only short range spin correlations and a trivial paramagnetic phase. We embed this model on the latest architecture of D-Wave's quantum annealer, the Advantage2 prototype, which uses the highly connected Zephyr graph. Using advanced embedding and calibration techniques, we are able to embed a kagome lattice with mixed open and periodic boundary conditions of 231 sites on the full graph of the currently available prototype. Through forward annealing experiments, we show that under a finite longitudinal field the system exhibits a one-third magnetization plateau, consistent with a classical spin liquid state of reduced entropy. An anneal-pause-quench protocol is then used to extract an experimental ensemble of states resulting from the equilibration of the model at finite transverse and longitudinal field. This allows us to construct a partial phase diagram and confirm that the system exits the constrained Hilbert space of the classical spin liquid when subjected to a transverse field. We connect our results to previous theoretical results and quantum Monte Carlo simulation, which helps us confirm the validity of the quantum simulation realized here. With these results, we are able to provide an understanding into the nature of the phase diagram of this model while extracting insight into the performance of the D-Wave quantum annealer to simulate nontrivial quantum systems in equilibrium.

Reentrant glassy systems are a class of disordered magnetic materials which can potentially host noncollinear spin state. Here, we focus on the role of site disorder on emergence of reentrant cluster glass state and the underlying mechanism for observation of anomalies in electrical transport properties of $\mathrm{T}{\mathrm{i}}_2\mathrm{FeAl}$. Structural and magnetic studies of $\mathrm{T}{\mathrm{i}}_2\mathrm{FeAl}$ (under our synthesis protocol) reveal that it hosts strong site disorder resulting in development of a reentrant cluster glass state (below10 K) along with a ferromagnetic ordering (around 30 K). Electrical resistivity in this alloy mimics a Kondo-like behavior along with the presence of weak localization effect at low temperatures. Remarkably, Hall resistivity measurements in glassy regime indicate a nontrivial, unconventional contribution which is attributed to the existence of noncollinear spin state. We believe that our study offers an ideal platform to understand the influence of disorder on magnetic ground state of such ternary alloys.

Relativistic forward scattering of electrons at finite temperature involves the incoherent superposition of diffraction patterns formed by different snapshots of thermal atomic displacements. In experiments, thermal vibrations lead to thermal diffuse scattering (TDS), partly dominating diffraction patterns of thick specimens. This study sheds light on the effects of TDS on solutions to the inverse scattering problem using combined real- and diffraction-space information acquired in a scanning transmission electron microscope (STEM) to retrieve the object's phase. Using frozen phonon multislice within the Einstein approximation, realistic ground truth data of 20-nm-thick ${\mathrm{SrTiO}}_3$ is generated and subjected to contemporary inverse multislice schemes to retrieve the projected Coulomb potential slicewise. We first classify phase retrieval algorithms as to their assumptions on periodicity along the incident beam direction, as well as pixelwise and parametrized reconstruction methods. It is found that pixelwise object reconstructions are capable of retrieving structural details qualitatively while being prone to contain TDS-related artifacts which can result in unphysical potentials. For pixelwise reconstructions of multiple independent specimen slices, we observe that the origin of TDS, i.e., thermal atomic displacements, starts to emerge naturally. However, the quantitative assessment tends to too small mean squared thermal displacements, also when reconstructing multiple object modes. Using an atomistically parametrized inversion strategy which exploits the explicit separation of thermal vibrations and potentials, temperature and chemistry of the specimen can be retrieved quantitatively with high accuracy.

We study the spread complexity in two-mode Bose-Einstein condensates and unveil that the long-time average of the spread complexity ${\overline{C}}_K$ can probe the dynamical transition from self-trapping to Josephson oscillation. When the parameter $\omega$ increases over a critical value ${\omega }_c$, we reveal that the spread complexity exhibits a sharp transition from lower to higher value, with the corresponding phase space trajectory changing from self-trapping to Josephson oscillation. Moreover, we scrutinize the eigenspectrum and uncover the relation between the dynamical transition and the excited state quantum phase transition, which is characterized by the emergence of singularity in the density of states at critical energy $E_c$. In the thermodynamical limit, the cross point $E_c\left(\omega \right)$ and the initial energy $E_0\left(\omega \right)$ determine the dynamical transition point ${\omega }_c$. Furthermore, we show that the different dynamical behavior for the initial state at a fixed point can be distinguished by the long-time average of the spread complexity, when the fixed point changes from unstable to stable. Finally, we also examine the sensitivity of ${\overline{C}}_K$ for the triple-well bosonic model which exhibits the transition from chaotic dynamics to regular dynamics.