Aluminum is an important component in many consumer goods, such as automobiles. Ore refinement and the production of end products incurs a significant energy cost. An alternative is to leverage liquid metal embrittlement (LME); here, a liquid metal alloys with a solid matrix to form a brittle alloy. By outlining the desired shape, LME can produce low-cost machined parts and take advantage of recycled stock. A famous example is the LME of aluminum via gallium. An issue that arises is the formation of aluminum oxide $\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$, either as a passivation layer or along the aluminum grain boundaries. It is not clear from the existing literature how this oxide layer would impact the LME through the application of gallium. In the current study, we examine the defect formation energies of gallium in $\alpha \text{−}{\mathrm{Al}}_2{\mathrm{O}}_3$ and its diffusion barriers as a function of gallium charge state. We find that while gallium in the $+3$ charge state is thermodynamically favored to insert into $\alpha \text{−}{\mathrm{Al}}_2{\mathrm{O}}_3$, there exists a high diffusion barrier that prevents it from traveling through the ${\mathrm{Al}}_2{\mathrm{O}}_3$ matrix.

Electron-vibration interactions in current-carrying nanodevices have been known to induce local heating and nonthermal vibration statistics simultaneously, while theoretical studies so far focus solely on one of them. Based on the quantum master equation, we study vibrationally inelastic electron transport in a double quantum dot device and find that the vibration bunching can be selectively excited for efficient charge and spin transport where the heat generation is inhibited. By introducing the nonequilibrium free energy, the extractable work under a thermal operation from nonthermal vibrations is clearly characterized and quantified. A spin transport channel with large work extraction while maintaining small heat generation rate is found. Furthermore, the extractable work is considerably enhanced by the vibration lasing transition. Our work reveals the relation between current-induced local heating and nonthermal vibration statistics and effects on extractable work, with the aim to control the distribution, storage, and conversion of the heat in nanodevices.

Motivated by the recent observations of electronic correlation effect M. Corasaniti et al. [Phys. Rev. B 104, L121112 (2021).] and topology-stabilized magnetic fluctuations N. C. drucker et al. [Nat. Commun. 14, 5182 (2023).] in the noncentrosymmetric magnetic Weyl semimetal candidate CeAlGe, we performed systematic studies on the local static and dynamic spin susceptibilities by ${}^{27}\mathrm{Al}$ nuclear magnetic resonance. Due to the large spin susceptibility from Ce-$4f$ electrons, the theoretically predicted responses from Weyl fermions are overwhelmed. A Knight-shift anomaly is observed below $T^{*}\sim 50$ K, a signature of the onset of coherent Kondo coupling. In addition, an anomalous peak is found in $1/T_{1}T$ near 15 K, well above the magnetic ordering temperature $T_N\approx 5$ K, which is probably a consequence of topology-stabilized magnetic fluctuations. These results highlight the interplay among electronic correlation, magnetism, and band topology in this family of Kondo Weyl semimetals.

The quantum many-body problem is an important topic in condensed matter physics. To efficiently solve the problem, several methods have been developed to improve the representation ability of wave functions. For the Fermi-Hubbard model under periodic boundary conditions, current state-of-the-art methods are neural network backflows and the hidden fermion Slater determinant. The backflow correction is an efficient way to improve the Slater determinant of free particles. In this work we propose a tensor representation of the backflow-corrected wave function; we show that for the spinless $t\text{−}V$ model, the energy precision is competitive or even lower than current state-of-the-art fermionic tensor network methods. For models with spin, we further improve the representation ability by considering backflows on fictitious particles with different spins, thus naturally introducing nonzero backflow corrections when the orbital and the particle have opposite spins. We benchmark our method on molecules in the STO-3G basis and the Fermi-Hubbard model with periodic and cylindrical boundary conditions. We show that the tensor representation of backflow corrections achieves competitive or even lower-energy results than current state-of-the-art neural network methods.

Metal-cluster compounds have recently attracted attention in the quest for novel low-dimensional multifunctional semiconductors owing to the structural diversity of metal-cluster geometries and the resulting broken symmetries. Based on first-principles calculations, we proposed a one-dimensional (1D) metal-cluster family of $X_4{\mathrm{OTe}}_9{\mathrm{I}}_4$ ($X$ = Nb, Ti) nanowires with high stability. Due to differences in the number of valence electrons of the metal atoms (Nb and Ti), these two nanowires exhibit distinct chain structures and physical properties. Our calculations revealed that ${\mathrm{Nb}}_4{\mathrm{OTe}}_9{\mathrm{I}}_4$ and ${\mathrm{Ti}}_4{\mathrm{OTe}}_9{\mathrm{I}}_4$ nanowires were direct- and indirect-band-gap semiconductors with moderate gaps of 1.32 and 1.25 eV, respectively. The off-center displacement of Nb ions in the optimized ${\mathrm{Nb}}_4{\mathrm{OTe}}_9{\mathrm{I}}_4$ nanowire induced intrinsic chain-direction ferroelectric ordering, whereas the ${\mathrm{Ti}}_4{\mathrm{OTe}}_9{\mathrm{I}}_4$ nanowire with a similar chain structure maintained a stable nonferroelectric structure. The structural evolution of the two nanowires under the tensile strain displayed different behaviors. When the tensile strain was applied, the ${\mathrm{Nb}}_4{\mathrm{OTe}}_9{\mathrm{I}}_4$ nanowire tended to shrink toward the cluster structure to stabilize the polar structure and produce the unexpected force release, whereas ${\mathrm{Ti}}_4{\mathrm{OTe}}_9{\mathrm{I}}_4$ nanowire was uniformly stretched before fracture. In addition, tunable magnetism was introduced into these two nonmagnetic 1D systems using carrier doping and alloying methods. On the one hand, the alloying process regulated the band gap of the material; on the other hand, it altered the spin-electronic properties of the system. Our calculations indicate that $X_4{\mathrm{OTe}}_9{\mathrm{I}}_4$ ($X=\mathrm{Nb}$, Ti) nanowires serve as representative 1D multifunctional materials, which are crucial for studying the structure-determined properties of low-dimensional materials.

Ferroelectric-dielectric superlattices have attracted renewed interest for their ability to frustrate the polar order, leading to the emergence of exotic polar textures. The electrostatic depolarization, thought to be responsible for the complex polar textures in these superlattices, can be alleviated by replacing the dielectric layer with a metallic one. One would thus expect that a close to uniform polarization state be recovered in the ferroelectric layer. However, here we show, using density-functional theory calculations, that metastable antipolar motions may still appear in superlattices combining multiferroic ${\mathrm{BiFeO}}_3$ and metallic ${\mathrm{SrRuO}}_3$ perovskite layers. We find that a complex oxygen octahedra tilt order, a so-called nanotwin phase, exists in ${\mathrm{BiFeO}}_3/{\mathrm{SrRuO}}_3$ superlattices and competes with a more conventional phase. It leads to a doubling of the chemical period along the out-of-plane direction, owing to the presence of an oxygen octahedra tilt-wave pattern and antipolar motions caused by trilinear energy couplings. We also show that out-of-plane polar displacements in the ${\mathrm{BiFeO}}_3$ layer may reverse the (anti)polar displacements thanks to a strong quadrilinear coupling term. The oxygen tilt-driven couplings identified here may open new ways to engineer and control polar displacements in superlattice-based polar metals and hybrid improper (anti)ferroelectrics.

Since the advent of time-reversal-invariant topological insulators, the generalization of topology concepts has led to the discovery of a wide range of topological states. These topological states may undergo topological phase transitions (TPTs) accompanied by discontinuous changes in topological invariants. In this Letter, by combining time- and angle-resolved photoemission spectroscopy measurements with first-principles calculations, we have demonstrated the existence of distinct TPTs in the unoccupied states above the Fermi level in the ${\mathit{M}}_2{\mathrm{Te}}_2\mathrm{P}$ ($M=\text{Ti}$, Zr, or Hf) family. These TPTs arise from the inversion of the transition metal $d$ and Te $p$ orbitals due to the enhancement of spin-orbit coupling and variation in crystal fields, as the transition metal changes from $3d$ to $4d$ and then to $5d$. Eventually, dual topological states are achieved in the $5d$ system ${\mathrm{Hf}}_2{\mathrm{Te}}_2\mathrm{P}$, where a type-III Dirac semimetal state coexists with a strong topological insulator state. Finally, we reveal a rapid relaxation process in the nonequilibrium population of the Dirac surface state due to the presence of an additional interband scattering channel in the bulk.

We propose that a large and tunable valley-selective Hall effect can be realized in a centrosymmetric system via light-induced breaking of inversion and time-reversal symmetries. This is demonstrated in graphene driven by bicircularly polarized light, which consists of a linear combination of left- and right-handed circularly polarized light with different frequencies. We also show that our Hall conductivity is two orders of magnitude larger than the maximum value obtained in noncentrosymmetric systems, and that the main valley can be switched by tuning a phase difference between the left- and right-handed circularly polarized light. Our results will enable us to generate and control the valley-selective Hall effect in centrosymmetric systems.

Switchable polarization makes ferroelectric materials widely usable in nonvolatile memories and electronic nanodevices. The coercive electric field, determining the polarization switching, is crucially important for the design and usage of ferroelectric devices. To prevent leakage and dielectric breakdown of the devices, it is necessary to reduce the coercive electric field. In this work, we propose a theoretical model to study the domain switching properties of epitaxial $\mathrm{PbTi}{\mathrm{O}}_3$ films within the framework of Landau's phenomenological theory, especially the multistep polarization switching in ferroelectric thin films near a phase boundary. Results indicate that substrate strains can significantly affect the domain structures and the domain switching process. Under specific substrate strain conditions (tensile misfit strain of 0%–0.8%), polydomains exist and ${180}^{\circ }$ polarization switching can be achieved via a two-step ${90}^{\circ }$ switching process. The coercive field required for a multistep switching process can be decreased by about 50% in comparison to that for single domains. The approach of reducing the electric field presents significant opportunities for the design and enhancement of devices based on ferroelectric materials across various applications.

Stacking fault energies (SFEs) are key parameters to understand the deformation mechanisms in metals and alloys, and prior knowledge of SFEs from ab initio calculations is crucial for alloy design. Machine learning (ML) algorithms used in the present work show a $\sim$ 80 times acceleration of generalized stacking fault energy predictions, which are otherwise computationally very expensive to get directly from density functional theory calculations, particularly for alloys. The origin of the features used for training the ML algorithms lies in the physics-based Friedel model, and the present work uncovers the connection between the physics of $d$ electrons and the deformation behavior of transition metals and alloys. Predictions based on the ML model agree with the experimental data. Our model can be helpful in accelerated alloy design by providing a fast method of screening materials in terms of stacking fault energies.

Free volume is one of the most important structural features closely associated with various glass phenomena and properties. However, precise determination of how free volume evolves with external tuning poses a considerable challenge. In this work, by using in situ high-pressure synchrotron x-ray diffraction in a diamond anvil cell, we investigate the effect of pressure on free volume in a relatively soft $\mathrm{L}{\mathrm{a}}_{75}\mathrm{A}{\mathrm{l}}_{25}$ metallic glass (MG). Our investigation quantitatively compares the pressure-dependent principal diffraction peak position and peak width variations with high accuracy between as-quenched and thermally annealed $\mathrm{L}{\mathrm{a}}_{75}\mathrm{A}{\mathrm{l}}_{25}$ metallic glass samples (each possessing different initial free-volume contents but under identical hydrostatic pressure conditions). The differences in compression and decompression behaviors are elucidated and discussed within the framework of free volume. It is revealed that free volume engages in the compression process with a linear, pressure-dependent reduction below ∼10 GPa, after which it reaches a saturated flat stage, maintaining a constant content up to 23.1 GPa. During decompression, an obvious hysteresis loop and permanent densification are observed. Although under hydrostatic pressure conditions, both $\mathrm{L}{\mathrm{a}}_{75}\mathrm{A}{\mathrm{l}}_{25}$ metallic glasses exhibit an inevitable buildup of local stress and/or strain once pressure is applied, and the annealed sample displays a notably faster rate of increase. Evident residual local stress and/or strain persists in the annealed sample after pressure release. Our findings underscore the complicated compression and decompression behavior in MGs if the pressure is high enough with respect to the sample bulk modulus. These complexities unveil many details regarding glass structures, especially the content and distribution of free volume, providing valuable insights to deepen our comprehension of free volume in glass structures.

Subsystem symmetries are of peculiar interest as their relation to many exotic phenomena. However, realistic models hosting such symmetries are rare. Here we propose an extended compass model that hosts subsystem symmetries and has potential experimental relevance to $3d$ transition metal compounds. The subsystem symmetries strongly constrain the mobility of spin excitations and lead to profound consequences. At the quantum critical point, we find the presence of a “critical Bose surface” along the entire $k_x$ and $k_y$ axes, and across this quantum critical point, we find a nodal-line spin liquid that undergoes nematic instability at low temperatures. In the ferroquadrupole phase, we find that one excitation is immobile individually analogous to “fractons”. We discuss the relevance of our model to transition metal compounds.

We study dimerization transitions in a frustrated spin-3 chain with next-nearest-neighbor and three-site interactions. We show that two independent coupling constants of the model are sufficient to fine-tune the system to the critical point in the Wess-Zumino-Witten $\mathrm{SU}{\left(2\right)}_6$ universality class. This critical point appears as the end point of an extended $\mathrm{SU}{\left(2\right)}_4$ critical line. This implies that the renormalization group flow leads to the critical theory with the largest level $k$ such that the number of relevant operators is reduced by one and the parity of the level is preserved. Furthermore, we argue that due to the presence of marginal operator there is only one point in the $\mathrm{SU}{\left(2\right)}_6$ universality class. In addition, we report the appearance of the nonmagnetic Ising transition between the topologically trivial uniform and dimerized phases. This transition takes place within the singlet sector, while the magnetic gap remains open.

We report a comprehensive set of density functional theory calculations on the family of layered antiferromagnetic manganese pnictides $(\mathrm{Ba},\mathrm{Ca},\mathrm{Sr}){\mathrm{Mn}}_2{(\mathrm{P},\mathrm{As},\mathrm{Sb})}_2$. We characterize all components to the linear magnetoelectric (ME) tensor $\alpha$, which are parsed into their contributions from spin and orbital moments for both lattice-mediated and their clamped-ion electronic analogs. Our main results show that the orbital magnetization components cannot be neglected in these systems. The ME response is dominated by electronic effects with total $\alpha$ values exceeding those of the prototypical ${\mathrm{Cr}}_2{\mathrm{O}}_3$ (i.e., $\alpha \simeq 6.79$ ps/m in ${\mathrm{BaMn}}_2{\mathrm{As}}_2$). We also identify a strong correlation with the computed ME susceptibility on pnictogen substitution in the trigonal subfamily albeit with weaker amplitudes ($\alpha \approx 0.2$–1.7 ps/m). Additionally, we provide the dependence of these predictions on the Hubbard $+U$ correction, at the level of the local density approximation, which shows large variations on the calculated ME coefficients in the tetragonal compounds highlighting the role of strong correlation in these compounds.

We theoretically studied the superconducting pairing in a single-orbital kagome lattice. By taking the electron-electron correlation as the pairing mechanism, we obtained the spin and charge fluctuations based on the random-phase approximation and calculated the preferred pairing function based on the linearized Eliashberg equation. It turns out that the frequency dependence of the Eliashberg equation is of great importance in this model, and may lead to spin-triplet and odd-frequency pairing state. We further found a robust $A_1$ pairing symmetry, with respect to the correlation strength and Fermi surface variation. This pairing state does not break the time-reversal symmetry and can be nodal or nodeless. We concluded that, in the recently discovered kagome superconductors, the preferred pairing symmetry is $A_1$, even if the pairing originates from the electron-electron interaction.

Symmetry properties of Cooper pairs play a pivotal role in studies on topological superconductivity. Unconventional superconductors, whose pairing symmetries are different from conventional Bardeen-Cooper-Schrieffer superconductors, have been paid attention to as a platform of topological superconductivity. However, pairing symmetries of most superconductors are actually the conventional one and these superconductors are usually considered to be topologically trivial. In this work, combining the real-space and the momentum space approaches developed recently, we conduct classifications of time-reversal symmetric topological superconductors with conventional pairing symmetries. Remarkably, we find topological superconducting phases in 199 out of 230 space groups. Our finding sheds light on superconductors with conventional pairing symmetries as candidates for topological superconductors.

By measuring the dynamical and conventional magnetization relaxation of ${\mathrm{Ba}}_{0.64}{\mathrm{K}}_{0.36}{\mathrm{Fe}}_2{\mathrm{As}}_2$ single crystals, we found a strong second peak effect on the magnetization hysteresis loops. It is found that there is a kink of magnetization at a field between the valley and maximum magnetization. Interestingly, the magnetization relaxation rate has a deep minimum at the field with the kink, indicating a diminished vortex creep. The relaxation rate at this field is clearly smaller than the so-called universal lower limit of the relaxation rate characterized by $S_0\approx G{i}^{1/2}(T/T_{\mathrm{c}})$. This diminished vortex creep is associated with the origin of the second magnetization peak effect and attributed to the strongly hindered flux motion when experiencing the transition from the quasi-ordered to disordered vortex phases.

Perturbed angular correlation spectroscopy combined with ab initio electronic structure calculations is used to unravel the structural phase transition path from the low-temperature polar structure to the high-temperature structural phase in ${\mathrm{Ca}}_3{\mathrm{Ti}}_2{\mathrm{O}}_7$, a hybrid improper ferroelectric. The experimental procedure, conducted at ISOLDE, explores the unique features of a local probe environment approach by monitoring the evolution of the electric field gradient tensor at the calcium sites. The local environments, observed above 1057 K, confirm a structural phase transition from the $A{2}_{1}am$ symmetry to an orthorhombic $Acaa$ symmetry in the ${\mathrm{Ca}}_3{\mathrm{Ti}}_2{\mathrm{O}}_7$ crystal lattice, disagreeing with the frequently reported avalanche structural transition from the polar $A{2}_{1}am$ phase to the aristotype $I4/mmm$ phase. Moreover, the EFG temperature dependency, within the $A{2}_{1}am$ temperature stability, is shown to be sensitive to the recently proposed ${\mathrm{Ca}}_3{\mathrm{Ti}}_2{\mathrm{O}}_7$ ferroelectric polarization decrease within the 500–800 K temperature range.

We have examined a range of point defects, Frenkel pairs, Schottky defects, and hydrogen-related defects in the ${\mathrm{PuO}}_2$ system (supercells of 96 and 768 atoms) using the onetep linear-scaling density functional theory code. Vacancy point defects related to oxygen are found to be more stable than those related to plutonium. The oxygen in the octahedral interstitial is higher in the formation energy than the plutonium in the same octahedral site, although the difference is less than 1 eV. We were also able to identify a stable peroxide species (1.57–2.67 eV) with a O-O distance of 1.46 Å. Of the Frenkel defects we studied, we found that the oxygen is more stable than the plutonium, whereas the Schottky stability changes as a function of supercell size. Finally, we examined a number of likely hydrogen sites in the ${\mathrm{PuO}}_2$ lattice: octahedral interstitial, oxygen edge, hydroxyl, oxygen vacancy, and plutonium vacancy. We report hydrogen which exists as a hydride at oxygen and plutonium vacancies to be relatively high in energy (2.69–3.81 and 13.71–15.54 eV, respectively). The hydrogen was found to exist as a radical at the octahedral interstitial site (2.43–3.38 eV) and which is somewhat higher formation energy than other studies find. We find that the hydrogen at the oxygen edge (as a ${\mathrm{H}}^{+}$ cation) and at the oxygen cube corner (as a hydroxyl) are both lower in energy (1.14–1.40 and 1.17–1.56 eV, respectively) as opposed to hydrogen in the octahedral interstitial site but again higher than found by other studies. We discuss the data in the context of potential hydrogen transport pathways and how that might be modified by radiation damage.