The nonequilibrium dynamics of disordered many-body quantum systems after a quantum quench unveils important insights about the competition between interactions and disorder, yielding, in particular, an interesting perspective toward the understanding of many-body localization. Still, the experimentally relevant effect of bond randomness in long-range interacting spin chains on their dynamical properties have so far not been investigated. In this Letter, we examine the entanglement entropy growth after a global quench in a quantum spin chain with randomly placed spins and long-range tunable interactions decaying with distance with power $\alpha$. Using a dynamical version of the strong disorder renormalization group we find for $\alpha >{\alpha }_c$ that the entanglement entropy grows logarithmically with time and becomes smaller with larger $\alpha$ as $S\left(t\right)=S_{p}ln\left(t\right)/\left(2\alpha \right)$. Here, $S_p=2ln2-1$. We present results of numerical exact diagonalization calculations for system sizes up to $N\sim 16$ spins, in good agreement with the analytical results for sufficiently large $\alpha >{\alpha }_c\approx 1.8$. For $\alpha <{\alpha }_c$, we find that the entanglement entropy grows as a power law with time, $S\left(t\right)\sim t^{\gamma \left(\alpha \right)}$ with $0<\gamma \left(\alpha \right)<1$ a decaying function of the interaction exponent $\alpha$.

In general, vibrational physics has been well described by quantum perturbation theory (QPT) to provide footprint characteristics for common crystals. However, despite weak phonon anharmonicity, the recently discovered cubic crystals (BAs and BP) have shown anomalous vibrational dynamics with elusive fundamental origin. Here, we developed a nonperturbative ab initio approach, together with spectroscopy and high-pressure experiments, to successfully determine the exact dynamic evolutions of the vibrational physics. We found that the local fluctuation and coupling isotopes significantly dictate the vibrational spectra, through the Brillouin zone folding that has previously been ignored in literature. By decomposing vibrational spectra into individual isotope eigenvectors, we observed both positive and negative contributions to Raman intensity from constitutional atoms (${}^{10}\mathrm{B}, {}^{11}\mathrm{B}, {}^{75}\mathrm{As}$, or ${}^{31}\mathrm{P}$). Importantly, our nonperturbative theory predicts that a vibrational resonance appears at high hydrostatic pressure due to broken translational symmetry, which was indeed verified by experimental measurement under a pressure up to 31.5 GPa. In this paper, we develop fundamental understandings for the anomalous lattice physics under the failure of QPT and provide an approach in exploring transport phenomena for materials of extreme properties.

A class of antiferromagnets with spin-polarized electron bands, yet zero net magnetization, called altermagnets, is attracting increasing attention due to their potential use in spintronics. Here, we study spin injection into an altermagnet via spin pumping from a ferromagnetic insulator. We find that the spin pumping behaves qualitatively differently depending on how the altermagnet is crystallographically oriented relative to the interface of the ferromagnetic insulator. The altermagnetic state can enhance or suppress spin pumping, which we explain in terms of the spin-split altermagnetic band structure and the spin-flip probability for the incident modes. Including the effect of interfacial Rashba spin-orbit coupling, we find that the spin-pumping effect is in general magnified, but that it can display a nonmonotonic behavior as a function of the spin-orbit coupling strength. We show that there exists an optimal value of the spin-orbit coupling strength which causes an order of magnitude increase in the pumped spin current, even for the crystallographic orientation of the altermagnet which suppresses the spin pumping.

We show that a local non-Hermitian perturbation in a Hermitian lattice system generically induces scale-free localization for the continuous-spectrum eigenstates. When the perturbation lies at a finite distance to the boundary, the scale-free eigenstates are promoted to exponentially localized modes, whose number is proportional to the distance. Furthermore, when the local non-Hermitian perturbation respects parity-time $\left(\mathcal{PT}\right)$ symmetry, the $\mathcal{PT}$ symmetry breaking is always accompanied by the emergence of scale-free or exponential localization. Intriguingly, we find a concise band-structure condition which tells not only when the continuous-spectrum $\mathcal{PT}$ breaking of scale-free modes can occur but also the precise $\mathcal{PT}$-breaking energy window. Our results uncover a series of unexpected generic phenomena induced by a local non-Hermitian perturbation, which has interesting interplay with $\mathcal{PT}$ symmetry.

Structural insight into nano-objects down to the atomic scale is one of the most important prerequisites to understand the properties of functional materials and will ultimately permit one to relate the size and shape of nanoparticles to their catalytic activity. We elucidate the potential of extracting structural information about a small ensemble of nanoparticles that are semiregularly arranged on a periodic array from coherent x-ray Bragg diffraction. The observed fringe pattern in the Pt(111) Bragg peak obviously originates from the mutual interference of the Bragg scattered wave field from individual nanoparticles in the nanoarray. Despite the absence of a symmetry center in the Bragg peak of the nanoarray, we identify the most prominent in-plane spatial frequencies of the latter by applying a Patterson map analysis to the Bragg peak superstructure. Integration along the in-plane reciprocal space direction over the relevant in-plane regions of interest results in Laue oscillations that arise from nanoparticle sets of similar heights in real space. A one-to-one comparison with real-space microscopic information obtained from scanning electron microscopy and atomic force microscopy suggests potential nanoparticle subsets as the origin for the x-ray intensity in these regions of interest by the good agreement in their height and direction-dependent in-plane interparticle distances, as also further supported by simulations. Nanoparticle arrays with well-defined tunable sizes and lateral distances may serve in the future to track structural changes in, e.g., sizes, relative positions, and tilts of smallest' catalysis-relevant nanoparticles during operando heterogeneous catalysis experiments in the 10-nm-size regime.

The fate of a single particle immersed in and interacting with a bath of other particles localized in a tilted lattice is investigated. For tilt values comparable to the tunneling rate a slow-down of the dynamics is observed without, however, a clear localization of the impurity. For a large tilt and strong interactions the motion of the impurity resembles that in the Kronig-Penney potential. The dynamics of the impurity depends on the initial distribution of majority particles. It shows delocalized dynamics for a regular, density-wave-like distribution and localization if majority particles are randomly distributed.

We report on elastic and inelastic neutron scattering from single-grain isotopically enriched samples to elucidate the local magnetic correlations between ${\mathrm{Tb}}^{3+}$ moments in quasicrystalline $i$-Tb-Cd. The inelastic neutron scattering measurements of the crystalline electric field excitations demonstrated that the ${\mathrm{Tb}}^{3+}$ moments are directed primarily along the local fivefold axes of the Tsai-type cluster as was found for the ${\mathrm{TbCd}}_6$ approximant phase. Based on the inelastic measurements, we consider a simple Ising-type model for the moment configurations on a single ${\mathrm{Tb}}^{3+}$ icosahedron and enumerate the lowest energy moment configurations. We then calculate the diffuse scattering from these configurations and compare with the experimental magnetic diffuse scattering measurements to identify the most likely single cluster moment configurations and find reasonable agreement between the broad features observed in our scattering simulations. We further use a heuristic glass model as well as large-scale Monte-Carlo simulations of a multicluster model to consider the role of higher-order (longer-range) intercluster correlations for magnetic frustration and the magnetic scattering.

We reinvestigate the phase transitions of the Ising model on the kagome lattice with antiferromagnetic nearest-neighbor and ferromagnetic next-nearest-neighbor interactions, which has a six-state-clock spin ice ground state and two consecutive Berezinskii-Kosterlitz-Thouless (BKT) phase transitions. Employing the classical Monte Carlo (MC) simulations, the phases are characterized by the magnetic order parameter and the critical temperatures are obtained by the finite-size scaling of related physical quantities. Moreover, we attempt to gain general information on the phase transitions from the MC process instead of MC results and successfully extract the correct transition points. Specifically, we focus on the selected data set of uncorrelated MC configurations and quantify the MC process using the distribution of two-configuration Hamming distances in this small data collection. This distribution is more than a quantity that features different behaviors in different phases but also nicely supports the same BKT scaling form as the order parameter, from which we successfully determine the two BKT transition points with surprisingly high accuracy. More strikingly, the distribution of Hamming distances can even determine the transition type without the help of the order parameter. We also discuss the connection between the phase transitions and the intrinsic dimension extracted from the Hamming distances, which is widely used in the growing field of machine learning and is reported to be able to detect critical points. Besides providing a new understanding of the spin ice transitions in the kagome lattice, we hope our proposal can be used to tackle the complicated phase transitions in the newly found compound HoAgGe.

The superconducting properties of two recently synthesized ternary silicides with unit formula $X_4\mathrm{CoSi}$ ($X=\mathrm{Nb}, \mathrm{Ta}$) are investigated through ab initio calculations combined with Eliashberg theory. Interestingly, their crystal structure comprises interlocking honeycomb networks of Nb/Ta atoms. ${\mathrm{Nb}}_4\mathrm{CoSi}$ is found to harbor better conditions for phonon-mediated superconductivity, as it possesses a higher density of states at the Fermi level, fostering stronger electron-phonon coupling. The superconducting critical temperatures ($T_c$) follow the same trend, with ${\mathrm{Nb}}_4\mathrm{CoSi}$ having a twice higher value than ${\mathrm{Ta}}_4\mathrm{CoSi}$. Furthermore, the calculated $T_c$ values (5.9 K vs 3.1 K) agree excellently with the experimentally obtained ones, establishing superconductivity in this new materials class as mediated by the electron-phonon coupling. Furthermore, my calculations show that the superconducting properties of these compounds do not simply correlate with the parameters of their honeycomb networks, contrary to proposals raised in the literature. Rather, their complete fermiology and phonon spectrum should be taken into account in order to explain their respective superconducting properties.

The influence of attractive boron impurities, embedded on a graphene sheet, on the phase diagrams of ${}^4\mathrm{He}$ and ${\mathrm{H}}_2$ adsorbed on top was studied using the diffusion Monte Carlo method. The doping of graphene was made by distributing the boron atoms following the same pattern found in an experimentally synthesized substrate. Our results show that while the different incommensurate solid phases of both adsorbates remain largely unchanged after doping, the liquid/gas equations of state are significantly different from the ones on pristine graphene. Doping graphene produces new translationally invariant stable phases for ${}^4\mathrm{He}$, depending on the concentration of boron impurities, but makes the ${\mathrm{H}}_2$ ground state to remain solid. In addition, several new registered phases appear for both adsorbates.

Nucleation of the pair condensate near surfaces above the upper critical magnetic field and the pair-condensate enhancement/suppression induced by changes in the electron-phonon interaction at interfaces are the most known examples of the surface superconductivity. Recently, another example has been reported when the surface enhancement of the critical superconducting temperature occurs due to quantum interference. In this case the pair states spread over the entire volume of the system while exhibiting the constructive interference near the surface. In the present work we investigate how an applied electric field impacts the interference-induced surface superconductivity. The study is based on a numerical solution of the self-consistent Bogoliubov-de Gennes equations for a one-dimensional attractive Hubbard model. Our results demonstrate that the surface superconducting characteristics, especially the surface critical temperature, are sensitive to the applied electric field and can be tailored by changing its magnitude.

Graphene is impervious to gases, so the question arises of how much pressure can few-layer graphene covering a slit withstand. Using the molecular dynamics model with a reduced number of degrees of freedom, a multilayer graphene sheet lying on an $h$-BN substrate with a slit of width $d$ is considered under external or internal pressure $p$. It has been established that at $p<p_0$, where $p_0$ is the critical pressure, a graphene sheet under pressure acquires a stationary profile and seals the slit. At $p>p_0$, the graphene sheet loses its connection with the substrate and the ability to seal the slit. The critical pressure is almost proportional to $1/d$ and decreases linearly with increasing temperature. An increase in the number of graphene layers in a graphene sheet slightly reduces $p_0$ only at $d<10$ nm, and for wider slits, the number of graphene layers does not affect $p_0$. This fact is explained by the membrane theory. The graphene sheet can seal the atmospheric pressure for a slit with a width of no more than 0.01 mm. Presented results are of interest for nanotechnologies using graphene membranes as sensors or resonators.

Recently, the emergence of polarity of so-called hard antiphase boundaries in strontium titanate was investigated using atomistic simulations based on machine-learned force fields. Comparing the resulting order parameter (OP) and polarization profiles to those obtained from numerical solutions based on a well-established Landau-Ginzburg-Devonshire (LGD) parametrization produces good agreement of the structural OP amplitudes but fails dramatically in reproducing the shape and pressure behavior of the domain wall (DW) polarization. While the atomistic simulations yield a nonzero DW polarization up to at least 120 kbar, LGD theory would predict a sharp transition to zero at a pressure as low as $4.6$ kbar. A semiquantitative agreement can be restored by adding so-called rotopolar couplings to the LGD potential and by considering the effects of nuclear quantum fluctuations. Additional evidence for the correctness of our extensions of the LGD approach is provided by comparing the temperature dependence of the DW polarization to recent experimental depolarization pyrocurrent measurements. Our results illustrate the importance of accounting for nuclear quantum effects beyond standard atomistic approaches in the investigation of DW properties.

Defects, i.e., inhomogeneities of the underlying lattice, are ubiquitous in magnetic materials and can have a crucial impact on their applicability in spintronic devices. For magnetic skyrmions, localized and topologically nontrivial spin textures, they give rise to a spatially inhomogeneous energy landscape and can lead to pinning, resulting in an exponentially increased dwell time at certain positions and typically a strongly reduced mobility. Using atomistic spin dynamics simulations, we reveal that under certain conditions, defects can instead enhance thermal diffusion of ferromagnetic skyrmions. By comparing with results for the diffusion of antiferromagnetic skyrmions and using a quasiparticle description based on the Thiele equation, we demonstrate that this surprising finding can be traced back to the partial lifting of the impact of the topological gyrocoupling, which governs the dynamics of ferromagnetic skyrmions in the absence of defects.

The van der Waals layered magnet $\alpha \text{−}{\mathrm{RuCl}}_3$ offers tantalizing prospects for the realization of Majorana quasiparticles. Efforts to understand this are, however, hampered by inconsistent magnetic and thermal transport properties likely coming from the formation of structural disorder during crystal growth, postgrowth processing, or upon cooling through the first order structural transition. Here, we investigate structural disorder in $\alpha \text{−}{\mathrm{RuCl}}_3$ using x-ray diffuse scattering and three-dimensional difference pair distribution function analysis. We develop a quantitative model that describes disorder in $\alpha \text{−}{\mathrm{RuCl}}_3$ in terms of rotational twinning and intermixing of the high- and low-temperature structural layer stacking. This disorder may be important to consider when investigating the detailed magnetic and electronic properties of this widely studied material.

Carrier density is one of the key controlling factors of material properties, particularly in controlling the essential correlations in strongly correlated materials. Typically, carrier density is externally tuned by doping or gating and remains fixed below room temperature. Strangely, the carrier density in correlated semimetals is often found to vary sensitively against weak external controls such as temperature, magnetic field, and pressure. Here, we develop a realistic simulation scheme that incorporates interatomic noncollinear magnetic correlation without a long-range order. Using the recently discovered nickelate superconductor as an example, we demonstrate a rather generic low-energy mechanism that in semimetals short-range correlation can reversely modulate the carrier density as well. Such a mutual influence between correlation and carrier density provides an extra ingredient for sensitive bifurcating behavior. This special feature of correlated semimetals explains their versatile carrier density at low energy and opens up new possibilities of functionalizing these materials.

We apply the recently developed slave fermion approach to study the doped Mott insulator in the one-band Hubbard and Hubbard-Heisenberg models. Our results produce several subtle features in the electron spectra and confirm the key role of antiferromagnetic (AFM) correlations in the appearance of the pseudogap. Upon hole doping, the electron spectra exhibit a single peak near the Fermi energy in the local approximation of the Hubbard model where AFM correlations are not included. When AFM correlations are included through an explicit mean-field Heisenberg interaction, a second peak emerges at slightly lower energy and pushes the other peak to higher energy, so that a pseudogap emerges between the two peaks at small doping. Both peaks grow rapidly with increasing doping and eventually merge together, where the pseudogap no longer exists. Detailed analyses of the spectral evolution with doping and the strength of the Heisenberg interaction confirm that the lower-energy peak comes from a polaronic mechanism due to the holon-spinon interaction in the AFM-correlated background and the higher-energy peak arises from the holon hybridization to form the electron quasiparticles. Thus, the pseudogap arises from the interplay of the polaronic and hybridization mechanisms. Our results are in good agreement with previous numerical calculations using the dynamical mean-field theory and its cluster extensions, but give a clearer picture of the underlying physics. Our work provides a promising perspective for clarifying the nature of doped Mott insulators and may serve as a starting point for more elaborate investigations in the future.