The recent discovery of shape memory behavior in Mg-Sc alloys has opened the door to the possibility of lightweight shape memory alloys. Very little is known, however, about martensitic phase transformations or about equilibrium phase stability in this alloy system. Here we report on a first-principles statistical mechanics study of zero Kelvin and finite temperature phase stability of hcp, bcc, and fcc based phases in the Mg-Sc binary. Our calculations reveal a rich array of phase transitions among the different low-temperature ordered and high-temperature disordered phases. Ground state orderings on hcp, bcc, and fcc belong to families of hierarchical structures containing rods of scandium atoms assembled in layers that repeat periodically. Both fcc and bcc are found to undergo a series of second-order phase transformations with increasing temperature until they completely disorder. A high degree of degeneracy is predicted at low and high temperatures among hcp, bcc, and fcc, a property that is likely to play an important role in the shape memory effects observed in this alloy.

${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_4/{\mathrm{La}}_2{\mathrm{CuO}}_4$ (LSCO15/LCO) bilayers with a precisely controlled thickness of $N$ unit cells (UCs) of the former and $M$ UCs of the latter ([$\text{LSCO15}\_N/\mathrm{LCO}\_M]$) were grown on (001)-oriented ${\mathrm{SrLaAlO}}_4$ (SLAO) substrates with pulsed laser deposition (PLD). X-ray diffraction and reciprocal space map (RSM) studies confirmed the epitaxial growth of the bilayers and showed that a [LSCO15_2/LCO_2] bilayer is fully strained, whereas a [LSCO15_2/LCO_7] bilayer is already partially relaxed. The in situ monitoring of the growth with reflection high energy electron diffraction (RHEED) revealed that the gas environment during deposition has a surprisingly strong effect on the growth mode and thus on the amount of disorder in the first UC of LSCO15 (or the first two monolayers of LSCO15 containing one ${\mathrm{CuO}}_2$ plane each). For samples grown in pure ${\mathrm{N}}_2\mathrm{O}$ gas (growth type B), the first LSCO15 UC next to the SLAO substrate is strongly disordered. This disorder is strongly reduced if the growth is performed in a mixture of ${\mathrm{N}}_2\mathrm{O}$ and ${\mathrm{O}}_2$ gas (growth type A). Electric transport measurements confirmed that the first UC of LSCO15 next to the SLAO substrate is highly resistive and shows no sign of superconductivity for growth type B, whereas it is superconducting for growth type A. Furthermore, we found, rather surprisingly, that the conductivity of the LSCO15 UC next to the LCO capping layer strongly depends on the thickness of the latter. A LCO capping layer with 7 UCs leads to a strong localization of the charge carriers in the adjacent LSCO15 UC and suppresses superconductivity. The magnetotransport data suggest a similarity with the case of weakly hole doped LSCO single crystals that are in a so-called ‘cluster-spin-glass state.’ We discussed several mechanisms that could lead to such a localization of holes that are embedded in a short-range ordered antiferromagnetic background for the case of a thick LCO capping layer with $M=7$ but not for a thin one with $M=2$.

Liquid-liquid crossover is promising and closely related to the atomic dynamics during heating and cooling processes. Here we reveal a reversible structural crossover in the liquid $\mathrm{G}{\mathrm{a}}_{85.8}\mathrm{I}{\mathrm{n}}_{14.2}$ eutectic alloys by using in situ synchrotron x-ray diffraction and ab initio molecular dynamics simulation. A kink always appears on the temperature dependent behaviors of density, ratio of the second peak position to the first in the pair correlation function, coordination number, heat capacity, free energy, and atomic diffusivity in the temperature range of about 400–550 K. It is likely ascribed to atomic rearrangements of Ga and In atoms from a relative random packing at high temperatures to a relative nonuniform packing at low temperatures, in which In atoms prefer to have more In neighbors. This observation will promote more understanding of the liquid structure of eutectic alloys.

Generally, a single scaling exponent, $D_f$, can characterize the fractal structures of metallic glasses according to the scaling power law. However, when the scaling power law is applied to liquid gallium upon compression, the results show multiple scaling exponents and the values are beyond 3 within the first four coordination spheres in real space, indicating that the power law fails to describe the fractal feature in liquid gallium. The increase in the first coordination number with pressure leads to the fact that first coordination spheres at different pressures are not similar to each other in a geometrical sense. This multiple scaling power behavior is confined within a correlation length of ξ ≈ 14–15 Å at applied pressure according to decay of $G$($r$) in liquid gallium. Beyond this length the liquid gallium system could roughly be viewed as homogeneous, as indicated by the scaling exponent, $D_s$, which is close to 3 beyond the first four coordination spheres.

The quantum phases of two-leg spin-$\frac{1}{2}$ ladders with skewed rungs are obtained using exact diagonalization of systems with up to 26 spins and by density-matrix renormalization-group calculations to 500 spins. The ladders have isotropic antiferromagnetic (AF) exchange $J_2>0$ between first neighbors in the legs, variable isotropic AF exchange $J_1$ between some first neighbors in different legs, and an unpaired spin per odd-membered ring when $J_1\gg J_2$. Ladders with skewed rungs and variable $J_1$ have frustrated AF interactions leading to multiple quantum phases: AF at small $J_1$, either ferromagnetic or AF at large $J_1$, as well as bond-order-wave phases or reentrant AF (singlet) phases at intermediate $J_1$.

Spin-orbit torques promise ultraefficient magnetization switching used for advanced devices based on emergent quasiparticles such as domain walls and skyrmions. Recently, the spin structure dynamics, materials, and systems with tailored spin-orbit torques are being developed. A method, which allows one to detect the acting torques in a given system as a function of the magnetization direction is the torque magnetometry method based on a higher harmonics analysis of the anomalous Hall effect. Here we show that the effective fields acting on magnetic domain walls that govern the efficiency of their dynamics require a sophisticated analysis taking into account the full angular dependence of the torques. Using a one-dimensional model, we compared the spin-orbit torque efficiencies by depinning measurements and spin torque magnetometry. We show that the effective fields can be accurately determined and we find good agreement. Thus, our method allows us now to rapidly screen materials and predict the resulting quasiparticle dynamics.

The properties of a phase with large correlation length can be strongly influenced by the underlying normal phase. We illustrate this by studying the half-filled two-dimensional Hubbard model using cellular dynamical mean-field theory with continuous-time quantum Monte Carlo. Sharp crossovers in the mechanism that favors antiferromagnetic correlations and in the corresponding local density of states are observed. These crossovers occur at values of the interaction strength $U$ and temperature $T$ that are controlled by the underlying normal-state Mott transition.

It is well known that the bulk physics of a topological phase constrains its possible edge physics through the bulk-edge correspondence. Therefore, the different types of edge theories that a topological phase can host constitute a universal piece of data which can be used to characterize topological order. In this paper, we argue that, beginning from only the fixed-point wave function (FPW) of a nonchiral topological phase and by locally deforming it, all possible edge theories can be extracted from its entanglement Hamiltonian (EH). We give a general argument, and concretely illustrate our claim by deforming the FPW of the Wen-plaquette model, the quantum double of ${\mathbb{Z}}_2$. In that case, we show that the possible EHs of the deformed FPW reflect the known possible types of edge theories, which are generically gapped but gapless if translational symmetry is preserved. We stress that our results do not require an underlying Hamiltonian—thus, this lends support to the notion that a topological phase is indeed characterized by only a set of quantum states and can be studied through its FPWs.

Using the method of contact resonance ultrasonic actuation (CRUA), we observed evidence of local structural rejuvenation at the surface of metallic glasses (MGs), arising from the increase of the vibration amplitude of the atoms after the resonance actuation. By adjusting the CRUA parameters, the size, pattern, and extent of the rejuvenated zones could be tailored. Nanoindentation tests revealed suppressed nucleation of shear bands after CRUA, originating from the homogenization of the local structure induced by the ultrasonic vibration. Compared with the structural homogenization from annealing, this method will not sacrifice the concentration of the free volume for the local structural constraint. These results are useful to understand the evolution of the microstructure and local structural rejuvenation of MGs, as well as the design of MGs with improved plasticity from the nanoscale to the microscale.

We demonstrate long trion spin lifetimes in a ${\mathrm{WSe}}_2$ monolayer of up to $150\mathrm{ns}$ at $5\mathrm{K}$. Applying a transverse magnetic field in time-resolved Kerr-rotation measurements reveals a complex composition of the spin signal of up to four distinct components. The Kerr-rotation signal can be well described by a model which includes inhomogeneous spin dephasing and by setting the trion spin lifetimes to the measured excitonic recombination times extracted from time-resolved reflectivity measurements. We observe a continuous shift of the Kerr resonance with the probe energy, which can be explained by an adsorbate-induced, inhomogeneous potential landscape of the ${\mathrm{WSe}}_2$ flake. A further indication of extrinsic effects on the spin dynamics is given by a change of both the trion spin lifetime and the distribution of $g$ factors over laboratory time. Finally, we detect a Kerr-rotation signal from the trion's higher-energy triplet state when the lower-energy singlet state is optically pumped by circularly polarized light. We explain this by the formation of dark trion states, which are also responsible for the observed long trion spin lifetimes.

We theoretically investigate the properties of a tunable Yagi-Uda nanoantenna composed of metal-dielectric (Ag-Ge) core-shell nanoparticles. We show that, due to the combination of two types of resonances in each nanoparticle, such hybrid Yagi-Uda nanoantenna can operate in two different regimes. Besides the conventional nonresonant operation regime at low frequencies, characterized by highly directive emission in the forward direction, there is another one at higher frequencies caused by a hybrid magneto-electric response of the core-shell nanoparticles. This regime is based on the excitation of the van Hove singularity, and emission in this regime is accompanied by high values of directivity and Purcell factor within the same narrow frequency range. Our analysis reveals the possibility of flexible dynamical tuning of the hybrid nanoantenna emission pattern via electron-hole plasma excitation by 100 fs pump pulse with relatively low peak intensities $\sim 200\mathrm{MW}{\mathrm{cm}}^{-2}$.

Many features of charge-$4e$ superconductors remain unknown because even the “mean-field Hamiltonian” describing them is an interacting model. Here we introduce an interacting model to describe a charge-$4e$ superconductor (SC) deep in the superconducting phase and explore its properties using quantum Monte Carlo (QMC) simulations. The QMC is sign-problem-free but only when a Majorana representation is employed. As a function of the chemical potential we observe two sharply-distinct behaviors: a “strong” quarteting phase in which charge-$4e$ quartets are tightly bound (like molecules) so that charge-$2e$ pairing does not occur even in the temperature $T\to 0$ limit, and a “weak” quarteting phase in which a further transition to a charge-$2e$ superconducting phase occurs at a lower critical temperature. Analogous issues arise in a putative $Z_4$ spin liquid with a pseudo-Fermi surface and other interacting models with composite order parameters. Under certain circumstances, we also identified a stable $T=0$ charge-$4e$ SC phase with gapless nodal quasiparticles. We further discuss possible relevance of our results to various experimental observations in $\frac{1}{8}$-doped LBCO.

We present a novel chiral sensing platform that combines a one-dimensional photonic crystal design with a birefringent surface defect. The platform sustains simultaneous transverse electric and transverse magnetic surface modes, which are exploited to generate chiral surface waves. The present design provides homogeneous and superchiral fields of both handednesses over arbitrarily large areas in a wide spectral range, resulting in the enhancement of the circular dichroism signal by more than two orders of magnitude, thus paving the road toward the successful combination of surface-enhanced spectroscopies and electromagnetic superchirality.

We define a class of “diagonal” $t–J$ ladders rotated by $\pi /4$ relative to the canonical lattice directions of the square lattice, and study it using density matrix renormalization group. Here, we focus on the two-leg cylinder with a doped hole concentration near $x=\frac{1}{4}$. At exactly $x=\frac{1}{4}$, the system forms a period 4 charge density wave and exhibits spin-charge separation. Slightly away from $\frac{1}{4}$ doping, we observe several topologically distinct types of solitons with well-defined fractionalized quantum numbers. Remarkably, given the absence of any obvious small parameter, the effective masses of the emergent solitons differ by several orders of magnitude.

In this work we introduce the Rytov approximation in the scope of high-energy electron scattering with the motivation of developing better linear models for electron scattering. Such linear models play an important role in tomography and similar reconstruction techniques. Conventional linear models, such as the phase grating approximation, have reached their limits in current and foreseeable applications, most importantly in achieving three-dimensional atomic resolution using electron holographic tomography. The Rytov approximation incorporates propagation effects which are the most pressing limitation of conventional models. While predominately used in the weak-scattering regime of light microscopy, we show that the Rytov approximation can give reasonable results in the inherently strong-scattering regime of transmission electron microscopy.

The intermediate-valence compound ${\mathrm{SmB}}_6$ is a well-known Kondo insulator, in which the hybridization of itinerant $5d$ electrons with localized $4f$ electrons leads to a transition from metallic to insulating behavior at low temperatures. Recent studies suggest that ${\mathrm{SmB}}_6$ is a topological insulator, with topological metallic surface states emerging from a fully insulating hybridized bulk band structure. Here, we locally probe the bulk magnetic properties of pure and $0.5\%$ Fe-doped ${\mathrm{SmB}}_6$ by muon spin rotation/relaxation methods. Below 6 K, the Fe impurity induces simultaneous changes in the bulk local magnetism and the electrical conductivity. In the low-$T$ insulating bulk state we observe a temperature-independent dynamic relaxation rate indicative of low-lying magnetic excitations driven primarily by quantum fluctuations.

The low energy behavior of a huge variety of one-dimensional interacting spinful fermionic systems exhibits spin-charge separation, described in the continuum limit by two sine-Gordon models decoupled in the charge and spin channels. Interaction is known to induce, besides the gapless Luttinger liquid phase, eight possible gapped phases, among which are the Mott, Haldane, charge-/spin-density, and bond-ordered wave insulators, and the Luther Emery liquid. Here we prove that some of these physically distinct phases have nontrivial topological properties, notably the presence of degenerate protected edge modes with fractionalized charge/spin. Moreover, we show that the eight gapped phases are in one-to-one correspondence with the symmetry-protected topological (SPT) phases classified by group cohomology theory in the presence of particle-hole symmetry P. The latter result is also exploited to characterize SPT phases by measurable nonlocal order parameters which follow the system evolution to the quantum phase transition. The implications on the appearance of exotic orders in the class of microscopic Hubbard Hamiltonians, possibly without P symmetry at higher energies, are discussed.

Heat management in thermoelectric and power devices as well as in random access memories poses a grand challenge and can make the difference between a working and an abandoned device design. Despite the prevalence of dislocations in all these technologies, the modeling of their thermal resistance is based on 50-year-old analytical approximations, whose simplicity was driven by practical limitations rather than physical insight. We introduce an efficient ab initio approach based on Green's functions computed by two-dimensional reciprocal space integration. By combining elasticity theory and density functional theory, we calculate the scattering strength of a ${90}^{\circ }$ misfit edge dislocation in Si. Because of the breakdown of the Born approximation, earlier literature models fail, even qualitatively. We find that a dislocation density larger than ${10}^9{\mathrm{cm}}^{-2}$ is necessary to substantially influence thermal conductivity at room temperature and above. We quantify how much of the reduction of thermal conductivity measured in nanograined samples can be explained by realistic dislocation concentrations.

The Aubry unpinned-pinned transition in the sliding of two incommensurate lattices occurs for increasing mutual interaction strength in one dimension and is of second order at $T=0$, turning into a crossover at nonzero temperatures. Yet, real incommensurate lattices come into contact in two dimensions, at finite temperature, generally developing a mutual Novaco-McTague misalignment, conditions in which the existence of a sharp transition is not clear. Using a model inspired by colloid monolayers in an optical lattice as a test two-dimensional (2D) case, simulations show a sharp Aubry transition between an unpinned and a pinned phase as a function of corrugation. Unlike one dimension, the 2D transition is now of first order, and, importantly, remains well defined at $T>0$. It is heavily structural, with a local rotation of moiré pattern domains from the nonzero initial Novaco-McTague equilibrium angle to nearly zero. In the temperature ($T$)-corrugation strength plane, the thermodynamical coexistence line between the unpinned and the pinned phases is strongly oblique, showing that the former has the largest entropy. This first-order Aubry line terminates with a novel critical point $T=T_c$, marked by a susceptibility peak. The expected static sliding friction upswing between the unpinned and the pinned phase decreases and disappears upon heating from $T=0$ to $T=T_c$. The experimental pursuit of this novel scenario is proposed.