Materials with high carrier mobility showing large magnetoresistance (MR) have recently received much attention because of potential applications in future high-performance magnetoelectric devices. Here, we report on an electron-hole-compensated half-Heusler semimetal LuPtBi that exhibits an extremely high electron mobility of up to $79000\mathrm{c}{\mathrm{m}}^2/\mathrm{V}\mathrm{s}$ with a nonsaturating positive MR as large as $3200\%$ at 2 K. Remarkably, the mobility at 300 K is found to exceed $10500\mathrm{c}{\mathrm{m}}^2/\mathrm{V}\mathrm{s}$, which is among the highest values reported in three-dimensional bulk materials thus far. The clean Shubnikov–de Haas quantum oscillation observed at low temperatures and the first-principles calculations together indicate that the high electron mobility is due to a rather small effective carrier mass caused by the distinctive band structure of the crystal. Our findings provide a different approach for finding large, high-mobility MR materials by designing an appropriate Fermi surface topology starting from simple electron-hole-compensated semimetals.

It is shown that the nonequilibrium self-energy of an interacting lattice-fermion model has a unique Lehmann representation. Based on the construction of a suitable noninteracting effective medium, we provide an explicit and numerically practicable scheme to construct the Lehmann representation for the self-energy, given the Lehmann representation of the single-particle nonequilibrium Green's function. This is of particular importance for an efficient numerical solution of Dyson's equation in the context of approximations where the self-energy is obtained from a reference system with a small Hilbert space. As compared to conventional techniques to solve Dyson's equation on the Keldysh contour, the effective-medium approach allows us to reach a maximum propagation time, which can be several orders of magnitude longer. This is demonstrated explicitly by choosing the nonequilibrium cluster-perturbation theory as a simple approach to study the long-time dynamics of an inhomogeneous initial state after a quantum quench in the Hubbard model on a $10\times 10$ square lattice. We demonstrate that the violation of conservation laws is moderate for weak Hubbard interaction and that the cluster approach is able to describe prethermalization physics.

I discuss the relationship between edge exponents in the statistics of work done, dynamical phase transitions, and the role of different kinds of excitations appearing when a nonequilibrium protocol is performed on a closed, gapped, one-dimensional system. I show that the edge exponent in the probability density function of the work is insensitive to the presence of interactions and can take only one of three values: $+1/2,-1/2$, and $-3/2$. It also turns out that there is an interesting interplay between spontaneous symmetry breaking or the presence of bound states and the exponents. For instantaneous global protocols, I find that the presence of the one-particle channel creates dynamical phase transitions in the time evolution.

We present a theoretical study of lifetimes of interface states (IS) on metal-organic interfaces PTCDA/Ag(111), NTCDA/Ag(111), PFP/Ag(111), and PTCDA/Ag(100), describing and explaining the recent experimental data. By means of unfolding the band structure of one of the interfaces under study onto the Ag(111) Brillouin zone we demonstrate that the Brillouin zone folding upon organic monolayer deposition plays a minor role in the phase space for electron decay, and hence weakly affects the resulting lifetimes. The presence of the unoccupied molecular states below the IS gives a small contribution to the IS decay rate, which is mostly determined by the change of the phase space of bulk states upon the energy shift of the IS. The calculated lifetimes follow the experimentally observed trends. In particular, we explain the trend of the unusual increase of the IS lifetimes with rising temperature.

Strain in a material induces shifts in vibrational frequencies. This phenomenon is a probe of the nature of the vibrations and interatomic potentials and can be used to map local stress/strain distributions via Raman microscopy. This method is standard for crystalline silicon devices, but due to the lack of calibration relations, it has not been applied to amorphous materials such as hydrogenated amorphous silicon $(a$-Si:H), a widely studied material for thin-film photovoltaic and electronic devices. We calculated the Raman spectrum of $a$-Si:H ab initio under different strains $\epsilon$ and found peak shifts $\mathrm{\Delta }\omega =\left(-460\pm 10{\mathrm{cm}}^{-1}\right)\mathrm{Tr}\epsilon$. This proportionality to the trace of the strain is the general form for isotropic amorphous vibrational modes, as we show by symmetry analysis and explicit computation. We also performed Raman measurements under strain and found a consistent coefficient of $-510\pm 120{\mathrm{cm}}^{-1}$. These results demonstrate that a reliable calibration for the Raman/strain relation can be achieved even for the broad peaks of an amorphous material, with similar accuracy and precision as for crystalline materials.

At the few or monolayer limit, layered materials define an interesting two-dimensional system with unique electronic and phonon properties. The electron band structure of monolayers can be drastically different from multilayers despite the weak van der Waals interaction between neighboring layers. In this Rapid Communication, we demonstrate that vibrational spectra of a $\mathrm{Mo}{\mathrm{S}}_2$ monolayer and a $\mathrm{W}{\mathrm{S}}_2$ monolayer are also renormalized when the interaction between them is artificially modulated. This is achieved by using a diamond-anvil cell to apply high pressures, up to 39 GPa onto $\mathrm{W}{\mathrm{S}}_2/\mathrm{Mo}{\mathrm{S}}_2$ heterobilayers. With increasing pressure, the out-of-plane Raman frequencies of the two individual monolayers repel each other, exhibiting coherent vibrations across the van der Waals gap with an optical-like and an acousticlike interlayer vibration mode. The discovery shows a crossover in lattice vibration from a two-dimensional system toward a three-dimensional system driven by enforced interlayer coupling.

We study the flat-band ferromagnetic phase of a topological Hubbard model within a bosonization formalism and, in particular, determine the spin-wave excitation spectrum. We consider a square lattice Hubbard model at $1/4$-filling whose free-electron term is the $\pi$-flux model with topologically nontrivial and nearly flat energy bands. The electron spin is introduced such that the model either explicitly breaks time-reversal symmetry (correlated flat-band Chern insulator) or is invariant under time-reversal symmetry (correlated flat-band ${\mathrm{Z}}_2$ topological insulator). We generalize for flat-band Chern and topological insulators the bosonization formalism [R. L. Doretto, A. O. Caldeira, and S. M. Girvin, Phys. Rev. B 71, 045339 (2005)] previously developed for the two-dimensional electron gas in a uniform and perpendicular magnetic field at filling factor $\nu =1$. We show that, within the bosonization scheme, the topological Hubbard model is mapped to an effective interacting boson model. We consider the boson model at the harmonic approximation and show that, for the correlated Chern insulator, the spin-wave excitation spectrum is gapless while, for the correlated topological insulator, gapped. We briefly comment on the possible effects of the boson-boson (spin-wave–spin-wave) coupling.

Recently, radially collapsed single-walled carbon nanotubes (SWCNTs) have been recognized as an analog of closed-edged bilayer graphene nanoribbons (GNRs). To explore this analogy, we first make detailed analyses of the radial deformation and collapse of armchair SWCNTs using the density functional theory with van der Waals corrections. The traditional threshold diameters dividing SWCNTs into the three regimes are obtained as $D_{\mathrm{meta}}=2.2\mathrm{nm}$ and $D_{\mathrm{abs}}=5.1\mathrm{nm}$, where deformed configurations can be stabilized (metastable) for tubes with diameter $D>D_{\mathrm{meta}}$ and are energetically more favorable than the cylindrical tube for $D>D_{\mathrm{abs}}$ (absolute stability). We find that the present result for $D_{\mathrm{abs}}$ is marginally in excellent agreement with the most plausible experimental result. We also identify, for the first time, other threshold diameters given by $D_{\mathrm{flat}1}=3.3\mathrm{nm}$ and $D_{\mathrm{flat}2}=4.4\mathrm{nm}$ in between $D_{\mathrm{meta}}$ and $D_{\mathrm{abs}}$, where the cross-sectional shape of a collapsed SWCNT is peanutlike for $D<D_{\mathrm{flat}1}$, either peanutlike or dumbbell-like for $D_{\mathrm{flat}1}<D<D_{\mathrm{flat}2}$, and dumbbell-like for $D>D_{\mathrm{flat}2}$. This bistability for tubes with $D$ between $D_{\mathrm{flat}1}$ and $D_{\mathrm{flat}2}$ implies that the most stable configuration of these collapsed tubes cannot necessarily be achieved by molecular dynamics simulation. Electronic structures of collapsed armchair SWCNTs are also investigated to find that substantial band gaps develop in the flattened armchair tubes with Bernal stacked opposing faces. These band gap openings of flattened SWCNTs are explored by exploiting their analogies to bilayer graphene and bilayer GNRs. We find in particular that band gaps of flattened armchair SWCNTs with dumbbell-like cross sections, whose width is denoted $W$, show a scale behavior, $\sim 1/W_{\mathrm{flat}}$, with $W_{\mathrm{flat}}=W-3.38\left(\mathrm{nm}\right)$, where $W_{\mathrm{flat}}$ is found to be the width of the flat region, consistent with recent theoretical analyses for a model of collapsed SWCNTs [T. Nakanishi and T. Ando, Phys. Rev. B 91, 155420 (2015)]. This behavior of band gaps is similar to that for monolayer zigzag GNRs (ZGNRs), $1/W$, where $W$ is the ribbon width, and is indicative of quantum confinement. The largest band gap of $130$ meV, which develops in the flattened armchair (30,30) SWCNT, is comparable to that for bilayer ZGNRs ($160$ meV), indicating that flattened armchair tubes could be used in place of ZGNRs in electronic device applications.

We present a comprehensive theoretical study of thermodynamic properties of superconductors with a dilute concentration of magnetic impurities, with focus on how the properties of the superconducting host change if the magnetic moments of the impurities order ferromagnetically. Scattering off the magnetic impurities leads to the formation of a band of Yu-Shiba-Rusinov states within the superconducting energy gap that drastically influences superconductivity. In the magnetically ordered system, the magnetization displays a sudden drop as a function of the impurity density or magnetic moment amplitude. The drop occurs as the spin-polarized impurity band crosses the Fermi level and is associated with a quantum phase transition first put forward by Sakurai for the single impurity case. Taking into account that the background magnetic field created by the ordered impurity moments enters as a Zeeman shift, we find that the superconducting phase transition changes from second order to first order for high enough impurity concentrations.

Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique. Quantitative analyses of the generated in situ Raman maps provide unique insight into the phase behavior of as-implanted a-Si. In particular, the occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were measured. The experimental results are linked with previously published papers on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a sequence for the development of deformation of a-Si under indentation loading. The sequence involves three distinct deformation mechanisms of a-Si: (1) reversible deformation, (2) increase in coordination defects (onset of plastic deformation), and (3) phase transformation. Estimated conditions for the occurrence of these mechanisms are given with respect to relevant intrinsic and extrinsic parameters, such as indentation stress, volumetric strain, and bond angle distribution (a measure for the structural order of the amorphous network). The induced volumetric strains are accommodated solely by reversible deformation of the tetrahedral network when exposed to small indentation stresses. At greater indentation stresses, the increased volumetric strains in the tetrahedral network lead to the formation of predominately fivefold coordination defects, which seems to mark the onset of irreversible or plastic deformation of the a-Si thin film. Further increase in the indentation stress appears to initiate the formation of sixfold coordinated atomic arrangements. These sixfold coordinated arrangements may maintain their amorphous tetrahedral structure with a high density of coordination defects or nucleate as a new crystalline β-tin phase within the a-Si network.

The angular dependence of the magnetization reversal in interconnected kagome artificial spin ice structures has been studied through experimental MOKE measurements and micromagnetic simulations. This reversal is mediated by the propagation of magnetic domain walls along the interconnecting bars, which either nucleate at the vertex or arrive following an interaction in a neighboring vertex. The physical differences in these processes show a distinct angular dependence allowing the different contributions to be identified. The configuration of the initial magnetization state, either locally or on a full sublattice of the system, controls the reversal characteristics of the array within a certain field window. This shows how the available magnetization reversal routes can be manipulated and the system can be trained.

The double perovskite ${\mathrm{Y}}_2{\mathrm{NiMnO}}_6$ displays ferromagnetic transition at $T_c\approx 81$ K. The ferromagnetic order at low temperature is confirmed by the saturation value of magnetization $\left(M_s\right)$ and also validated by the refined ordered magnetic moment values extracted from neutron powder diffraction data at 10 K. This way, the dominant $\mathrm{Mn}^{4+}$ and $\mathrm{Ni}^{2+}$ cationic ordering is confirmed. The cation-ordered $P{2}_1/n$ nuclear structure is revealed by neutron powder diffraction studies at 300 and 10 K. Analysis of the frequency-dependent dielectric constant and equivalent circuit analysis of impedance data take into account the bulk contribution to the total dielectric constant. This reveals an anomaly which coincides with the ferromagnetic transition temperature $\left(T_c\right)$. Pyrocurrent measurements register a current flow with onset near $T_c$ and a peak at 57 K that shifts with temperature ramp rate. The extrinsic nature of the observed pyrocurrent is established by employing a special protocol measurement. It is realized that the origin is due to reorientation of electric dipoles created by the free charge carriers and not by spontaneous electric polarization at variance with recently reported magnetism-driven ferroelectricity in this material.

We investigate the influence of the interfacial Dzyaloshinskii-Moriya interaction (DMI) on the propagation of Damon-Eshbach spin waves in micrometer-sized Pt(2 nm)/Co(0.4 nm)/Py(5 nm)/MgO(5 nm) stripes. We use time-resolved scanning Kerr microscopy to image the spin waves excited by a microwave antenna and to directly access their dispersion. The presence of an interfacial DMI manifests itself in an asymmetry in the dispersion for counterpropagating spin waves which reverses sign upon reversal of the direction of the externally applied magnetic field. From this asymmetry we deduce the strength of the interfacial DMI. Micromagnetic simulations confirm that the observed difference in the wave numbers and the signature of the asymmetry are characteristic for the occurrence of an interfacial DMI at the Pt/Co interface and cannot be explained by the uniaxial perpendicular magnetic anisotropy field originating from the same interface.

The high-pressure melting curve of titanium has been studied up to 120 GPa and $\sim 3500$ K using both laser-heated diamond anvil cells and ab initio molecular dynamic simulations. Several theoretical and experimental melting diagnostics, including x-ray diffraction, are tested and compared. Using the most accurate on both sides, a fair agreement can be reached between experiments and simulations. The observation of temperature plateaus, a melting diagnostic proposed for laser-heated diamond anvil cell experiments, is not reliable here. The melting curve obtained here is higher (by 450 K at most) than previously reported by Errandonea et al. [Phys. Rev. B 63, 132104 (2001)] using laser-heated diamond anvil cell with optical detection of melting but also significantly lower than the one estimated in multiphase thermodynamic models based on shock compression data.

We describe the features of magnonic crystals based upon antiferromagnetic elements. Our main results are that with a periodic modulation of either magnetic fields or system characteristics, such as the anisotropy, it is possible to tailor the spin-wave spectra of antiferromagnetic systems into a band-like organization that displays a segregation of allowed and forbidden bands. The main features of the band structure, such as bandwidths and band gaps, can be readily manipulated. Our results provide a natural link between two steadily growing fields of spintronics: antiferromagnetic spintronics and magnonics.

We investigate the evolution of the electronic structure of ${\mathrm{NiS}}_{2-x}{\mathrm{Se}}_x$ alloys with varying temperature and composition $x$ by using the combined approach of density-functional theory and dynamical mean-field theory. Adopting realistic alloy structures containing S and Se dimers, we map their electronic correlation strength on the phase diagram and observe the metal-insulator transition (MIT) at the composition $x=0.5$, which is consistent with the experimental measurements. The temperature dependence of the local magnetic susceptibility is found to show a typical Curie-Weiss-like behavior in the insulating phase while it shows a constant Pauli-like behavior in the metallic phase. A comparison of the electronic structures for ${\mathrm{NiS}}_2$ and ${\mathrm{NiSe}}_2$ in different lattice structures suggests that the MIT in this alloy system can be classified as of bandwidth-control type, where the change in the hybridization strength between Ni $d$ and chalcogen $p$ orbitals is the most important parameter.

The competition between Kondo screening and indirect magnetic exchange is studied for a system with geometrical frustration using dynamical mean-field theory (DMFT). We systematically scan the weak- to strong-coupling regime of the periodic Anderson model on the triangular lattice for a wide range of fillings $n$. The magnetic phase diagram is derived using a site-dependent DMFT approach by self-consistent mapping onto three independent single-impurity models corresponding to the three correlated $f$ orbitals in the unit cell. At half-filling, the system is a nonmagnetic Kondo insulator for all considered interaction strengths $U>0$, which immediately develops into a nonmagnetic metallic Kondo-singlet phase for fillings slightly below half-filling. On the other hand, indirect magnetic exchange between the $f$ moments results in antiferromagnetic order at lower fillings. The antiferromagnetic and Kondo-singlet phases are separated in the $U\text{−}n$ phase diagram by an extended region of partial Kondo screening, i.e., a phase in which the magnetic moment at one site in the unit cell is Kondo-screened while the remaining two are coupled antiferromagnetically. At even lower fillings, the system crosses over from a local-moment to a mixed-valence regime in which the minimization of the kinetic energy in a strongly correlated system gives rise to a metallic and partially polarized ferromagnetic state.

Single crystals of $\mathrm{Ca}{\left(\mathrm{F}{\mathrm{e}}_{1-x}\mathrm{R}{\mathrm{u}}_x\right)}_2\mathrm{A}{\mathrm{s}}_2(0\le x\le 0.065)$ and $\mathrm{C}{\mathrm{a}}_{1-y}\mathrm{L}{\mathrm{a}}_y{\left(\mathrm{F}{\mathrm{e}}_{0.973}\mathrm{R}{\mathrm{u}}_{0.027}\right)}_2\mathrm{A}{\mathrm{s}}_2(0\le y\le 0.2)$ have been synthesized and studied with respect to their structural, electronic, and magnetic properties. The partial substitution of Fe by Ru induces a decrease of the $c$-axis constant leading for $x\le 0.023$ to a suppression of the coupled magnetic and structural (tetragonal to orthorhombic) transitions. At $x_{\mathrm{cr}}=0.023$ a first-order transition to a collapsed tetragonal (CT) phase is found, which behaves like a Fermi liquid and which is stabilized by further increase of $x$. The absence of superconductivity near $x_{\mathrm{cr}}$ is consistent with truly hydrostatic pressure experiments on undoped $\mathrm{CaF}{\mathrm{e}}_2\mathrm{A}{\mathrm{s}}_2$. Starting in the CT regime at $x=0.027$, we investigate the additional effect of electron doping by partial replacement of Ca by La. Most remarkably, with increasing $y$ the CT phase transition is destabilized and the system is tuned back into a tetragonal ground state at $y$ $\ge$ 0.08. This effect is ascribed to a weakening of interlayer As-As bonds by electron doping. Upon further electron doping filamentary superconductivity with $T_c$ of 41 K at $y=0.2$ is observed.

The composition and reconstruction of oxide surfaces can be deterministically controlled via ambient conditions. We demonstrate that such intrinsic alterations can have a crucial effect on the surface dipole and reactivity, even for surfaces with the same crystallographic plane. The surface dipole potential drops of ${\mathrm{BaTiO}}_3,{\mathrm{SrTiO}}_3,{\mathrm{LaFeO}}_3$, and ${\mathrm{TiO}}_2$ surfaces with various reconstructions and compositions are shown to vary by as much as 5 V, leading to significant variation of the band edge positions at these surfaces. These variations are shown to correlate with the calculated oxygen binding energy, demonstrating how oxide surface reactivity can be substantially manipulated using environmental changes.