We report a high magnetic field study up to 55 T of the parent and the nearly optimally doped iron-pnictide superconductor ${\mathrm{Ca}}_{10}\left({\mathrm{Pt}}_3{\mathrm{As}}_8\right)\left(\right({\mathrm{Fe}}_{1-x}{\mathrm{Pt}}_x{)}_2{\mathrm{As}}_2{)}_5$ [$x=0$ and 0.078(6)] using magnetic torque, tunnel diode oscillator technique, and transport measurements. We determine the superconducting phase diagram, revealing an anisotropy of the irreversibility field up to a factor of 10 near $T_c$ and signatures of multiband superconductivity. Unexpectedly, we find a prominent anomaly in magnetic torque close to 22 T, when the magnetic field is applied perpendicular to the ($ab$) planes, which becomes significantly more pronounced as the temperature is lowered to 0.33 K. We suggest that this field-induced transition, observed both in the magnetically ordered parent compound and a nonordered superconducting sample, is a signature of a spin-flop-like transition associated not with long-range order but driven by antiferromagnetic fluctuations of magnetic moments aligned preferentially out of the conducting planes at low temperatures.

The properties of the entanglement entropy (EE) of low-lying excitations in one-dimensional disordered interacting systems are studied. The ground state EE shows a clear signature of localization, while low-lying excitations show a significantly longer localization length. The dependence of the localization as a function of interaction strength and sample length is studied using the density matrix renormalization group (DMRG). This behavior corresponds to the presence of the predicted many-particle critical energy in the vicinity of the ground state energy. The implications of these results on experiments are discussed.

In this work we employ ab initio electronic structure theory at a very high level to resolve a long standing experimental controversy; the interaction between helium and the MgO (100) surface has been studied extensively by other groups, employing diverse experimental approaches. Nevertheless, the binding energy of the lowest bound state is still unclear: the existence of a state at around $-$5.5 meV is well established but a state at $-$10 meV has also been reported. The MgO (100)-He system captures the fundamental physics involved in many adsorption problems; the weak binding is governed by long-range electronic correlation for which a fully predictive theory applicable to the solid state has been elusive. The above-mentioned experimental controversy can now be resolved on the basis of the calculations presented in this work. We performed three-dimensional vibrational dynamics calculations on a highly accurate potential-energy surface. The latter was constructed using a method which systematically approaches the exact limit in its treatment of electronic correlation. The outcome is clear: our calculations do not support the existence of a bound state around $-$10 meV.

Absorption spectra of strongly coupled intersubband cavity polaritons have been measured, using a tunable midinfrared quantum cascade laser, with high angular and spectral resolution. Pronounced linewidth narrowing of the polaritons around the anticrossing was found, with polariton linewidths narrower (4.2 meV) than both the bare intersubband transition linewidth and empty cavity linewidth (6.2 and 6 meV, respectively), at room temperature. This is due to variations in the degree of spatial averaging of the in-plane quantum-well disorder as the polariton's extended coherence length is increased by the photonic coupling over the value corresponding to the bare intersubband transition coherence length.

A superconductor is a natural source of spin-entangled spatially separated electron pairs. Although the first Cooper-pair splitter devices have been realized recently, an experimental confirmation of the spin state and the entanglement of the emitted electron pairs has been lacking up to now. In this paper, a method is proposed to confirm the spin-singlet character of individual split Cooper pairs. Two quantum dots (QDs), each of them holding one spin-prepared electron, serve as the detector of the spin state of a single Cooper pair that is forced to split when it tunnels out from the superconductor to the QDs. The number of charges on the QDs, measured at the end of the procedure, carries information on the spin state of the extracted Cooper pair. The method relies on the experimentally established toolkit of QD-based spin qubits: resonant spin manipulation, Pauli blockade, and charge measurement.

We present an atomistic model that accounts for a range of anomalous thermodynamic properties of the fcc $\delta$ phase of Pu-Ga alloys in terms of the Invar mechanism. Two modified embedded atom method potentials are employed to represent competing electronic states in $\delta$-Pu, each of which has an individual configuration dependence as well as distinct interactions with gallium. Using classical Monte Carlo simulations, we compute the temperature dependence of various thermodynamic properties for different dilute gallium concentrations. The model reproduces the observed effects of excessive volume reduction along with a rapid shift in thermal expansion from negative to positive values with increasing gallium concentration. It also predicts progressive stiffening upon dilute-gallium alloying, while the calculated thermal softening is nearly independent of the gallium concentration in agreement with resonant ultrasound spectroscopy measurements in the literature. Analysis of the local structure predicted by the model indicates that the distribution of the gallium atoms is not completely random in the $\delta$ phase due to the presence of short-range order associated with the Invar mechanism. This effect is consistent with the nanoscale heterogeneity in local gallium concentration which is observed in recent extended x-ray absorption fine structure spectroscopy experiments. Implications of the Invar effect for phase stability and physical interpretations of the two states are also discussed.

The slow $\beta$ relaxation is understood to be a universal feature of glassy dynamics. Its presence in bulk metallic glasses (BMGs) is evidence of a broad relaxation time spectrum that extends to deep within the glassy state. Despite the breadth of research devoted to this phenomenon, its microscopic origin is still not fully understood. The low-temperature aging behavior and atomic structural rearrangements of a ${\mathrm{Au}}_{49}$${\mathrm{Cu}}_{26.9}$${\mathrm{Si}}_{16.3}$${\mathrm{Ag}}_{5.5}$${\mathrm{Pd}}_{2.3}$ BMG are investigated in the regime of the slow $\beta$ relaxation by employing an ensemble of experimental techniques such as high-intensity synchrotron x-ray scattering, modulated differential scanning calorimetry (MDSC), dynamic mechanical analysis (DMA), impulse excitation, and dilatometry. Evidence of a distinct slow $\beta$-relaxation regime is seen in the form of (1) an excess wing of the DMA loss modulus beginning at $\sim$50 ${}^{\circ }$C, (2) a crossover effect of elastic modulus with isothermal aging at 50${}^{\circ }$C, and (3) a broad, nonreversing and largely irreversible sub-$T_g$ endotherm in the MDSC results. Atomic rearrangements occurring at the onset of the measured slow $\beta$-relaxation temperature regime were found to be confined mainly to the short-range order length scale while no significant atomic rearrangements occur on the length scale of the medium-range order. Furthermore, evidence is presented that suggests the crossover effect in Young's modulus is due to the evolution of chemical short-range order. These results support the emergent picture of a dynamically heterogeneous glassy structure, in which low-temperature relaxation occurs through atomic rearrangements confined mostly to the short-range order length scale.

We use finite-difference time-domain modeling to investigate plasma generation induced by multiphoton absorption of intense laser light in dielectrics with tiny inhomogeneities. Plasma generation is found to be strongly amplified around nanometer-sized inhomogeneities as present in glasses. Each inhomogeneity acts as the seed of a plasma structure growing against the direction of light propagation. Plasma structures originating from randomly distributed inhomogeneities are found to interact strongly and to organize in regularly spaced planes oriented perpendicularly to the laser polarization. We discuss similarities between our results and nanogratings in fused silica written by laser beams with spatially homogeneous as well as radial and azimuthal polarizations.

A three-dimensional (3D) symmetry-protected topological (SPT) phase by definition must have symmetry-protected nontrivial boundary states; namely, its two-dimensional (2D) boundary must be either gapless or degenerate. In this work we demonstrate that once we couple a 3D SPT phase to a lattice dynamical $Z_2$ gauge field, in many cases the $Z_2$ vison line excitation (line defect) can be viewed as a ‘one-dimensional (1D) boundary” of the 3D SPT phase, and this line defect is guaranteed to have a gapless or degenerate spectrum, which is also protected by the symmetry of the SPT phase.

We develop a variational Monte Carlo (VMC) method for electron-phonon coupled systems. The VMC method has been extensively used for investigating strongly correlated electrons over the last decades. However, its applications to electron-phonon coupled systems have been severely restricted because of its large Hilbert space. Here, we propose a variational wave function with a large number of variational parameters, which is suitable and tractable for systems with electron-phonon coupling. In the proposed wave function, we implement an unexplored electron-phonon correlation factor, which takes into account the effect of the entanglement between electrons and phonons. The method is applied to systems with diagonal electron-phonon interactions, i.e., interactions between charge densities and lattice displacements (phonons). As benchmarks, we compare VMC results with previous results obtained by the exact diagonalization, the Green function Monte Carlo method and the density matrix renormalization group for the Holstein and Holstein-Hubbard model. From these benchmarks, we show that the present method offers an efficient way to treat strongly coupled electron-phonon systems.

Strain-modulated anisotropic electronic charge transfers in perovskite ${\mathrm{Pr}}_{0.67}$${\mathrm{Sr}}_{0.33}$${\mathrm{MnO}}_3$ thin films were investigated using polarization dependent x-ray absorption near-edge structure at the Mn $K$ absorption edge and half-integer diffraction. The strain from the lattice mismatch between the film and the substrate affects the ${\mathrm{MnO}}_6$ octahedron tilt pattern in thin films, which modifies the Mn-O bond length and bond angles, and charge transfer properties. The probability of charge transfer from O to Mn is anisotropic along the in-plane and out-of-plane directions, which is enhanced in the direction with compressive strain due to a larger overlap of Mn 3$d$ and O 2$p$ orbitals as a result of a shorter Mn-O bond length. These results were further verified using the ab initio FEFF calculations and Curie temperature calculation.

$\mathrm{Hg}{\mathrm{Ba}}_2\mathrm{Cu}{\mathrm{O}}_{4+\delta }$ (Hg1201) has been shown to be a model cuprate for scattering, optical, and transport experiments, but angle-resolved photoemission spectroscopy (ARPES) data are still lacking owing to the absence of a charge-neutral cleavage plane. We report on progress in achieving the experimental conditions for which quasiparticles can be observed in the near-nodal region of the Fermi surface. The $d$-wave superconducting gap in near-optimally-doped Hg1201 is found to have a maximum of 39 meV. At low temperature, a kink is detected in the nodal dispersion at approximately 51 meV below the Fermi level, an energy that is different from other cuprates with comparable T${}_c$. The superconducting gap, Fermi surface, and nodal band renormalization measured here provide a crucial momentum-space complement to other experimental probes.

The tetragonal rare-earth transition-metal silicide system with three-dimensional crystallographic structure $R_5{T}_4{\mathrm{Si}}_{10}$, where $R$ is Dy, Ho, Er, Tm, and Lu, and $T=\mathrm{Ir}$ and Rh, has been shown to exhibit fascinating charge-density-wave (CDW) phase transitions, a phenomenon largely found in otherwise low-dimensional systems. In this study, we report the investigations of CDW in Dy${}_5$Ir${}_4$Si${}_{10}$ at different temperatures using transmission electron microscopy techniques including electron diffraction and dark-field imaging. Incommensurate superlattice spots along the $c$ axis were observed in the electron-diffraction patterns when the sample was cooled below the CDW transition temperature at $\sim$208 K. CDW becomes commensurate with further cooling and configurations of CDW dislocations convincingly show that the CDW phase transition is accompanied by a concomitant cell-doubling crystallographic structural phase transition. Intriguingly, the cell-doubling transition is featured by a broken inversion symmetry along the $c$ axis and a disparity in the CDW-modulation vectors with opposite signs, which gives rise to two sets of CDW domains with reversed contrasts. The profound physics underlining this notable domain-contrast behavior is discussed.

A one-dimensional lattice with strong spin-orbit interactions (SOIs) and a Zeeman magnetic field is shown to lead to the formation of a helical charge-density-wave (CDW) state near half filling. The interplay between the magnetic field, SOI constants, and the CDW gap seems to support Majorana bound states under appropriate values of the external parameters. An explicit calculation of the quasiparticles' wave functions supports the formation of a localized zero-energy state, bounded to the sample end points. Symmetry classification of the system is provided. The relative value of the density of states shows a precise zero-energy peak at the center of the band in the nontrivial topological regime.

We investigated the atomic and electronic structure of the K-adsorbed graphene/Au/Ni(111) surface by using density-functional calculations. The role of the K adsorbates is verified as a simple donor: the adsorption of K induces a rigid shift of the graphene $\pi$ bands with preserving the quasifreestanding Dirac-cone shape. The $\pi$ character of the Dirac-cone bands, however, undergoes some weakening due to the hybridization with Ni $d$ bands, especially in the energy range of 0.5–0.8 eV (0.1–0.3 eV) below the Fermi level for the majority (minority) spin band structure. This weakening of the $\pi$ character could possibly account for the reduced photoemission intensity of the Dirac cone, which was experimentally reported as a band gap of 0.6 eV.

We present a theoretical study of the plasmon and coupled plasmon-phonon modes induced by intraband electron-electron interaction in graphene in the presence of driving dc electric field. We find that the electric field dependence of these collective excitation modes in graphene differs significantly from that in a conventional two-dimensional electron gas with a parabolic energy spectrum. This is due mainly to the fact that graphene has a linear energy spectrum and the Fermi velocity of electrons in graphene is much larger than the drift velocity of electrons. The obtained results demonstrate that the plasmon and coupled plasmon-phonon modes in graphene can be tuned by applying not only the gate voltage but also the source-to-drain field. The manipulation of plasmon and coupled plasmon-phonon modes by source-to-drain voltage can let graphene be more conveniently applied as an advanced plasmonic material.

The recent observation of charge fractionalization in single Tomanga-Luttinger liquids (TLLs) [H. Kamata et al., Nat. Nanotechnol. 9, 177 (2014)] opens new routes for a systematic investigation of this exotic quantum phenomenon. In this Rapid Communication we perform measurements on two adjacent TLLs and put forward an accurate theoretical framework to address the experiments. The theory is based on the plasmon scattering approach and can deal with injected charge pulses of arbitrary shape in TLL regions. We accurately reproduce and interpret the time-resolved multiple fractionalization events in both single and double TLLs. The effect of intercorrelations between the two TLLs is also discussed.

A spectroscopic pump-probe method to determine the spatial shape of bound quantum states in semiconductor quantum dots is proposed. The method uses intraband transitions between the bound states and unbound continuum states in the host medium. The developed theoretical scheme is applicable to quantum dots embedded in bulk material and with some modification also for other nanostructures. In particular, the analyzed pump-probe spectra exhibit specific spectral signatures for different spatial extensions of the quantum dot confinement potential.

We discuss how electron-electron interactions renormalize the spin-orbit induced anticrossings between different subbands in ballistic quantum wires. Depending on the ratio of spin-orbit coupling and subband spacing, electron-electron interactions can either increase or decrease anticrossing gaps. When the anticrossings are closing due to a special combination of Rashba and Dresselhaus spin-orbit couplings, their gap approaches zero as an interaction dependent power law of the spin-orbit couplings, which is a consequence of Luttinger liquid physics. Monitoring the closing of the anticrossings allows us to directly measure the related renormalization group scaling dimension in an experiment. If a magnetic field is applied parallel to the spin-orbit coupling direction, the anticrossings experience different renormalizations. Since this difference is entirely rooted in electron-electron interactions, unequally large anticrossings also serve as a direct signature of Luttinger liquid physics. Electron-electron interactions furthermore increase the sensitivity of conductance measurements to the presence of anticrossing.