We present linear polarization-dependent soft-x-ray absorption spectroscopy data at the Ce $M_{4,5}$ edges of Cd- and Sn-doped ${\mathrm{CeCoIn}}_5$. The $4f$ ground-state wave functions have been determined for their superconducting, antiferromagnetic, and paramagnetic ground states. The absence of changes in the wave functions in $\mathrm{CeCo}{\left({\mathrm{In}}_{1-x}{\mathrm{Cd}}_x\right)}_5$ suggests that the $4f$-conduction-electron ($cf$) hybridization is not affected by global Cd doping, thus supporting the interpretation of magnetic droplets nucleating long-range magnetic order. This is contrasted by changes in the wave function due to Sn substitution. Increasing Sn in $\mathrm{CeCo}{\left({\mathrm{In}}_{1-y}{\mathrm{Sn}}_y\right)}_5$ compresses the $4f$ orbitals into the tetragonal plane of these materials, suggesting enhanced $cf$ hybridization with the in-plane In(1) atoms and a homogeneous altering of the electronic structure. As these experiments show, the $4f$ wave functions are a very sensitive probe of small changes in the hybridization of $4f$ and conduction electrons, even conveying information about direction dependencies.

Two known representatives of the split-vacancy complexes in diamond, the negatively charged silicon-vacancy ${\mathrm{SiV}}^{-}$ and recently discovered germanium-vacancy ${\mathrm{GeV}}^{-}$ defects, were comparatively studied for their photoluminescence (PL) and complementary optical absorption spectra. The observed strong difference between luminescence and absorption spectra indicates a strong frequency defect, that is the difference of binding energies of impurity atom in the ground and excited electronic states, in these color centers. The presence of frequency defect is well supported by first-principle calculations. The obtained results accompanied with isotopic effects shed light on the structure of these centers in the ground and excited electronic states that would open the doorway to their theoretical description.

The adsorption of small organic molecules onto vicinal Au-stabilized Si(111) surfaces is shown to be a versatile route towards controlled growth of ordered organic-metal hybrid one-dimensional nanostructures. Density functional theory is used to investigate the site-specific adsorption of toluene-3,4-dithiol (TDT) molecules onto the clean Si(553)-Au surface and onto a co-doped surface whose steps are passivated by hydrogen. We find that the most reactive sites involve bonding to silicon at the step edge or on the terraces, while gold sites are relatively unfavored. H passivation and TDT adsorption both induce a controlled charge redistribution within the surface layer, causing the surface metallicity, electronic structure, and chemical reactivity of individual adsorption sites to be substantially altered.

We propose a spin-selective coherent electron transfer in a silicon quantum dot array. Oscillating magnetic fields and temporally controlled gate voltages are utilized to separate the electron wave function into different quantum dots depending on the spin state. We introduce a nonadiabatic protocol based on $\pi$ pulses and an adiabatic protocol which offer fast electron transfer and robustness against the error in the control-field pulse area, respectively. We also study a shortcut-to-adiabaticity protocol which compromises these two protocols. We show that this scheme can be extended to multielectron systems straightforwardly and used for nonlocal manipulations of electrons.

Orbital effects of a magnetic field in a proximitized semiconductor nanowire are studied in the context of the spatial extent of Majorana bound states. We develop an analytical model that explains the impact of concurring effects of paramagnetic coupling of the nanowire bands via the kinetic energy operator and spin-orbit interaction on the Majorana modes. We find that the perpendicular field, so far considered to be detrimental to the Majorana fermion formation, is, in fact, helpful in establishing the topological zero-energy modes in a finite system due to significant decrease in the Majorana decay length.

The spin-$\frac{1}{2}$ Heisenberg model on a kagome lattice is a typical frustrated quantum spin system. The basic structure of a kagome lattice is also present in the kagome-strip lattice in one dimension, where a similar type of frustration is expected. We thus study the magnetization plateaus of the spin-$\frac{1}{2}$ Heisenberg model on a kagome-strip chain with three-independent antiferromagnetic exchange interactions using the density-matrix renormalization-group method. In a certain range of exchange parameters, we find twelve kinds of magnetization plateaus, nine of which have magnetic structures breaking translational and/or reflection symmetry spontaneously. The structures are classified by an array of five-site unit cells with specific bond-spin correlations. In a case with a nontrivial plateau, namely a 3/10 plateau, we find long-period magnetic structure with a period of four unit cells.

The Hida model, defined on a honeycomb lattice, is a spin-1/2 Heisenberg model of aniferromagnetic hexagons (with nearest-neighbor interaction, $J_A>0)$ coupled via ferromagnetic bonds (with exchange interaction, $J_F<0)$. It applies to the spin-gapped organic materials, $\mathrm{m}\text{−}\mathrm{MPYNN}·X$ (for $X=\mathrm{I},{\mathrm{BF}}_4,{\mathrm{ClO}}_4)$, and for $|J_F|\gg J_A$, it reduces to the spin-1 kagome Heisenberg antiferromagnet (KHA). Motivated by the recent finding of the trimerized singlet (TS) ground state for spin-1 KHA, we investigate the evolution of the ground state of the Hida model from weak to strong $J_F/J_A$ using mean-field triplon analysis and Schwinger boson mean-field theory. Our triplon analysis of the Hida model shows that its uniform hexagonal singlet (HS) ground state (for weak $J_F/J_A)$ gives way to the dimerized hexagonal singlet (D-HS) ground state for $|J_F|/J_A\gtrsim 1.26$ (which for strong $J_F/J_A$ approaches the TS state). From the Schwinger boson calculations, we find that the evolution from the uniform HS phase for spin-1/2 Hida model to the TS phase for spin-1 KHA happens through two quantum phase transitions: (1) the spontaneous dimerization transition at $J_F/J_A\sim -0.28$ from the uniform HS to D-HS phase and (2) the moment formation transition at $J_F/J_A\sim -1.46$, across which the pair of spin-1/2's on every FM bond begins to appear as a bound moment that tends to spin-1 for large negative $J_F$'s. The TS ground state of spin-1 KHA is thus adiabatically connected to the D-HS ground state of the Hida model. Our calculations imply that the $\mathrm{m}\text{−}\mathrm{MPYNN}·X$ salts realize the D-HS phase at low temperatures, which can be ascertained through neutron diffraction.

Vector spin glasses are known to show two different kinds of phase transitions in the presence of an external field: the so-called de Almeida–Thouless and Gabay–Toulouse lines. While the former has been studied to some extent on several topologies (fully connected, random graphs, finite-dimensional lattices, chains with long-range interactions), the latter has been studied only in fully connected models, which however are known to show some unphysical behaviors (e.g., the divergence of these critical lines in the zero-temperature limit). Here we compute analytically both these critical lines for XY spin glasses on random regular graphs. We discuss the different nature of these phase transitions and the dependence of the critical behavior on the field distribution. We also study the crossover between the two different critical behaviors, by suitably tuning the field distribution.

Describing superfluid turbulence at intermediate scales between the intervortex distance and the macroscale requires an acceptable equation of motion for the density of quantized vortex lines $\mathcal{L}$. The closure of such an equation for superfluid inhomogeneous flows requires additional inputs besides $\mathcal{L}$ and the normal and superfluid velocity fields. In this paper, we offer a minimal closure using one additional anisotropy parameter $I_{l0}$. Using the example of counterflow superfluid turbulence, we derive two coupled closure equations for the vortex line density and the anisotropy parameter $I_{l0}$ with an input of the normal and superfluid velocity fields. The various closure assumptions and the predictions of the resulting theory are tested against numerical simulations.

We have studied carbon-doped magnesium diboride nanoparticles using ${}^{13}\mathrm{C}$ and ${}^{11}\mathrm{B}$ NMR in the normal and superconducting states. Measurements of the line shape reveal the role of carbon as a flux-pinning center and, combined with Knight shift measurements, suggest the doping procedure favors the chemical substitution scenario. We perform ab initio calculations on a structure with a single carbon-boron substitution which yield results that match the experimental data. The ${}^{13}\mathrm{C}$ and ${}^{11}\mathrm{B}$ Knight shift data are used to extract the spin susceptibility, which indicates a BCS pairing mechanism; however, we do not observe the Hebel-Slichter coherence peak from 1/$T_1$ data, which we hypothesize is due to a pair-breaking mechanism present in the boron planes.

We propose that the quasi-one-dimensional molybdenum selenide compound ${\mathrm{Tl}}_{2-x}{\mathrm{Mo}}_6{\mathrm{Se}}_6$ is a time-reversal-invariant topological superconductor induced by intersublattice pairing, even in the absence of spin-orbit coupling (SOC). No noticeable change in superconductivity is observed in Tl-deficient $\left(0\le x\le 0.1\right)$ compounds. At weak SOC, the superconductor prefers the triplet $d$ vector lying perpendicular to the chain direction and two-dimensional $E_{2u}$ symmetry, which is driven to a nematic order by spontaneous rotation symmetry breaking. The locking energy of the $d$ vector is estimated to be weak and hence the proof of its direction would rely on tunneling or phase-sensitive measurements.

The two-dimensional $XY$ model is the first well-studied system with topological point defects. On the other hand, although topological line defects are common in three-dimensional systems, the evolution mechanism of line defects is not fully understood. The six domains in hexagonal manganites converge to vortex lines in three dimensions. Using phase-field simulations, we predicted that during the domain coarsening process, the vortex-line network undergoes three types of basic topological changes, i.e., vortex-line loop shrinking, coalescence, and splitting. It is shown that the vortex-antivortex annihilation controls the scaling dynamics.

We report on the effects of hydrostatic pressure (HP) on the charge density wave observed in underdoped cuprates. We studied ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6.6}(T_c=61$ K) using high-resolution inelastic x-ray scattering (IXS), and reveal an extreme sensitivity of the phonon anomalies related to the charge density wave (CDW) order to HP. The amplitudes of the normal state broadening and superconductivity-induced phonon softening at ${\mathbf{Q}}_{\text{CDW}}$ rapidly decrease as HP is applied, resulting in the complete suppression of signatures of the CDW below $\sim 10$ kbar. Additional IXS measurements on ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6.75}$ demonstrate that this very rapid effect cannot be explained by pressure-induced modification of the doping level and highlight the different role of external pressure and doping in tuning the phase diagram of the cuprates. Our results provide insights into the mechanisms underlying the CDW formation and its interplay with superconductivity.

Plate impact experiments in the 100–250 GPa pressure range were done on a $\langle 100\rangle$ single-crystal MgO preheated before compression to 1850 K. Hot Mo(driver)-MgO targets were impacted with Mo or Ta flyers launched by the Caltech two-stage light-gas gun up to 7.5 km/s. Radiative temperatures and shock velocities were measured with 3%–4% and 1%–2% uncertainty, respectively, by a six-channel pyrometer with 3-ns time resolution, over a 500–900-nm spectral range. MgO shock front reflectivity was determined in additional experiments at 220 and 248 GPa using $\approx 50/50$ high-temperature sapphire beam splitters. Our measurements yield accurate experimental data on the mechanical, optical, and thermodynamic properties of B1 phase MgO from 102 GPa and 3900 K to 248 GPa and 9100 K, a region not sampled by previous studies. Reported Hugoniot data for MgO initially at ambient temperature, $T=298$ K, and the results of our current Hugoniot measurements on samples preheated to 1850 K were analyzed using the most general methods of least-squares fitting to constrain the Grüneisen model. This equation of state (EOS) was then used to construct maximum likelihood linear Hugoniots of MgO with initial temperatures from 298 to 2400 K. A parametrization of all EOS values and best-fit coefficients was done over the entire range of relevant particle velocities. Total uncertainties of all the EOS parameters and correlation coefficients for these uncertainties are also given. The predictive capabilities of our updated Mie-Grüneisen EOS were confirmed by (1) the good agreement between our Grüneisen data and five semiempirical $\gamma \left(V\right)$ models derived from porous shock data only or from combined static and shock data sets, (2) the very good agreement between our 1-bar Grüneisen values and $\gamma \left(T\right)$ at ambient pressure recalculated from reported experimental data on the adiabatic bulk modulus $K_s\left(T\right)$, and (3) the good agreement of the brightness temperatures, corrected for shock reflectivity, with the corresponding values calculated using the current EOS or predicted by other groups via first-principles molecular dynamics simulations. Our experiments showed no evidence of MgO melting up to 250 GPa and 9100 K. The highest shock temperatures exceed the extrapolated melting curve of Zerr and Boehler by $>3300$ K and the upper limit for the melting boundary predictions of Aguado and Madden by $>2600$ K and those of Strachan et al. by $>2100$ K. We show that the potential for superheating in our shock experiments is negligible and therefore out data put a lower limit on the melting curve of B1 phase MgO in $P\text{−}T$ space close to the set of consistent independent predictions by Sun et al., Liu et al., and de Koker and Stixrude.

We introduce a class of aperiodic arrays of electric dipoles generated from the distribution of prime numbers in complex quadratic fields (Eisenstein and Gaussian primes) as well as quaternion primes (Hurwitz and Lifschitz primes), and study the nature of their scattering resonances using the vectorial Green's matrix method. In these systems we demonstrate several distinctive spectral properties, such as the absence of level repulsion in the strongly scattering regime, critical statistics of level spacings, and the existence of critical modes, which are extended fractal modes with long lifetimes not supported by either random or periodic systems. Moreover, we show that one can predict important physical properties, such as the existence spectral gaps, by analyzing the eigenvalue distribution of the Green's matrix of the arrays in the complex plane. Our results unveil the importance of aperiodic correlations in prime number arrays for the engineering of gapped photonic media that support far richer mode localization and spectral properties compared to usual periodic and random media.

We investigate theoretically and numerically the possibility of existence of Fano and acoustic-induced transparency (AIT) resonances in a simple though realistic one-dimensional acoustic structure made of solid-fluid layers inserted between two fluids. These resonances are obtained by combining appropriately the zeros of transmission (antiresonance) induced by the solid layers and the local resonances induced by the solid or combined solid-fluid layers with surface free boundary conditions. In particular, we show the possibility of trapped modes, also called bound states in continuum, which have recently found a high renewal interest. These modes appear as resonances with zero width in the transmission spectra as well as in the density of states (DOS). We consider three different structures: (i) a single solid layer inserted between two fluids. This simple structure shows the possibility of existence of trapped modes, which are discrete modes of the solid layer that lie in the continuum modes of the surrounding fluids. We give explicit analytical expressions of the dispersion relation of these eigenmodes of the solid layer which are found independent of the nature of the surrounding fluids. By slightly detuning the angle of incidence from that associated to the trapped mode, we get a well-defined Fano resonance characterized by an asymmetric Fano profile in the transmission spectra. (ii) The second structure consists of a solid-fluid-solid triple layer embedded between two fluids. This structure is found more appropriate to show both Fano and acoustic-induced transparency resonances. We provide detailed analytical expressions for the transmission and reflection coefficients that enable us to deduce a closed-form expression of the dispersion relation giving the trapped modes. Two situations can be distinguished in the triple-layer system: in the case of a symmetric structure (i.e., the same solid layers) we show, by detuning the incidence angle $\theta$, the possibility of existence of Fano resonances that can be fitted following a Fano-type expression. The variation of the Fano parameter that describes the asymmetry of such resonances as well as their width versus $\theta$ is studied in detail. In the case of an asymmetric structure (i.e., different solid layers), we show the existence of an incidence angle that enables to squeeze a resonance between two transmission zeros induced by the two solid layers. This resonance behaves like an AIT resonance, its position and width depend on the nature of the fluid and solid layers as well as on the difference between the thicknesses of the solid layers. (iii) In the case of a periodic structure (phononic crystal), we show that trapped modes and Fano resonances give rise, respectively, to dispersionless flat bands with zero group velocity and nearly flat bands with negative or positive group velocities. The analytical results presented here are obtained by means of the Green's function method which enables to deduce in closed form: dispersion curves, transmission and reflection coefficients, DOS, as well as the displacement fields. The proposed solid-fluid layered structures should have important applications for designing acoustic mirrors and acoustic filters as well as supersonic and subsonic materials.

We introduce a method “DMT” for approximating density operators of 1D systems that, when combined with a standard framework for time evolution (TEBD), makes possible simulation of the dynamics of strongly thermalizing systems to arbitrary times. We demonstrate that the method performs well for both near-equilibrium initial states (Gibbs states with spatially varying temperatures) and far-from-equilibrium initial states, including quenches across phase transitions and pure states.

We present a detailed analysis of the conditions that result in unity absorption in metamaterial absorbers to guide the design and optimization of this important class of functional electromagnetic composites. Multilayer absorbers consisting of a metamaterial layer, dielectric spacer, and ground plane are specifically considered. Using interference theory, the dielectric spacer thickness and resonant frequency for unity absorption can be numerically determined from the functional dependence of the relative phase shift of the total reflection. Further, using transmission line theory in combination with interference theory we obtain analytical expressions for the unity absorption resonance frequency and corresponding spacer layer thickness in terms of the bare resonant frequency of the metamaterial layer and metallic and dielectric losses within the absorber structure. These simple expressions reveal a redshift of the unity absorption frequency with increasing loss that, in turn, necessitates an increase in the thickness of the dielectric spacer. The results of our analysis are experimentally confirmed by performing reflection-based terahertz time-domain spectroscopy on fabricated absorber structures covering a range of dielectric spacer thicknesses with careful control of the loss accomplished through water absorption in a semiporous polyimide dielectric spacer. Our findings can be widely applied to guide the design and optimization of the metamaterial absorbers and sensors.

We demonstrate a generalized notion of eigenstate thermalization for translation-invariant quasifree fermionic models: the vast majority of eigenstates satisfying a finite number of suitable constraints (e.g., fixed energy and particle number) have the property that their reduced density matrix on small subsystems approximates the corresponding generalized Gibbs ensemble. To this end, we generalize analytic results by H. Lai and K. Yang [Phys. Rev. B 91, 081110(R) (2015)] and illustrate the claim numerically by example of the Jordan-Wigner transform of the XX spin chain.