An absolute stress-density path for shocklessly compressed copper is obtained to over 450 GPa. A magnetic pressure drive is temporally tailored to generate shockless compression waves through over 2.5-mm-thick copper samples. The free-surface velocity data is analyzed for Lagrangian sound velocity using the iterative Lagrangian analysis (ILA) technique, which relies upon the method of characteristics. We correct for the effects of strength and plastic work heating to determine an isentropic compression path. By assuming a Debye model for the heat capacity, we can further correct the isentrope to an isotherm. Our determination of the isentrope and isotherm of copper represents a highly accurate pressure standard for copper to over 450 GPa.

We report measurements of the specific heat and electrical resistivity of $\mathrm{C}{\mathrm{a}}_3{\left(\mathrm{I}{\mathrm{r}}_{0.91}\mathrm{C}{\mathrm{o}}_{0.09}\right)}_4\mathrm{S}{\mathrm{n}}_{13}$ in comparison to $\mathrm{C}{\mathrm{a}}_3\mathrm{I}{\mathrm{r}}_4\mathrm{S}{\mathrm{n}}_{13}$. The Co substitution was chosen to suppress the structural anomaly $T^{*}=38\mathrm{K}$ reported in $\mathrm{C}{\mathrm{a}}_3\mathrm{I}{\mathrm{r}}_4\mathrm{S}{\mathrm{n}}_{13}$. While the superconducting transition temperature of $\mathrm{C}{\mathrm{a}}_3{\left(\mathrm{I}{\mathrm{r}}_{0.91}\mathrm{C}{\mathrm{o}}_{0.09}\right)}_4\mathrm{S}{\mathrm{n}}_{13}$ is slightly higher than in the stoichiometric parent compound $\mathrm{C}{\mathrm{a}}_3\mathrm{I}{\mathrm{r}}_4\mathrm{S}{\mathrm{n}}_{13}$, and it displays a stronger superconducting coupling strength, the absence of a structural phase transition allows us to determine the spectral distribution of phonon states and its relation to superconductivity. The phonon density of states $F$(ω) and the spectral electron-phonon scattering function ${a_{tr}}^{2}F\left(\omega \right)$ are determined by deconvolution of the specific heat and electrical resistivity, respectively. A dominant mode appears in both histograms at $\hslash \omega =12\mathrm{meV}$, which indicates that this phonon mode is responsible for the superconductivity in $\mathrm{C}{\mathrm{a}}_3{\left(\mathrm{I}{\mathrm{r}}_{0.91}\mathrm{C}{\mathrm{o}}_{0.09}\right)}_4\mathrm{S}{\mathrm{n}}_{13}$. The data suggest that superconductivity in this material class can be conclusively explained within a conventional strong -coupling phonon-mediated scenario.

We report on measurements of the sound velocity and attenuation in a single crystal of the candidate quantum-spin-ice material ${\mathrm{Yb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ as a function of temperature and magnetic field. The acoustic modes couple to the spins magnetoelastically and, hence, carry information about the spin correlations that sheds light on the intricate magnetic phase diagram of ${\mathrm{Yb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ and the nature of spin dynamics in the material. Particularly, we find a pronounced thermal hysteresis in the acoustic data with a concomitant peak in the specific heat indicating a possible first-order phase transition at about 0.17 K. At low temperatures, the acoustic response to magnetic field saturates hinting at the development of magnetic order. The experimental data are consistent with a first-order phase transition from a cooperative paramagnet to a ferromagnet below $T\approx 0.17$ K, as shown by fitting the data with a phenomenological mean-field theory.

The Kondo resonance of an organic molecule containing a Co atom is investigated by scanning tunneling spectroscopy and ab initio calculations on a Ag(100) surface. High resolution mapping of the line shape shows evidence of local nonradially symmetric variations of the Fano factor and the Kondo amplitude, revealing a strong influence of the molecular ligand. We show that the decay of the amplitude of the Kondo resonance is determined by the spatial distribution of the ligand's orbital being hybridized with the singly occupied Co $d_{z^2}$ orbital, forming together the singly occupied Kondo-active orbital.

We present thermoelectric power and resistivity measurements in the ferromagnet ${\mathrm{UGe}}_2$ as a function of temperature and magnetic field. At low temperature, huge quantum oscillations are observed in the thermoelectric power as a function of the magnetic field applied along the $a$ axis. The frequencies of the extreme orbits are determined and an analysis of the cyclotron masses is performed following different theoretical approaches for quantum oscillations detected in the thermoelectric power. They are compared to those obtained by Shubnikov–de Haas experiments on the same crystal and previous de Haas–van Alphen experiments. The agreement of the different probes confirms thermoelectric power as an excellent probe to extract simultaneously both microscopic and macroscopic information on the Fermi surface properties. Band structure calculations of ${\mathrm{UGe}}_2$ in the ferromagnetic state are compared to the experiment.

We study (2+1)-dimensional phases with topological order, such as fractional quantum Hall states and gapped spin liquids, in the presence of global symmetries. Phases that share the same topological order can then differ depending on the action of symmetry, leading to symmetry-enriched topological (SET) phases. Here, we present a $K$-matrix Chern-Simons approach to identify distinct phases with Abelian topological order, in the presence of unitary or antiunitary global symmetries. A key step is the identification of a smooth edge sewing condition that is used to check if two putative phases are indeed distinct. We illustrate this method by classifying $Z_2$ topological order ($Z_2$ spin liquids) in the presence of an internal $Z_2$ global symmetry for which we find six distinct phases. These include two phases with an unconventional action of symmetry that permutes anyons leading to symmetry-protected Majorana edge modes. Other routes to realizing protected edge states in SET phases are identified. Symmetry-enriched Laughlin states and double-semion theories are also discussed. Somewhat surprisingly, we observe that (i) gauging the global symmetry of distinct SET phases leads to topological orders with the same total quantum dimension, and (ii) a pair of distinct SET phases can yield the same topological order on gauging the symmetry.

We reveal the emergence of metallic Kondo clouds in an atomistic carbon quantum dot, realized as a single-atom junction in a suitably patterned graphene nanoflake. Using density functional dynamical mean-field theory (DFDMFT) we show how correlation effects lead to striking features in the electronic structure of our device, and how those are enhanced by the electron-electron interactions when graphene is patterned at the atomistic scale. Our setup provides a well-controlled environment to understand the principles behind the orbital-selective Kondo physics and the interplay between orbital and spin degrees of freedom in carbon-based nanomaterials, which indicate new pathways for spintronics in atomically patterned graphene.

We investigate the nonequilibrium insulator-metal transition driven in a $\mathrm{SmNi}{\mathrm{O}}_3$ thin film by coherent optical excitation of the $\mathrm{LaAl}{\mathrm{O}}_3$ substrate lattice. By probing the transient optical properties over a broad frequency range $\left(100-800\mathrm{c}{\mathrm{m}}^{-1}\right)$, we analyze both the time-dependent metallic plasma and the infrared optical phonon line shapes. We show that the light-induced metallic phase in $\mathrm{SmNi}{\mathrm{O}}_3$ has the same carrier density as the equilibrium metallic phase. We also report that the $\mathrm{LaAl}{\mathrm{O}}_3$ substrate acts as a transducer only at the earlier time delays, as the vibrations are driven coherently. No long-lived structural rearrangement takes place in the substrate. Finally, we show that the transient insulator-metal transition occurs both below and above the Néel temperature. We conclude that the supersonic melting of magnetic order measured with ultrafast x rays is not the driving force of the formation of the metallic phase. We posit that the insulator-metal transition may origin from the rearrangement of ordered charges at the interface propagating into the film.

In this paper, we present a detailed study of the boron impurity in $3C$-SiC (${\mathrm{B}}_{Si}$) in the cluster (CL) and supercell (SC) approximations, using representative local, gradient-corrected, and hybrid density functionals. Comparison of the theoretical spin-Hamiltonian parameters, calculated in the CL approximation using nonlocal density functionals, with the corresponding experimental values for the so-called shallow boron in SiC has proved that the latter is the ${\mathrm{B}}_{Si}^0$ defect. We analyze the motional effects in the electron paramagnetic resonance spectra, as well as the site dependence of the symmetry and SH parameters of ${\mathrm{B}}_{Si}^0$. The dependencies of the calculated structural and energetic parameters on the size of the model space both for SC and CL methods are presented. The calculated relative formation energies and transition energy levels for the neutral ${\mathrm{B}}_{Si}$ and ${\mathrm{B}}_C$ centers reveal substantial finite-size effects. A simple extrapolation scheme indicates that the supercells with up to ${10}^5$ atoms are required to achieve the desired accuracy level of 0.1 eV. Calculations suggest that ${\mathrm{B}}_C$ impurity is a hyperdeep acceptor, which acts as the electron trap rather than increases the $p$-type conductivity.

We present a comprehensive study of the electronic, magnetic, and optical properties of ${\mathrm{CuGa}}_{1-x}{\mathrm{Fe}}_x{\mathrm{S}}_2$, as a promising candidate for intermediate-band (IB) solar cells. We use hybrid exchange-correlation functional within the density functional theory framework, and show that Fe doping induces unoccupied states 1.6–1.9 eV above the valence band. The IBs significantly enhance the optical absorption in lower energy part of the spectrum. We find that at moderate $n$-type co-doping concentration, the added charge occupies part of the IB in the gap, but large concentrations lower the energy of the occupied IB toward the valence band. Moreover, we show that Fe impurities tend to cluster within the compound and they choose antiferromagnetic ordering. The findings can have a significant effect in understanding this material and help to synthesize more efficient IB solar cells.

Predicting the ground states for surface adsorption is a challenging problem because the number of degrees of freedom involved in the process is very high. Most of the studies deal with some specific arrangements of adsorbates on a given surface, but very few of them actually attempt to find the ground states for different adatom coverage. In this work, we show the effectiveness of the cluster expansion method to predict the “ground states” resulting from chemisorption of oxygen and fluorine atom on the surface of monolayer black phosphorus or phosphorene. For device applications, we find that in addition to band-gap tuning, controlled chemisorption can change the unique anisotropic carrier effective mass for both the electrons and holes and even rotate them by ${90}^{\circ }$, which can be useful for exploring unusual quantum Hall effect and electronic devices based on phosphorene.

We consider thermoelectric transport properties of the edge states of a two-dimensional topological insulator in a double quantum point contact geometry coupled to two thermally biased reservoirs. Both spin-preserving and spin-flipping tunneling processes between opposite edges are analyzed in the presence of electron-electron interactions. We demonstrate that the simultaneous presence of spin-flipping processes and interactions gives rise to a finite longitudinal spin current. Moreover, its sign and amplitude can be tuned by means of gate voltages with the possibility to generate a pure spin current, with a vanishing charge current.

$\mathrm{B}{\mathrm{a}}_8\mathrm{S}{\mathrm{i}}_{39}\mathrm{G}{\mathrm{e}}_7$ and $\mathrm{B}{\mathrm{a}}_8\mathrm{S}{\mathrm{i}}_{29}\mathrm{G}{\mathrm{e}}_{17}$ have been studied at high pressure using x-ray diffraction and x-ray absorption spectroscopy (XAS) at the Ge $K$ edge. In $\mathrm{B}{\mathrm{a}}_8\mathrm{S}{\mathrm{i}}_{39}\mathrm{G}{\mathrm{e}}_7$, a transition is observed similar to the one in $\mathrm{B}{\mathrm{a}}_8\mathrm{S}{\mathrm{i}}_{46}$, apparently isostructural. However, the XAS data analysis shows that the transformation is related to the off-centering of the Ba atoms. A theoretical model based on a Landau potential suggests that this transition is second order, with a symmetry-breaking mechanism related to the Ba displacement probably initiated by the vacancy creation or local distortion predicted theoretically. This analysis gives a coherent picture of the phase transition mechanism. In the case of $\mathrm{B}{\mathrm{a}}_8\mathrm{S}{\mathrm{i}}_{29}\mathrm{G}{\mathrm{e}}_{17}$, such phase transition is not observed as the Ba atoms appear already off-center at ambient pressure.

The continuous electron bombardment of a sample during transmission electron microscopy (TEM) drives atomic-scale transformations. In earlier studies the transformations appeared to proceed as if the sample was held at an elevated temperature, and, indeed, the hypothesis of an electron-beam-induced virtual temperature has gained traction in the scientific community. However, the sample is not significantly heated by the electron beam, meaning the processes are not activated by thermal vibrations. Instead, individual collisions between the electrons and the target atoms, and/or excitations of the electronic system, lead to the observed transformations. It is not a priori clear what virtual temperature can be assigned to the conditions under the electron irradiation, or even if such a temperature can be defined at all. Here, we attempt to measure the virtual temperature, specific to this system, by comparing the relative population of the three different divacancy defect states in single-layer graphene to the Boltzmann distribution using calculated energy levels of the defect states. The experiment is conducted using aberration-corrected high-resolution TEM at an acceleration voltage of 80 kV. Atomistic simulations are used to learn about the energetics of the defects. We find that the measured populations cannot be fitted to the Boltzmann distribution, and consequently no universal virtual temperature can be assigned to the system.

The low-frequency response of systems near a many-body localization transition can be dominated by rare regions that are locally critical or “in the other phase.” It is known that in one dimension, these rare regions can cause the dc conductivity and diffusion constant to vanish even inside the delocalized thermal phase. Here, we present a general analysis of such Griffiths effects in the thermal phase near the many-body localization transition: we consider both one-dimensional and higher-dimensional systems, subject to quenched randomness, and discuss both linear response (including the frequency- and wave-vector-dependent conductivity) and more general dynamics. In all the regimes we consider, we identify observables that are dominated by rare-region effects. In some cases (one-dimensional systems and Floquet systems with no extensive conserved quantities), essentially all long-time local observables are dominated by rare-region effects; in others, generic observables are instead dominated by hydrodynamic long-time tails throughout the thermal phase, and one must look at specific probes, such as spin echo, to see Griffiths behavior.

The structural and magnetic properties of one atomic layer thin nanostructures of Ni deposited on fcc Fe monolayer stripes on Ir(111) have been studied by (spin-resolved) scanning tunneling microscopy measurements. Ni grows dominantly in fcc stacking on Ir(111), whereas it forms a dense reconstruction pattern on Fe/Ir(111), with bridge site dislocation lines separating triangularly shaped fcc and hcp regions. In the interior of the Ni nanostructures, fcc and hcp areas are of comparable size, but the fcc stacking dominates at the edges. The magnetic nanoskyrmion lattice of Fe/Ir(111) undergoes a transition to ferromagnetism where covered with a single layer of Ni. The Ni/Fe bilayer islands show an out-of-plane easy axis and can be switched by external magnetic fields of only 1.0 T–1.5 T.

In this work, we present a nuclear magnetic resonance (NMR) study of the spin dynamics in the rare-earth-based low-dimensional molecular magnetic chains $\mathrm{Eu}{\left(\mathrm{hfac}\right)}_3\mathrm{NITEt}$ and $\mathrm{Gd}{\left(\mathrm{hfac}\right)}_3\mathrm{NITEt}$ (in short, Eu-Et and Gd-Et). Although both samples are based on the same chemical building block, [(${\mathrm{hfac})}_3\mathrm{NITEt}]$, their magnetic properties change dramatically when the ${\mathrm{Eu}}^{3+}$ ion, which is nonmagnetic at low temperatures, is substituted by the magnetic ${\mathrm{Gd}}^{3+}$ ion. The present proton NMR investigation shows that, down to the lowest investigated temperature ($T=1.5$ K for Gd-Et and $T=3$ K for Eu-Et), the Eu-Et chain behaves as a one-dimensional Heisenberg model with antiferromagnetic exchange coupling ($J=-20$ K) between $s=1/2$ organic radicals, and has a $T$-independent exchange frequency (${\omega }_e=2.6\times {10}^{12}$ rad/s). In the Gd-Et chain, in contrast, a competition arises between nearest-neighbor ferromagnetic coupling and next-nearest-neighbor antiferromagnetic coupling; moreover, two phase transitions have previously been found, in agreement with Villain's conjecture: a first transition, at $T_0=2.2$ K, from a high temperature paramagnetic phase to a chiral spin liquid phase, and a second transition, at $T_N=1.9$ K, to a three-dimensional helical spin solid phase. Contrary to the Eu-Et chain (whose three-dimensional ordering temperature is estimated to insurge at very low, $T_N\approx 0.3$ K), critical spin dynamics effects have been measured in the Gd-Et chain on approaching $T_N=1.9$ K: namely, a divergence of the proton nuclear spin-lattice relaxation rate $1/T_1$, which in turn produces a sudden wipe-out of the NMR signal in a very narrow ($\mathrm{\Delta }T\sim 0.04$ K) temperature range above $T_N$. Below $T_N$, an inhomogeneous broadening of the NMR line indicates a complete spin freezing. At $T_0=2.2$ K, instead, such critical effects are not observed because NMR measurements probe the two-spin correlation function, while the chiral spin liquid phase transition is associated with a divergence of the four-spin correlation function.

During ultrafast demagnetization after the excitation of ferromagnetic films with femtosecond laser pulses, the angular momentum of the electronic system is transferred to the lattice via electron-phonon scatterings. The actual amount of transfer is calculated for Ni and Fe by considering spin-phonon eigenmodes, which have a sharp angular momentum. Because the considered Hamiltonian is not isotropic, the total angular momentum is not conserved.

The time evolution of magnetization induced by circularly polarized light in an $S=1$ Heisenberg chain with large easy-plane anisotropy is studied numerically and analytically. Results at constant light frequency $\mathrm{\Omega }={\mathrm{\Omega }}_0$ are interpreted in terms of absorption lines of the electronic spin resonance spectrum. The application of time-dependent frequency $\mathrm{\Omega }=\mathrm{\Omega }\left(t\right)$ light, so called chirping, is shown to be an efficient procedure in order to obtain within a short time a large, controlled value of the magnetization $M^z$. Furthermore, comparison with a two-level model provides a qualitative understanding of the induced magnetization process.

We perform a micromagnetic study of the synchronization dynamics in nanoconstriction-based spin Hall nano-oscillator (SHNO) arrays. The simulation reveals that efficient synchronization in this kind of system is possible, and indicates that the synchronization is mediated by a combination of linear coupling through the overlap of localized modes and parametric coupling through propagating spin waves which are excited by the second harmonic oscillation in the SHNOs. Due to the anisotropic spin wave dispersion in the studied system, the synchronization properties decisively depend on the geometrical alignment of the SHNO array with respect to the external field. We find that, by utilizing the directional spin wave emission and correspondingly optimizing the alignment of the SHNO array, the synchronization is enhanced with a significant increase of the phase-locking bandwidth.