We have performed in situ synchrotron x-ray diffraction studies of the iridium-hydrogen system up to 125 GPa. At 55 GPa, a phase transition in the metal lattice from the fcc to a distorted simple cubic phase is observed. The new phase is characterized by a drastically increased volume per metal atom, indicating the formation of a metal hydride, and substantially decreased bulk modulus of 190 GPa (383 GPa for pure Ir). Ab initio calculations show that the hydrogen atoms occupy the face-centered positions in the metal matrix, making this the first known noninterstitial noble metal hydride and, with a stoichiometry of ${\mathrm{IrH}}_3$, the one with the highest volumetric hydrogen content. Computations also reveal that several energetically competing phases exist, which can all be seen as having distorted simple cubic lattices. Slow kinetics during decomposition at pressures as low as 6 GPa suggest that this material is metastable at ambient pressure and low temperatures.

The electronic properties of single walled carbon nanotubes (SWNTs) can change with a slight deformation, such as the one caused by the pressure of one SWNT crossing over the other in an “$X$” shape. The effect, however, is extremely localized. We present a tip-enhanced Raman investigation of the extremely localized semiconductor-to-metal transition of SWNTs in such a situation, where we can see how the Fano interaction, which is a Raman signature of metallic behavior, grows towards the junction and is localized within a few nanometers of its vicinity. After exploring the deconvoluted components of the $G$-band Raman mode, we were able to reveal the change in electronic properties of a SWNT at extremely high spatial resolution along its length.

Spin-split two-dimensional electronic states have been observed on ultrathin Sn(001) films grown on InSb(001) substrates. Angle-resolved photoelectron spectroscopy (ARPES) performed on these films revealed Dirac-cone-like linear dispersion around the $\overline{\Gamma }$ point of the surface Brillouin zone, suggesting nearly massless electrons belonging to 2D surface states. The states disperse across a band gap between bulklike quantum well states in the films. Moreover, both circular dichroism of ARPES and spin-resolved ARPES studies show helical spin polarization of the Dirac-cone-like surface states, suggesting a topologically protected character as in a bulk topological insulator (TI). These results indicate that a quasi-3D TI phase can be realized in ultrathin films of zero-gap semiconductors.

By a combined angle-resolved photoemission spectroscopy and density functional theory study, we discover that the surface metallicity is polarity driven in ${\mathrm{SmB}}_6$. Two surface states, not accounted for by the bulk band structure, are reproduced by slab calculations for coexisting ${\mathrm{B}}_6$ and Sm surface terminations. Our analysis reveals that a metallic surface state stems from an unusual property, generic to the (001) termination of all hexaborides: the presence of boron $2p$ dangling bonds, on a polar surface. The discovery of polarity-driven surface metallicity sheds new light on the 40-year old conundrum of the low-temperature residual conductivity of ${\mathrm{SmB}}_6$, and raises a fundamental question in the field of topological Kondo insulators regarding the interplay between polarity and nontrivial topological properties.

As nanomagnetic devices scale to smaller sizes, spin-orbit coupling due to the broken structural inversion symmetry at interfaces becomes increasingly important. Here, we study interfacial spin-orbit coupling effects in magnetic bilayers using a simple Rashba model. The spin-orbit coupling introduces chirality into the behavior of the electrons and through them into the energetics of the magnetization. In the derived form of the magnetization dynamics, all of the contributions that are linear in the spin-orbit coupling follow from this chirality, considerably simplifying the analysis. For these systems, an important consequence is a correlation between the Dzyaloshinskii-Moriya interaction and the spin-orbit torque. We use this correlation to analyze recent experiments.

In scanning tunneling experiments on semiconductor surfaces, the energy scale within the tunneling junction is usually unknown due to tip-induced band bending. Here, we experimentally recover the zero point of the energy scale by combining scanning tunneling microscopy with Kelvin probe force spectroscopy. With this technique, we revisit shallow acceptors buried in GaAs. Enhanced acceptor-related conductance is observed in negative, zero, and positive band-bending regimes. An Anderson-Hubbard model is used to rationalize our findings, capturing the crossover between the acceptor state being part of an impurity band for zero band bending and the acceptor state being split off and localized for strong negative or positive band bending, respectively.

We performed temperature dependent x-ray linear dichroism (XLD) experiments on an iron pnictide system, $\mathrm{Ba}({\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x{)}_2{\mathrm{As}}_2$ with $x=0.00$, 0.05, 0.08, and 0.10 to experimentally verify the existence of orbital ordering (OO). Substantial XLD was observed in polarization dependent x-ray absorption spectra of Fe $L$ edges. By exploiting the difference in the temperature dependent behaviors, OO, and structure contributions to XLD could be clearly separated. The observed OO signal indicates different occupation numbers for $d_{yz}$ and $d_{zx}$ orbitals and supports the existence of ferro-OO. The results are also consistent with the theoretical prediction. Moreover, we find substantial OO signal well above the structural and magnetic transition temperatures, which suggests the existence of strong OO fluctuations up to high temperatures.

We investigate with angle-resolved photoelectron spectroscopy the changes of the Fermi surface and the main bands from the paramagnetic state to the antiferromagnetic (AFM) state occurring below 72 K in ${\mathrm{Fe}}_{1.06}\mathrm{Te}$. The evolution is completely different from that observed in Fe pnictides, as nesting is absent. The AFM state is a rather good metal, in agreement with our magnetic band structure calculation. On the other hand, the paramagnetic state is very anomalous with a large pseudogap of $\sim 65\mathrm{meV}$ on the electron pocket that closes in the AFM state. We discuss this behavior in connection with spin fluctuations existing above the magnetic transition and the correlations predicted in the spin-freezing regime of the incoherent metallic state.

Motivated by the fully gapped superconductivity in iron-based superconductors with uncompensated electron pockets, we propose a spin singlet, but orbital triplet analogue of the superfluid phase of ${}^3\mathrm{He}\mathrm{\text{−}}\mathrm{B}$. We show that orbital triplets with a nominal $d$-wave symmetry at the iron sites can transform as $s$-wave pairs under rotations about the selenium sites. Linear combinations of such $d_{xy}$ and $d_{x^2-y^2}$ triplets form a fully gapped, topological superconductor. Raman-active excitations are predicted to develop below the superconducting transition temperature.

We introduce the idea of emergent lattices, where a simple lattice decouples into two weakly coupled lattices as a way to stabilize spin liquids. In ${\mathrm{LiZn}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$, the disappearance of $2/3$ of the spins at low temperatures suggests that its triangular lattice decouples into an emergent honeycomb lattice weakly coupled to the remaining spins, and we suggest several ways to test this proposal. We show that these orphan spins act to stabilize the spin liquid in the $J_1$-$J_2$ honeycomb model and also discuss a possible 3D analogue, ${\mathrm{Ba}}_2{\mathrm{MoYO}}_6$ that may form a “depleted fcc lattice.”

We study the quasi-instantaneous change of electron density in the unit cells of LiH and ${\mathrm{NaBH}}_4$ in response to a nonresonant strong optical field. We determine for the first time the related transient electron density maps, applying femtosecond x-ray powder diffraction as a structure probe. The light-induced charge relocation in ${\mathrm{NaBH}}_4$ exhibits an electron transfer from the anion (${\mathrm{BH}}_4^{-}$) to the ${\mathrm{Na}}^{+}$ cation. In contrast, LiH displays the opposite behavior, i.e., an increase of the ionicity of LiH in the presence of the strong electric field. This behavior originates from strong electron correlations in LiH, as is evident from a comparison with quasiparticle band structures calculated within the Coulomb-hole-plus-screened-exchange formalism.

Oxygen vacancies are an important type of defect in transition metal oxides. In ${\mathrm{SrTiO}}_3$ they are believed to be the main donors in an otherwise intrinsic crystal. At the same time, a relatively deep gap state associated with the vacancy is widely reported. To explain this inconsistency we investigate the effect of electron correlation in an oxygen vacancy (OV) in ${\mathrm{SrTiO}}_3$. When taking correlation into account, we find that the OV-induced localized level can at most trap one electron, while the second electron occupies the conduction band. Our results offer a natural explanation of how the OV in ${\mathrm{SrTiO}}_3$ can produce a deep in-gap level (about 1 eV below the conduction band bottom) in photoemission, and at the same time be an electron donor. Our analysis implies that an OV in ${\mathrm{SrTiO}}_3$ should be fundamentally regarded as a magnetic impurity, whose deep level is always partially occupied due to the strong Coulomb repulsion. An OV-based Anderson impurity model is derived, and its implications are discussed.

The linearity of quantum mechanics leads, under the assumption that the wave function offers a complete description of reality, to grotesque situations famously known as Schrödinger’s cat. Ways out are either adding elements of reality or replacing the linear evolution by a nonlinear one. Models of spontaneous wave function collapses took the latter path. The way such models are constructed leaves the question of whether such models are in some sense unique, i.e., whether the nonlinear equations replacing Schrödinger’s equation are uniquely determined as collapse equations. Various people worked on identifying the class of nonlinear modifications of the Schrödinger equation, compatible with general physical requirements. Here we identify the most general class of continuous wave function evolutions under the assumption of no-faster-than-light signaling.

Quantum corrections to three-point functions of scalar single trace operators in planar $\mathcal{N}=4$ Super-Yang-Mills theory are studied using integrability. At one loop, we find new algebraic structures that not only govern all two-loop corrections to the mixing of the operators but also automatically incorporate all one-loop diagrams correcting the tree-level Wick contractions. Speculations about possible extensions of our construction to all loop orders are given. We also match our results with the strong coupling predictions in the classical (Frolov-Tseytlin) limit.

In this Letter we analyze the consequences, for the LHC, of gauge and third family Yukawa coupling unification with a particular set of boundary conditions defined at the grand unified theory (GUT) scale, which we characterize as effective “mirage” mediation. We perform a global ${\chi }^2$ analysis including the observables $M_W$, $M_Z$, $G_F$, ${\alpha }_{em}^{-1}$, ${\alpha }_s(M_Z)$, $M_t$, $m_b(m_b)$, $M_{\tau }$, $\mathrm{BR}(B\to X_s\gamma )$, $\mathrm{BR}(B_s\to {\mu }^{+}{\mu }^{-})$, and $M_h$. The fit is performed in the minimal supersymmetric standard model in terms of 10 GUT scale parameters, while $\tan \beta$ and $\mu$ are fixed at the weak scale. We find good fits to the low energy data and a supersymmetry spectrum which is dramatically different than previously studied in the context of Yukawa unification.

We calculate next-to-leading order (NLO) QCD corrections to electroweak Higgs boson plus three jet production. Both vector boson fusion (VBF) and Higgs-strahlung type contributions are included along with all interferences. The calculation is implemented within the Matchbox NLO framework of the Herwig++ event generator.

We report a novel insulator-insulator transition arising from the internal charge degrees of freedom in the two-dimensional quarter-filled organic salt $\beta \mathrm{\text{−}}(meso\mathrm{\text{−}}\mathrm{DMBEDT}\mathrm{\text{−}}\mathrm{TTF}{)}_2{\mathrm{PF}}_6$. The optical conductivity spectra above $T_c=70\mathrm{K}$ display a prominent feature of the dimer Mott insulator, characterized by a substantial growth of a dimer peak near 0.6 eV with decreasing temperature. The dimer peak growth is rapidly quenched as soon as a peak of the charge order appears below $T_c$, indicating a competition between the two insulating phases. Our infrared imaging spectroscopy has further revealed a spatially competitive electronic phase far below $T_c$, suggesting a nature of quantum phase transition driven by material-parameter variations.

A spatial avalanche model is introduced, in which avalanches increase stability in the regions where they occur. Instability is driven globally by a driving process that contains shocks. The system is typically subcritical, but the shocks occasionally lift it into a near- or supercritical state from which it rapidly retreats due to large avalanches. These shocks leave behind a signature—a distinct power-law crossover in the avalanche size distribution. The model is inspired by landslide field data, but the principles may be applied to any system that experiences stabilizing failures, possesses a critical point, and is subject to an ongoing process of destabilization that includes occasional dramatic destabilizing events.

Discontinuous shear thickening (DST) observed in many dense athermal suspensions has proven difficult to understand and to reproduce by numerical simulation. By introducing a numerical scheme including both relevant hydrodynamic interactions and granularlike contacts, we show that contact friction is essential for having DST. Above a critical volume fraction, we observe the existence of two states: a low viscosity, contactless (hence, frictionless) state, and a high viscosity frictional shear jammed state. These two states are separated by a critical shear stress, associated with a critical shear rate where DST occurs. The shear jammed state is reminiscent of the jamming phase of granular matter. Continuous shear thickening is seen as a lower volume fraction vestige of the jamming transition.

We present possible indications for flavor separation during the QCD crossover transition based on continuum extrapolated lattice QCD calculations of higher order susceptibilities. We base our findings on flavor-specific quantities in the light and strange quark sector. We propose a possible experimental verification of our prediction, based on the measurement of higher order moments of identified particle multiplicities. Since all our calculations are performed at zero baryochemical potential, these results are of particular relevance for the heavy-ion program at the LHC.