The two-dimensional layered perovskite Sr2IrO4 was proposed to be a spin-orbit Mott insulator, where the effect of Hubbard interaction is amplified on a narrow J eff = 1/2 band due to strong spinorbit coupling. On the other hand, the three-dimensional orthorhombic perovskite (Pbnm) SrIrO3 remains metallic. To understand the physical origin of the metallic state and possible transitions to insulating phases, we construct a tight-binding model for SrIrO3. The band structure possesses a line node made of J eff = 1/2 bands below the Fermi level. As a consequence, instability towards magnetic ordering is suppressed and the system remains metallic. This line node, originating from the underlying crystal structure, turns into a pair of three-dimensional nodal points on the introduction of a staggered potential or spin-orbit coupling strength between alternating layers. Increasing this potential beyond a critical strength induces a transition to a strong topological insulator, followed by another transition to a normal band insulator. We propose that materials constructed with alternating Ir-and Rh-oxide layers along the (001) direction, such as Sr2IrRhO6, are candidates for a strong topological insulator.

There has been a rapidly growing interest on the interplay between spin-orbit coupling (SOC) and Hubbard interaction U in correlated materials. A current consensus is that the stronger the SOC, the smaller is the critical interaction U c required for a spin-orbit Mott insulator, because the atomic SOC splits a band into different total angular momentum bands narrowing the effective bandwidth. It was further claimed that at large enough SOC, the stronger the SOC, the weaker the U c because in general the effective SOC is enhanced with increasing electron-electron interaction strength. Contrary to this expectation, we find that, in orthorhombic perovskite oxides (Pbnm), the stronger the SOC, the bigger the U c . This is originated from a line of Dirac node in J e f f = 1/2 bands near the Fermi level inherited from a combination of the lattice structure and a large SOC. Due to this protected line of nodes, there are small hole and electron pockets in SrIrO 3 , and such a small density of states makes Hubbard interaction less efficient in building a magnetic insulator. The full phase diagram in U vs. SOC is obtained, where non-magnetic semimetal, magnetic metal, and magnetic insulator are found. Magnetic ordering patterns beyond U c are also presented. We further discuss implications of our finding in relation to other perovskites such as SrRhO 3 and SrRuO 3 .

Strong coupling between light and matter is possible with a variety of organic materials. In contrast to the simpler inorganic case, organic materials often have a complicated spectrum, with vibrationally dressed electronic transitions. Strong coupling to light competes with this vibrational dressing, and if strong enough, can suppress the entanglement between electronic and vibrational degrees of freedom. By exploiting symmetries, we can perform exact numerical diagonalization to find the polaritonic states for intermediate numbers of molecules, and use these to define and validate accurate expressions for the lower polariton states and strong-coupling spectrum in the thermodynamic limit. Using this approach, we find that vibrational decoupling occurs as a sharp transition above a critical matter-light coupling strength. We also demonstrate how the polariton spectrum evolves with the number of molecules, recovering classical linear optics results only at large N . arXiv:1608.08929v3 [cond-mat.mes-hall]

The electronic stopping power of H and He moving through gold is obtained to high accuracy using time-evolving density-functional theory, thereby bringing usual first-principles accuracies into this kind of strongly coupled, continuum non-adiabatic processes in condensed matter. The two key unexplained features of what observed experimentally have been reproduced and understood: (i) The non-linear behaviour of stopping power versus velocity is a gradual crossover as excitations tail into the d-electron spectrum; and (ii) the low-velocity H/He anomaly (the relative stopping powers are contrary to established theory) is explained by the substantial involvement of the d electrons in the screening of the projectile even at the lowest velocities where the energy loss is generated by s-like electron-hole pair formation only.Non-adiabatic processes are at the heart of aspects of science and technology as important as radiation damage of materials in the nuclear and space industries, and radiotherapy in medicine. Yet, in spite of a long history, the quantitative understanding of non-adiabatic processes in condensed matter and our ability to perform predictive theoretical simulations of processes coupling many adiabatic energy surfaces is very much behind what accomplished for adiabatic situations, for which first-principles calculations provide predictions of varied properties within a few percent accuracy. Substantial progress has been made for weakly non-adiabatic problems such as the chemistry of vibrationally excited molecules landing on metal surfaces [1], but not in the stronger coupling regime of radiation damage. Recently, the electronic stopping power for swift ions in gold has been carefully characterized by experiments [2-4], showing flagrant discrepancies with the established paradigm for such problems [5,6], and only qualitative agreement with time-dependent tight-binding studies [7], and with detailed studies for protons based on first principles [8], leaving very fundamental questions unanswered in spite of the apparent simplicity of the system. Most notably the H/He anomaly: the present understanding predicts a stopping power for H higher than for He at low velocities [6], which strongly contradicts the recent experiments [4].A particle moving through a solid material interacts with it and loses its kinetic energy to both the nuclei and the electrons inside it. At projectile velocities between 0.1 and 1 atomic units (a.u. henceforth) both the nuclear and the electronic contributions to the stopping power (energy lost by the projectile per unit length) are sizeable [7]. Based on the jellium model (homogeneous electron gas) the electronic stopping power, S e , is predicted to be S e ∝ v for a slow projectile traversing a metallic medium [9,10]. Such behaviour has been observed experimentally in many sp-bonded metals [11,12], and the jellium model has allowed deep understanding of the dynamic screening of the projectile and its relation to stopping [13]. Even the jellium prediction of an oscillation of the ...

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