Direct coupling of light to valley current.

The coupling of circularly polarized light to local band structure extrema ("valleys") in two dimensional semiconductors promises a new electronics based on the valley degree of freedom. Such pulses, however, couple only to valley charge and not to the valley current, precluding lightwave manipulation of this second vital element of valleytronic devices. Contradicting this established wisdom, we show that the few cycle limit of circularly polarized light is imbued with an emergent vectorial character that allows direct coupling to the valley current.

Light-Shaping of Valley States.

The established paradigm to create valley states, excitations at local band extrema ("valleys"), is through selective occupation of specific valleys via circularly polarized laser pulses. Here we show a second way exists to create valley states, not by valley population imbalance but by "light-shaping" in momentum space, i.e.

Giant and Controllable Valley Currents in Graphene by Double Pumped THz Light.

The field of valleytronics considers the creation and manipulation of "valley states", charge excitations characterized by a particular value of the crystal momentum in the Brillouin zone. Here we show, using the example of minimally gapped (≤40 meV) graphene, that there exist lightforms that create almost perfect valley contrasting current states (up to ∼80% valley purity) in the absence of a valley contrasting charge excitation. These "momentum streaked" THz waveforms act by deforming the excited state population in momentum space such that current flows at one valley yet is blocked at the conjugate valley.

Making a case for femto-phono-magnetism with FePt.

In the field of femtomagnetism, magnetic matter is controlled by ultrafast laser pulses; here, we show that coupling phonon excitations of the nuclei to spin and charge leads to femto-phono-magnetism, a powerful route to control magnetic order at ultrafast times. With state-of-the-art theoretical simulations of coupled spin, charge, and lattice dynamics, we identify strong nonadiabatic spin-phonon coupled modes that dominate early time spin dynamics. Activating these phonon modes that we show leads to an additional (up to 40% extra) loss of moment in iron-platinum occurring within 40 femtoseconds of the pump laser pulse.

Perfect and Controllable Nesting in Minimally Twisted Bilayer Graphene.

Parallel ("nested") regions of a Fermi surface (FS) drive instabilities of the electron fluid, for example, the spin density wave in elemental chromium. In one-dimensional materials, the FS is trivially fully nested (a single nesting vector connects two "Fermi dots"), while in higher dimensions only a fraction of the FS consists of parallel sheets. We demonstrate that the tiny angle regime of twist bilayer graphene (TBLG) possesses a phase, accessible by interlayer bias, in which the FS consists entirely of nestable "Fermi lines", the first example of a completely nested FS in a two-dimensional (2D) material.

Laser-Induced Intersite Spin Transfer.

Laser pulses induce spin-selective charge flow that we show to generate dramatic changes in the magnetic structure of materials, including a switching of magnetic order from antiferromagnetic (AFM) to transient ferromagnetic (FM) in multisub-lattice systems. The microscopic mechanism underpinning this ultrafast switching of magnetic order is dominated by spin-selective charge transfer from one magnetic sublattice to another. Because this spin modulation is purely optical in nature (i.

Anomalous Dirac point transport due to extended defects in bilayer graphene.

Charge transport at the Dirac point in bilayer graphene exhibits two dramatically different transport states, insulating and metallic, that occur in apparently otherwise indistinguishable experimental samples. We demonstrate that the existence of these two transport states has its origin in an interplay between evanescent modes, that dominate charge transport near the Dirac point, and disordered configurations of extended defects in the form of partial dislocations. In a large ensemble of bilayer systems with randomly positioned partial dislocations, the distribution of conductivities is found to be strongly peaked at both the insulating and metallic limits.

An anomalous interlayer exciton in MoS.

The few layer transition metal dichalcogenides are two dimensional materials that have an intrinsic gap of the order of ≈2 eV. The reduced screening in two dimensions implies a rich excitonic physics and, as a consequence, many potential applications in the field of opto-electronics. Here we report that a layer perpendicular electric field, by which the gap size in these materials can be efficiently controlled, generates an anomalous inter-layer exciton whose binding energy is independent of the gap size.

Mediators of the relation between sexual victimization and distress: Comparison to bereavement.

Objective: The purposes of this research were (a) to examine relationship quality and neuroticism as mediators of the relation between past sexual victimization and current distress in 2 samples of college students and (b) to examine the specificity of the mediated effects by assessing whether these variables also mediated the relation between the most common potentially traumatic event in both samples (past bereavement) and current distress. This study improved on prior research by using longitudinal data, assessing multiple mediators, assessing specificity of mediated effects, and replicating results across 2 samples.

Method: Participants in both studies were undergraduate students in psychology courses (Ns = 1,528 and 1,084, respectively).

Social Causation Versus Social Erosion: Comparisons of Causal Models for Relations Between Support and PTSD Symptoms.

Social support is a robust correlate of posttraumatic stress disorder (PTSD) symptoms and of general psychological distress (Ozer, Best, Lipsey, & Weiss, 2003). The nature of the causal relationship between support and PTSD remains the subject of debate, with 2 models, social erosion and social causation, often used to explain findings. Despite extensive research using these models, no studies of which we are aware have included tests of both models within the same series of analyses, across more than 2 time points, in veterans.

Using reinforcement sensitivity to understand longitudinal links between PTSD and relationship adjustment.

There is limited research testing longitudinal models of how posttraumatic stress disorder (PTSD) severity leads to impaired relationship adjustment. The present study evaluated 2 potential mechanisms among a longitudinal sample of National Guard soldiers deployed to the Iraq War: (1) sensitivity to cues associated with punishment within intimate relationships and (2) sensitivity to cues associated with incentives in intimate relationships. Participants were surveyed by mail 1 year after an extended 16-month combat deployment and again 2 years later.

Buffering the responses of avoidantly attached romantic partners in strain test situations.

Strain tests are unique contexts that have important implications for relationships, but they have rarely been studied in social interactions. We investigate how more avoidant individuals (responders) react when their romantic partners (askers) request cooperation with an important plan/goal that requires a major sacrifice from responders. As predicted, more avoidant responders were less accommodating when asked to sacrifice and showed drops in trust and commitment following the strain test discussion.

Sexual victimization history predicts academic performance in college women.

College women frequently report having experienced sexual victimization (SV) in their lifetime, including child sexual abuse and adolescent/adult sexual assault. Although the harmful mental health sequelae of SV have been extensively studied, recent research suggests that SV is also a risk factor for poorer college academic performance. The current studies examined whether exposure to SV uniquely predicted poorer college academic performance, even beyond contributions from three well-established predictors of academic performance: high school rank, composite standardized test scores (i.

Excitons in Organics Using Time-Dependent Density Functional Theory: PPV, Pentacene, and Picene.

We apply the bootstrap kernel within time-dependent density functional theory to study the one-dimensional chain of polymer polyphenylenevinylene and molecular crystals of picene and pentacene. The absorption spectra of poly(p-phenylenevinylene) has a bound excitonic peak that is well-reproduced. Pentacene and picene, electronically similar materials, have remarkably different excitonic physics, and this difference is also well captured.

Spectrum for nonmagnetic mott insulators from power functional within reduced density matrix functional theory.

We demonstrate that reduced density matrix functional theory (RDMFT), in conjunction with the power functional, can successfully treat the nonmagnetic insulating state of the transition metal oxides NiO and MnO, finding for both a gapped single particle spectrum. While long-range spin order is thus not necessary for qualitative agreement with experiment, we find that it is required for good agreement with the X-ray photoemission spectroscopy and Bremsstrahlung isochromat spectroscopy data. We further examine the nature of the natural orbitals in the materials, finding that they display significant Hubbard localization and are, as a consequence, very far from the corresponding Kohn-Sham orbitals.

Social resources mediate the relations between attachment dimensions and distress following potentially traumatic events.

Insecure adult attachment dimensions are consistently related to poorer posttrauma adjustment, but these relations have rarely been examined prospectively or across a wide range of potentially traumatic events. In addition, the factors mediating these relations are not yet fully understood. Therefore, the first aim of this study was to assess whether anxious and avoidant attachment dimensions assessed preevent would predict changes in adjustment (e.

Spin-crossover and massive anisotropy switching of 5d transition metal atoms on graphene nanoflakes.

In spin crossover phenomena, the magnetic moment of a molecule is switched by external means. Here we theoretically predict that several 5d-transition metals (TMs) adsorbed on finite graphene flakes undergo a spin crossover, resulting from multiple adsorption minima, that are absent in the zero-dimensional limit of benzene and the two-dimensional limit of graphene. The different spin states are stable at finite temperature and can be reversibly switched with an electric field.

Magnetic anisotropy of graphene quantum dots decorated with a ruthenium adatom.

The creation of magnetic storage devices by decoration of a graphene sheet by magnetic transition-metal adatoms, utilizing the high in-plane versus out-of-plane magnetic anisotropy energy (MAE), has recently been proposed. This concept is extended in our density-functional-based modeling study by incorporating the influence of the graphene edge on the MAE. We consider triangular graphene flakes with both armchair and zigzag edges in which a single ruthenium adatom is placed at symmetrically inequivalent positions.

Spectral density and metal-insulator phase transition in Mott insulators within reduced density matrix functional theory.

We present a method for calculating the spectrum of periodic solids within reduced density matrix functional theory. This method is validated by a detailed comparison of the angular momentum projected spectral density with that of well-established many-body techniques, finding very good agreement in all cases. The physics behind the pressure induced insulator-metal phase transition in MnO is investigated.

Further development of the temporal model of control.

The temporal model of control (Frazier, Berman, & Steward, 2001) posits that different temporal aspects of control (i.e., past, present, and future) have markedly different relations with adjustment and need to be clearly distinguished from each other.

Prevalence and effects of life event exposure among undergraduate and community college students.

The purposes of this study were to assess lifetime and recent exposure to various life events among undergraduate and community college students and to assess the relation between event exposure and a broad range of outcomes (i.e., mental and physical health, life satisfaction, grade point average).

Beyond Criterion A1: the effects of relational and non-relational traumatic events.

Trauma research has historically focused on Criterion A1 traumas, neglecting many other negative interpersonal events that have been shown to lead to posttraumatic stress disorder (PTSD; S. L. Anders, P.