Microscopic linear response theory of spin relaxation and relativistic transport phenomena in graphene

We present a unified theoretical framework for the study of spin dynamics and relativistic transport phenomena in disordered two-dimensional Dirac systems with pseudospin-spin coupling. The formalism is applied to the paradigmatic case of graphene with uniform Bychkov-Rashba interaction and shown to capture spin relaxation processes and associated charge-to-spin interconversion phenomena in response to generic external perturbations, including spin density fluctuations and electric fields. A controlled diagrammatic evaluation of the generalized spin susceptibility in the diffusive regime of weak spin-orbit interaction allows us to show that the spin and momentum lifetimes satisfy the standard Dyakonov-Perel relation for both weak (Gaussian) and resonant (unitary) nonmagnetic disorder. Finally, we demonstrate that the spin relaxation rate can be derived in the zero-frequency limit by exploiting the SU(2) covariant conservation laws for the spin observables. Our results set the stage for a fully quantum-mechanical description of spin relaxation in both pristine graphene samples with weak spin-orbit fields and in graphene heterostructures with enhanced spin-orbital effects currently attracting much attention

Optimal Charge-to-Spin Conversion in Graphene on Transition-Metal Dichalcogenides

When graphene is placed on a monolayer of semiconducting transition metal dichalcogenide (TMD) its band structure develops rich spin textures due to proximity spin-orbital effects with interfacial breaking of inversion symmetry. In this work, we show that the characteristic spin winding of low-energy states in graphene on a TMD monolayer enables current-driven spin polarization, a phenomenon known as the inverse spin galvanic effect (ISGE). By introducing a proper figure of merit, we quantify the efficiency of charge-to-spin conversion and show it is close to unity when the Fermi level approaches the spin minority band. Remarkably, at high electronic density, even though subbands with opposite spin helicities are occupied, the efficiency decays only algebraically. The giant ISGE predicted for graphene on TMD monolayers is robust against disorder and remains large at room temperature

Covariant Conservation Laws and the Spin Hall Effect in Dirac-Rashba Systems

We present a theoretical analysis of two-dimensional Dirac-Rashba systems in the presence of disorder and external perturbations. We unveil a set of exact symmetry relations (Ward identities) that impose strong constraints on the spin dynamics of Dirac fermions subject to proximity-induced interactions. This allows us to demonstrate that an arbitrary dilute concentration of scalar impurities results in the total suppression of nonequilibrium spin Hall currents when only Rashba spin-orbit coupling is present. Remarkably, a finite spin Hall conductivity is restored when the minimal Dirac-Rashba model is supplemented with a spin–valley interaction. The Ward identities provide a systematic way to predict the emergence of the spin Hall effect in a wider class of Dirac-Rashba systems of experimental relevance and represent an important benchmark for testing the validity of numerical methodologies

Coupled Charge-Spin Transport and Spin–Orbit Phenomena in 2D Dirac Materials

The advent of 2D layered materials, boasting high-crystal quality and rich electronic properties, has provided a unique arena for exploring exotic condensed-matter phenomena, including the emergence of ultra-relativistic Dirac fermions in graphene, topological insulating phases in WS_{2}, long-lived excitons in group-VI dichalcogenides and unconventional superconductivity in twisted bilayer graphene. The enhancement of spin-orbit effects in heterointerfaces, built from the vertical stacking of different 2D layers, is recently attracting much attention. A series of crucial experiments have demonstrated the induction of strong spin-orbit effects in graphene sheets proximity-coupled to group-VI dichalcogenides. Owing to a combination of room-temperature spin transport over long distances and gate-tunable spin orbit interactions, such systems hold great promise for all-electrical generation and manipulation of spin currents, which is key to the realisation of the next generation of spintronics devices. To fully unlock the potential of 2D Dirac materials for spintronics, these recent experimental findings call for the formulation of a solid theoretical framework which can underpin them, but also—and more importantly—predict novel phenomena. This thesis aims to develop the foundations of such a framework, with a focus on spin dynamics and coupled charge-spin transport in 2D Dirac materials with strong proximity-induced interactions. A number of key results are established. We show that charge-to-spin interconversion in 2D Dirac materials can be understood in terms of exact symmetry relations (Ward identities). Depending on the specific spin-orbit interactions present in a 2D Dirac system, the symmetry relations dictate the relative contributions of the so-called spin-Hall effect (SHE) and inverse spin Galvanic effect (ISGE). In particular, for materials with interfacial breaking of mirror symmetry and unbroken (broken) sublattice symmetry, the SHE contribution is suppressed (sizable), whereas the ISGE contribution stays typically large and robust in both scenarios. The extrinsic SHE has its origin in a peculiar skew scattering mechanism—emerging from the non-coplanar spin texture of spin–orbit-coupled Dirac bands—and can be tuned by a gate voltage. We propose a diagrammatic approach to obtain the coupled charge/spin diffusion equations, as well as the spin relaxation times and the charge-to-spin interconversion rates. We supplement this study with a density matrix-based approach, allowing one to gain more insight into the delicate competition of the various energy scales present in realistic systems, and to calculate the spin relaxation time anisotropy of experimental relevance. Finally, we examine ferromagnetic 2D Dirac materials, through a unified theory of charge carrier transport combining semiclassical and fully-quantum mechanical approaches. We identify an experimental signature that characterises the crossover from the nonquantised anomalous Hall effect to the topologically-nontrivial quantum anomalous Hall effect, which can help future experimental efforts to unlock this fascinating quantum state of matter with Dirac fermions

“I Wasn’t Expecting It”: High School Experiences and Navigating Belonging in the Transition to College

For emerging adults transitioning to college, normative social and contextual shifts present challenges that are largely a productive aspect of development. But not all students have the same experiences, nor do all students manage similar experiences in similar ways. Black and Latinx emerging adults transitioning to Historically White Institutions must adjust not only to college life but also to feeling different and, sometimes, isolated. There is a dearth of qualitative work examining how students of color make meaning of their racial-ethnic experiences on campus. Our article draws on a mixed-methods study of Black and Latinx emerging adults’ transition to college to investigate how high school racial-ethnic contexts shape students’ interpretations of experiences of difference on college campuses. There was substantial variation in how Black and Latinx students interpreted experiences of difference on campus and coped with their feelings of otherness, and this variation was predicted by racial-ethnic high school context

Discriminating the Presence of Psychological Distress in Patients Suffering from Psoriasis: An Application of the Clinimetric Approach in Dermatology.

none 4 si Psoriasis is a chronic dermatologic disease that negatively impacts physical and mental health of patients as well as their social and work life. The aim of this study is to illustrate, by a clinimetric approach the differences in psychological distress and well-being between patients with mild and moderate to severe psoriasis. Seventy patients with psoriasis were evaluated using the Structured Clinical Interview for DSM-IV (SCID-I), the Diagnostic Criteria for Psychosomatic Research (DCPR), along with the following self-report instruments: the Symptoms Questionnaire (SQ), the Psychological Well-being scales (PWB) and the Temperament and Character Inventory (TCI). Illness severity was evaluated using the Psoriasis Area and Severity Index (PASI). While no differences were reported between groups in terms of psychiatric diagnoses, patients with greater severity (PASI >10) presented higher rates of demoralization (61.5%) and Type A behavior (53.8%) than subjects with mild severity (17.5% and 21.1%, respectively). Patients with moderate/severe psoriasis also reported impaired levels of psychological well-being in terms of lower autonomy, environmental mastery, personal growth and purpose in life. Furthermore, according to TCI, patients with severe psoriasis reported greater harm avoidance and lower self-directness than individuals with milder psoriasis levels. Overall results highlighted the need in psoriasis care of a more comprehensive psychological and psychosomatic assessment not limited to the customary psychiatric diagnostic criteria. none Offidani, Emanuela; Del Basso, Donatella; Prignago, Francesca; Tomba, Elena Offidani, Emanuela; Del Basso, Donatella; Prignago, Francesca; Tomba, Elen

Political Activism and Mental Health Among Black and Latinx College Students

Objectives: The current study investigates the utility of political activism as a protective factor against experiences of racial/ethnic (R/E) discrimination that negatively affect stress, anxiety, and depressive symptoms among Black and Latinx college freshmen at predominately White institutions. Method: Data come from the Minority College Cohort Study, a longitudinal investigation of Black and Latinx college students (N = 504; 44% Black). We conducted multiple regression analyses for each mental health indicator and tested for interaction effects. Results: For Black and Latinx students, the relationship between R/E microaggressions and end of freshman year stress varied by political activism. For Black students, the relationship between R/E microaggressions and end of the year anxiety varied by political activism. There was a significant interaction effect for depressive symptoms among Latinx students. Conclusions: Political activism serves as a protective factor to mitigate the negative effect of R/E discrimination on stress and depressive symptoms for Latinx students. For Black students, higher levels of political activism may exacerbate experiences of R/E microaggressions and relate to more stress and anxiety compared with Black students who are less politically involved. Findings point to the need for a deeper understanding of phenomenological variation in experiences of microaggressions among R/E minorities and how students leverage political activism as an adaptive coping strategy to mitigate race-related stress during college