Coherent anti-Stokes Raman spectroscopy of single and multi-layer graphene

Spontaneous Raman spectroscopy is a powerful characterization tool for graphene research. Its extension to the coherent regime, despite the large nonlinear third-order susceptibility of graphene, has so far proven challenging. Due to its gapless nature, several interfering electronic and phononic transitions concur to generate its optical response, preventing to retrieve spectral profiles analogous to those of spontaneous Raman. Here we report stimulated Raman spectroscopy of the G-phonon in single and multi-layer graphene, through coherent anti-Stokes Raman Scattering. The nonlinear signal is dominated by a vibrationally non-resonant background, obscuring the Raman lineshape. We demonstrate that the vibrationally resonant coherent anti-Stokes Raman Scattering peak can be measured by reducing the temporal overlap of the laser excitation pulses, suppressing the vibrationally non-resonant background. We model the spectra, taking into account the electronically resonant nature of both. We show how coherent anti-Stokes Raman Scattering can be used for graphene imaging with vibrational sensitivity.

Correction: Corrigendum: p-wave triggered superconductivity in single-layer graphene on an electron-doped oxide superconductor

Nature Communications 8: Article number: 14024 (2017); Published: 19 January 2017; Updated: 1 March 2017 The present address for U. Sassi is incorrect in this Article. This author does not have a present address. The correct full affiliation details for this author are given below: Cambridge Graphene Centre, University of Cambridge, Cambridge CB3 0FA, UK.

p-wave triggered superconductivity in single-layer graphene on an electron-doped oxide superconductor

Electron pairing in the vast majority of superconductors follows the Bardeen-Cooper-Schrieffer theory of superconductivity, which describes the condensation of electrons into pairs with antiparallel spins in a singlet state with an s-wave symmetry. Unconventional superconductivity was predicted in single-layer graphene (SLG), with the electrons pairing with a p-wave or chiral d-wave symmetry, depending on the position of the Fermi energy with respect to the Dirac point. By placing SLG on an electron-doped (non-chiral) d-wave superconductor and performing local scanning tunnelling microscopy and spectroscopy, here we show evidence for a p-wave triggered superconducting density of states in SLG. The realization of unconventional superconductivity in SLG offers an exciting new route for the development of p-wave superconductivity using two-dimensional materials with transition temperatures above 4.2 K.

Complex angular momentum theory of state-to-state integral cross sections: resonance effects in the F + HD → HF(v′ = 3) + D reaction

State-to-state reactive integral cross sections (ICSs) are often affected by quantum mechanical resonances, especially in the neighborhood of a reactive threshold.

Theoretical reaction kinetics astride the transition between moderate and deep tunneling regimes: the F + HD case

For the reaction between F and HD, giving HF + D and DF + H, the rate constants, obtained from rigorous quantum scattering calculations at temperatures ranging from 350 K down to 100 K, show deviations from the Arrhenius behavior that have been interpreted in terms of tunneling of either H or D atoms through a potential energy barrier. The interval of temperature investigated extends from above to below a crossover value Tc, a transition temperature separating the moderate and deep quantum tunneling regimes. Below Tc, the rate of the H or D exchange reaction is controlled by the prevalence of tunneling over the thermal activation mechanism. In this temperature range, Bell's early treatment of quantum tunneling, based on a semiclassical approximation for the barrier permeability, provides a reliable tool to quantitatively account for the contribution of the tunneling effect. This treatment is here applied for extracting from rate constants properties of the effective tunneling path, such as the activation barrier height and width. We show that this is a way of parametrizing the dependence of the apparent activation energy on temperature useful for both calculated and experimental rate constants in an ample interval of temperature, from above to below Tc, relevant for modelization of astrophysical and in general very low-temperature environments.

Long-term psychometric outcomes of facial lipoatrophy therapy: forty-eight-week observational, nonrandomized study

The aim of this observational, prospective, nonrandomized study was to assess long-term psychometric outcomes of surgical treatment of HIV-related facial lipoatrophy. Two hundred ninety-nine participants (70.8% male) consecutively attending the Metabolic Clinic of Modena and Reggio Emilia University from November 2005 to July 2006, undergoing surgical interventions for HIV-related facial lipoatrophy were enrolled. Fifty-four (18.1%) underwent facial lipofilling, which consists of the harvesting of a small, intact parcel of fatty tissue with processing that removes the nonviable components and of the transport of fatty parcels through a small cannula to implant the graft in a manner that provides nutrition and anchors the fat to the host tissue. After an initial lipofilling, 24 (8%) needed polylactic acid injections to correct cheek asymmetry, 91 (30.4%) received only polylactic acid infiltrations, and 130 (43.5%) polyacrylamide infiltrations only. Subjective outcome measures were face aesthetic satisfaction, body image perception, depression evaluated by a visual analogue scale (VAS), the Assessment of Body Change and Distress questionnaire (ABCD), and by the Beck Depression Inventory questionnaire, respectively. Objective measure was cheek thickness evaluated by a 7.5-MHz frequency ultrasound probe perpendicular to the skin surface at the nasolabial fold, the corner of the mouth, the zygomatic arch, and centrally between these points in the buccal fat pad area. Both subjective and objective variables were evaluated at baseline and 48 weeks after end of surgical treatment. All 299 participants had significant improvement of the aesthetic satisfaction for the face (VAS from 2.9 +/- 2.1 to 6.2 +/- 2.1, p < 0.0001), of body image satisfaction (ABCD question 7 from 3.8 +/- 1 to 3.1 +/- 1 p < 0.0001 and ABCD question 8 from 70.7 +/- 16.7 to 77.2 +/- 17.2 p < 0.0001), of depression score (Beck score from 11.4 +/- 8.3 to 9.4 +/- 7.8 p = 0.001). Participants experienced a significant augmentation of both cheeks' thickness (right cheek from 4.3 +/- 1.9 mm to 9.5 +/- 3 mm p < 0.0001, left cheek from 4.4 +/- 2 mm to 9.6 +/- 3.1 mm, p < 0.0001). Our data suggest that facial surgery is an important option in the treatment of HIV-related lipoatrophy as an integral part of the management of HIV infection, because of the important and lasting psychological benefits.

Overlapping resonances and Regge oscillations in the state-to-state integral cross sections of the F+H2 reaction

A Regge pole analysis is employed to explain the oscillatory patterns observed in numerical simulations of integral cross section for the F+H(2)(v=0,j=0)-->HF(v(')=2,j(')=0)+H reaction in the translational collision energy range 25-50 meV. In this range the integral cross section for the transition, affected by two overlapping resonances, shows nearly sinusoidal oscillations below 38 meV and a more structured oscillatory pattern at larger energies. The two types of oscillations are related to the two Regge trajectories which (pseudo) cross near the energy where the resonances are aligned. Simple estimates are given for the periods of the oscillations.

Interacting resonances in the F+H2 reaction revisited: Complex terms, Riemann surfaces, and angular distributions

We study the effect of overlapping resonances on the angular distributions of the reaction F+H2(v=0,j=0)-->HF(v=2,j=0)+H in the collision energy range from 5 to 65 meV, i.e., under the reaction barrier. Reactive scattering calculations were performed using the hyperquantization algorithm on the potential energy surface of Stark and Werner [J. Chem. Phys. 104, 6515 (1996)]. The positions of the Regge and complex energy poles are obtained by Pade reconstruction of the scattering matrix element. The Sturmian theory is invoked to relate the Regge and complex energy terms. For two interacting resonances, a two-sheet Riemann surface is contracted and inverted. The semiclassical complex angular momentum analysis is used to decompose the scattering amplitude into the direct and resonance contributions.