Thermal difference reflectivity of tilted 2D Dirac materials

Deviation from perfect conical dispersion in Dirac materials, such as the presence of mass or tilting, enhances control and directionality of electronic transport. To identify these signatures, we analyze the thermal derivative spectra of optical reflectivity in doped massive tilted Dirac systems. The density of states and chemical potential are determined as preliminary steps to calculate the optical conductivity tensor at finite temperature using thermal convolution. Changes in reflection caused by temperature variations enable clear identification of critical frequencies in the optical response. By measuring these spectral features in the thermoderivative spectrum, energy gaps and band structure tilting can be determined. A comparison is presented between the spectra of various low-energy Dirac Hamiltonians. Our findings suggest that thermal difference spectroscopy holds promise as a valuable technique for probing interband transitions of 2D Dirac fermion

Ballistic guided electrons against disorder in graphene nanoribbons

Graphene nanoribbons (GNRs) are natural waveguides for electrons in graphene. Nevertheless, unlike micron-sized samples, conductance is nearly suppressed in these narrow graphene stripes, mainly due to scattering with edge disorder generated during synthesis or cut. A possible way to circumvent this effect is to define an internal waveguide that isolates specific modes from the edge disorder and allows ballistic conductance. There are several proposals for defining waveguides in graphene; in this manuscript, we consider strain folds and scalar potentials and numerically evaluate these proposals' performance against edge and bulk disorder. Using the Green's function approach, we calculate conductance and the local density of states (LDOS) of zigzag GNRs and characterize the performance of these different physical waveguiding effects in both types of disorder. We found a general improvement in the electronic conductance of GNR due to the presence of the internal waveguiding, with the emergence of plateaus with quasi-ballistic properties and robustness against edge disorder. These findings are up to be applied in modern nanotechnology and being experimentally tested.Comment: 7 pages, 5 figure

Tuning the pseudospin polarization of graphene by a pseudo-magnetic field

One of the intriguing characteristics of honeycomb lattices is the appearance of a pseudo-magnetic field as a result of mechanical deformation. In the case of graphene, the Landau quantization resulting from this pseudo-magnetic field has been measured using scanning tunneling microscopy. Here we show that a signature of the pseudo-magnetic field is a local sublattice symmetry breaking observable as a redistribution of the local density of states. This can be interpreted as a polarization of graphene's pseudospin due to a strain induced pseudo-magnetic field, in analogy to the alignment of a real spin in a magnetic field. We reveal this sublattice symmetry breaking by tunably straining graphene using the tip of a scanning tunneling microscope. The tip locally lifts the graphene membrane from a SiO$_2$ support, as visible by an increased slope of the $I(z)$ curves. The amount of lifting is consistent with molecular dynamics calculations, which reveal a deformed graphene area under the tip in the shape of a Gaussian. The pseudo-magnetic field induced by the deformation becomes visible as a sublattice symmetry breaking which scales with the lifting height of the strained deformation and therefore with the pseudo-magnetic field strength. Its magnitude is quantitatively reproduced by analytic and tight-binding models, revealing fields of 1000 T. These results might be the starting point for an effective THz valley filter, as a basic element of valleytronics.Comment: Revised manuscript: streamlined the abstract and introduction, added methods to supplement, Nano Letters, 201

Pharmacological and Non-Pharmacological Agents versus Bovine Colostrum Supplementation for the Management of Bone Health Using an Osteoporosis-Induced Rat Model

Osteoporosis is defined by loss of bone mass and deteriorated bone microarchitecture. The present study compared the effects of available pharmacological and non-pharmacological agents for osteoporosis [alendronate (ALE) and concomitant supplementation of vitamin D (VD) and calcium (Ca)] with the effects of bovine colostrum (BC) supplementation in ovariectomized (OVX) and orchidectomized (ORX) rats. Seven-month-old rats were randomly allocated to: (1) placebo-control, (2) ALE group (7.5 μg/kg of body weight/day/5 times per week), (3) VD/Ca group (VD: 35 μg/kg of body weight/day/5 times per week; Ca: 13 mg/kg of body weight/day/3 times per week), and (4) BC supplementation (OVX: 1.5 g/day/5 times per week; ORX: 2 g/day/5 times per week). Following four months of supplementation, bone microarchitecture, strength and bone markers were evaluated. ALE group demonstrated significantly higher Ct.OV, Ct.BMC, Tb.Th, Tb.OV and Tb.BMC and significantly lower Ct.Pr, Tb.Pr, Tb.Sp, Ct.BMD and Tb.BMD, compared to placebo (p < 0.05). BC presented significantly higher Ct.Pr, Ct.BMD, Tb.Pr, Tb.Sp, and Tb.BMD and significantly lower Ct.OV, Ct.BMC, Tb.Th, Tb.OV and Tb.BMC compared to ALE in OVX rats (p < 0.05). OVX rats receiving BC experienced a significant increase in serum ALP and OC levels post-supplementation (p < 0.05). BC supplementation may induce positive effects on bone metabolism by stimulating bone formation, but appear not to be as effective as ALE

Strained graphene structures: from valleytronics to pressure sensing

Due to its strong bonds graphene can stretch up to 25% of its original size without breaking. Furthermore, mechanical deformations lead to the generation of pseudo-magnetic fields (PMF) that can exceed 300 T. The generated PMF has opposite direction for electrons originating from different valleys. We show that valley-polarized currents can be generated by local straining of multi-terminal graphene devices. The pseudo-magnetic field created by a Gaussian-like deformation allows electrons from only one valley to transmit and a current of electrons from a single valley is generated at the opposite side of the locally strained region. Furthermore, applying a pressure difference between the two sides of a graphene membrane causes it to bend/bulge resulting in a resistance change. We find that the resistance changes linearly with pressure for bubbles of small radius while the response becomes non-linear for bubbles that stretch almost to the edges of the sample. This is explained as due to the strong interference of propagating electronic modes inside the bubble. Our calculations show that high gauge factors can be obtained in this way which makes graphene a good candidate for pressure sensing.Comment: to appear in proceedings of the NATO Advanced Research Worksho