Tuning the Pseudospin Polarization of Graphene by a Pseudomagnetic Field

in Nano Letters (2017), 17

One of the intriguing characteristics of honeycomb lattices is the appearance of a pseudomagnetic field as a result of mechanical deformation. In the case of graphene, the Landau quantization resulting ... [more ▼]

One of the intriguing characteristics of honeycomb lattices is the appearance of a pseudomagnetic field as a result of mechanical deformation. In the case of graphene, the Landau quantization resulting from this pseudomagnetic field has been measured using scanning tunneling microscopy. Here we show that a signature of the pseudomagnetic 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 pseudomagnetic 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 SiO2 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 pseudomagnetic 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 pseudomagnetic 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. [less ▲]

Desorption of H2O from Flat and Stepped Pt(111)

in Journal of Physical Chemistry. C, Nanomaterials and interfaces (2009), 113(2), 691-697

To investigate the effect of steps on H2O binding on a nominal Pt(111) surface, we used thermal desorption spectroscopy of water adsorbed on purposefully nanostructured surfaces: a rippled surface ... [more ▼]

To investigate the effect of steps on H2O binding on a nominal Pt(111) surface, we used thermal desorption spectroscopy of water adsorbed on purposefully nanostructured surfaces: a rippled surface containing densely packed (100)-microfaceted and (111)-microfaceted steps was created using grazing incidence ion bombardment, and a surface with triangular mounds mainly consisting of (111)-microfaceted steps was fabricated through hornoepitaxial growth. These morphologies are determined by scanning tunneling microscopy. We find two additional high -temperature H2O desorption peaks using the rippled surface, whereas only the peak with the highest desorption temperature is present on the (111)-microfaceted mound. Thus, water preferentially binds to steps and especially favors (111)-microfaceted ones. Furthermore, the large step concentration on our nanostructured surfaces precludes the coexistence of a condensed and a diluted phase in a monolayer of water and suppresses the formation of crystalline ice multilayers during heating. [less ▲]