Disorder-induced magnetooscillations in bilayer graphene at high bias

Energy spectrum of biased bilayer graphene near the bottom has a "Mexican-hat"-like shape. For the Fermi level within the Mexican hat we predict that, apart from conventional magnetooscillations which vanish with temperature, there are additional magnetooscillations which are weakly sensitive to temperature. These oscillations are also insensitive to a long-range disorder. Their period in magnetic field scales with bias, V, as V^2. The origin of these oscillations is the disorder-induced scattering between electron-like and hole-like Fermi-surfaces, specific for Mexican hat.Comment: 5 pages, 2 figure

Scattering of plasmons at the intersection of two metallic nanotubes: Implications for tunnelling

We study theoretically the plasmon scattering at the intersection of two metallic carbon nanotubes. We demonstrate that for a small angle of crossing, $\theta \ll 1$, the transmission coefficient is an oscillatory function of $\lambda/\theta$, where $\lambda$ is the interaction parameter of the Luttinger liquid in an individual nanotube. We calculate the tunnel density of states, $\nu(\omega,x)$, as a function of energy, $\omega$, and distance, $x$, from the intersection. In contrast to a single nanotube, we find that, in the geometry of crossed nanotubes, conventional "rapid" oscillations in $\nu(\omega,x)$ due to the plasmon scattering acquire an aperiodic "slow-breathing" envelope which has $\lambda/\theta$ nodes.Comment: 4 pages, 2 figures (revised version

The photon absorption edge in superconductors and gapped 1D systems

Opening of a gap in the low-energy excitations spectrum affects the power-law singularity in the photon absorption spectrum $A(\Omega)$. In the normal state, the singularity, $A(\Omega)\propto [D/(\Omega-\Omega_{\rm th})]^\alpha$, is characterized by an interaction-dependent exponent $\alpha$. On the contrary, in the supeconducting state the divergence, $A(\Omega)\propto (D/\Delta)^\alpha(\Omega-\tilde{\Omega}_{\rm th})^{-1/2}$, is interaction-independent, while threshold is shifted, $\tilde{\Omega}_{\rm th}=\Omega_{\rm th}+\Delta$; the ``normal-metal'' form of $A(\Omega)$ resumes at $(\Omega-\tilde{\Omega}_{\rm th})\gtrsim \Delta\exp(1/\alpha)$. If the core hole is magnetic, it creates in-gap states; these states transform drastically the absorption edge. In addition, processes of scattering off the magnetic core hole involving spin-flip give rise to inelastic absorption with one or several {\it real} excited pairs in the final state, yielding a structure of peaks in $A(\Omega)$ at multiples of $2\Delta$ above the threshold frequency. The above conclusions apply to a broad class of systems, e.g., Mott insulators, where a gap opens at the Fermi level due to the interactions.Comment: 6 pages, 5 figures; published versio