Quantum nature of edge magnetism in graphene.

It is argued that the subtle crossover from decoherence-dominated classical magnetism to fluctuation-dominated quantum magnetism is experimentally accessible in graphene nanoribbons. We show that the width of a nanoribbon determines whether the edge magnetism is on the classical side, on the quantum side, or in between. In the classical regime, decoherence is dominant and leads to static spin polarizations at the ribbon edges, which are well described by mean-field theories.

Magnetic correlations in short and narrow graphene armchair nanoribbons.

Electronic states at the ends of a narrow armchair nanoribbon give rise to a pair of nonlocally entangled spins. We propose two experiments to probe these magnetic states, based on magnetometry and tunneling spectroscopy, in which correlation effects lead to a striking, nonlinear response to external magnetic fields. On the basis of low-energy theories that we derive here, it is remarkably simple to assess these nonlinear signatures for magnetic edge states.

Helical modes in carbon nanotubes generated by strong electric fields.

Helical modes, conducting opposite spins in opposite directions, are shown to exist in metallic armchair nanotubes in an all-electric setup. This is a consequence of the interplay between spin-orbit interaction and strong electric fields. The helical regime can also be obtained in chiral metallic nanotubes by applying an additional magnetic field.

Method for replica symmetry breaking at and near T=0 with application to the Sherrington-Kirkpatrick model.

We describe a method which allows the treatment of high orders of replica symmetry breaking (RSB) at low temperatures as well as at T=0 directly, without a need for approximations or scaling assumptions. It yields the low-temperature order function q(a,T) in the full range 0 < or = a < infinity and is complete in the sense that all observables can be calculated from it. The behavior of some observables and the finite RSB theory itself is analyzed as the continuous RSB limit is approached.