Nonequilibrium charge dynamics of light-driven rings threaded by a magnetic flux

We study theoretically the charge polarization and the charge current dynamics of a mesoscopic ring driven by short asymmetric electromagnetic pulses and threaded by an external static magnetic flux. It is shown that the pulse-induced charge polarization and the associated light-emission is controllable by tuning the external magnetic flux. Applying two mutually perpendicular pulses triggers a charge current in the ring. The interplay between this nonequilibrium and the persistent currents is investigated and the conditions under which the pulses stop the persistent current are identified.Comment: 6 pages, 2 figures; submitted to EP

Stacking domains and dislocation networks in marginally twisted bilayers of transition metal dichalcogenides

We apply a multiscale modeling approach to study lattice reconstruction in marginally twisted bilayers of transition metal dichalcogenides (TMD). For this, we develop DFT-parametrized interpolation formulae for interlayer adhesion energies of MoSe$_2$, WSe$_2$, MoS$_2$, and WS$_2$, combine those with elasticity theory, and analyze the bilayer lattice relaxation into mesoscale domain structures. Paying particular attention to the inversion asymmetry of TMD monolayers, we show that 3R and 2H stacking domains, separated by a network of dislocations develop for twist angles $\theta^{\circ}<\theta^{\circ}_P\sim 2.5^{\circ}$ and $\theta^{\circ}<\theta^{\circ}_{AP}\sim 1^{\circ}$ for, respectively, bilayers with parallel (P) and antiparallel (AP) orientation of the monolayer unit cells and suggest how the domain structures would manifest itself in local probe scanning of marginally twisted P- and AP-bilayers

Competing Nematic, Anti-ferromagnetic and Spin-flux orders in the Ground State of Bilayer Graphene

We analyze the phase diagram of the Bilayer graphene (BLG) at zero temperature and doping. Assuming that at the high energies the electronic system of BLG can be described within a weak coupling theory (consistent with the experimental evidence), we systematically study the evolution of the couplings with going from high to low energies. The divergences of the couplings at some energies indicates the tendency towards certain symmetry breakings. Carrying out this program, we found that the phase diagram is determined by microscopic couplings defined on the short distances (initial conditions). We explored all plausible space of these initial conditions and found that the three states have the largest phase volume of the initial couplings: nematic, antiferromagnetic and spin flux (a.k.a quantum spin Hall). In addition, ferroelectric and two superconducting phases and appear only near the very limits of the applicability of the weak coupling approach. The paper also contains the derivation and analysis of the renormalization group equations and the group theory classification of all the possible phases which might arise from the symmetry breakings of the lattice, spin rotation, and gauge symmetries of graphene.Comment: 19 pages, 16 figure

Spectroscopic Signatures of Electronic Excitations in Raman Scattering in Thin Films of Rhombohedral Graphite

Rhombohedral graphite features peculiar electronic properties, including persistence of low-energy surface bands of a topological nature. Here, we study the contribution of electron-hole excitations towards inelastic light scattering in thin films of rhombohedral graphite. We show that, in contrast to the featureless electron-hole contribution towards Raman spectrum of graphitic films with Bernal stacking, the inelastic light scattering accompanied by electron-hole excitations in crystals with rhombohedral stacking produces distinct features in the Raman signal which can be used both to identify the stacking and to determine the number of layers in the film.Comment: 15 pages in preprint format, 4 figures, accepted versio

Anomalously strong pinning of the filling factor nu=2 in epitaxial graphene

We explore the robust quantization of the Hall resistance in epitaxial graphene grown on Si-terminated SiC. Uniquely to this system, the dominance of quantum over classical capacitance in the charge transfer between the substrate and graphene is such that Landau levels (in particular, the one at exactly zero energy) remain completely filled over an extraordinarily broad range of magnetic fields. One important implication of this pinning of the filling factor is that the system can sustain a very high nondissipative current. This makes epitaxial graphene ideally suited for quantum resistance metrology, and we have achieved a precision of 3 parts in 10^10 in the Hall resistance quantization measurements

Weak ferroelectric charge transfer in layer-asymmetric bilayers of 2D semiconductors

In bilayers of two-dimensional (2D) semiconductors with stacking arrangements which lack inversion symmetry charge transfer between the layers due to layer-asymmetric interband hybridisation can generate a potential difference between the layers. We analyse bilayers of transition metal dichalcogenides (TMDs) - in particular, WSe$_2$ - for which we find a substantial stacking-dependent charge transfer, and InSe, for which the charge transfer is found to be negligibly small. The information obtained about TMDs is then used to map potentials generated by the interlayer charge transfer across the moir\'e superlattice in twistronic bilayers.Comment: To appear in Scientific Report

Spin-orbit coupling effect on quantum Hall ferromagnets with vanishing Zeeman energy

We present the phase diagram of a ferromagnetic quantum Hall effect liquid in a narrow quantum well with vanishing single-particle Zeeman splitting, $\epsilon_{{\rm Z}}$ and pronounced spin-orbit coupling. Upon decreasing $\epsilon_{{\rm Z}}$, the spin-polarization field of a liquid takes, first, the easy-axis configuration, followed by the formation of a helical state, which affects the transport and NMR properties of a liquid and the form of topological defects in it. The analysis is extended over high odd integer filling factors.Comment: This revised version takes into account easy-axis terms in the energy and offers a corrected phase diagram of the ferromagnetic QHE liquid. Analysis is extended over higher filling factor