On the role of electron-phonon interaction in the resistance anisotropy of two-dimensional electrons in GaAs heterostructures

A contribution of the electron-phonon interaction into the energy of a unidirectional charge ordered state (stripe phase) of two-dimensional electrons in GaAs heterostructures is analyzed. The dependence of the energy on the direction of the electron density modulation is calculated. It is shown that in electrons layers situated close to the (001) surface the interference between the piezoelectric and the deformation potential interaction causes a preferential orientation of the stripes along the [110] axis.Comment: 9 pages, accepted for publication in Journal of Physics: Condensed Matte

Strong enhancement of third harmonic generation in a double layer graphene system caused by electron-hole pairing

A manifestation of electron-hole pairing in nonlinear electromagnetic response of a double layer graphene system is studied. It is shown that the pairing causes the appearance of a number of peaks in the frequency dependence of the intensity of the third harmonic generation (THG). The highest peak corresponds to \hbar\omega = (2/3)\Delta, where \omega\ is the incident wave frequency, and \Delta\ is the order parameter of the electron-hole pairing. The absolute value of the THG intensity in the systems with electron-hole pairing is in several orders of magnitude greater than the THG intensity in the unpaired state. It is shown that huge enhancement of the THG intensity occurs both in the double monolayer and double bilayer graphene systems.Comment: 7 page

Superconductivity of electron-hole pairs in a bilayer graphene system in a quantizing magnetic field

The state with a spontaneous interlayer phase coherence in a graphene based bilayer quantum Hall system is studied. This state can be considered as a gas of superfluid electron-hole pairs with the components of the pair belonging to different layers. Superfluid flux of such pairs is equivalent to two electrical supercurrents in the layers. It is shown that the state with the interlayer phase coherence emerges in the graphene system if a certain imbalance of the Landau level filling factors of the layers is created. We obtain the temperature of transition into the superfluid state, the maximum interlayer distance at which the phase coherence is possible, and the critical values of the supercurrent. The advantages of use of graphene systems instead of GaAs heterostructures for the realization of the bilayer electron-hole superconductivity is discussed.Comment: 16 pages, 8 figure

Vortex generation in a superfluid gas of dipolar chains in crossed electric and magnetic fields

Crossed electric and magnetic fields influence dipolar neutral particles in the same way as the magnetic field influences charged particles. The effect of crossed fields is proportional to the dipole moment of the particle (inherent or induced). We show that this effect is quite spectacular in a multilayer system of polar molecules. In this system molecules may bind in chains. At low temperature the gas of chains becomes the superfluid one. The crossed fields then induce vortices in the superfluid gas of chains. The density of vortices is proportional to the number of particles in the chain. The effect can be used for monitoring the formation and destruction of chains in multilayer dipolar gases.Comment: To appear in Low Temperature Physics/Fizika Nizkikh Temperatur, 2020, v. 46, No.