Multilayer Electron Systems Research Articles

PL spectroscopy of Fermi electrons in regime of the quantum Hall effect

The influence of the interlayer coupling on formation of the quantized Hall phase at the filling factor ν = 2 was studied in the multilayer GaAs/AlGaAs heterostructures. The disorder broaden Gaussian photoluminescence line due to the localized electrons was found in the quantized Hall phase of the isolated multi-quantum well structure. On the other hand, the quantized Hall phase of the weakly-coupled multilayers emitted an asymmetrical line similar to that one observed in the metallic electron systems. We demonstrated that the observed asymmetry indicates a formation of the Fermi surface in the quantized Hall phase of the multilayer electron system due to the interlayer percolation. A sharp decrease of the single-particle scattering time associated with the extended states on the Fermi surface was observed at the filling factor ν = 2 .

Charge ordering and interlayer phase coherence in quantum Hall superlattices

The possibility of the existence of states with a spontaneous interlayer phase coherence in multilayer electron systems in a high perpendicular magnetic field is investigated. It is shown that phase coherence can be established in such systems only within individual pairs of adjacent layers, while such coherence does not exist between layers of different pairs. The conditions for stability of a state with interlayer phase coherence against transition to a charge-ordered state are determined. It is shown that in a system with N⩽10 layers there is stability at any value of the interlayer distance d. For N>10 there are two intervals of stability: at sufficiently large and at sufficiently small d. For N→∞ the stability interval in the region of small d vanishes.

Spontaneous interlayer coherence in multilayer electron systems in strong magnetic fields

It is predicted that in multilayer system which is homogeneous in the direction normal to layers the interaction of electrons from different layers leads to spontaneous breaking of homogeneity in this direction. The alternation of paired and unpaired layers corresponds to the ground state of the system.

Electronic properties and quantum Hall effect in multi-layer electron systems

We analyze the effect that the interaction between electrons has on the properties of a multi-layer electron system. We consider the case corresponding to filling factor unity in each layer. In the case of an infinity superlattice, the system presents ferromagnetic, canted antiferromagnetic or paramagnetic interlayer spin correlations depending on the sample parameters. We have obtained that these three ground states are quantum Hall effect (QHE) phases, because of the existence of a finite activation energy. In the ferromagnetic phase the gap is due to the intrawell exchange energy, whereas in the paramagnetic phase the gap appears due to the spatial modulation of the interwell coherence. We have also studied the properties of multi-layer systems as a function of the number of electron sheets, NL. We find that the magnetic coupling of the electron layers depends strongly on the even/odd character of NL.

Interlayer Magnetic Coupling and the Quantum Hall Effect in Multilayer Electron Systems

We study the effect that the electron-electron interaction has on the properties of a multilayer electron system. We consider the case corresponding to filling factor unity in each layer. We find that as a function of the sample parameters the system has ferromagnetic, canted antiferromagnetic or paramagnetic interlayer spin correlations. These three ground states are QHE phases, because of the existence of a finite activation energy. In the ferromagnetic phase the gap is due to the intrawell exchange energy, whereas in the paramagnetic phase the gap appears due to the spatial modulation of the interwell coherence.

Hierarchy of fractional quantum Hall states in multi-layer electron systems

It is shown that the recursion relations for the filling fractions of fractional quantum Hall states in double-layer electron systems proposed by M Greiter and I A McDonald can be expressed in a `matrix continued fraction form'. We extend this matrix continued fraction form to multi-layer electron systems and show that under some physical restrictions the matrix continued fraction form is reduced to the usual numerical continued fraction.

Localization and Metal-Insulator Transition in Multilayer Quantum Hall Structures

We study the phase structure and Hall conductance quantization in weakly coupled multilayer electron systems in the integer quantum Hall regime. We derive an effective field theory and perform a two-loop renormalization group calculation. It is shown that (i) finite interlayer tunnelings (however small) give rise to successive metallic and insulating phases and metal-insulator transitions in the unitary universality class; (ii) the Hall conductivity is not renormalized in the metallic phases in the 3D regime; and (iii) the Hall conductances are quantized in the insulating phases. In the bulk quantum Hall phases, the effective field theory describes the transport on the surface.

Fractional quantum Hall effect in multilayer electron systems

We present several novel quasi-two-dimensional electron systems with an additional degree of freedom. These include systems which contain two or more layers of electrons in close proximity so that interlayer Coulomb interactions are strong, and thick-layer electron systems in wide parabolic wells. The magneto-transport data in these systems exhibit new phenomena: examples include the observation of a fractional quantum Hall state at the even-denominator v= 1 2 filling and an insulating phase reentrant around the v=1/3 fractional state in a double-layer electron system in a wide quantum well.