Slow relaxation of magnetoresistance in AlGaAs–GaAs quantum well structures quenched in a magnetic field

Abstract

We observed a slow relaxation of magnetoresistance in response to applied magnetic field in selectively doped p-GaAs-AlGaAs structures with partially filled upper Hubbard band. We have paid a special attention to exclude the effects related to temperature fluctuations. Though this effect is important, we have found that the general features of slow relaxation still persist. This behavior is interpreted as related to the properties of the Coulomb glass formed by charged centers with account of spin correlations, which are sensitive to an external magnetic field. Variation of the magnetic field changes numbers of impurity complexes of different types. As a result, it effects the shape and depth of the polaron gap formed at the states belonging to the percolation cluster responsible for the conductance. The suggested model explains both the qualitative behavior and the order of magnitude of the slowly relaxing magnetoresistance.

Temperature-dependent disorder and magnetic field driven disorder: Experimental observations for doped GaAs/AlGaAs quantum well structures

“…The properly selected doping of both wells and barriers facilitates a creation of double occupied states in a controlled way due to tunneling of carriers from the barriers to the wells. In our earlier work we reported long-term relaxations within the response to external magnetic field for GaAs/AlGaAs structures doped by Be which we explained as the Coulomb glass effects [4], [5]. An important ingredient of our explanation was related to an effect of magnetic field on the charge distribution within the Coulomb glass.…”

“…Thus, after initial exponential increase of σ, it is followed by a steep decrease due to steep increase of 1/τ . Then, an increase of 1/τ with temperature increase is naturally restricted by some effective value (1/τ ) max which leads to a saturation of σ(T ) at the value σ ≃ e 2 m(1/τ max ) (5) b) Magnetic field driven disorder. The main effect of the external magnetic field H on the relation between A + andà 0 centers is related to the Zeeman energy µ B gH (where µ B is Bohr magneton while g is g-factor) which should be paid for a creation of A + center due to on-site spin correlation on the center (see Fig.5).…”

Low frequency excitations in the Coulomb Glass: Numerical analysis using the avalanche method

“…In our opinion, these avalanches have some similarities with metastable systems discussed in [23][24][25][26]. However, the final state of the avalanche in [28] is not always a real 1e stable state of the whole Coulomb Glass (at least for dipole excitations) due to initial excitation that is still present in the system.…”

“…The discussed computation shows that there are quite a lot of realizations of pairs of metastable states that differ only locally and thus are in some way similar to metastable clusters that are discussed in [23][24][25][26].…”

“…Another attempts to describe low-frequency properties of Coulomb Glass were made in [23][24][25][26]. The authors assumed that the Coulomb Glass contains local areas that can exist in one of two states with close energies and act as local metastable systems.…”