Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Memory effects in ac hopping conductance in the quantum Hall effect
  regime: Possible manifestation of DX$^-$ centers   Using simultaneous measurements of the attenuation and velocity of surface
acoustic waves propagating along GaAs/Al$_{0.3}$Ga$_{0.7}$As heterostructures,
complex ac conductance of the latters has been determined. In the magnetic
fields corresponding to the middles of the Hall plateaus both the ac
conductance, $\sigma (\omega)$, and the sheet electron density, $n_s$, in the
two-dimensional conducting layer turn out to be dependent on the samples'
cooling rate. As a result, the sample ``remembers'' the cooling conditions. The
complex conductance is strongly dependent on an infrared illumination which
also changes both $\sigma (\omega)$ and $n_s$. Remarkably, the correlation
between $\sigma (\omega)$ and $n_s$ is \emph{universal}, i.e. it is independent
of the way to change these quantities. The results are attributed to
two-electron defects (so-called $DX^-$ centers) located in the Si doped layer.

21
The categories of this paper are: adap-org
0
The categories of this paper are: hep-ph
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
5
The categories of this paper are: gr-qc
23
The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
25
The categories of this paper are: patt-sol
3
The categories of this paper are: physics
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin
1
The categories of this paper are: cs
8
The categories of this paper are: hep-ex
35
The categories of this paper are: mtrl-th