Studies of low-frequency noise in the c-axis resistance of lightly doped La2-x SrxCuO4 (x = 0.03) have revealed
distinct switching fluctuations at low temperatures and in magnetic fields B of up to 9 T parallel to the c-axis of
the crystal. The switching noise is modulated by some slower events and becomes less prominent with increasing
temperature T. Our results demonstrate the existence of multiple metastable states in the presence of B. The
overall behavior of the noise is consistent with the picture of microscopic segregation of doped holes into hole-rich
regions separated by undoped domains in CuO2 planes. It also strongly suggests that interactions should be
included in possible theoretical models to describe the data.
Studies of low-frequency resistance noise show that the glassy freezing of the two-dimensional electron system (2DES) in Si in the vicinity of the metal-insulator transition (MIT) persists in parallel magnetic fields B of up to 9 T. At low B, both the glass transition density ng and nc, the critical density for the MIT, increase with B such that the width of the metallic glass phase (nc < ns < n g) increases with B. At higher B, where the 2DES is spin polarized, nc and ng no longer depend on B. Our results demonstrate that charge, as opposed to spin, degrees of freedom are responsible for glassy ordering of the 2DES near the MIT.
Studies of low-frequency resistance noise demonstrate that glassy freezing occurs in a two-dimensional electron system in silicon in the
vicinity of the metal-insulator transition (MIT). The width of the metallic glass phase, which separates the 2D metal and the (glassy) insulator, depends strongly on disorder, becoming extremely small
in high-mobility (low-disorder) samples. The glass transition is manifested by a sudden and dramatic slowing down of the electron dynamics, and by a very abrupt change to the sort of statistics characteristic of complicated multistate systems. In particular, the behavior of the second spectrum, an important fourth-order noise
statistic, indicates the presence of long-range correlations between fluctuators in the glassy phase, consistent with the hierarchical picture of glassy dynamics.
A giant and nonlinear Zeeman splitting in diluted magnetic semiconductors (DMS) offers a unique opportunity to examine quantum Hall ferromagnetism (QHF) since crossing of Landau levels (LL) can be achieved in moderately strong (Btot ≈ 1 T) total magnetic fields. We carried out magnetoresistance studies on modulation-doped, gated heterostructures of Cd1-xMnxTe/Cd1-yMgyTe:I. We put into evidence the formation of ISing quantum Hall ferromagnet with Curie temperature Tc as high as 2 K. QHF in our device is manisfested by anomalous magnetoresistance maxima, their hysteretic behavior, and time-dependent resistance, similar to earlier observations in III-V heterostructures. However, in our system these phenomena are much stronger, especially when either 2- or 1-, and 0+ LL are brought into coincidence. The magnitude of the QHF spikes depends dramatically on the history of the sample, shows hysteresis when either magnetic field or gate voltage are swept, stretched exponential-time evolution characteristic of glassy systems, and strong Barkhausen noise reflecting the dynamics of ferromagnetic domains. Our study indicates that these metastabilities stem from the electronic systems itself as an effect of slow dynamics of ferromagnetic domains, while the nuclear spin polarization plays a rather minor role.