Recent advances in III(1-x)Mn(x)V ferromagnetic semiconductors (for example in Ga(1-x)Mn(x)As) have demonstrated that electrical control of their spin properties can be used for manipulation and detection of magnetic signals. The Mn(2+) ions in these alloys provide magnetic moments, and at the same time act as a source of valence-band holes that mediate the Mn(2+)-Mn(2+) interactions. This coupling results in the ferromagnetic phase. In earlier workit was shown that the ferromagnetic state can be enhanced or suppressed by varying the carrier density. Here we demonstrate that, by using hydrostatic pressure to continuously tune the wavefunction overlap, one can control the strength of ferromagnetic coupling without any change in the carrier concentration. Tuning the exchange coupling by this process increases the magnetization spectacularly, and can even induce the ferromagnetic phase in an initially paramagnetic alloy. These results may open new directions for strain-engineering of nanodevices.

Quantum point contacts implemented in p-type GaAs/AlGaAs heterostructures are investigated by low-temperature electrical conductance spectroscopy measurements. Besides one-dimensional conductance quantization in units of 2e2 /h a pronounced extra plateau is found at about 0.7(2e 2 /h) which possesses the characteristic properties of the so-called "0.7 anomaly" known from experiments with n-type samples. The evolution of the 0.7 plateau in high perpendicular magnetic field reveals the existence of a quasi-localized state and supports the explanation of the 0.7 anomaly based on self-consistent charge localization. These observations are robust when lateral electrical fields are applied which shift the relative position of the electron wavefunction in the quantum point contact, testifying to the intrinsic nature of the underlying physics. [12]. An alternative explanation suggests that the conductance is suppressed due to Coulomb repulsion from a quasi-localized state in the QPC [13,14], and restored to the 2e 2 /h full value at low temperatures due to the Kondo effect. The emergence of such a quasi-localized state in QPCs has been predicted based on spin-density functional theory (SDFT) calculations [15,16], and quantum Monte Carlo calculations [17]. Kondo-like physics has indeed been observed in QPCs [18].The more pronounced carrier-carrier interactions in low-dimensional hole systems [19,20] compared to their n-type counterparts make p-doped systems especially suitable for investigating many-body effects such as the 0.7 anomaly [21]. While previous studies [9,[21][22][23][24] focused on Si-doped (311) structures with an anisotropic in-plane Fermi surface, we present data on C-doped (100) samples. We performed conductance spectroscopy measurements of hole QPCs oriented along the high symmetry crystallographic directions parallel to the cleaved edges of the wafer at magnetic fields applied perpendicular to the plane of the two-dimensional hole gas (2DHG). We found that the 0.7 anomaly gradually evolves into a Coulomb resonance-like peak at high magnetic fields accompanied by a Coulomb blockade diamond observed in the finite bias conductivity. In symmetrically designed QPCs both features are insensitive to a lateral displacement of the wavefunction in the QPC channel. This provides experimental evidence for the intrinsic origin of the quasi-localized state.Measurements were performed on five QPCs with different geometries, all based on the same wafer material. The host heterostructure consists of a 5 nm undoped GaAs cap layer, followed by a 15 nm thick, homogeneously C-doped layer of AlGaAs separated from the 2DHG formed in the electronically isotropic (100) plane by a 25 nm thick, undoped AlGaAs spacer layer [25]. Prior to sample fabrication the quality of the 2DHG (n = 4×10 11 cm −2 , µ = 120'000 cm 2 /Vs) was characterized by standard magnetotransport measurements at 4.2 K [26]. Typical values for the interaction parameter r s = E int /E F are r s > 5.Investigations of the 0.7 anomaly in hole systems are experim...

We demonstrate the universal 1/f type current noise in Ag based, nanofilamentary resistive switches which arises from internal resistance fluctuations.

The dynamics of resistive switchings in nanometer-scale metallic junctions formed between an inert metallic tip and an Ag film covered by a thin Ag2S layer are investigated. Our thorough experimental analysis and numerical simulations revealed that the resistance change upon a switching bias voltage pulse exhibits a strongly non-exponential behaviour yielding markedly different response times at different bias levels. Our results demonstrate the merits of Ag2S nanojunctions as nanometer-scale non-volatile memory cells with stable switching ratios, high endurance as well as fast response to write/erase, and an outstanding stability against read operations at technologically optimal bias and current levels.