The sheet resistance as a function of temperature, magnetic field and its orientation for atomically flat SrTiO 3 / LaAlO 3 interfaces with carrier densities of ϳ3 ϫ 10 13 cm −2 is reported. At low magnetic fields superconductivity is observed below 130 mK. The temperature dependence of the high field magnetoresistance and its strong anisotropy suggest possible magnetic ordering below 35 K. The origin of this ordering and its possible relation to superconductivity are discussed.

Three antibiotics were isolated from a CH2Cl2 extract of the liquid culture of Pseudomonas fluorescens strain PFM2. Two of the antibiotics were identified as 2,4-diacetylphloroglucinol and pyoluterin. The structure elucidation, absolute stereochemistry, synthesis, and biological activities of the new antibiotic (+)-(S)- dihydroaeruginoic acid [1] are reported.

We report sub-meV (as low as 0.6meV) low-temperature photoluminescence linewidth and high low-temperature electron mobility (μ∼1−1.5×106cm2∕Vs) of GaAs quantum wells in AlGaAs barriers grown by standard metalorganic vapor phase epitaxy. These records values are achieved by epitaxial growth on (100) slightly misoriented substrates [⩽0.6 degrees off-(100) GaAs substrates] in combination with a high V/III ratio for AlGaAs growth. Such small misorientations are sufficient to drastically modify the optical and transport properties as well as the growth mode and surface morphologies of both GaAs and AlGaAs epitaxial layers, allowing greater interface quality and reduced impurity incorporation. The quantum wells so obtained show optical properties comparable to high-quality samples grown by molecular beam epitaxy. In addition, the slight misorientation considerably reduces the impact of substrate temperature on electron mobility, which allows achieving high values of μ within a much broader range of growth temperatures.

We have measured the temperature dependence of the conductance in long V-groove quantum wires (QWRs) fabricated in GaAs/AlGaAs heterostructures. Our data is consistent with recent theories developed within the framework of the Luttinger liquid model, in the limit of weakly disordered wires. We show that for the relatively low level of disorder in our QWRs, the value of the interaction parameter g ∼ = 0.66, which is the expected value for GaAs. However, samples with a higher level of disorder show conductance with stronger temperature dependence, which does not allow their treatment in the framework of perturbation theory. Fitting such data with perturbation-theory models leads inevitably to wrong (lower) values of g. The electrical conductance through noninteracting clean quantum wires (QWRs) containing a number of one-dimensional subbands is quantized in the universal unit, as observed in narrow constrictions in 2D electron gas (2DEG) systems [2,3]. For such short and clean narrow wires, the e-e interactions described by the so-called Luttinger liquid (LL) model [4] do not affect the value of the conductance, namely it is temperature and length independent as indeed was shown experimentally [2,3]. In the presence of disorder in sufficiently long QWRs, suppression of the conductance is expected at low temperatures. A number of theoretical papers addressing this issue [5,6,7,8] predict a negative correction to the conductance versus temperature G(T ), which increases with T and obeys a power law: T g−1 , where g < 1 is an interaction parameter.The validity of the implications of the LL theory has been recently demonstrated in a number of experiments [9,10]. The most evident proofs of the predictions were shown in tunnelling experiments performed in T-shaped cleaved-edged overgrown GaAs quantum wires [9] and in carbon nanotubes [10]. Earlier non-tunnelling experiments, in which suppression of conductance occurs in the linear response regime, did not unambiguously prove the validity of the theory, and the value of the g parameter could not be deduced from the experimental data [11,12,13]. Several complications are encountered in such experiments. For sufficiently disordered wires, where the correction to G(T ) is expected to be large, the value of the conductance at the plateau is not well defined due to the specific realization of the disordered potential in the wire, as was the case for the long wires of Tarucha et al. [11]. Moreover, in the intermediate regime, namely for disorder level for which the conductance plateau could be well defined but the corrections to G(T ) are already significant for a relatively narrow temperature range, g cannot be extracted by applying a perturbation theory. If however, the disorder is very weak so that the plateaus are well defined at all temperatures [11,12], the variation of its value versus temperature is so weak that the g parameter cannot be reliably determined. Therefore, if one wishes to compare G(T ) to the theory, a wire possessing just the right amount of disorder is ...

Pseudomonas fluorescens strain PFM2, antagonistic to Septoria tritici, also inhibited growth of several other phytopathogenic bacteria and fungi in vitro. Three inhibitory compounds were extracted from liquid glycerol‐peptone‐phosphate medium in which strain PFM2 was grown for 4 weeks. The compound recovered in greatest quantity (70 mg/1) was identified as 2,4‐diacetylphloroglucinol. The other two antibiotics, which were produced in small amounts (< 5 mg/l), were not identified. A similar pattern of inhibition against the different bacteria and fungi was exhibited by both 2,4‐diacetylphloroglucinol and strain PFM2 when grown in a medium of the same composition as that in which the antibiotic was produced.