W. Plesiewicz

Millikelvin studies of mixed-valence HgSe : Fe

Resistivity and magnetic susceptibility measurements of HgSe:Fe have been performed down to 30 mK and in the magnetic field range 50 mOe-3 kOe. Previously observed high conductivities of HgSe:Fe in the mixed valence region of Fe donors have been found to remain unchanged down to the lowest measured temperatures, indicating a minor influence of the resonant scattering and Kondo effect. This points to a weak k-d hybridization and substantiates classification of HgSe:Fe as an inhomogeneous mixed-valence system in which intersite Coulomb interactions impose spatial correlations in positions of charged centers. A resistive and inductive indication of superconductivity has been detected in some samples. The phenomenon is assigned to the presence of Hg-related superconducting inclusions and the associated proximity effect. This interpretation explains the field and temperature dependence of the resistivity and magnetic susceptibility, as well as being consistent with a sensitivity of the effect on deviations from stoichiometry and on annealing in Se vapor.

Conductivity in a spin-polarized band near the metal-insulator critical point

Abstract Millikelvin conductivity measurements of semimagnetic n-Cd 0.95 Mn 0.5 Se and p-Hg 0.915 Mn 0.085 Te in the region of the insulator-to-metal transition induced by the magnetic field are presented. The results of CdMnSe can be quantitatively explained on both sides of the transition by Finkelsteins renormalization group equations suitable for a spin-polarized Fermi liquid. The temperature dependence of the variable-range hopping conductivity in p-HgMnTe is consistent with the presence of a Coulomb anomaly at the Fermi level.

Second-harmonic generation in a spin-glass microstructure

Abstract We studied magnetoconductance of microregions containing 2d electron-gas adjacent to a grain-boundary plane in bicrystals of Hg0.79Cd0.19Mn0.02Te. In addition to weak localization magnetoresistance and universal conductance fluctuations persisting up to ∼ 1 K, strongly nonlinear-current voltage characteristics were detected in the vicinity of spin-glass freezing occurring at 100 mK.

Critical Behavior of the Hall Coefficient and Dielectric Susceptibility near the Anderson-Mott Transition in p-Hg1−xMnxTe

Results of millikelvin measurements of magnetoresistance, Hall effect, and dielectric susceptibility near the magnetic field-induced non-metal-metal transition are presented for Hg0.92Mn0.08Te. The critical behavior is discussed in terms of the Anderson-Mott transition, driven by electron-electron interactions in a spin-polarized band.

Magnetic Field Driven Insulator-to-Metal Transition in Semimagnetic Semiconductors

Results of millikelvin magnetoresistance measurements of anisotropic p-Hg 0.915 Mn 0.085 Te and isotropic n-Gd 0.95 Mn 0.05 Se are presented and interpreted in terms of Anderson-Mott transition in a spin polarized band.

Mesoscopic phenomena in a dilute magnetic semiconductor Hg1−x−yCdyMnxTe

Abstract Microscopic four-contact probes to inversion layers adjacent to grain-boundaries of semimagnetic HgCdMnTe have been photolithographically patterned. Magnetoresistance measurements performed on these structures revealed aperiodic conductance fluctuations of the magnitude of the order of e 2 h . Analysis of both fluctuation amplitude and their mean period indicated that the studied system was in mesoscopic regime. Additionally, strongly nonlinear current-voltage characteristics were detected in the vicinity of the spin-glass freezing occurring at T = 100 mK.

Absence of resonant scattering in mixed valent Hg1χ-FeχSe

Abstract Resistivity and magnetic susceptibility of Hg 1-χ Fe χ Se have been measured down to 30 mK, in the magnetic field range of 50 mOe - 3 kOe. The data substantiate the classification of Hg l-χ Fe χ Se as an inhomogeneous mixed valence system in which inter-site Coulomb interactions among Fe resonant donors charges impose their spatial correlations, thereby reducing the efficiency of electron scattering. Resistive of superconductivity have been observed in some samples. The phenomenon is assigned to the presence of Hg-related inclusions and the associated proximity effect.

Fundamental high-field transport properties of a GaAs/AlGaAs modulation doped heterostructure

Abstract Quantum Hall effect studies of GaAs/AlGaAs modulation doped heterostructures with electron mobilities of 2 × 10 5 cm 2 /V·s are presented. The heterostructures were grown by a MBE system in Beijing, China. The measurements have been performed up to 18 T at 1.9 K and up to 6 T down to 50 mK.