Magnetoresistivity and acoustoelectronic effects in a tilted magnetic field in p -Si/SiGe/Si structures with an anisotro
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C PROPERTIES OF SOLID
Magnetoresistivity and Acoustoelectronic Effects in a Tilted Magnetic Field in pSi/SiGe/Si Structures with an Anisotropic g Factor I. L. Drichkoa, *, I. Yu. Smirnova, A. V. Suslovb, O. A. Mironovc, and D. R. Leadleyd a
Ioffe Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia *email: [email protected] b National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA c Warwick SEMINANO R & D Centre, University of Warwick Science Park, Coventry CV4 7EZ, UK dDepartment of Physics, University of Warwick Science Park, Coventry CV4 7AL, UK Received November 17, 2009
Abstract—Magnetoresistivity ρxx and ρxy and the acoustoelectronic effects are measured in pSi/SiGe/Si with an impurity concentration p = 1.99 × 1011 cm–2 in the temperature range 0.3–2.0 K and an tilted magnetic field up to 18 T. The dependence of the effective g factor on the angle of magnetic field tilt θ to the normal to the plane of a twodimensional pSi/SiGe/Si channel is determined. A firstorder ferromagnet–paramagnet phase transition is observed in the magnetic fields corresponding to a filling factor ν = 2 at θ ≈ 59°–60°. DOI: 10.1134/S1063776110090189
INTRODUCTION The rather interesting kinetic properties of pSi/SiGe/Si structures have been attracting attention of researchers for the last two decades [1–6]. The quantum well in pSi/Si1 – xGex/Si is located in the strained Si1 – xGex layer; therefore, the triply degener ate (without regard for spin) valence band of SiGe splits into three bands due to spin–orbit coupling and mechanical stresses. The charge carriers are repre sented by heavy holes, whose band is formed by atomic states with quantum numbers L = 1, S = 1/2, and J = 3/2. This should result in a strong anisotropy of the effective g factor: g* ≈ 4.5 if a magnetic field is normal to the plane of the quantum well and g* ≈ 0 if a magnetic field is parallel to the plane of the quantum well [7]. In such structures in a magnetic field normal to the plane of the quantum well, the values of parameter m* and g* factor are such that the relationship g*μBB ≈ បωc holds true; here, μB is the Bohr magneton, ωc = eB/m*c is the cyclotron frequency, e is the electron charge, B is the magnetic field, m* is the effective hole mass, and c is the velocity of light. As a result, resistiv ity ρxx oscillations only with odd filling factors ν = 1, 3, 5, … are experimentally observed in magnetic field B. ρxx(B) oscillations at ν = 2 are observed only in some samples. The specific features of conductivity in the magnetic field corresponding to ν = 2 are comprehen sively studied in this work. The formation of pinned Wigner glass was revealed in pSi/SiGe/Si with a low impurity concentration (p = 8.2 × 1010 cm–2) in the quantum limit in a perpen
dicular magnetic field [8], and a giant positive magne toresistivity was observed in this structure in a parallel magnetic field [9]. This magnetoresistivity was caused by the interaction of the orbital motion
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