Magnetoresistivity in a tilted magnetic field in p -Si/SiGe/Si heterostructures with an anisotropic g -factor. Part II
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LECTRONIC PROPERTIES OF SOLID
Magnetoresistivity in a Tilted Magnetic Field in pSi/SiGe/Si Heterostructures with an Anisotropic gFactor. Part II1 I. L. Drichkoa, I. Yu. Smirnova, A. V. Suslovb, O. A. Mironovc, and D. R. Leadleyd a
Ioffe Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia b National High Magnetic Field Laboratory Tallahassee, FL 32310, USA cWarwick SEMINANO R&D Centre, University of Warwick Science Park Coventry CV4 7EZ, UK d Department of Physics, University of Warwick Coventry CV4 7AL, UK email: [email protected] Received October 25, 2011
Abstract—The magnetoresistance components ρxx and ρxy are measured in two pSi/SiGe/Si quantum wells that have an anisotropic gfactor in a tilted magnetic field as a function of the temperature, field, and tilt angle. Activation energy measurements demonstrate the existence of a ferromagnetic–paramagnetic (F–P) transition for the sample with the hole density p = 2 × 1011 cm–2. This transition is due to the crossing of the 0↑ and 1↓ Landau levels. However, in another sample with p = 7.2 × 1010 cm–2, the 0↑ and 1↓ Landau levels coincide for angles θ = 0–70°. Only for θ > 70° do the levels start to diverge which, in turn, results in the energy gap opening. DOI: 10.1134/S1063776112080067 1
1. INTRODUCTION Magnetotransport measurements on dilute pSi/SiGe/Si structures, with twodimensional hole gas (2DHG) densities about 1011 cm–2, have revealed an unusual phenomenon at the filling factor ν = 3/2, the socalled “reentrant” metalinsulator transition [1–6]. This phenomenon manifests itself as an addi tional peak of the magnetoresistance ρxx(T, θ) at ν = 3/2. The peak demonstrates an insulatortype behav ior, i.e., its magnitude increases with decreasing the sample temperature [3, 5]. The authors of [2] explained this appearance by the presence of smooth longrange potential fluctuations having a magnitude comparable to the Fermi energy. But in [3–5], the magnetoresistance anomaly was attributed to a crossing of the Landau levels (LLs) with different spin directions 0↑ and 1↓ as the magnetic field increased. It appears that some pSi/SiGe/Si sys tems show a magnetoresistance anomaly at ν = 3/2 that depends on the tilt angle between the magnetic field and the sample normal [6], whereas in other pSi/SiGe/Si systems, this anomaly is not manifested at all [4]. The third set of pSi/SiGe/Si systems have such anomaly in ρxx at ν = 3/2, but it is independent of the tilt angle [3]. In our earlier article [7], we analyzed the conductiv ity at ν = 2 in tilted magnetic fields in a sample with p = 2 × 1011 cm–2 and demonstrated the presence of a ferromagnetic–paramagnetic (F–P) transition at a tilt angle of about 60°. We note that we did not observe any 1 The article is published in the original.
significant variation of the conductivity at ν = 3/2; a resistivity peak of the reentranttransition type occurred in this region of the filling factor. We there fore focused our research on the ν = 2 region, i.e., the vicinity of
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