Dynamic behavior of correlated electrons in the insulating doped semiconductor Si:P
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At low energy scales charge transport in the insulating Si:P is dominated byactivated hopping between the localized donor electron states.Theoretical models for a disordered electronic system with a long-range Coulomb interaction are appropriate to interpret the electric conductivity spectra. With a novel and advanced method [2,3], we perform broadband phase sensitive measurements of thereflection coefficient from 45 MHz up to 5 GHz, employing a vectornetwork analyzer with a 2.4 mm coaxial sensor, which is terminatedby the sample under test. While the material parameters(conductivity and permittivity) can be easily extracted from theobtained impedance data if the sample is metallic, no directsolution is possible if the material under investigation is aninsulator. Focusing on doped semiconductors with largely varyingconductivity and dielectric function, we present a closed calibration and evaluationprocedure with an optimized theoretical and experimental complexity, based on the rigoroussolution for the electromagnetic field inside theinsulating sample, combined with the variational principle]. Basically nolimiting assumptions are necessary in a strictly defined parameter range. As an application of our new method, we have measured the complex broadband microwaveconductivity of Si:P in a broad range ofphosphorus concentration n/n_c from 0.56 to 0.9 relative to thecritical value n_c=3.5x10^{18} cm^{-3} of the metal-insulator transition driven by doping at temperatures down to 1.1 K, and studied unresolved issues of fundamental research concerning the electronic correlations and the metal-insulator transition.Verknüpfung zu Publikationen oder weiteren Datensätzen
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Journal of Applied Physics, 103 (2008), S. 084902-1-8 , Physica Status Solidi C, 5 (2008), S. 703-707