Glassy behavior of a two-dimensional electron system in Si in parallel magnetic fields

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Studies of low-frequency resistance noise show that the glassy freezing of the two-dimensional electron system (2DES) in Si in the vicinity of the metal-insulator transition (MIT) persists in parallel magnetic fields B of up to 9 T. At low B, both the glass transition density ng and nc, the critical density for the MIT, increase with B such that the width of the metallic glass phase (nc < ns < ng) increases with B. At higher B, where the 2DES is spin polarized, nc and ng no longer depend on B. Our results demonstrate that charge, as opposed to spin, degrees of freedom are responsible for glassy ordering of the 2DES near the MIT.