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Additional file 1: Supplementary Materials.

We use millimeter wave radiation to manipulate the populations of the energy levels of a single crystal molecular magnet Fe8. When a continuous wave radiation is in resonance with the transitions from the ground state to the first excited state, the equilibrium magnetization exhibits a dip. The position of this dip varies linearly with the radiation frequency. Our results provide a lower bound of 0.17 ns for transverse relaxation time and suggest the possibility that single-molecule magnets might be utilized for quantum computation., 16 pages, 3 figures

Physical Review Letters

We report Hall sensor measurements of the magnetic relaxation of Mn$_{12}$-acetate as a function of magnetic field applied along the easy axis of magnetization for a series of closely-spaced temperatures between 0.24 K and 1.9 K. We map out a region in the $H-T$ plane where ground state tunneling is observed, a region where tunneling proceeds via thermally-assisted tunneling, and a crossover region where both participate in the relaxation. We observe the occasional absence of ground-state tunneling under conditions where one would expect it to be present, and suggest a resolution to the enigma., Comment: 5 pages including 4 figures. Minor revisions to clarify explanations

Physical Review Letters

Measurements in magnetic fields applied at a small angle with respect to the 2D plane of the electrons of a low-density silicon MOSFET indicate that the Hall coefficient is independent of parallel field from H=0 to $H>H_{sat}$, the field above which the longitudinal resistance saturates and the electrons have reached full spin-polarization. This implies that the mobilities of the spin-up and spin-down electrons remain comparable at all magnetic fields, and suggests there is strong mixing of spin-up and spin-down electron states., 4 pages, 2 figures

We report measurements of the resistance of silicon MOSFETs as a function of temperature in high parallel magnetic fields where the 2D system of electrons has been shown to be fully spin-polarized. A magnetic field suppresses the metallic behavior observed in the absence of a magnetic field. In a field of 10.8 T, insulating behavior is found for densities up to n_s approximately 1.35 x 10^{11} cm^{-2} or 1.5 n_c; above this density the resistance is a very weak function of temperature, varying less than 10% between 0.25 K and 1.90 K. At low densities the resistance goes to infinity more rapidly as the temperature is reduced than in zero field and the magnetoresistance diverges as T goes to 0., 4 pages, including 4 figures. References added

This paper has been withdrawn by the authors. Measurements at many different angles spanning a broad range of electron densities indicate that the observed doubling of the period of Shubnikov-de Haas oscillations, which we had attributed to a transition to a new spin-ordered phase, is also consistent with an alternative explanation. A full interpretation of our data will be posted at a later date., This paper has been withdrawn. Measurements at different angles spanning a broad range of electron densities indicate that the doubling of the period of SdH oscillations, which we had attributed to a transition to a new spin-ordered phase, is also consistent with an alternative explanation. A full paper will be posted at a later date

The response to a parallel magnetic field of the very dilute insulating two-dimensional system of electrons in silicon MOSFET's is dramatic and similar to that found on the conducting side of the metal-insulator transition: there is a large initial increase in resistivity with increasing field, followed by saturation to a value that is approximately constant above a characteristic magnetic field of about one Tesla. This is unexpected behavior in an insulator that exhibits Efros-Shklovskii variable-range hopping in zero field, and appears to be a general feature of very dilute electron systems., Comment: References added and updated. To be published in Phys. Rev. B