Parallel Magnetic Field Tuning of Valley Splitting in AlAs Two-Dimensional Electrons (2008)
Gokmen, T., Padmanabhan, Medini, Gunawan, O., Shkolnikov, Y. P., Vakili, K., De Poortere, E. P., ...
We demonstrate that, in a quasi-two-dimensional electron system confined to an AlAs quantum well and occupying two conduction-band minima (valleys), a parallel magnetic field can couple to the...
Anomalous giant piezoresistance in AlAs 2D electrons with anti-dot lattices (2007)
Gunawan, O., Gokmen, T., Shkolnikov, Y. P., De Poortere, E. P., Shayegan, M.
An AlAs two-dimensional electron system patterned with an anti-dot lattice exhibits a giant piezoresistance (GPR) effect, with a sign opposite to the piezoresistance observed in the unpatterned...
Valley polarization and susceptibility of composite fermions around nu=3/2 (2007)
Bishop, N. C., Padmanabhan, M., Vakili, K., Shkolnikov, Y. P., De Poortere, E. P., Shayegan, M.
We report magnetotransport measurements of fractional quantum Hall states in an AlAs quantum well around Landau level filling factor nu = 3/2, demonstrating that the quasiparticles are composite...
Two-dimensional electrons occupying multiple valleys in AlAs (2006)
Shayegan, M., De Poortere, E. P., Gunawan, O., Shkolnikov, Y. P., Tutuc, E., Vakili, K.
Two-dimensional electrons in AlAs quantum wells occupy multiple conduction-band minima at the X- points of the Brillouin zone. These valleys have large effective mass and g-factor compared to the...
High-mobility AlAs quantum wells with out-of-plane valley occupation (2006)
Vakili, K., Shkolnikov, Y. P., Tutuc, E., De Poortere, E. P., Padmanabhan, M., Shayegan, M.
Employing state-of-the-art molecular beam epitaxy techniques to grow thin, modulation-doped AlAs quantum wells, we have achieved a low temperature mobility of 5.5 m$^2$/Vs with out-of-plane...
Dependence of persistent gaps at Landau level crossings on relative spin (2006)
Vakili, K., Gokmen, T., Gunawan, O., Shkolnikov, Y. P., De Poortere, E. P., Shayegan, M.
We report measurements of the quantum Hall state energy gap at avoided crossings between Landau levels originating from different conduction band valleys in AlAs quantum wells. These gaps exhibit an...
Valley susceptibility of an interacting two-dimensional electron system (2006)
Gunawan, O., Shkolnikov, Y. P., Vakili, K., Gokmen, T., De Poortere, E. P., Shayegan, M.
We report direct measurements of the valley susceptibility, the change of valley population in response to applied symmetry-breaking strain, in an AlAs two-dimensional electron system. As the...
Observation of Quantum Hall Valley Skyrmions (2005)
Shkolnikov, Y. P., Misra, S., Bishop, N. C., De Poortere, E. P., Shayegan, M.
We report measurements of the interaction-induced quantum Hall effect in a spin-polarized AlAs two-dimensional electron system where the electrons occupy two in-plane conduction band valleys. Via the...
Spin-dependent resistivity at transitions between integer quantum Hall states (2005)
Vakili, K., Shkolnikov, Y. P., Tutuc, E., Bishop, N. C., De Poortere, E. P., Shayegan, M.
The longitudinal resistivity at transitions between integer quantum Hall states in two-dimensional electrons confined to AlAs quantum wells is found to depend on the spin orientation of the...
Shayegan, M., Karrai, K., Shkolnikov, Y. P., Vakili, K., De Poortere, E. P., Manus, S.
We demonstrate the use of a piezoelectric actuator to apply, at low temperatures, uniaxial stress in the plane of a two-dimensional electron system confined to a modulation-doped AlAs quantum well....
Giant low-temperature piezoresistance effect in AlAs two-dimensional electrons (2004)
Shkolnikov, Y. P., Vakili, K., De Poortere, E. P., Shayegan, M.
We present piezoresistance measurements in modulation doped AlAs quantum wells where the two-dimensional electron system occupies two conduction band valleys with elliptical Fermi contours. Our data...
Spin susceptibility of two-dimensional electrons in narrow AlAs quantum wells (2004)
Vakili, K., Shkolnikov, Y. P., Tutuc, E., De Poortere, E. P., Shayegan, M.
We report measurements of the spin susceptibility in dilute two-dimensional electrons confined to a 45$\AA$ wide AlAs quantum well. The electrons in this well occupy an out-of-plane conduction-band...
Shkolnikov, Y. P., Vakili, K., De Poortere, E. P., Shayegan, M.
We report measurements of the spin susceptibility, $\chi\propto g_v g^*m^*$, in an AlAs two-dimensional electron system where, via the application of in-plane stress, we transfer electrons from one...
Ballistic transport in AlAs two-dimensional electrons (2004)
Gunawan, O., Shkolnikov, Y. P., De Poortere, E. P., Tutuc, E., Shayegan, M.
We report the observation of commensurability oscillations in an AlAs two-dimensional electron system where two conduction-band valleys with elliptical in-plane Fermi contours are occupied. The...
Realization of an Interacting Two-Valley AlAs Bilayer System (2003)
Vakili, K., Shkolnikov, Y. P., Tutuc, E., De Poortere, E. P., Shayegan, M.
By using different widths for two AlAs quantum wells comprising a bilayer system, we force the X-point conduction-band electrons in the two layers to occupy valleys with different Fermi contours,...
Field-Effect Persistent Photoconductivity (2003)
De Poortere, E. P., Shkolnikov, Y. P., Shayegan, M.
We report a persistent increase or decrease in the two-dimensional electron density of AlAs or GaAs quantum wells flanked by AlGaAs barriers, brought about by illuminating the samples at T ~ 4 K...
Magnetic Field Induced Spin Polarization of AlAs Two-dimensional Electrons (2002)
De Poortere, E. P., Tutuc, E., Shkolnikov, Y. P., Vakili, K., Shayegan, M.
Two-dimensional (2D) electrons in an in-plane magnetic field become fully spin polarized above a field B_P, which we can determine from the in-plane magnetoresistance. We perform such measurements in...
Valley splitting of AlAs two-dimensional electrons in a perpendicular magnetic field (2002)
Shkolnikov, Y. P., De Poortere, E. P., Tutuc, E., Shayegan, M.
By measuring the angles at which the Landau levels overlap in tilted magnetic fields (the coincidence method), we determine the splitting of the conduction-band valleys in high-mobility...