Quantum Hall effect in dual-gated graphene bilayers with tunable layer density imbalance (2009)
We study the magnetotransport properties of dual-gated graphene bilayers, in which the total density and layer density imbalance are independently controlled. As the bilayer is imbalanced we observe...
Gokmen, T., Padmanabhan, Medini, Vakili, K., Tutuc, E., Shayegan, M.
We measure the effective mass (m*) of interacting two-dimensional electrons confined to a 4.5 nm-wide AlAs quantum well. The electrons in this well occupy a single out-of-plane conduction band valley...
Giant frictional drag in strongly interacting bilayers near filling factor one (2008)
Tutuc, E., Pillarisetty, R., Shayegan, M.
We study the frictional drag in high mobility, strongly interacting GaAs bilayer hole systems in the vicinity of the filling factor $\nu=1$ quantum Hall state (QHS), at the same fillings where the...
Dynamics of Density Imbalanced Bilayer Holes in the Quantum Hall Regime (2008)
Misra, S., Bishop, N. C., Tutuc, E., Shayegan, M.
We report magnetotransport measurements on bilayer GaAs hole systems with unequal hole concentrations in the two layers. At magnetic fields where one layer is in the integer quantum Hall state and...
Spin susceptibility of interacting two-dimensional electrons with anisotropic effective mass (2008)
Gokmen, T., Padmanabhan, Medini, Tutuc, E., Shayegan, M., De Palo, Stefania, Moroni, Saverio, ...
We report measurements of the spin susceptibility in dilute (rs up to 10) AlAs two-dimensional (2D) electrons occupying a single conduction-band valley with an anisotropic in-plane Fermi contour,...
Spin Susceptibility of Interacting Two-dimensional Electrons with Anisotropic Effective Mass (2007)
Gokmen, T., Padmanabhan, Medini, Tutuc, E., Shayegan, M., De Palo, S., Moroni, S., ...
We report measurements of the spin susceptibility in dilute (rs up to 10) AlAs two-dimensional (2D) electrons occupying a single conduction-band valley with an anisotropic in-plane Fermi contour,...
Tunneling between Dilute GaAs Hole Layers (2007)
Misra, S., Bishop, N. C., Tutuc, E., Shayegan, M.
We report interlayer tunneling measurements between very dilute two-dimensional GaAs hole layers. Surprisingly, the shape and temperature-dependence of the tunneling spectrum can be explained with a...
Strong Aharonov-Bohm oscillations in GaAs two-dimensional holes (2006)
Habib, B., Tutuc, E., Shayegan, M.
We measured Aharonov-Bohm resistance oscillations in a shallow two-dimensional GaAs hole ring structure, defined by local anodic surface oxidation. The amplitude of the oscillations is about 10% of...
Pinning modes and interlayer correlation in high magnetic field bilayer Wigner solids (2006)
Wang, Zhihai, Chen, Yong P., Engel, L. W., Tsui, D. C., Tutuc, E., Shayegan, M.
We report studies of pinning mode resonances in the low total Landau filling (\nu) Wigner solid of a series of bilayer hole samples with negligible interlayer tunneling, and with varying interlayer...
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...
Zeeman splitting of interacting two-dimensional electrons with two effective masses (2006)
Vakili, K., Tutuc, E., Shayegan, M.
We have realized an AlAs two-dimensional electron system in which electrons occupy conduction-band valleys with different Fermi contours and effective masses. In the quantum Hall regime, we observe...
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...
Interaction and disorder in bilayer counterflow transport at filling factor one (2005)
We study high mobility, interacting GaAs bilayer hole systems exhibiting counterflow superfluid transport at total filling factor $\nu=1$. As the density of the two layers is reduced, making the...
Anomalous Spin Polarization of GaAs Two-Dimensional Hole Systems (2005)
Winkler, R., Tutuc, E., Papadakis, S. J., Melinte, S., Shayegan, M., Wasserman, D., ...
We report measurements and calculations of the spin-subband depopulation, induced by a parallel magnetic field, of dilute GaAs two-dimensional (2D) hole systems. The results reveal that the shape of...
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...
Faniel, S., Tutuc, E., De Poortere, E. P., Gustin, C., Vlad, A., Melinte, S., ...
We report thermopower measurements of interacting GaAs bilayer hole systems. When the carrier densities in the two layers are equal, these systems exhibit a reentrant insulating phase near the...
Spin Splitting in GaAs (100) Two-Dimensional Holes (2004)
Habib, B., Tutuc, E., Melinte, S., Shayegan, M., Wasserman, D., Lyon, S. A., ...
We measured Shubnikov-de Haas (SdH) oscillations in GaAs (100) two-dimensional holes to determine the inversion asymmetry-induced spin splitting. The Fourier spectrum of the SdH oscillations contains...
Negative differential Rashba effect in two-dimensional hole systems (2004)
Habib, B., Tutuc, E., Melinte, S., Shayegan, M., Wasserman, D., Lyon, S. A., ...
We demonstrate experimentally and theoretically that two-dimensional (2D) heavy hole systems in single heterostructures exhibit a \emph{decrease} in spin-orbit interaction-induced spin splitting with...
Spin Polarization Dependence of the Coulomb Drag at Large $r_{s}$ (2004)
Pillarisetty, R., Noh, H., Tutuc, E., De Poortere, E. P., Tsui, D. C., Shayegan, M.
We find that the temperature dependence of the drag resistivity ($\rho_{D}$) between two dilute two-dimensional hole systems exhibits an unusual dependence upon spin polarization. Near the apparent...
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...
Coulomb Drag near the metal-insulator transition in two-dimensions (2004)
Pillarisetty, R., Noh, H., Tutuc, E., De Poortere, E. P., Lai, K., Tsui, D. C., ...
We studied the drag resistivity between dilute two-dimensional hole systems, near the apparent metal-insulator transition. We find the deviations from the $T^{2}$ dependence of the drag to be...
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...
Tutuc, E., Shayegan, M., Huse, D. A.
We study interacting GaAs bilayer hole systems, with very small interlayer tunneling, in a counterflow geometry where equal currents are passed in opposite directions in the two, independently...
A Laterally Modulated 2D Electron System in the Extreme Quantum Limit (2003)
Melinte, Sorin, Berciu, Mona, Zhou, C., Tutuc, E., Papadakis, S. J., Harrison, C., ...
We report on magnetotransport of a two-dimensional electron system (2DES), located 32 nm below the surface, with a surface superlattice gate structure of periodicity 39 nm imposing a periodic...
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,...
Layer charge instability in unbalanced bilayer systems in the quantum Hall regime (2003)
Tutuc, E., Pillarisetty, R., Melinte, S., De Poortere, E. P., Shayegan, M.
Measurements in GaAs hole bilayers with unequal layer densities reveal a pronounced magneto-resistance hysteresis at the magnetic field positions where either the majority or minority layer is at...
Critical Resistance of the Quantum Hall Ferromagnet in AlAs 2D Electrons (2003)
De Poortere, E. P., Tutuc, E., Shayegan, M.
Magnetic transitions in AlAs two-dimensional electrons give rise to sharp resistance spikes within the quantum Hall effect. Such spikes are likely caused by carrier scattering at magnetic domain...
In-Plane Magnetodrag between Dilute Two-Dimensional Systems (2003)
Pillarisetty, R., Noh, Hwayong, Tutuc, E., De Poortere, E. P., Tsui, D. C., Shayegan, M.
We performed in-plane magnetodrag measurements on dilute double layer two-dimensional hole systems, at in-plane magnetic fields that suppress the apparent metallic behavior, and to fields well above...
Tutuc, E., Melinte, S., De Poortere, E. P., Shayegan, M., Winkler, R.
We report measurements and calculations of the spin-polarization, induced by a parallel magnetic field, of interacting, dilute, two-dimensional electron systems confined to GaAs/AlGaAs...
Role of density imbalance in an interacting bilayer hole system (2002)
Tutuc, E., Melinte, S., De Poortere, E. P., Pillarisetty, R., Shayegan, M.
We study interacting GaAs hole bilayers in the limit of zero tunneling. When the layers have equal densities, we observe a phase coherent bilayer quantum Hall (QH) state at total filling factor...
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...
Spin polarization and transition from metallic to insulating behavior in 2D systems (2002)
Tutuc, E., De Poortere, E. P., Papadakis, S. J., Shayegan, M.
We have made quantitative measurements of the spin polarization of two-dimensional (2D) GaAs (100) electrons and GaAs (311)A holes, as a function of an in-plane magnetic field. The functional form of...
Frictional Drag between Two Dilute Two-Dimensional Hole Layers (2002)
Pillarisetty, R., Noh, Hwayong, Tsui, D. C., De Poortere, E. P., Tutuc, E., Shayegan, M.
We report drag measurements on dilute double layer two-dimensional hole systems in the regime of r_s=19~39. We observed a strong enhancement of the drag over the simple Boltzmann calculations of...
Spin polarization and g-factor of a dilute GaAs two-dimensional electron system (2001)
Tutuc, E., Melinte, S., Shayegan, M.
The effective g-factor ($g^{*}$) of a dilute interacting two-dimensional electron system is expected to increase with respect to its bare value as the density is lowered, and to eventually diverge as...
Anomalous Rashba spin splitting in two-dimensional hole systems (2001)
Winkler, R., Noh, H., Tutuc, E., Shayegan, M.
It has long been assumed that the inversion asymmetry-induced Rashba spin splitting in two-dimensional (2D) systems at zero magnetic field is proportional to the electric field that characterizes the...
Resistance Spikes at Transitions between Quantum Hall Ferromagnets (2000)
De Poortere, E. P., Tutuc, E., Papadakis, S. J., Shayegan, M.
We report a new manifestation of first-order magnetic transitions in two-dimensional electron systems. This phenomenon occurs in aluminum arsenide quantum wells with sufficiently low carrier...
Tutuc, E., De Poortere, E. P., Papadakis, S. J., Shayegan, M.
Using a novel technique, we make quantitative measurements of the spin polarization of dilute (3.4 to 6.8*10^{10} cm^{-2}) GaAs (311)A two-dimensional holes as a function of an in-plane magnetic...