Electronic and spin properties of Rashba billiards

Ballistic electrons confined to a billiard and subject to spin--orbit coupling of the Rashba type are investigated, using both approximate semiclassical and exact quantum--mechanical methods. We focus on the low--energy part of the spectrum that has negative eigenvalues. When the spin precession length is smaller than the radius of the billiard, the low--lying energy eigenvalues turn out to be well described semiclassically. Corresponding eigenspinors are found to have a finite spin polarization in the direction perpendicular to the billiard plane.Comment: 5 pages, 2 figure

In-plane magnetoelectric response in bilayer graphene

A graphene bilayer shows an unusual magnetoelectric response whose magnitude is controlled by the valley-isospin density, making it possible to link magnetoelectric behavior to valleytronics. Complementary to previous studies, we consider the effect of static homogeneous electric and magnetic fields that are oriented parallel to the bilayer's plane. Starting from a tight-binding description and using quasi-degenerate perturbation theory, the low-energy Hamiltonian is derived including all relevant magnetoelectric terms whose prefactors are expressed in terms of tight-binding parameters. We confirm the existence of an expected axion-type pseudoscalar term, which turns out to have the same sign and about twice the magnitude of the previously obtained out-of-plane counterpart. Additionally, small anisotropic corrections to the magnetoelectric tensor are found that are fundamentally related to the skew interlayer hopping parameter $\gamma_4$. We discuss possible ways to identify magnetoelectric effects by distinctive features in the optical conductivity.Comment: 14 pages, 7 figure

Tracking the energies of one-dimensional subband edges in quantum point contacts using dc conductance measurements

The semiconductor quantum point contact has long been a focal point for studies of one-dimensional electron transport. Their electrical properties are typically studied using ac conductance methods, but recent work has shown that the dc conductance can be used to obtain additional information, with a density-dependent Land\'{e} effective g-factor recently reported [T.-M. Chen et al, Phys. Rev. B 79, 081301 (2009)]. We discuss previous dc conductance measurements of quantum point contacts, demonstrating how valuable additional information can be extracted from the data. We provide a comprehensive and general framework for dc conductance measurements that provides a path to improving the accuracy of existing data and obtaining useful additional data. A key aspect is that dc conductance measurements can be used to map the energy of the 1D subband edges directly, giving new insight into the physics that takes place as the spin-split 1D subbands populate. Through a re-analysis of the data obtained by Chen et al, we obtain two findings. The first is that the 2-down subband edge closely tracks the source chemical potential when it first begins populating before dropping more rapidly in energy. The second is that the 2-up subband populates more rapidly as the subband edge approaches the drain potential. This second finding suggests that the spin-gap may stop opening, or even begin to close again, as the 2-up subband continues populating, consistent with recent theoretical calculations and experimental studies.Comment: Published version available at http://iopscience.iop.org/0953-8984/23/36/362201 15 pages, 3 figure

Reply to Comment on "Strongly Correlated Fractional Quantum Hall Line Junctions"

In two recent articles [PRL 90, 026802 (2003); PRB 69, 085307 (2004)], we developed a transport theory for an extended tunnel junction between two interacting fractional-quantum-Hall edge channels, obtaining analytical results for the conductance. Ponomarenko and Averin (PA) have expressed disagreement with our theoretical approach and question the validity of our results (cond-mat/0602532). Here we show why PA's critique is unwarranted.Comment: 1 page, no figures, RevTex