December 2011

Abstracts of the QSIT Lunch Seminar, December 1, 2011

Carbon nanotubes in electric and magnetic fields

Jelena Klinovaja, Condensed Matter Theory and Quantum Computing Group, University of Basel

Abstract:  We derive an effective low-energy theory for metallic (armchair and nonarmchair) single-wall nanotubes in the presence of an electric field perpendicular to the nanotube axis, and in the presence of magnetic fields, taking into account spin-orbit interactions and screening effects on the basis of a microscopic tight-binding model [1,2]. The interplay between electric field and spin-orbit interaction allows us to tune armchair nanotubes into a helical conductor in both Dirac valleys. Metallic nonarmchair nanotubes are gapped by the surface curvature, yet helical conduction modes can be restored in one of the valleys by a magnetic field along the nanotube axis. If in proximity with a superconductor, helical modes give rise to Majorana bound states. Furthermore, we discuss electric dipole spin resonance in carbon nanotubes, and find that the Rabi frequency shows a pronounced dependence on the momentum along the nanotube.

References:

[1] J. Klinovaja, M. Schmidt, B. Braunecker, and D. Loss, Phys. Rev. Lett. 106, 156809 (2011)
[2] J. Klinovaja, M. Schmidt, B. Braunecker, and D. Loss, Phys. Rev. B 84, 085452 (2011)

Site-controlled QDs for nanophotonics

by Arun Mohan, Quantum Optoelectronics Group, ETH Zurich

Semiconductor quantum dots (QDs) constitute a unique class of photonic materials, offering atomic-like spectral features in a solid-state matrix. They have been at the forefront of exploratory physics and have also been employed in various optoelectronic applications. In spite of its widespread use, the strain driven formation of the Stranski-Krastanow (S-K) QDs, limits the control over the QD position, shape, size and composition profile. In this respect site-controlled QDs grown into pyramidal recesses offer superior control over the structural and spectral design [1]. Nanophotonic applications that utilize the unique properties of site-controlled QDs is discussed [2].

References:

[1] Mohan A, Gallo P, Felici M, et al., Small 6, 1268-1272  (2010)
[2] Mohan A, Felici M, Gallo P, et al., Nature Photon. 4, 302-306 (2010)