Wurtzite quantum wires with strong spatial confinement: polarization anisotropies in single wire spectroscopy

We report GaAs/AlGaAs nanowires in the one-dimensional (1D) quantum limit. The ultrathin wurtzite GaAs cores between 20-40\,nm induce large confinement energies of several tens of meV, allowing us to experimentally resolve up to four well separated subband excitations in microphotoluminescence spectroscopy. Our detailed experimental and theoretical polarization-resolved study reveals a strong diameter-dependent anisotropy of these transitions: We demonstrate that the polarization of the detected photoluminescence is governed by the symmetry of the wurtzite 1D quantum wire subbands on the one hand, but also by the dielectric mismatch of the wires with the surrounding material on the other hand. The latter effect leads to a strong attenuation of perpendicularly polarized light in thin dielectric wires, making the thickness of the AlGaAs shell an important factor in the observed polarization behavior. Including the dielectric mismatch to our k.p-based simulated polarization-resolved spectra of purely wurtzite GaAs quantum wires, we find an excellent agreement between experiment and theory

Very weak bonds to artificial atoms formed by quantum corrals

We explored the bonding properties of the quantum corral (a circle of 48 iron atoms placed on a copper surface) reported by Crommie et al. in 1993, along with variants, as an artificial atom using an atomic force microscope (AFM). The original corral geometry confines 102 electrons to 28 discrete energy states, and we found that these states can form a bond to the front atom of the AFM with an energy of about 5 millielectron volts. The measured forces are about 1/1000 of typical forces in atomically resolved AFM. The confined electrons showed covalent attraction to metal tips and Pauli repulsion to CO-terminated tips. The repulsion at close distance was evident from the response of corral states created by deliberately placing single iron atoms inside the corral. The forces scaled appropriately with a 24-atom corral

Wurtzite Quantum Wires with Strong Spatial Confinement: Polarization Anisotropies in Single-Wire Spectroscopy

We report GaAs/(Al, Ga)As nanowires in the one-dimensional (1D) quantum limit. The ultrathin wurtzite GaAs cores between 20 and 40 nm induce large confinement energies of several tens of millielectronvolts, allowing us to experimentally resolve up to four well-separated subband excitations in microphotoluminescence spectroscopy. Our detailed experimental and theoretical polarization-resolved study reveals a strong diameter-dependent anisotropy of these transitions: We demonstrate that the polarization of the detected photoluminescence is governed, on the one hand, by the symmetry of the wurtzite 1D quantum wire subbands but also, on the other, by the dielectric mismatch of the wires with the surrounding material. The latter effect leads to a strong attenuation of perpendicularly polarized light in thin-dielectric wires, making the thickness of the (Al, Ga)As shell an important factor in the observed polarization behavior. Including the dielectric mismatch to our k center dot p-based simulated polarization-resolved spectra of purely wurtzite GaAs quantum wires, we find excellent agreement between experiment and theory. These findings reveal insights relevant to spectroscopic studies of the 1D quantum regime and the design of photonic quantum wire applications such as lasers and hopefully open up paths for selective subband excitations