Terahertz technology has recently emerged as a highly sought-after and versatile scientific tool in many fields, including medical imaging, security screening, and wireless communication. However, scientific progress has been hindered by the lack of sources and detectors in this frequency range, thereby known as the terahertz gap. Here, we show that carbon nanotube quantum dots coupled to antennas are extremely sensitive, broad-band, terahertz quantum detectors with spectral resolution. Their response is due to photon-assisted single-electron tunneling and it is substantially enhanced by a novel radiation-induced nonequilibrium cooling of the electrons, causing a sharp height increase of the Coulomb oscillation peaks.

Coulomb staircases and quantum siz b effects in tunnelling spectroscopy on ligand-stabilized metal clusters J. G. A. D u b o is1, J, W . G e r r i ts e n 1, S. E. S h a f r a n ju k 1'2, E. J. G. B oon1 G. Schm id3 and H. van K em pen1

Andreev reflection point-contact spectroscopy is performed on a bilayer consisting of 50-nm degenerately doped Si backed with Nb. Due to the short mean free path both injection into and transport across the Si layer are diffusive, in contrast to the ballistic conditions prevailing in clean metal layers. Nevertheless a large Andreev signal is observed in the point-contact characteristics, not reduced by elastic scattering in the Si layer or by interface scattering, but only limited by the transmission coefficient of the metal-semiconductor point contact. Two peaks in the Andreev reflection probability are visible, marking the values of the superconducting energy gap at the interface on the Nb and Si sides. This interpretation is supported by a method of solving the Bogolubov equations analytically using a simplified expression for the variation of the order parameter close to the interface. This observation enables a comparison with theoretical predictions of the gap discontinuity in the proximity effect. It is found that the widely used de Gennes model does not agree with the experimental data.

A resonant chiral tunneling (CT) across a graphene junction (GJ) induced by an external electromagnetic field (EF) is studied. Modulation of the electron and hole wavefunction phases ϕ by the external EF during the CT processes strongly impacts the CT directional diagram. Therefore the a.c. transport characteristics of GJs depend on the EF polarization and frequency considerably. The GJ shows great promises for various nanoelectronic applications working in the THz diapason.

A photon-assisted Fano resonance in a two-branch single wall carbon nanotube junction ͑NJ͒ is considered. The NJ branches are misaligned by a finite angle and represent two coupled one-dimensional quantum dots where quantized electron states are formed. The inter-dot tunneling coupling causes a Fano resonance. When an external electromagnetic field ͑EF͒ is applied, the interdot tunneling becomes photon assisted. The resulting dc conductivity of each NJ branch shows series of satellite singularities arising in addition to the steady state Fano peaks. Magnitudes and positions of the singularities depend on the frequency, amplitude, and polarization of the EF, which may be used for sensing purposes.