arXiv subjects

A. Ishii

Publications and source records attributed to A. Ishii.

22 records · Page 2Linked to original sources

arXiv2014

Stark effect of excitons in individual air-suspended carbon nanotubes

We investigate electric-field induced redshifts of photoluminescence from individual single-walled carbon nanotubes. The shifts scale quadratically with field, while measurements with different excitation powers and energies show that effects from heating and relaxation pathways are small. We attribute the shifts to the Stark effect, and characterize nanotubes with different chiralities. By taking into account exciton binding energies for air-suspended tubes, we find that theoretical predictions are in quantitative agreement.

cond-mat.mes-hall↗

arXiv2013

Giant circular dichroism in individual carbon nanotubes induced by extrinsic chirality

Circular dichroism is widely used for characterizing organic and biological materials, but measurements at a single molecule level are challenging because differences in absorption for opposite helicities are small. Here we show that extrinsic chirality can induce giant circular dichroism in individual carbon nanotubes, with degree of polarization reaching 65%. The signal has a large dependence on the incidence angle, consistent with the interpretation that mirror symmetry breaking by the optical wave vector is responsible for the effect. We propose that field-induced charge distribution results in an efficient polarization conversion, giving rise to the giant dichroism. Our results highlight the possibility of polarization manipulation at the nanoscale for applications in integrated photonics and novel metamaterial designs.

cond-mat.mes-hall↗

arXiv2013

Spontaneous exciton dissociation in carbon nanotubes

Simultaneous photoluminescence and photocurrent measurements on individual single-walled carbon nanotubes reveal spontaneous dissociation of excitons into free electron-hole pairs. Correlation of luminescence intensity and photocurrent shows that a significant fraction of excitons are dissociating during their relaxation into the lowest exciton state. Furthermore, the combination of optical and electrical signals also allows for extraction of the absorption cross section and the oscillator strength. Our observations explain the reasons for photoconductivity measurements in single-walled carbon nanotubes being straightforward despite the large exciton binding energies.

cond-mat.mes-hall↗

arXiv2012

Unusual linewidth dependence of coherent THz emission measured from intrinsic Josephson junction stacks in the hot-spot regime

We report on measurements of the linewidth Δf of THz radiation emitted from intrinsic Josephson junction stacks, using a Nb/AlN/NbN integrated receiver for detection. Previous resolution limited measurements indicated that Δf may be below 1 GHz - much smaller than expected from a purely cavity-induced synchronization. While at low bias we found Δf to be not smaller than ? 500 MHz, at high bias, where a hotspot coexists with regions which are still superconducting, Δf turned out to be as narrow as 23 MHz. We attribute this to the hotspot acting as a synchronizing element. Δf decreases with increasing bath temperature, a behavior reminiscent of motional narrowing in NMR or ESR, but hard to explain in standard electrodynamic models of Josephson junctions.

cond-mat.supr-con↗