Yuhei Miyauchi

Cross-polarized absorption peaks of isolated single-walled carbon nanotubes (SWNTs) were observed by polarized photoluminescence excitation (PLE) spectroscopy. Using a simple theory for PL anisotropy, the observed PLE spectra are decomposed into ``pure'' components of the photoexcitation for incident light polarized parallel and perpendicular to the SWNT axis. For several $(n,m)$ SWNTs, distinct peaks corresponding to perpendicular excitation were observed. The measured transition energies for p

Photoluminescence phenomena normally obey Stokes' law of luminescence according to which the emitted photon energy is typically lower than its excitation counterparts. Here we show that carbon nanotubes break this rule under one-photon excitation conditions. We found that the carbon nanotubes exhibit efficient near-infrared photoluminescence upon photoexcitation even at an energy lying >100-200 meV below that of the emission at room temperature. This apparently anomalous phenomenon is attributed

We have studied photoluminescence and resonant Raman scattering of single-walled carbon nanotubes (SWNTs) consisting of carbon-13 $({\mathrm{SW}}^{13}\mathrm{CNTs})$ synthesized from a small amount of isotopically modified ethanol. There was almost no change in the Raman spectra shape for ${\mathrm{SW}}^{13}\mathrm{CNTs}$ except for a downshift of the Raman shift frequency by the square root of the mass ratio $12∕13$. By comparing photoluminescence excitation spectra of ${\mathrm{SW}}^{13}\mathr

Single-walled carbon nanotubes (SWNTs) are extremely thin cylinders of hexagonal carbon networks with diameters on the order of 1 nm. Over the past decade, optical properties of SWNTs, dominated by correlated electron–hole bound states known as excitons, have been intensively studied. The exciton photophysics of SWNTs is relevant to nearly all optical phenomena observed in SWNTs, and their detailed understanding is critical for the development of future optoelectronic devices using SWNTs. Here w

Monolayers of transition metal dichalcogenides (TMDC) have recently emerged as excellent platforms for exploiting new physics and applications relying on electronic valley degrees of freedom in two-dimensional (2D) systems. Here, we demonstrate that Coulomb screening by 2D carriers plays a critical role in excitonic valley pseudospin relaxation processes in naturally carrier-doped WSe₂ monolayers (1L-WSe₂). The exciton valley relaxation times were examined using polarizatio

We evaluated the radiative lifetimes and the one-dimensional exciton coherence lengths in single-walled carbon nanotubes (SWNTs). The radiative lifetimes determined from simultaneous measurements of photoluminescence (PL) lifetimes and PL quantum yields range from $\ensuremath{\sim}3$ to 10 ns, and slightly increase with the tube diameter. The exciton coherence lengths in SWNTs are of the order of 10 nm, as deduced from the experimentally obtained radiative lifetimes, and they are about ten time