Spin-Orbit Effects on Exciton Complexes in Diamond.

Ultrafine splittings are found in the optical absorption spectra of boron-doped diamond measured with high resolution. An analytical model of an exciton complex is developed, which permits assigning all absorption lines and sizing the interactions among the constituent charges and crystal field. We conclude that the entry of split-off holes in the acceptor-bound exciton fine structure yields two triplets separated by a spin-orbit splitting of 14.3 meV. Our findings thereby resolve a long-standing controversy [R. Sauer et al., Revised fine splitting of excitons in diamond, Phys. Rev. Lett. 84, 4172 (2000).PRLTAO0031-900710.1103/PhysRevLett.84.4172; M. Cardona et al., Comment on "Revised fine splitting of excitons in diamond,", Phys. Rev. Lett. 86, 3923 (2001).PRLTAO0031-900710.1103/PhysRevLett.86.3923; R. Sauer and K. Thonke, Sauer and Thonke reply, Phys. Rev. Lett. 86, 3924 (2001).PRLTAO0031-900710.1103/PhysRevLett.86.3924], revealing the underlying physics common in diverse semiconductors, including diamond.

Broadband sum frequency generation spectroscopy of dark exciton states in hBN-encapsulated monolayer WSe2.

We demonstrate that broadband sum frequency generation (SFG) spectroscopy based on a partially incoherent supercontinuum light source can elucidate dark p-series excitons in monolayer WSe2 encapsulated between hexagonal boron nitride (hBN) slabs. The observed 2p exciton peak energy is a few meV higher than that predicted by the Rytova-Keldysh potential model, which is originated from the Berry phase effect. Interestingly, although the radiative relaxation of the 2p exciton is weaker, the 2p exciton peak is broader than the 1s and 2s peaks, which indicates its faster dephasing than the 1s and 2s excitons. Measuring the excitation intensity and temperature dependence, we clarified that this broader linewidth is not caused by excitation- or phonon-induced dephasing, but rather by exciton-electron scattering.

Superradiance-to-Polariton Crossover of Wannier Excitons with Multiple Resonances.

We demonstrated the superradiance-to-polariton crossover of the blue excitons in Cu_{2}O by varying the sample thicknesses instead of controlling the cavity quality factor. The crossover behavior was compared with unprecedented calculations based on the nonlocal optical response theory with the inclusion of three exciton resonances. The crossover thickness, found to be 177±2 nm, was smaller than the predicted value for a single resonance by a factor of 5. The fact that there was much larger longitudinal-transverse splitting (40±5 meV) than in the bulk implies a surprisingly fast radiative recombination even without a cavity structure.

Ultranarrow optical absorption and two-phonon excitation spectroscopy of Cu2O paraexcitons in a high magnetic field.

We show that in a magnetic field B the otherwise forbidden lowest exciton in Cu2O (paraexciton of Gamma(2)(+) symmetry) gives rise to a narrow absorption line of 80 neV at a temperature of 1.2 K. The B2 dependence of the field-induced oscillator strength and the low energy shift DeltaE with increasing field strength are measured. From two-phonon excitation spectroscopy measurements we derive by a merely kinematical analysis a very reliable value for the paraexciton mass. A blueshift and a broadening of the absorption line are observed for increasing excitation intensity. These observations are discussed in connection with a Bose-Einstein condensation of paraexcitons in Cu2O.