Picosecond quantum-beat spectroscopy of quadrupole polaritons inCu2O

Abstract

Quantum beats in picosecond time-resolved resonance Quorescence are investigated in Cu20 for the yellow 1S quadrupole exciton polariton. In order to obtain information on the coherence of the resonant intermediate polariton states, we have studied the electric-dipole allowed lightscattering processes involving one and two I'3 phonons. A quantitative analysis provides excitonpolariton coherence times of about 1 ns at 2 K, decreasing with higher temperatures and larger wave vectors due to phonon scattering. From the magnetic-field dependence, low-field g values are determined with high accuracy. The measurements permit a clear distinction between Raman and hot-luminescence-like contributions to the scattering intensity. The strong eKect of the spectral width of the excitation pulse on the time behavior of the scattering, as well as the temperature dependence of the coherence time, indicate that it is essential to take into account the polariton character.

Transversal-Longitudinal Splittings of Quadrupole-Active Exciton Level in Cu2O Crystal

“…In this case, however, polariton propagation effects do not lead to an additional beat structure. This is due to the fact that in the Raman process polariton states with different wave vectors interact with different phonons and do not interfere [35,36]. It has to be mentioned that in the last decade the exchange splitting of dipole-active quantum well excitons was considered [37,38].…”

Propagation Hanle effect of quadrupole polaritons in Cu2O

“…The total energy relaxation time or the population lifetime is usually measured by time-resolved luminescence spectroscopy. [11][12][13][14][15] As was emphasized in Ref. 13 the quantum beat method allows one to distinguish between coherent Raman scattering and incoherent hot luminescence.…”

Cuprous Oxide (Cu2O): A Unique System Hosting Various Excitonic Matter and Exhibiting Large Third-Order Nonlinear Optical Responses

“…Quadrupole polaritons in Cu 2 O may offer an alternative route to "long-lived" BEC. Unlike well-studied excitons in this semiconductor, a quadrupole polariton is relatively unexplored since its first discovery using coherent quantum beat spectroscopy [Frohlich et al (1991); Langer et al (1995)]. The measured lifetime of quadrupole polaritons is about 2 ns and this much longer lifetime arises from the above noted dipole-forbidden nature of Cu 2 O.…”

“…12(b)]. The propagating nature of the quadrupole polariton was first observed in the variation of the beat period using coherent quantum beat spectroscopy under resonant one-photon excitation [Frohlich et al (1991); Langer et al (1995)]. By contrast, a dark orthoexciton does not directly couple to the radiation field.…”

“…Most of the previous experiments directed at excitonic BEC in Cu 2 O were carried out using one-photon excitation [Fortin et al (1993); Hulin et al (1980); Snoke et al (1987;; Snoke & Negoita (2000); Wolfe et al (1995)]. In contrast, quadrupole polaritons can be generated using resonant excitation involving either one or two photons [Frohlich et al (1991);Goto et al (1997); Ideguchi et al (2008);Jang & Ketterson (2007);Jang et al (2008a);Langer et al (1995); Sun et al (2001); Tayagaki et al (2006)]. Rather than trying to cool the highly nonequilibrium state which follows nonresonant excitation, thermalization of the system under resonant excitation involves a subsequent heating induced by acoustic phonon absorption.…”