Brodbeck S, De Liberato S, Amthor M, Klaas M, Kamp M, Worschech L, Schneider C, Höfling S
Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen-Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, United Kingdom.
Phys Rev Lett. 2017 Jul 14;119(2):027401. doi: 10.1103/PhysRevLett.119.027401. Epub 2017 Jul 12.
The dipole coupling strength g between cavity photons and quantum well excitons determines the regime of light matter coupling in quantum well microcavities. In the strong coupling regime, a reversible energy transfer between exciton and cavity photon takes place, which leads to the formation of hybrid polaritonic resonances. If the coupling is further increased, a hybridization of different single exciton states emerges, which is referred to as the very strong coupling regime. In semiconductor quantum wells such a regime is predicted to manifest as a photon-mediated electron-hole coupling leading to different excitonic wave functions for the two polaritonic branches when the ratio of the coupling strength to exciton binding energy g/E_{B} approaches unity. Here, we verify experimentally the existence of this regime in magneto-optical measurements on a microcavity characterized by g/E_{B}≈0.64, showing that the average electron-hole separation of the upper polariton is significantly increased compared to the bare quantum well exciton Bohr radius. This yields a diamagnetic shift around 0 detuning that exceeds the shift of the lower polariton by 1 order of magnitude and the bare quantum well exciton diamagnetic shift by a factor of 2. The lower polariton exhibits a diamagnetic shift smaller than expected from the coupling of a rigid exciton to the cavity mode, which suggests more tightly bound electron-hole pairs than in the bare quantum well.
腔光子与量子阱激子之间的偶极耦合强度g决定了量子阱微腔中光与物质的耦合机制。在强耦合机制下，激子与腔光子之间会发生可逆的能量转移，这会导致混合极化激元共振的形成。如果耦合进一步增强，不同单激子态之间会出现杂化，这被称为极强耦合机制。在半导体量子阱中，当耦合强度与激子束缚能的比值g/E₈接近1时，预计这种机制会表现为光子介导的电子 - 空穴耦合，从而导致两个极化激元分支具有不同的激子波函数。在此，我们通过对一个g/E₈≈0.64的微腔进行磁光测量，实验验证了这种机制的存在，结果表明，与裸量子阱激子玻尔半径相比，上极化激元的平均电子 - 空穴间距显著增大。这在零失谐附近产生了一个抗磁位移，该位移比下极化激元的位移大1个数量级，比裸量子阱激子的抗磁位移大2倍。下极化激元的抗磁位移比刚性激子与腔模耦合预期的要小，这表明其电子 - 空穴对的束缚比裸量子阱中的更紧密。
