激子的“灰色”BCS凝聚和内约瑟夫森效应
"Gray" BCS condensate of excitons and internal Josephson effect
摘要：
最近有人提出，在稀释极限中由激子形成的玻色-爱因斯坦凝聚体必须是暗的，即，不与光子耦合。在这里，我们表明，在密度增加，暗激子凝聚体必须获得一个明亮的组件，由于载流子交换，其中暗激子变亮。然而，这需要大于阈值的密度，该阈值似乎落在稀激子气体和致密电子-空穴等离子体之间的相分离的禁限区域中。类似BCS的凝结很可能发生在致密的一面，因此必须有一个黑暗和一个明亮的成分-这使得它成为“灰色”。应该可以在这两个相干分量之间诱导内部约瑟夫森效应，光致发光的振荡作为这种“灰色”BCS类激子凝聚体存在的有力证据。
英文摘要：
It has been recently suggested that the Bose-Einstein condensate formed by excitons in the dilute limit must be dark, i.e., not coupled to photons. Here, we show that, under a density increase, the dark exciton condensate must acquire a bright component due to carrier exchange in which dark excitons turn bright. This however requires a density larger than a threshold which seems to fall in the forbidden region of the phase separation between a dilute exciton gas and a dense electron-hole plasma. The BCS-like condensation which is likely to take place on the dense side, must then have a dark and a bright component - which makes it "gray". It should be possible to induce an internal Josephson effect between these two coherent components, with oscillations of the photoluminescence as a strong proof of the existence for this "gray" BCS-like exciton condensate.
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