Resonant spin orientation at the exciton level anticrossing in InP quantum dots

Abstract

Resonant spin orientation of excitons was observed under linearly polarized quasiresonant excitation around two anticrossing points of excitons in InP quantum dots ͑QDs͒. Under the longitudinal and tilted magnetic fields of 1.5 and 2.5 T, two anticrossings of bright and dark excitons take place. At the anticrossing points, bright and dark excitons mix with each other and the wave function mixing induces the resonant spin orientation. Time-resolved circular polarization clearly showed the resonant spin orientation due to mixing of bright and dark excitons at the anticrossing points. Dark excitons can work as the carrier and spin reservoir because of their long lifetime. We demonstrated that magnetic field can control the spin entanglement and the resonant spin orientation of QDs.

Spin orientation of excitons, trions and tetraons in charge tunable InP quantum dots

“…1(b). In the Faraday configuration, bright excitons and dark excitons change their energies depending on δ 1 = 0.038 meV, and δ 2 = 0 meV, the electron g-factor, g e,z = 1.5 and g e,x = 1.5, and the hole g-factor, g h,x = 0.25 and g h,z = 1.05, for InP QDs in the present sample [1].…”

“…Magnetic field-dependent circular polarization of photoluminescence (PL) in InP QDs strongly depends on the charging condition. In neutral InP QDs, the resonant spin orientation due to mixing of bright exciton and dark exciton dominates over the spin polarization of an exciton [1]. On the other hand, in InP QDs doped by 1 electron or 2 electrons, thermal spin orientation of a hole dominates over the spin polarization of a trion and a tetraon, but small electron-hole exchange interaction reduces the thermal spin orientation of a hole at low temperatures.…”

Spin relaxation in charge-tunable InP quantum dots

“…31 Our previous study on the resonant spin orientation has clarified that the generation ratio between the bright and dark excitons is around 2:1 for the quasiresonant excitation at 1.771 eV. 32 Without magnetic field, dark excitons are nonluminescent and do not contribute to c . However, a transverse magnetic field causes mixing between bright and dark excitons.…”

Магнитная Циркулярная Поляризация Фотолюминесценции Экситонов

“…Наблюдать антипересечение экситонных подуровней удается в квантовых точках с небольшими значения-ми δ 0 , как это, например, было сделано в структу-рах с самоорганизованными квантовыми точками InP, у которых δ 0 = 0.14 meV [43]. С другой стороны, в сферических нанокристаллах и нанообъектах " точка-в-стержне" CdS/CdSe обменная константа δ 0 составляет 2−5 meV, антипересечение возможно только в очень сильных полях; более того, при низкой температуре экситоны X e−hh скапливаются только на нижних, темных…”