Yong-min Kim

Pressure effect on magneto-optical properties in CdTe/(Cd, Mn)Te single quantum wells with high Mn concentration

The pressure effect on the magnetic field induced type I–type II transition is studied in a CdTe/Cd1−xMnxTe (x=0.24) single quantum well. Photoluminescence measurements under hydrostatic pressures up to 1.07 GPa and long pulsed magnetic fields up to 60 T with a pulse duration of 2 s are reported. The pressures were generated in a plastic diamond anvil cell. A bend toward lower energies (additional red shift) is observed above 28.5 T in magnetic field dependence of the exciton energy for a 13 A thick quantum well. We attribute this red shift to a phenomenon preceding the type I–type II transition after a comparison with a simple quantum mechanical calculation. The onset field of the additional red shift increases by 3.4 T by applying a pressure of 1.07 GPa. Spin–spin coupling between the exciton and the Mn ion in the interface region is also investigated and found to be enhanced by pressure.

Spectral anomalies of exciton photoluminescence at v = 1 and 2/3 in a modulation-doped n-type CdTe/(Cd, Mg, Mn)Te single quantum well

Spin-polarized magnetophotoluminescence measurements have been conducted in a modulation-doped n-type CdTe/(Cd, Mg, Mn)Te single quantum well at 1.5 K under 2 s long pulsed magnetic fields up to 60 T. For the σ - polarization, a new peak was observed to emerge at ν ∼ 1 on the higher energy side of a main peak. The former peak became larger than the latter with increasing magnetic field, while the latter peak had a local maximum at ν ∼ 0.9 and attenuated. Furthermore, magnetic field dependence of the latter peak energy showed step-like behavior around ν ∼ 0.9. The intensity of the former peak was observed to increase monotonically with field, showed a kink at v ∼ 2/3 and saturated, i.e. showed a shoulder-like structure there. With changing the angle between the direction of the sample surface normal and the magnetic field, both features at ν ∼ 1 and 2/3 exhibited tendencies to fade out, which suggests that the former is associated with spin-singlet charged exciton and the latter with fractional quantum Hall effect at v = 2/3.

High-pressure and high-magnetic-field study of energy transfer from excitons into local d electrons in a CdTe/(Cd, Mn)Te quantum well structure

Photoluminescence measurements have been conducted for a CdTe/Cd1-xMnx Te (x = 0.4) single-quantum-well structure at low temperatures under pressures to 0.49 GPa and magnetic fields to 60 T. At the ambient pressure, a new emission was induced by the application of a magnetic field. The emission has been assigned to exciton emission from the barrier layer, which is suppressed below 9 T due to the energy transfer from the exciton to local d electrons. At 0.49 GPa, the emission recovered at 44 T. In the field region where the energy transfer occurs, an anomalous red-shift of the exciton energy was observed clearly for the case of the ambient pressure. The alloy potential fluctuation effect and the magnetopolaron effect are examined as candidates for the mechanism to cause this phenomenon.

Interface local spin states in a CdTe/(Cd, Mn)Te quantum well

Magneto-photoluminescence spectra obtained experimentally for a 1.9 nm thick CdTe quantum well with semi-magnetic barriers of Cd1−xMnx Te( x =0 :24) in the range of a magnetic 6eld B = 0–50 Tand applied pressure up to 1 :5 GPa have been analyzed through the interface � -potential model. In the model, the interface potential is expressed as A�� (z ±Lw=2), where � is the spin projection ±1=2 and Lw is the quantum well width. Our results show that the amplitude of the interface potential A is saturated at 15 Tand is not changed up to 50 T . T his behavior is described well by the modi6ed Brillouin function, which suggests that the magnetic ions in the interface region are isolated rather than clustered, in contrast to those in the barrier layers. The potential amplitude A is found to be enhanced by the pressure. c

Pressure effect on the exchange interaction in the interface region of a CdTe/CdMnTe quantum-well structure

Exchange interaction of an exciton in a quantum well with magnetic ions in the interface region and pressure effect on the interaction are investigated for a 1.9 nm thick CdTe/Cd 1 -x Mn x Te (x = 0.24) single quantum well (SQW). Photoluminescence has been measured at 4 K under magnetic fields to 60 T generated by a motor-generator driven long-pulsed magnet and hydrostatic pressures to 2.45 GPa produced in a diamond anvil cell (DAC) with a plastic body. An additional red shift is observed in a Zeeman shift for the SQW above 30T. This structure has enabled us to evaluate the above-mentioned interaction quite accurately and to find that pressure enhances it.