Browsing by Author "Oszwaldowski, R."

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Conventional vs Unconventional Magnetic Polarons: ZnMnTe/ZnSe and ZnTe/ZnMnSe Quantum Dots
(2014-01-01)
Barman, B.
;
Tsai, Y.
;
Scrace, T.
;
Murphy, J. R.
;
Cartwright, A. N.
We used time resolved photoluminescence (TRPL) spectroscopy to compare the properties of magnetic polarons in two related, spatially indirect, II-VI epitaxially grown quantum dot systems. In sample A (ZnMnTe/ZnSe), the photoexcited holes are confined in the magnetic ZnMnTe quantum dots (QDs), while the electrons remain in the surrounding non-magnetic ZnSe matrix. In sample B (ZnTe/ZnMnSe) on the other hand, the holes are confined in the non-magnetic ZnTe QDs and the electrons move in the magnetic ZnMnSe matrix. The magnetic polaron formation energies, E-MP, in these samples were measured from the temporal red-shift of the excitonic emission peak. The magnetic polarons in the two samples exhibit distinct characteristics. In sample A, the magnetic polaron is strongly bound with E-MP = 35 meV. Furthermore, E-MP has unconventionally weak dependence of on both temperature T and magnetic field B-appl. In contrast, magnetic polarons in sample B show conventional characteristics with E-MP decreasing with increasing temperature and increasing external magnetic field. We attribute the difference in magnetic polaron properties between the two types of QDs to the difference in the location of the Mn ions in the respective structures.
Robust Coherent Magneto-optical Properties of Columnar Type-II Quantum Dots in ZnTe/ZnSe and ZnMnTe/ZnSe Systems
(2011-01-01)
Whiteside, V. R.
;
Sellers, I. R.
;
Eginligil, M.
;
Oszwaldowski, R.
;
Petrou, A.
We present recent experimental results that show strong optical AB effects in the magneto-photoluminescence of columnar II-VI quantum dots (QDs). The AB effects manifest themselves as oscillations in the photoluminescence energy and intensity with magnetic field. It will be shown that this coherent behavior is remarkably robust, persisting at 180K. We, also, present results for a magnetic system, ZnMnTe QDs. These magnetic type-II systems also display evidence of robust magnetic ordering. This behavior is attributed to the formation of magnetic polarons caused by the exchange interaction between strongly localized holes and Mn ions within the QDs. Time-resolved PL measurements display evidence of magnetic polarons up to 200K with a binding energy of approximately 40 meV.
Robust magnetic polarons in type-II (Zn, Mn) Te/ZnSe magnetic quantum dots
(2010-11-18)
Sellers, I. R.
;
Oszwaldowski, R.
;
Whiteside, V. R.
;
Eginligil, M.
;
Petrou, A.
We present a magneto-optical study of magnetic polarons in type-II (Zn, Mn) Te quantum dots. The polarons are formed due to the exchange coupling between the spins of the holes and those of the Mn ions, both of which are localized in the dots. In our photoluminescence studies, the magnetic polarons are detected at temperatures up to similar to 150 K, with a formation energy of similar to 40 meV. The emission from these dots exhibits an unusually small Zeeman shift with applied magnetic field (similar to 2 meV at 8 T) and at the same time a very large circular polarization. We attribute this apparently contradictory behavior by a low and weakly temperature-dependent magnetic susceptibility due to antiferromagnetic coupling of the Mn spins.
Robust magnetic polarons in type-II (Zn, Mn) Te/ZnSe magnetic quantum dots
(2010-11-18)
Sellers, I. R.
;
Oszwaldowski, R.
;
Whiteside, V. R.
;
Eginligil, M.
;
Petrou, A.
We present a magneto-optical study of magnetic polarons in type-II (Zn, Mn) Te quantum dots. The polarons are formed due to the exchange coupling between the spins of the holes and those of the Mn ions, both of which are localized in the dots. In our photoluminescence studies, the magnetic polarons are detected at temperatures up to similar to 150 K, with a formation energy of similar to 40 meV. The emission from these dots exhibits an unusually small Zeeman shift with applied magnetic field (similar to 2 meV at 8 T) and at the same time a very large circular polarization. We attribute this apparently contradictory behavior by a low and weakly temperature-dependent magnetic susceptibility due to antiferromagnetic coupling of the Mn spins.
Time-resolved magnetophotoluminescence studies of magnetic polaron dynamics in type-II quantum dots
(2015-07-24)
Barman, B.
;
Oszwaldowski, R.
;
Schweidenback, L.
;
Russ, A. H.
;
Pientka, J. M.
We used continuous wave photoluminescence (cw-PL) and time-resolved photoluminescence (TR-PL) spectroscopy to compare the properties of magnetic polarons (MP) in two related spatially indirect II-VI epitaxially grown quantum dot systems. In the ZnTe/(Zn, Mn)Se system the holes are confined in the nonmagnetic ZnTe quantum dots (QDs), and the electrons reside in the magnetic (Zn, Mn)Se matrix. On the other hand, in the (Zn, Mn)Te/ZnSe system, the holes are confined in the magnetic (Zn, Mn)Te QDs, while the electrons remain in the surrounding nonmagnetic ZnSe matrix. The magnetic polaron formation energies E-MP in both systems were measured from the temporal redshift of the band-edge emission. The magnetic polaron exhibits distinct characteristics depending on the location of the Mn ions. In the ZnTe/(Zn, Mn)Se system the magnetic polaron shows conventional behavior with E-MP decreasing with increasing temperature T and increasing magnetic field B. In contrast, E-MP in the (Zn, Mn)Te/ZnSe system has unconventional dependence on temperature T and magnetic field B; E-MP is weakly dependent on T as well as on B. We discuss a possible origin for such a striking difference in the MP properties in two closely related QD systems.