Coherent Aharonov-Bohm oscillations in type-II (Zn,Mn)Te/ZnSe quantum dots

Abstract

The magneto-photoluminescence of type-II (ZnMn)Te quantum dots is presented. As a result of the type-II band alignment Aharonov-Bohm (AB) oscillations in the photoluminescence intensity are evident, confirming previous predictions for the suitability of this geometry to control the optical Aharonov-Bohm effect. Moreover, the system demonstrates an interesting interplay between the AB effect and the spin polarization in diluted magnetic semiconductor quantum dots. The intensity of the AB oscillations increases with both magnetic field and the degree of optical polarization, indicating the suppression of spin fluctuations improves the coherence of the system. * isellers@buffalo.edu 2The Aharonov-Bohm (AB) effect describes a phase shift induced upon a charged particle as it moves in a closed trajectory in the presence of a magnetic field [1]. Despite the fact that the AB effect is a property of charged particles it has been shown that for neutral excitons in semiconductor nano-rings, a non-zero electric dipole moment exists [2,3], which is adequate to create AB oscillations. Such behavior results from the inherent differences in confinement potential and effective mass of the particles comprising the exciton, the electron and hole, and leads to different trajectories for each of the charge carriers, resulting in a measurable AB effect. Type-II quantum dots (QDs) have been predicted to be particularly amenable to exhibiting such AB effects because of the enhanced polarization of the electron and hole due to the spatial separation of the carriers in such systems [3,4].In this work we present experimental evidence of AB oscillations i n the magnetophotoluminescence (MPL) of type-II (ZnMn)Te/ZnSe QDs. In this system the hole is strongly confined within the (ZnMn)Te QD while the electron resides in the ZnSe matrix, confined only through coulomb attraction to the hole. Although the AB effect has been observed optically for charged excitons in In(Ga)As QDs [5] and neutral excitons in both Type-II GaAs/InP [6] and Zn(SeTe ) QDs [7,8], and also in capacitance [10] and magnetization measurements [11] in InAs quantum rings, this is the first time such effects have been observed in a diluted magnetic semiconductor (DMS) system. In DMS systems the application of a magnetic field strongly aligns the Mn spins, thus polarizing the emission through the carrier-Mn exchange [12]. At saturation polarization the carrier spins will also be preferentially aligned, significantly reducing the spin disorder in the system [9,10].The samples studied were grown by MBE on (001) GaAs substrates. The GaAs buffer layer was planarized at 580ºC before the temperature was reduced to 300ºC to deposit a ZnSe buffer. The active layers were grown by migration enhanced epitaxy initiated by the growth of several mono-layers of ZnSe followed by the deposition of the (ZnMn)Te QDs. In the sample described here, five 2.6 ML 3 (ZnMn)Te QD layers were grown, separated by narrow (5 nm) ZnSe spacer layers. The QD density of each layer was estimated from atomic for...

Luminescence of Cd0.7Mn0.3Te crystals in magnetic field: Linewidth, Landau quantization, and carrier effective mass

“…We can conclude that in the case of luminescence of semimagnetic Cd 0.7 Mn 0.3 Te magnetic fluctuations influence the FWHM(B) magn. value [30] 0.125 0.124 kp method, Kane [31] through the value of scattering potential, as also suggested in [24].…”

“…with the strength of spin fluctuation change in magnetic field of a single Mn 2+ ion √ ∆M 2 = kT (∂M/∂B) [24] (Fig. 3, line 6), 2. with the quantity close to the mean-squared angular deviation of a single spin from alignment with the field 1 − ( S z /S 0 ) 2 [25] (Fig.…”

Optical Aharonov-Bohm effect on Wigner molecules in type-II semiconductor quantum dots

“…[21][22][23][24][25] In these systems, holes are confined inside a quantum dot and electrons are in a ring-shaped region surrounding the quantum dot, as depicted in the inset of Fig. 1 (the roles of electron and hole are exchanged in the case of InP/GaAs).…”

“…[21][22][23][24][25] For the holes, only the heavy-hole band (total angular momentum j = 3/2, j z = ±3/2) is considered because the confinement in the z direction splits it from the light-hole band (j = 3/2, j z = ±1/2). 38 The wave functions of the electron and hole are written as…”

Enhancement and narrowing of the Aharonov-Bohm oscillations due to built-in electric field in stacked type-II ZnTe/ZnSe quantum dots: Spectral analysis

“…4,5,6 It was predicted that the AB effect for the dipole can be observed via optical emission of radially polarized excitons in nanorings and disk-like type-II quantum dots (QDs) -so-called excitonic AB effectdue to the interaction of the dipole associated with the polarized excitons with the vector potential 7,8 . The experimental verification of the AB signature of such spatially indirect excitons 9,10-12 inspired further interest in both theoretical [13][14][15][16][17][18][19] and experimental [20][21][22][23][24][25][26] research.…”