Thermal Tuning and Inversion of Excitonic Zeeman Splittings in Colloidal Doped CdSe Quantum Dots

Abstract

Variable-temperature magnetic circular dichroism (MCD) spectroscopy is used to measure excitonic Zeeman splittings in colloidal Co(2+)- and Mn(2+)-doped CdSe quantum dots with low dopant concentrations. The data demonstrate that the competition between intrinsic and exchange contributions to the excitonic Zeeman splittings in doped quantum dots can be tuned using temperature, from being dominated by exchange at low temperatures to being dominated by intrinsic Zeeman interactions at room temperature, with inversion at easily accessible temperatures and fields. These results may have relevance to spin-based information processing technologies that rely on manipulating carrier spins in quantum dots.

Magnetic Circular Dichroism in Nanomaterials: New Opportunity in Understanding and Modulation of Excitonic and Plasmonic Resonances

“…Since early 1990s, MCD technique has found its efficiency in direct measurement of excited state Zeeman splitting, [68][69][70][71] which is the basis for determination of the g-factor of excitons in semiconductor nanocrystals [72][73][74][75] and demonstration of the sp-d exchange interactions in diluted magnetic semiconductor nanocrystals. [34,[76][77][78][79][80][81] Very recently, MCD has displayed its new opportunities in analyzing fine structure in semiconductor nanoclusters. [81][82][83]…”

“…The giant Zeeman splitting effect is the key characteristic of DMSs, which is the origin for intense MCD activity corresponding to the band edge of semiconductor nanocrystals. With the advantage of direct demonstration of Zeeman splitting, MCD provides a powerful tool to qualitatively examine the presence of sp-d exchange interactions, [34,74,78,[92][93][94][95] which lays the foundation for manipulating magneto-optical properties for technological applications. Reproduced with permission.…”

Excitonic Zeeman splittings in colloidal CdSe quantum dots doped with single magnetic impurities

“…Following the approach of ref. 32, the data in Figure 2D were fit to Equation 2, where x eff is the effective Mn 2+ concentration, N 0 (α-β) describes the bulk sp-d exchange (1.5 eV), 33 Figure 2D show a global best fit to these data, yielding x eff = 0.00030 ± 0.00002, which corresponds to 0.40 Mn 2+ /QD and the doping statistics plotted in Figure 1B.…”

Impurity incorporation and exchange interactions in Co2+-doped CdSe/CdS core/shell nanoplatelets

“…In the case of hh 1 e 1 -X, the MCD amplitude drops with increasing temperature and the sign of the MCD signal swaps at T = 48 K. Such a behavior has been previously observed for the excited state of lowest energy in CdSe nanocrystals with extreme low Mn 2+ content and explained by the competition between (temperature-independent) intrinsic and (temperature-dependent) giant Zeeman splitting, which exhibit opposite sign. 77,78 It is important to note that the modest magneto-optical response observed is caused by both the low Co 2+ content and the small overlap γ between the charge carrier wavefunctions and the dopants due to the core/shell structure. Both, lh 1 e 1 -X and so 1 e 1 -X exhibit opposite sign compared to the data of hh 1 e 1 -X for T < 48 K. The deviation between hh 1 e 1 -X (and lh 1 e 1 -X) and the Brillouin fit can be explained by the competition between giant and intrinsic Zeeman splittings.…”