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Proceedings Paper

Exciton magnetic polaron physics in magnetically doped colloidal nanocrystals (Conference Presentation)
Author(s): William Rice
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Paper Abstract

Strong quantum confinement in semiconductors compresses 
the wavefunctions of band carriers to nanometer-scale volumes, significantly enhancing their interactions with dopants. In magnetically doped 
semiconductors, where paramagnetic dopants couple to band carriers via strong sp–d spin 
exchange, giant magneto-optical effects can be 
realized using few, or even single, 
impurity spins. Importantly, however, thermodynamic spin fluctuations become increasingly relevant in this few-spin limit: the statistical N^1/2 fluctuations of N 
spins are expected to generate giant effective magnetic fields 
B_eff, which dramatically impacts carrier spin dynamics, 
 even in the absence of an applied field. Here, I present measurements of both the initial and final stages of exciton magnetic polarons (EMPs) in lightly doped Cd_1-xMn_xSe colloidal nanocrystals. In the first section, I show our ultrafast spectroscopic investigations of the large B_eff in this system. At B_applied= 0T, extremely rapid 
(300–600 GHz) electron spin precession is 
observed, indicating B_eff∼15−30 T [1]. In the second part of the talk, I show our work on fully-formed EMPs. Using the highly sensitive technique of resonant photoluminescence, we directly measure the EMP binding energy to be tens of meV. Temperature- and field-dependent studies reveal that the exchange field is approximately 10 T, which agrees with theoretical estimates [2]. Taken together, the measurements of initial, ultrafast coherent dynamics and final, static formation states, give us a comprehensive picture of EMPs in doped nanocrystals. [1] W. D. Rice et al. Nature Nanotech. 11, 137 (2016). [2] W. D. Rice et al. Nano Lett. 17, 3068 (2017).

Paper Details

Date Published: 18 September 2018
Proc. SPIE 10732, Spintronics XI, 107320R (18 September 2018); doi: 10.1117/12.2319335
Show Author Affiliations
William Rice, Univ. of Wyoming (United States)

Published in SPIE Proceedings Vol. 10732:
Spintronics XI
Henri-Jean Drouhin; Jean-Eric Wegrowe; Manijeh Razeghi; Henri Jaffrès, Editor(s)

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