TY - JOUR
T1 - Revealing giant internal magnetic fields due to spin fluctuations in magnetically doped colloidal nanocrystals
AU - Rice, William D.
AU - Liu, Wenyong
AU - Baker, Thomas A.
AU - Sinitsyn, Nikolai A.
AU - Klimov, Victor I.
AU - Crooker, Scott A.
N1 - Funding Information:
We gratefully thank D. R. Yakovlev and D. L. Smith for helpful discussions and insight. W.D.R. acknowledges support from the Los Alamos LDRD programme. W.L., T.A.B., and V.I.K. are supported by the Office of Chemical Sciences, Biosciences, and Geosciences of the Department of Energy Office of Basic Energy Sciences. All optical measurements were performed at the National High Magnetic Field Laboratory, which is supported by NSF DMR-1157490.
Funding Information:
We gratefully thank D. R. Yakovlev and D. L. Smith for helpful discussions and insight. W.D.R. acknowledges support from the Los Alamos LDRD programme.W.L., T.A.B., and V.I.K. are supported by the Office of Chemical Sciences, Biosciences, and Geosciences of the Department of Energy Office of Basic Energy Sciences. All optical measurements were performed at the National High Magnetic Field Laboratory, which is supported by NSF DMR-1157490.
PY - 2016/2/1
Y1 - 2016/2/1
N2 - Strong quantum confinement in semiconductors can compress the wavefunctions of band electrons and holes to nanometre-scale volumes, significantly enhancing interactions between themselves and individual dopants. In magnetically doped semiconductors, where paramagnetic dopants (such as Mn 2+, Co 2+ and so on) couple to band carriers via strong sp-d spin exchange, giant magneto-optical effects can therefore be realized in confined geometries using few or even single impurity spins. Importantly, however, thermodynamic spin fluctuations become increasingly relevant in this few-spin limit. In nanoscale volumes, the statistical fluctuations of N spins are expected to generate giant effective magnetic fields B eff, which should dramatically impact carrier spin dynamics, even in the absence of any applied field. Here we directly and unambiguously reveal the large B eff that exist in Mn 2+ -doped CdSe colloidal nanocrystals using ultrafast optical spectroscopy. At zero applied magnetic field, extremely rapid (300-600â €...GHz) spin precession of photoinjected electrons is observed, indicating B eff â 1/4 15 â '30 T for electrons. Precession frequencies exceed 2 THz in applied magnetic fields. These signals arise from electron precession about the random fields due to statistically incomplete cancellation of the embedded Mn 2+ moments, thereby revealing the initial coherent dynamics of magnetic polaron formation, and highlighting the importance of magnetization fluctuations on carrier spin dynamics in nanomaterials.
AB - Strong quantum confinement in semiconductors can compress the wavefunctions of band electrons and holes to nanometre-scale volumes, significantly enhancing interactions between themselves and individual dopants. In magnetically doped semiconductors, where paramagnetic dopants (such as Mn 2+, Co 2+ and so on) couple to band carriers via strong sp-d spin exchange, giant magneto-optical effects can therefore be realized in confined geometries using few or even single impurity spins. Importantly, however, thermodynamic spin fluctuations become increasingly relevant in this few-spin limit. In nanoscale volumes, the statistical fluctuations of N spins are expected to generate giant effective magnetic fields B eff, which should dramatically impact carrier spin dynamics, even in the absence of any applied field. Here we directly and unambiguously reveal the large B eff that exist in Mn 2+ -doped CdSe colloidal nanocrystals using ultrafast optical spectroscopy. At zero applied magnetic field, extremely rapid (300-600â €...GHz) spin precession of photoinjected electrons is observed, indicating B eff â 1/4 15 â '30 T for electrons. Precession frequencies exceed 2 THz in applied magnetic fields. These signals arise from electron precession about the random fields due to statistically incomplete cancellation of the embedded Mn 2+ moments, thereby revealing the initial coherent dynamics of magnetic polaron formation, and highlighting the importance of magnetization fluctuations on carrier spin dynamics in nanomaterials.
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U2 - 10.1038/nnano.2015.258
DO - 10.1038/nnano.2015.258
M3 - Article
AN - SCOPUS:84957845532
VL - 11
SP - 137
EP - 142
JO - Nature Nanotechnology
JF - Nature Nanotechnology
SN - 1748-3387
IS - 2
ER -