Direct Measurements of Magnetic Polarons in Cd${}_{1-x}$Mn${}_x$Se Nanocrystals from Resonant Photoluminescence

Abstract

In semiconductors, quantum confinement can greatly enhance the interaction between band carriers (electrons and holes) and dopant atoms. One manifestation of this enhancement is the increased stability of exciton magnetic polarons in magnetically-doped nanostructures. In the limit of very strong 0D confinement that is realized in colloidal semiconductor nanocrystals, a single exciton can exert an effective exchange field $B_{\mathrm{ex}}$ on the embedded magnetic dopants that exceeds several tesla. Here we use the very sensitive method of resonant photoluminescence (PL) to directly measure the presence and properties of exciton magnetic polarons in colloidal Cd${}_{1-x}$Mn${}_x$Se nanocrystals. Despite small Mn${}^{2+}$ concentrations ($x$=0.4-1.6\%), large polaron binding energies up to $\sim$26~meV are observed at low temperatures via the substantial Stokes shift between the pump laser and the resonant PL maximum, indicating nearly complete alignment of all Mn${}^{2+}$ spins by $B_{\mathrm{ex}}$. Temperature and magnetic field-dependent studies reveal that $B_{\mathrm{ex}}\approx$ 10~T in these nanocrystals, in good agreement with theoretical estimates. Further, the emission linewidths provide direct insight into the statistical fluctuations of the Mn${}^{2+}$ spins. These resonant PL studies provide detailed insight into collective magnetic phenomena, especially in lightly-doped nanocrystals where conventional techniques such as nonresonant PL or time-resolved PL provide ambiguous results.

12 pages, 8 figures, Nano Letters articles ASAP (2017)

References in corpus (5)

• Tunable magnetic exchange interactions in manganese-doped inverted core/shell ZnSe/CdSe nanocrystals
• Tailoring Magnetism in Quantum Dots
• Magnetic polaron formation and exciton spin relaxation in single CdMnTe quantum dots
• Förster energy transfer of dark excitons enhanced by a magnetic field in an ensemble of CdTe colloidal nanocrystals
• Bound magnetic polarons in the very dilute regime

Cited by in corpus (3)

• Magneto-optics of excitons interacting with magnetic ions in CdSe/CdMnS colloidal nanoplatelets
• Bright-Dark Exciton Interplay Evidenced by Spin Polarization in CdSe/CdMnS Nanoplatelets
• Unveiling Photoluminescence Signatures of Magneto-Optical Coupling in Layered Hybrid Manganese Chloride Perovskites