Light-Induced Spontaneous Magnetization in Doped Colloidal Quantum Dots

Beaulac, Rémi; Schneider, Lars; Archer, Paul; Bacher, G.; Gamelin, Daniel R.

doi:10.1126/science.1174419

Cited by 314 publications

(368 citation statements)

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“…In diluted magnetic semiconductors (DMSs), exchange interactions between localized magnetic impurities and delocalized charge carriers give rise to various technologically important effects including giant spin splittings of the semiconductor band structure, [1][2][3] exciton spin polarization, [4][5][6][7] spin-polarized electrical currents, 8,9 excitonic magnetic polarons, [10][11][12][13][14][15][16] and carrier-controlled magnetism. [17][18][19][20] Within the past decade, attention has turned to magnetically doped semiconductor nanostructures like colloidal or self-assembled DMS quantum dots (QDs), 10,[21][22][23] motivated in part by potential quantum optics or information processing technologies.…”

Section: Introductionmentioning

confidence: 99%

Orbital pathways for Mn2+-carriersp−dexchange in diluted magnetic semiconductor quantum dots

et al. 2011

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Abstract. Manganese-carrier magnetic exchange interactions in strongly quantum confined -conduction-band-electron interaction is described well using the recently proposed ferromagnetic kinetic s-s exchange pathway. Antiferromagnetic kinetic s-d exchange interactions previously proposed to become dominant in quantum confined diluted magnetic semiconductors (DMSs) have been evaluated quantitatively by both DFT and perturbation theory and are found to be weak compared to the ferromagnetic s-s interaction, even in these strongly confined QDs. The magnitudes of the mean-field exchange parameters are found to be nearly independent of quantum confinement over this range of QD diameters, and the dominant orbital pathways are not fundamentally altered by quantum confinement.i.

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Section: Introductionmentioning

confidence: 99%

Orbital pathways for Mn2+-carriersp−dexchange in diluted magnetic semiconductor quantum dots

et al. 2011

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“…In turn, these aligned local moments act back on the exciton's spin, which lowers the exciton's energy, further localizes the exciton, and further stabilizes the polaron. The stability and binding energy of EMPs therefore depends on the detailed interplay between many factors including the exciton lifetime, the polaron formation time, the exchange field B ex , sample dimensionality, and temperature.EMPs and collective magnetic phenomena have been experimentally studied in a variety of Mn 2+ -doped semiconductor nanostructures, including CdMnSe and CdMnTe-based epilayers and quantum wells [34][35][36][37][38][39][40][41][42], selfassembled CdMnSe and CdMnTe quantum dots grown by molecular-beam epitaxy [14][15][16][18][19][20][21][22][23][24][25], and most recently in CdMnSe nanocrystals synthesized via colloidal techniques [8,28]. Common measurement techniques include the analysis of conventional (i.e., non-resonant) PL [8, 14, 15,18,21,28,39] and time-resolved PL [8, 16,28,34,35,40].…”

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confidence: 99%

“…Common measurement techniques include the analysis of conventional (i.e., non-resonant) PL [8, 14, 15,18,21,28,39] and time-resolved PL [8, 16,28,34,35,40].…”

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Direct Measurements of Magnetic Polarons in Cd_1–xMn_xSe Nanocrystals from Resonant Photoluminescence

et al. 2017

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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 Bex 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 Cd1−xMnxSe nanocrystals. Despite small Mn 2+ concentrations (x=0.4-1.6%), large polaron binding energies up to ∼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 Bex. Temperature and magnetic field-dependent studies reveal that Bex ≈ 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.Advances in the colloidal synthesis of magneticallydoped nanomaterials have sparked a renewed focus on low-dimensional magnetic semiconductors [1][2][3][4][5][6][7][8]. The interesting magnetic properties of these materials originates in the strong sp-d exchange interactions that exist between carrier spins (i.e., band electrons and holes with s-and p-type wavefunctions) and the local 3d spins of embedded paramagnetic dopant atoms such as Mn, Co,. At the microscopic level, the strength of this interaction for a dopant located at position r i scales with the probability density of the carrier envelope wavefunctions at that point: |ψ e,h (r i )| 2 . As such, local spin-spin interactions can be greatly enhanced by strong quantum confinement, which compresses carrier wavefunctions to nanometer-scale volumes and therefore increases |ψ e,h (r)| 2 . The extent to which these exchange interactions can be enhanced and controlled via quantum confinement is an area of significant current interest and has recently been studied in a variety of magnetically-doped semiconductor nanostructures, including nanoribbons [12, 13], nanoplatelets [14], epitaxial quantum dots [14][15][16][18][19][20][21][22][23][24][25][26], and colloidal nanocrystals [1-8, 27, 28, 30].A particularly striking consequence of sp-d interactions in II-VI semiconductors is the formation of exciton magnetic polarons (EMPs), wherein the effective magnetic exchange field from a single photogenerated exciton -B ex -induces the collective and spontaneous ferromagnetic alignment of the magnetic dopants within its wavefunction envelope, generating a net local...

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“…Doping of bulk materials is a very well developed field, which underpins most of our present technologies, since the properties of materials for lighting, electronic and optoelectronic applications are largely controlled by dopants. In contrast, the precise doping of NCs is still an underdeveloped field, which is however booming and has delivered great successes and many novel materials in recent years [28,[91][92][93][94][95][96][97][98][99][100]. Fig.…”

Section: Composition Effects: Tailoring the Property Gamutmentioning

confidence: 99%

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

Rabouw

Donegá

2016

Topics in Current Chemistry Collections

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Colloidal semiconductor nanocrystals have attracted continuous worldwide interest over the last three decades owing to their remarkable and unique sizeand shape-, dependent properties. The colloidal nature of these nanomaterials allows one to take full advantage of nanoscale effects to tailor their optoelectronic and physical-chemical properties, yielding materials that combine size-, shape-, and composition-dependent properties with easy surface manipulation and solution processing. These features have turned the study of colloidal semiconductor nanocrystals into a dynamic and multidisciplinary research field, with fascinating fundamental challenges and dazzling application prospects. This review focuses on the excited-state dynamics in these intriguing nanomaterials, covering a range of different relaxation mechanisms that span over 15 orders of magnitude, from a few femtoseconds to a few seconds after photoexcitation. In addition to reviewing the state of the art and highlighting the essential concepts in the field, we also discuss

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Light-Induced Spontaneous Magnetization in Doped Colloidal Quantum Dots

Cited by 314 publications

References 28 publications

Orbital pathways for Mn2+-carriersp−dexchange in diluted magnetic semiconductor quantum dots

Orbital pathways for Mn2+-carriersp−dexchange in diluted magnetic semiconductor quantum dots

Direct Measurements of Magnetic Polarons in Cd_1–xMn_xSe Nanocrystals from Resonant Photoluminescence

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

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Light-Induced Spontaneous Magnetization in Doped Colloidal Quantum Dots

Cited by 314 publications

References 28 publications

Orbital pathways for Mn2+-carriersp−dexchange in diluted magnetic semiconductor quantum dots

Orbital pathways for Mn2+-carriersp−dexchange in diluted magnetic semiconductor quantum dots

Direct Measurements of Magnetic Polarons in Cd1–xMnxSe Nanocrystals from Resonant Photoluminescence

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

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Product

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Direct Measurements of Magnetic Polarons in Cd_1–xMn_xSe Nanocrystals from Resonant Photoluminescence