Localized exciton magnetic polarons in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Cd</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mi mathvariant="normal">−</mml:mi><mml:mi mathvariant="italic">x</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Mn</mml:mi></mml:mrow><mml:mrow><mm

Mackh, G.; Ossau, W.; Yakovlev, D. R.; Waag, A.; Landwehr, G.; Hellmann, Robert; Göbel, E. O.

doi:10.1103/physrevb.49.10248

Cited by 148 publications

(104 citation statements)

References 22 publications

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“…In order to estimate the polaron binding energy we use a simple thermodynamic model, where the emission linewidth, w, should vary as w= (2ε p k B T) 1/2 [30], where ε p is the polaron binding energy, T is the temperature and k B is the Boltzman constant. Using this model for typical emission lines of width 5meV at T=5K, the polaron binding energy is equal to ~ 30meV, which is significantly larger than binding energies of EMPs observed typically for bulk CdMnTe [19] and CdMnTe QWs [22].…”

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confidence: 97%

Optical studies of zero-field magnetization of CdMnTe quantum dots: Influence of average size and composition of quantum dots

Gurung

Maćkowski

Jackson

et al. 2004

Journal of Applied Physics

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We show that through the resonant optical excitation of spin-polarized excitons into CdMnTe magnetic quantum dots, we can induce a macroscopic magnetization of the Mn impurities. We observe very broad (4 meV linewidth) emission lines of single dots, which are consistent with the formation of strongly confined exciton magnetic polarons. Therefore we attribute the optically induced magnetization of the magnetic dots results to the formation of spin-polarized exciton magnetic polarons. We find that the photo-induced magnetization of magnetic polarons is weaker for larger dots which emit at lower energies within the QD distribution. We also show that the photo-induced magnetization is stronger for quantum dots with lower Mn concentration, which we ascribe to weaker Mn-Mn interaction between the nearest neighbors within the dots. Due to particular stability of the exciton magnetic polarons in QDs, where the localization of the electrons and holes is comparable to the magnetic exchange interaction, this optically induced spin alignment persists to temperatures as high as 160 K.

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confidence: 97%

Optical studies of zero-field magnetization of CdMnTe quantum dots: Influence of average size and composition of quantum dots

Gurung

Maćkowski

Jackson

et al. 2004

Journal of Applied Physics

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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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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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“…Thus, the diffusion model [7] is in conflict with the experimental findings [1][2][3][4], as they point to the exponential dependence of E p on t.…”

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confidence: 94%

“…

Consider a carrier trapped at t = O in a localized state.

…”

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confidence: 99%

“…Progress in the application of short light pulses for monitoring of dynamical processes has made it possible to trace the emerging of exciton magnetic polarons (EMP) after optical injection of carriers across the band gap in diluted magnetic semiconductors (DMS) [1][2][3][4][5][6]. In this paper we discuss mechanisms which might account for the fast dynamics of the polaron formation in DMS.…”

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Formation Time of Magnetic Polarons

et al. 1995

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It is shown that non-scalar spin-spin interactions rather than spinlattice coupling or spin diffusion control the dynamics of the magnetization formation visible in time-resolved luminescence and SQUID magnetometry.PACS numbers: 78.55.Et, 75.50.Rr Progress in the application of short light pulses for monitoring of dynamical processes has made it possible to trace the emerging of exciton magnetic polarons (EMP) after optical injection of carriers across the band gap in diluted magnetic semiconductors (DMS) [1][2][3][4][5][6]. In this paper we discuss mechanisms which might account for the fast dynamics of the polaron formation in DMS.Consider a carrier trapped at t = O in a localized state. Its adiabatic wave function is described by a Schródinger equation which contains: (i) kinetic energy, taken here in the one-band effective-mass approximation, (ii) potential energy that includes the localizing and confining potential, (iii) a nonlinear term HM = HM(r, t), which describes the exchange interaction with the time-dependent polarization of the surrounding localized spins, Here J = α or Q is the electron-or hole-magnetic ion exchange integral, while g and M0 (H) denote the Lande factor and the equilibrium magnetization of the localized spins, respectively. The molecular field H* produced by the carrier and experienced by the ionic spins appears at t = 0, and is then given by Finally, G(r, t) is the response function of the spins. As a starting point we assume that it can be described by Bloch equations with the diffusion term included.

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Localized exciton magnetic polarons inCd1−xMn

Cited by 148 publications

References 22 publications

Optical studies of zero-field magnetization of CdMnTe quantum dots: Influence of average size and composition of quantum dots

Optical studies of zero-field magnetization of CdMnTe quantum dots: Influence of average size and composition of quantum dots

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

Formation Time of Magnetic Polarons

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Localized exciton magnetic polarons inCd1−xMn

Cited by 148 publications

References 22 publications

Optical studies of zero-field magnetization of CdMnTe quantum dots: Influence of average size and composition of quantum dots

Optical studies of zero-field magnetization of CdMnTe quantum dots: Influence of average size and composition of quantum dots

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

Formation Time of Magnetic Polarons

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Product

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