Model for the Mn acceptor in GaAs

We derive an effective Hamiltonian for Ga1−xMnxAs in the dilute limit, where Ga1−xMnxAs can be described in terms of spin F = 3/2 polarons hopping between the Mn sites and coupled to the local Mn spins. We determine the parameters of our model from microscopic calculations using both a variational method and an exact diagonalization within the so-called spherical approximation. Our approach treats the extremely large Coulomb interaction in a non-perturbative way, and captures the effects of strong spin-orbit coupling and Mn positional disorder. We study the effective Hamiltonian in a mean field and variational calculation, including the effects of interactions between the holes at both zero and finite temperature. We study the resulting magnetic properties, such as the magnetization and spin disorder manifest in the generically non-collinear magnetic state. We find a well formed impurity band fairly well separated from the valence band up to xactive < ∼ 0.015 for which finite size scaling studies of the participation ratios indicate a localization transition, even in the presence of strong on-site interactions, where xactive < xnom is the fraction of magnetically active Mn. We study the localization transition as a function of hole concentration, Mn positional disorder, and interaction strength between the holes.

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“…These values are very close to the numbers used for the central cell corrections in Ref. [39] and Ref. [40].…”

Section: Variational Calculation Of the Baldereschi-lipari Wavefusupporting

confidence: 85%

Disorder, spin-orbit, and interaction effects in diluteGa1−xMnxAs

et al. 2005

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“…(iii) The remaining part of the Mn Ga binding energy is due to the spin-dependent hybridization of Mn d-states with neighboring As p-states. Its contribution, which has been directly inferred from spectroscopic measurements of uncoupled Mn Ga impurities [17,18], is again comparable to the binding energy of the hydrogenic single-acceptor potential. Combining (i)-(iii) accounts for the experimental binding energy of the Mn Ga acceptor of 0.1 eV.…”

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confidence: 63%

Microscopic Analysis of the Valence Band and Impurity Band Theories of (Ga,Mn)As

et al. 2010

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We analyze microscopically the valence and impurity band models of ferromagnetic (Ga,Mn)As. We find that the tight-binding Anderson approach with conventional parameterization and the full potential LDA+U calculations give a very similar picture of states near the Fermi energy which reside in an exchange-split sp-d hybridized valence band with dominant orbital character of the host semiconductor; this microscopic spectral character is consistent with the physical premise of the k ·p kinetic-exchange model. On the other hand, the various models with a band structure comprising an impurity band detached from the valence band assume mutually incompatible microscopic spectral character. By adapting the tight-binding Anderson calculations individually to each of the impurity band pictures in the single Mn impurity limit and then by exploring the entire doping range we find that a detached impurity band does not persist in any of these models in ferromagnetic (Ga,Mn)As.PACS numbers: 75.10. Lp,75.30.Hx,75.50.Pp Over more than four decades, (Ga,Mn)As has evolved from a pioneering direct gap p-doped semiconductor [1] into an archetypical degenerate semiconductor with holemediated ferromagnetism [2][3][4]. Paramagnetic insulating Ga 1−x Mn x As materials prepared in the 1970's by melt growth showed valence band (VB) to impurity band (IB) activation, with a non-systematic filamentary metallic conduction being observed at the highest studied dopings of x ∼ 0.1% and ascribed to sample inhomogeneities [5]. The degenerate semiconductor regime was not reached in these materials. A comprehensive experimental assessment of basic doping only trends became possible in the late 1990's with the development of epitaxial (Ga,Mn)As films [2, 7-9] which can be doped well beyond the equilibrium Mn solubility limit while avoiding phase segregation and maintaining a high degree of uniformity. Transport measurements on such films confirmed the insulating characteristics and the presence of the IB for x 0.1%. For higher concentrations, 0.5 x 1.5%, no clear signatures of activation from the VB to the IB have been detected in the dc transport, suggesting that the bands start to overlap and mix, yet the materials remain insulating. At x ∼ 1.5%, the low-temperature conductivity of the films increase abruptly by several orders of magnitude and the material becomes a bulk degenerate semiconductor. The onset of ferromagnetism occurs on the insulating side of the transition at x ∼ 1% and the Curie temperature gradually increases with increasing doping, reaching ∼190 K at the accessible substitutional Mn Ga doping of x ∼ 8%.One physical scenario for ferromagnetic (Ga,Mn)As, termed the VB picture, has an exchange-split band structure comprising the impurity band merged into the valence band. The states at the Fermi energy, E F , retain the predominant orbital character of the host semiconductor and are moderately hybridized with the localized Mn d-electrons. This description, quantified by a variety of theoretical methods, has been a fruitful basi...

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“…A simple interpretation of this spectral feature can be constructed by assuming that the QD contains a Mn impurity in the A 0 configuration, i.e. a hole bound to an A − center [16,17,18]. This acceptor state is characterized in bulk GaAs by an anti-ferromagnetic "p-d" exchange between the 3d 5 Mn spin S = 5/2 and the hole spin J h = 3/2.…”

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confidence: 99%

Optically Probing the Fine Structure of a Single Mn Atom in an InAs Quantum Dot

et al. 2007

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We report on the optical spectroscopy of a single InAs/GaAs quantum dot (QD) doped with a single Mn atom in a longitudinal magnetic field of a few Tesla. Our findings show that the Mn impurity is a neutral acceptor state A 0 whose effective spin J = 1 is significantly perturbed by the QD potential and its associated strain field. The spin interaction with photo-carriers injected in the quantum dot is shown to be ferromagnetic for holes, with an effective coupling constant of a few hundreds of µeV, but vanishingly small for electrons.PACS numbers: 71.35. Pq, 78.67.Hc,75.75.+a,78.55.Cr The spin state of a single magnetic impurity could be envisaged as a primary building block of a nanoscopic spin-based device [1,2] in particular for the realization of quantum bits [3]. However probing and manipulating such a system require extremely high sensitivity. Several techniques have been successfully developed over the last few years to address a single or few coupled spins: electrical detection [4,5], scanning tunneling microscopy (STM) [6,7,8,9], magnetic resonance force microscopic [10], optical spectroscopy [11]. Recently, Besombes et al. [12,13,14,15] have investigated the spin state of a single Mn +2 ion embedded in a single II-VI self-assembled quantum dot (QD). In this system the magnetic impurity is an isoelectronic center in a 3d 5 configuration with spin S = 5/2. The large exchange interaction between the spin of the photocreated carriers confined inside the dot and the Mn magnetic moment induces strong modifications of the QD photoluminescence (PL) spectrum: 2S + 1 = 6 discrete lines are observed, reflecting the Mn spin state at the instant when the exciton recombines.The case of the Mn ion is different in GaAs, since the impurity is an acceptor in this matrix with a rather large activation energy (113 meV). Two types of Mn centers exist in GaAs, the A 0 and the A − states. In low doped GaAs (below 10 19 cm −2 ), the former is dominant. It corresponds to the 3d 5 + h configuration, where h is a hole bound to the Mn ion with a Bohr radius around 1 nm [16]. When considering a single Mn impurity in InAs QD several issues arise: the impurity configuration, its possible change when photo-carriers are captured, the influence on the binding energy of excitonic complexes, the strength and sign of the effective exchange interaction with each of the carriers (electron or hole) in the QD S-shell. In this Letter, we report the first evidences of a single Mn impurity in an individual InAs QD which enable us to answer most of the above questions. In particular, we find that the formation of excitons, biexciton and trions is weakly perturbed by the impurity center, whereas the effective exchange coupling with the Mn impurity (found in the A 0 configuration) is ferromagnetic for holes (a few 100 µeV's) and almost zero for the electrons.The sample was grown by molecular beam epitaxy on a semi-insulating GaAs [001] substrate. The Mn-doped quantum layer was embedded inbetween an electron reservoir and a Schottky gate. This des...

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Model for the Mn acceptor in GaAs

Cited by 124 publications

References 22 publications

Disorder, spin-orbit, and interaction effects in diluteGa1−xMnxAs

Disorder, spin-orbit, and interaction effects in diluteGa1−xMnxAs

Microscopic Analysis of the Valence Band and Impurity Band Theories of (Ga,Mn)As

Optically Probing the Fine Structure of a Single Mn Atom in an InAs Quantum Dot

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