Individual Cr atom in a semiconductor quantum dot: Optical addressability and spin-strain coupling

Abstract

International audienceWe demonstrate the optical addressability of the spin of an individual chromium atom (Cr) embedded in a semiconductor quantum dot. The emission of Cr-doped quantum dots and their evolution in magnetic field reveal a large magnetic anisotropy of the Cr spin induced by local strain. This results in the zero field splitting of the 0, ±1, and ±2 Cr spin states and in a thermalization on the magnetic ground states 0 and ±1. The observed strong spin to strain coupling of Cr is of particular interest for the development of hybrid spin-mechanical devices where coherent mechanical driving of an individual spin in an oscillator is needed. The magneto-optical properties of Cr-doped quantum dots are modeled by a spin Hamiltonian including the sensitivity of the Cr spin to the strain and the influence of the quantum dot symmetry on the carrier-Cr spin coupling

Spin dynamics of an individual Cr atom in a semiconductor quantum dot under optical excitation

“…Because of the large magnetic anisotropy of the Cr spin, D 0 S 2 z , induced by the local bi-axial strain in self-assembled QDs, the Cr spin thermalizes to its magnetic ground states S z =0 and S z =±1. The exchange interaction with the spin of the confined bright exciton | ± 1 splits the Cr spin states S z =±1 and three main lines (labeled (1), (2) and (3)) are observed in the PL spectra [1]. Most of the dots also present a low symmetry (lower than C 2v ) and the central line associated with S z =0 (line (2)), is split and linearly polarized along two orthogonal directions, by (i) the long-range e-h exchange interaction in a QD with an in-plane shape anisotropy and/or (ii) the short range e-h exchange interaction in the presence of valence band mixing.…”

“…The variety of magnetic transition elements that could be incorporated in semiconductors gives a large choice of electronic and nuclear spins as well as orbital momentum [10,11]. In this context, growth and optical addressing of II-VI semiconductor quantum dots (QDs) containing an individual Cr atom were achieved recently [1].Cr is incorporated in II-VI compounds as Cr 2+ ions carrying a localized electronic spin S = 2 and an orbital momentum L = 2 [12]. In addition, most of the Cr isotopes have no nuclear spin.…”

“…The variety of magnetic transition elements that could be incorporated in semiconductors gives a large choice of electronic and nuclear spins as well as orbital momentum [10,11]. In this context, growth and optical addressing of II-VI semiconductor quantum dots (QDs) containing an individual Cr atom were achieved recently [1].…”

“…1(b), this line presents a longer lifetime. It arises from a dark exciton (| ± 2 ) which acquires some oscillator strength by a mixing with a bright exciton interacting with the same Cr spin state [1]. This dark/bright exciton mixing is induced by the e-h exchange interaction in a confining potential of low symmetry [19].…”

“…We used recently developed singly Cr-doped CdTe/ZnTe quantum dots (A. Lafuente-Sampietro et al, [1]) to access the spin of an individual magnetic atom. Auto-correlation of the photons emitted by the quantum dot under continuous wave optical excitation reveals fluctuations of the localized spin with a timescale in the 10 ns range.…”