arXiv subjects

Joel Cibert

Publications and source records attributed to Joel Cibert.

15 recordsLinked to original sources

arXiv2025

Cathodoluminescence Study of a Quantum Dot in a Nanowire for Single-Photon Emission

Cathodoluminescence in a scanning electron microscope was applied to a semiconductor quantum dot in a nanowire able to emit single photons. We show that cathodoluminescence can be used not only for imaging and spectroscopy, but also to measure the correlation function and characterize the purity of the single-photon emitter. The electron beam can be manipulated to minimize the collection of parasitic luminescence. At cryogenic temperatures, we observed that the thermal budget, as measured via the phonon sidebands, is close to that of non-resonant micro-photoluminescence. This makes cathodoluminescence an efficient tool in the quest of novel single-photon sources.

physics.optics↗

arXiv2025

Calibration-free measurement of the phonon temperature around a single emitter

The emission properties of a localized solid-state emitter are strongly influenced by its environment. The coupling to acoustic phonons impacts the coherence of the emitter and its temperature dependence, and also results in the apparition of phonon sidebands besides the sharp zero-phonon line. Here, we present a method for measuring the absolute temperature of a localized emitter by directly plotting the ratio of the Stokes and anti-Stokes components of the phonon sideband as a function of the shift from the zero-phonon line. This approach requires no calibration and knowledge of the system, making it applicable to a wide range of emitters and materials. We validate the method using a CdSe quantum dot in a ZnSe nanowire. We thus show that the quantum dot is significantly heated under non-resonant excitation when increasing the incident power at low temperature and is ascribed to the drop in thermal conductivity at these temperatures.

physics.optics↗

arXiv2023

Brightness and purity of a room-temperature single-photon source in the blue-green range

Single-photon sources are crucial for developing secure telecommunications. However, most systems operate at cryogenic temperatures. Here, we discuss a promising solid-state system emitting single photons at room temperature in the blue-green range, allowing for quantum communications in free space and underwater. The active element is a core-shell ZnSe tapered nanowire embedding a single CdSe quantum dot grown by molecular beam epitaxy. A patterned substrate enables a thorough study of the one and same nanowire by different methods. Our source exhibits anti-bunching with g(2)(0) < 0.3 near the centre of the photoluminescence line and shows high brightness. This work paves the way for developing single-photon sources operating at non-cryogenic temperatures.

physics.optics↗

arXiv2021

Regulated dynamics with two-monolayer steps in vapor-solid-solid growth of nanowires

The growth of ZnTe nanowires and ZnTe-CdTe nanowire heterostructures is studied by \emph{in situ} transmission electron microscopy. We describe the shape, and the change of shape, of the solid gold nanoparticle during vapor-solid-solid growth. We show the balance between one-monolayer and two-monolayer steps which characterizes the vapor-liquid-solid and vapor-solid-solid growth modes of ZnTe. We discuss the role of the mismatch strain and lattice coincidence between gold and ZnTe on the predominance of two-monolayer steps during vapor-solid-solid growth, and on the subsequent self-regulation of the step dynamics. Finally, the formation of an interface between CdTe and ZnTe is described.

cond-mat.mtrl-sci↗

arXiv2019

Light / heavy hole switching with correlated characterization on a single quantum dot : Probing the light hole / heavy hole switching with correlated magneto-optical spectroscopy and chemical analysis on a single quantum dot

A whole series of complementary studies have been performed on the same, single nanowire containing a quantum dot: cathodoluminescence spectroscopy and imaging, micro-photoluminescence spectroscopy under magnetic field and as a function of temperature, and energy-dispersive X-ray spectrometry and imaging. The ZnTe nanowire was deposited on a Si 3 N 4 membrane with Ti/Al patterns. The complete set of data shows that the CdTe quantum dot features the heavy-hole state as a ground state, although the compressive mismatch strain promotes a light-hole ground state as soon as the aspect ratio is larger than unity (elongated dot). A numerical calculation of the whole structure shows that the transition from the heavy-hole to the light-hole configuration is pushed toward values of the aspect ratio much larger than unity by the presence of a (Zn,Mg)Te shell, and that the effect is further enhanced by a small valence band offset between the semiconductors in the dot and around it.

cond-mat.mes-hall↗

arXiv2018

Nanowire growth and sublimation: CdTe quantum dots in ZnTe nanowires

The role of the sublimation of the compound and of the evaporation of the constituents from the gold nanoparticle during the growth of semiconductor nanowires is exemplified with CdTe-ZnTe heterostructures. Operating close to the upper temperature limit strongly reduces the amount of Cd present in the gold nanoparticle and the density of adatoms on the nanowire sidewalls. As a result, the growth rate is small and strongly temperature dependent, but a good control of the growth conditions allows the incorporation of quantum dots in nanowires with sharp interfaces and adjustable shape, and it minimizes the radial growth and the subsequent formation of additional CdTe clusters on the nanowire sidewalls, as confirmed by photoluminescence. Uncapped CdTe segments dissolve into the gold nanoparticle when interrupting the flux, giving rise to a bulb-like (pendant-droplet) shape attributed to the Kirkendall effect.

cond-mat.mtrl-sci↗

arXiv2014

Strain in crystalline core-shell nanowires

The strain configuration induced by the lattice mismatch in a core-shell nanowire is calculated analytically, taking into account the crystal anisotropy and the difference in stiffness constants of the two materials. The method is applied to nanowires with the wurtzite structure or the zinc-blende structure with the hexagonal / trigonal axis along the nanowire, and the results are compared to available numerical calculations and experimental data. It is also applied to multishell nanowires, and to core-shell nanowires grown along the $<001>$ axis of cubic semiconductors.

cond-mat.mes-hall↗

arXiv2013

X-ray magnetic circular dichroism in (Ge,Mn) compounds: experiments and modeling

X-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) spectra at the L$_{2,3}$ edges of Mn in (Ge,Mn) compounds have been measured and are compared to the results of first principles calculation. Early \textit{ab initio} studies show that the Density Functional Theory (DFT) can very well describe the valence band electronic properties but fails to reproduce a characteristic change of sign in the L$_{3}$ XMCD spectrum of Mn in Ge$_3$Mn$_5$, which is observed in experiments. In this work we demonstrate that this disagreement is partially related to an underestimation of the exchange splitting of Mn 2$p$ core states within the local density approximation. It is shown that the change in sign experimentally observed is reproduced if the exchange splitting is accurately calculated within the Hartree-Fock approximation, while the final states can be still described by the DFT. This approach is further used to calculate the XMCD in different (Ge,Mn) compounds. It demonstrates that the agreement between experimental and theoretical spectra can be improved by combining state of the art calculations for the core and valence states respectively.

cond-mat.mtrl-sci↗

arXiv2013

Optical properties of single ZnTe nanowires grown at low temperature

Optically active gold-catalyzed ZnTe nanowires have been grown by molecular beam epitaxy, on a ZnTe(111) buffer layer, at low temperature 350\degree under Te rich conditions, and at ultra-low density (from 1 to 5 nanowires per micrometer^{2}. The crystalline structure is zinc blende as identified by transmission electron microscopy. All nanowires are tapered and the majority of them are <111> oriented. Low temperature micro-photoluminescence and cathodoluminescence experiments have been performed on single nanowires. We observe a narrow emission line with a blue-shift of 2 or 3 meV with respect to the exciton energy in bulk ZnTe. This shift is attributed to the strain induced by a 5 nm-thick oxide layer covering the nanowires, and this assumption is supported by a quantitative estimation of the strain in the nanowires.

cond-mat.mtrl-sci↗

arXiv2012

Electric-field control of the magnetic anisotropy in an ultrathin (Ga,Mn)As/(Ga,Mn)(As,P) bilayer

We report on the electric control of the magnetic anisotropy in an ultrathin ferromagnetic (Ga,Mn)As/(Ga,Mn)(As,P) bilayer with competing in-plane and out-of-plane anisotropies. The carrier distribution and therefore the strength of the effective anisotropy is controlled by the gate voltage of a field effect device. Anomalous Hall Effect measurements confirm that a depletion of carriers in the upper (Ga,Mn)As layer results in the decrease of the in-plane anisotropy. The uniaxial anisotropy field is found to decrease by a factor ~ 4 over the explored gate-voltage range, so that the transition to an out-of-plane easy-axis configuration is almost reached.

cond-mat.mtrl-sci↗

arXiv2010

Spin waves in magnetic quantum wells with Coulomb interaction and $sd$ exchange coupling

We theoretically describe the spin excitation spectrum of a two dimensional electron gas embedded in a quantum well with localized magnetic impurities. Compared to the previous work, we introduce equations that allow to consider the interplay between the Coulomb interaction of delocalized electrons and the $sd$ exchange coupling between electrons and magnetic impurities. Strong qualitative changes are found : mixed waves propagate below the single particle continuum, an anticrossing gap is open at a specific wavevector and the kinetic damping due to the electron motion strongly influences the coupling strength between electrons and impurities spins.

cond-mat.mes-hall↗

arXiv2009

Growth of (Ge,Mn) nanocolumns on GaAs(100): the role of morphology and co-doping on magnetotransport

Changing the morphology of the growing surface and the nature of residual impurities in (Ge,Mn) layers - by using different substrates - dramatically changes the morphology of the ferromagnetic Mn-rich inclusions and the magnetotransport properties. We obtained p-type layers with nanocolumns, either parallel or entangled, and n-type layers with spherical clusters. Holes exhibit an anomalous Hall effect, and electrons exhibit a tunneling magnetoresistance, both with a clear dependence on the magnetization of the Mn-rich inclusions; holes exhibit orbital MR, and electrons show only the normal Hall effect, and an additional component of magnetoresistance due to weak localization, all three being independent of the magnetic state of the Mn rich inclusions. Identified mechanisms point to the position of the Fermi level of the Mn-rich material with respect to the valence band of germanium as a crucial parameter in such hybrid layers.

cond-mat.mtrl-sci↗

arXiv2008

Magnetization dynamics down to zero field in dilute (Cd,Mn)Te quantum wells

The evolution of the magnetization in (Cd,Mn)Te quantum wells after a short pulse of magnetic field was determined from the giant Zeeman shift of spectroscopic lines. The dynamics in absence of magnetic field was found to be up to three orders of magnitude faster than that at 1 T. Hyperfine interaction and strain are mainly responsible for the fast decay. The influence of a hole gas is clearly visible: at zero field anisotropic holes stabilize the system of Mn ions, while in a magnetic field of 1 T they are known to speed up the decay by opening an additional relaxation channel.

cond-mat.mtrl-sci↗

arXiv2008

From diluted magnetic semiconductors to self-organized nanocolumns of GeMn in Germanium

While achieving high Curie temperatures (above room temperature) in diluted magnetic semiconductors remains a challenge in the case of well controlled homogeneous alloys, several systems characterized by a strongly inhomogeneous incorporation of the magnetic component appear as promising. Incorporation of manganese into germanium drastically alters the growth conditions, and in certain conditions of low temperature Molecular Beam Epitaxy it leads to the formation of well organized nanocolumns of a Mn-rich material, with a crystalline structure in epitaxial relationship with the Mn-poor germanium matrix. A strong interaction between the Mn atoms in these nanocolums is demonstrated by x-ray absorption spectroscopy, giving rise to a ferromagnetic character as observed through magnetometry and x-ray magnetic circular dichroism. Most interesting, intense magneto-transport features are observed on the whole structure, which strongly depend on the magnetic configuration of the nanocolumns.

cond-mat.mtrl-sci↗

arXiv2003

Hall effect and magnetoresistance in p-type ferromagnetic semiconductors

Recent works aiming at understanding magnetotransport phenomena in ferromagnetic III-V and II-VI semiconductors are described. Theory of the anomalous Hall effect in p-type magnetic semiconductors is discussed, and the relative role of side-jump and skew-scattering mechanisms assessed for (Ga,Mn)As and (Zn,Mn)Te. It is emphasized that magnetotransport studies of ferromagnetic semiconductors in high magnetic fields make it possible to separate the contributions of the ordinary and anomalous Hall effects, to evaluate the role of the spins in carrier scattering and localization as well as to determine the participation ratio of the ferromagnetic phase near the metal-insulator transition. A sizable negative magnetoresistance in the regime of strong magnetic fields is assigned to the weak localization effect.

cond-mat.mtrl-sci↗