Marius Millot

Electron cyclotron effective mass in indium nitride

We report on cyclotron effective mass measurement in indium nitride epilayers grown on c-sapphire, using the thermal damping of Shubnikov-de-Haas oscillations obtained in the temperature range 2–70 K and under magnetic field up to 60 T. We unravel an isotropic electron cyclotron effective mass equal to 0.062±0.002m0 for samples having electron concentration near 1018 cm−3. After nonparabolicity and polaron corrections we estimate a bare mass at the bottom of the band equal to 0.055±0.002m0.

Analysis of laser shock experiments on precompressed samples using a quartz reference and application to warm dense hydrogen and helium

Megabar (1 Mbar = 100 GPa) laser shocks on precompressed samples allow reaching unprecedented high densities and moderately high ∼103–104 K temperatures. We describe here a complete analysis framework for the velocimetry (VISAR) and pyrometry (SOP) data produced in these experiments. Since the precompression increases the initial density of both the sample of interest and the quartz reference for pressure-density, reflectivity, and temperature measurements, we describe analytical corrections based on available experimental data on warm dense silica and density-functional-theory based molecular dynamics computer simulations. Using our improved analysis framework, we report a re-analysis of previously published data on warm dense hydrogen and helium, compare the newly inferred pressure, density, and temperature data with most advanced equation of state models and provide updated reflectivity values.

Evidence of type-I direct recombination in InP/GaP quantum dots via magnetoluminescence

Photoluminescence from InP quantum dots within a GaP matrix is investigated as a function of magnetic field. By fitting the magnetoluminescence data to the energy states of the electrons and holes confined in quantum dots in a perpendicular magnetic field, the electron-hole reduced effective mass is determined to be 0.094m0. The diamagnetic shift in the luminescence peak gives an average exciton radius of about 5 nm, smaller than the dot radius. These results indicate that the recombining electrons are primarily composed of states originating from the InP Γ valley although the conduction band discontinuity between the InP and the GaP barrier is expected to be very small or even negative.

Er3+ luminescence as a sensor of high pressure and strong external magnetic fields

In this paper, we present the preliminary results of the combined effect of high pressure (up to 7.5 GPa) and strong external magnetic fields (up to 28.5 T) on the photoluminescence (PL) properties of Er3+–Yb3+ co-doped single-crystal thin films of well-oriented KY(WO4)2 at low temperatures. Measurements were carried out under pulsed magnetic field, exciting the Er3+ ions via upconversion mechanisms by a Ti:sapphire laser with the external magnetic field applied along the crystallographic b axis. The detailed study of the green 4S3/2→4I15/2 Er3+ PL after infrared excitation around 1 μm as a function of pressure and external magnetic field reveals the potential applicability of this system as sensor of high magnetic fields, high pressure and low temperature, simultaneously.

Red-green luminescence in indium gallium nitride alloys investigated by high pressure optical spectroscopy

We performed optical absorption and photoluminescence experiments under high pressure up to 10 GPa on two good quality InGaN epilayers with ∼40% indium. The pressure coefficient of about 30 meV/GPa for the absorption edge is close to the bandgap pressure coefficients of InN and GaN, indicating similar pressure dependence of the fundamental band gap in the whole composition range. In contrast, the pressure coefficient of the photoluminescence peak energy shows much weaker pressure dependence which we attribute to an increasing role of highly localized defects when the conduction band approaches the Fermi level stabilization energy at higher indium contents.

New diamond anvil cell for optical and transport measurements under high magnetic fields up to 60 T

We present here a new diamond anvil cell designed to combine high hydrostatic pressure up to 10 GPa, non-destructive, pulsed magnetic fields up to 60 T and low temperature as low as 2 K. Both optical and transport measurements are now achievable. Magneto-photoluminescence set-up under pressure is described in great detail. We report photoluminescence experiments on oriented ruby single crystals exhibiting direct observation of the intrinsic Zeeman splitting of excited states under pressure.

Pressure dependence of Raman modes in double wall carbon nanotubes filled with α-Fe

The preparation of highly anisotropic one-dimensional (1D) structures confined into carbon nanotubes (CNTs) in general is a key objective in CNTs research. In this work, the capillary effect was used to fill double wall carbon nanotubes with iron. The samples are characterized by Mössbauer and Raman spectroscopy, transmission electron microscopy, scanning area electron diffraction, and magnetization. In order to investigate their structural stability and compare it with that of single wall carbon nanotubes (SWNTs), elucidating the differences induced by the inner-outer tube interaction, unpolarized Raman spectra of tangential modes of double wall carbon nanotubes (DWNTs) filled with 1D nanocrystallin α-Fe excited with 514 nm were studied at room temperature and elevated pressure. Up to 16 GPa we find a pressure coefficient for the internal tube of 4.3 cm−1 GPa−1 and for the external tube of 5.5 cm−1 GPa−1. In addition, the tangential band of the external and internal tubes broadens and decreases in amplitude. All findings lead to the conclusion that the outer tube acts as a protection shield for the inner tubes (at least up 16 GPa). Structural phase transitions were not observed in this range of pressure.

Photoluminescence of InP/GaP quantum dots under extreme conditions

We present here high-field magneto-photoluminescence experiments on self-assembled InP/GaP quantum dots under high pressure, at cryogenic temperature. We unveil and discuss a very low pressure coefficient (PC) for the direct exciton and the quenching of the strong luminescence at 1.2 GPa. In fact, the magneto-fingerprints, interpreted in the classic Fock–Darwin framework, give access to the evolution of charge carriers confinement and unravel an increase of the exciton effective mass, involved in the low effective PC.