Jean Leotin

LNCMI-CNRS · Physics

Highly aligned, packed, and doped carbon nanotube (CNT) fibers with electrical conductivities approaching that of copper have recently become available. These fibers are promising for high-power electrical applications that require light-weight, high current-carrying capacity cables. However, a microscopic understanding of how doping affects the el...

We present a compact, portable, terahertz time-domain magneto-spectrometer which consists of a table-top pulsed magnet and a fast terahertz time-domain system. The magnet operates at room temperature. An electronically controlled optical sampling (“ECOPS”) technique acquires 3000 pulse traces per second.

We report on the fabrication of monolayer MoS2 coated gold nano-antennas combining chemical vapor deposition, e-beam lithography surface patterning, and a soft lift-off/transfer technique. The optical properties of these hybrid plasmonic-excitonic nanostructures are investigated using spatially resolved photoluminescence spectroscopy. Off- and in-r...

We have developed a mini-coil pulsed magnet system with direct optical access, ideally suited for nonlinear and ultrafast spectroscopy studies of materials in high magnetic fields up to 30 T. The apparatus consists of a small coil in a liquid nitrogen cryostat coupled with a helium flow cryostat to provide sample temperatures down to below 10 K. Di...

The GaP/AlP/GaP heterostructure has an indirect gap both in real as well as momentum space, making the first order radiative recombination doubly forbidden. Nevertheless, we have observed relatively efficient emission from these structures. This paper comprehensively studies the origin of this improved light emission through a detailed analysis of...

To study low-energy magnetic dynamics and excitations in condensed matter systems in high magnetic fields, we are developing a unique terahertz time-domain magneto-optical spectroscopy system. The system is based on a compact single-shot terahertz spectroscopy setup using an echelle optic combined with a repetitive mini-coil pulsed magnet.

We have observed intense superfluorescent emission from a high-density electron-hole plasma in semiconductor quantum wells in high magnetic fields up to 30 T by developing a unique magneto-optical system with a table-top mini-coil pulsed magnet.

Magnetization measurements have been performed on single-crystalline Fe$_{1.1}$Te in pulsed magnetic fields $\mathbf{H}\perp\mathbf{c}$ up to 53 T and temperatures from 4.2 to 65 K. At $T=4.2$ K, a non-reversible reorientation of the antiferromagnetic moments is observed at $\mu_0H_R=48$ T as the pulsed field is on the rise. No anomaly is observed...

In this paper we present a compact THz Magneto-spectrometer based on an all-fiber OSCAT system with rapid scan mode. We investigate properties of graphite and p-Ge samples in magnetic fields up to 10T.

We present a novel approach for terahertz time-domain spectroscopy of magneto-optic phenomena. The setup used in this work combines a tabletop pulsed magnet and a standard terahertz time-domain spectroscopy system. The approach is based on repetitive operation of the pulsed magnet and step-wise increment of the delay time of the time-domain spectro...

In this paper, we report a correction to the model potential of the Ga acceptor in germanium, evidenced by high-magnetic-field photoconductivity measurements. We found that under high magnetic fields the chemical shift of the binding energy of Ga acceptors vanishes, contrary to the results given by the generally accepted theory. To fit our data, we...

Terahertz time-domain magneto-optics using pulsed magnetic fields is demonstrated with two different approaches. The first uses a fiber coupled high-speed delay line in combination with a long duration pulsed magnet. The second uses a table-top short duration pulsed magnet scanned repetitively and a step-scan readout of the THz electric field.

We report on oscillatory magnetoabsorption experiments on several indium nitride (InN) epilayers under a pulsed magnetic field up to 56 T. This optical technique is uniquely suited to probe the bulk electronic structure in the vicinity of the fundamental band edge by Landau level spectroscopy. We discuss these results in light of two recent studies...

In this paper we present a portable quantum cascade laser (QCL) based infrared magnetospectrometer covering the spectral range from 5 to 120 μm. The variation of the excitation wavelength is enabled by an easy change of the QCL plug-in modules, while the use of any other external source is also possible. The performance of the setup is illustrated...

We present time-resolved cyclotron resonance spectra of holes in p-Ge measured during single magnetic field pulses by using a rapid-scanning, fiber-coupled terahertz time-domain spectroscopy system. The key component of the system is a rotating monolithic delay line featuring four helicoid mirror surfaces. It allows measurements of THz spectra at u...

We present a magneto-transmission experimental set up covering the spectral region from 5 to 120 μm. Interchangeable quantum cascade lasers are used as excitation sources. The performance of the setup is illustrated via cyclotron resonance studies of InGaAs/GaAs QWs under magnetic fields up to 60T.

We present time-resolved cyclotron resonance spectra of holes in p-germanium measured during a single magnetic field pulse by using a rapid-scanning, fiber-coupled THz time-domain spectroscopy system.

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 +/- 0.002m(0) for samples having electro...

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 classi...

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 i...

We report here first magneto-photoluminescence investigations under high pressure up to 6 GPa on III–VI layered semiconductor InSe. Both diamagnetism and magnetic field induced gap opening driven by Landau quantization became observable by using a 60 T pulsed magnet. The pressure-induced enhancement of the diamagnetic coefficient is consistent with...

We report a systematic study of the cyclotron resonance CR absorption of two-dimensional holes in strained InGaAs/GaAs quantum wells QWs in the quantum limit. The energies of the CR transitions are traced as a function of magnetic field up to 55 T. A remarkable CR line splitting was evidenced when the resonant field exceeds 20 T. We analyze our dat...

We have studied the magnetotransport properties of p-InMnAs layers in strong (up to 30 T) pulsed magnetic fields. The p-InMnAs layers were obtained by laser plasma deposition with subsequent annealing by radiation of a pulsed ruby laser. Under anomalous Hall effect conditions in a strong magnetic field (above 20 T), the Hall resistance in the param...

Cyclotron resonance, quantum Hall effect, and Shubnikov de Haas oscillations measurements of quasi-two-dimensional (2-D) electrons in modulation-doped AIP quantum wells are investigated. This study enables to clarify the electronic structure of quasi-lattice matched AIP/GaP quantum wells that are epitaxially grown on (100)-oriented GaP substrate. T...

Transmission spectra, T(H), of linearly polarized electromagnetic waves through YFeO(3), weak ferromagnet, measured at frequencies nu=96-1000 GHz in long-pulsed magnetic fields (H||k||c-axis, Faraday geometry) exhibit strong rotation of the polarization plane near the quasiferromagnetic AFMR as well as low frequency impurity modes. New ascending im...

A detailed study of inter-subband energy transitions in AlP quantum wells (QWs) based on valley-symmetry and effective-mass measurements using THz cyclotron resonance and quantum transport in AlP/GaP QWs is presented. We show that AlP/GaP QWs can serve as the basis for THz devices emitting in the 30-60 mum wavelength range that is inaccessible by o...

We investigate the properties of quasi-two-dimensional electrons in a wide range of modulation-doped AlP quantum wells (between 3 and 15 nm) with GaP barriers by measuring cyclotron resonance, quantum Hall effect, and Shubnikov–de Haas oscillations. The degeneracy of the three X valleys is lifted due to both strain and confinement: In wider wells t...

We report on the investigation of the conduction band (CB) of AlP by high magnetic field cyclotron resonance (CR) and transport in a two-dimensional electron gas (2DEG) confined in AlP/ GaP. We found that for QW width <4nm the ground state subband is a single Xz valley with cyclotron mass m z c /m0= 0.3±0.02, whereas, for wider QW, > 10nm thick, th...

The magnetotransport properties of a two-dimensional (2D) electron-hole system localized on a single type II broken-gap heterointerface have been studied in a pulsed magnetic field up to 35 T. The step-like decrease of the driving current indicates a conductivity path through localized states of the 2D system. Up to ∼20 T, Hall resistance (Rxy) is...

In this paper we present a very compact THz cyclotron resonance spectrometer that operates in the range 3 to 30 THz. This range is covered by choosing, respectively, several GaAs/AlGaAs quantum cascade lasers (QCL) for excitation, and either by Boron doped Silicon or Gallium doped Germanium photoconductors for detection. The system is made portable...

Transmission polarization control spectra T(B) of YFeO3 weak ferromagnet measured in long-pulsed magnetic fields in Faraday geometry exhibit strong effects of polarization plane rotation near the quasiferromagnetic AFMR as well as low frequency impurity modes. New ascending impurity branch including five lines was observed at high magnetic field (1...

We investigate the properties of quasi-two-dimensional electrons in AlP quantum wells by measuring cyclotron resonance, quantum Hall effect, and Shubnikov de Haas oscillations in modulation-doped AlP-GaP type-II quantum wells. We find that in wide AlP wells, the lowest conduction band states are in the Xx and Xy valleys transverse to the growth dir...

We investigate the properties of quasi-two-dimensional electrons in AlP quantum wells by measuring cyclotron resonance, quantum Hall effect, and Shubnikov de Haas oscillations in modulation-doped AlP-GaP type-II quantum wells. We find that in wide AlP wells, the lowest conduction band states are in the Xt valleys transverse to the growth direction,...

The development of THz spectroscopy and imaging based on intersubband transitions in Quantum Cascade Lasers (QCL) is precluded to date in the wavelength range 20-60 mum (15-5 THz) because of the reststrahl band of currently used GaAs alloy materials. One option to overcome this limitation is to use AlP/GaP Quantum wells grown on a GaP substrate, bu...

Magnetotransport properties of p-InMnAs layers are studied in pulsed magnetic fields up to 30 T. Samples were prepared by the laser deposition and annealed by ruby laser pulses. Well annealed samples show p-type conductivity while they were n-type before the annealing. Surprisingly the anomalous Hall effect resistance in paramagnetic state (T>40 K)...

THz cyclotron resonance measurements In wide AlP/GaP multi-quantum wells gives a cyclotron mass m*=0.52 m₀ and X_xy-valley-symmetry for the ground state subband. In addition, twofold valley degeneracy is found from magneto-transport measurements.

The dependence of photoconductivity on the magnetic field has been studied for Si:B blocked-impurity-band (BIB) structures with the boron impurity concentration of ∼1018 cm−3 in the active layer. Measurements were performed in the magnetic field B up to 30 T with the pulse length of 0.8 s in the temperature range T = 4.2−9 K, under irradiation of s...

In this paper we present a very compact cyclotron resonance (CR) spectrometer based on a GaAs/AlGaAs quantum cascade laser emitting at 11.4μm. We show its operation under magnetic fields up to 60 T and in temperatures up to 80K. We, finally, illustrate our spectrometer with the measurements of InAs_xSb_1-x alloy.

The magnetic-field dependence of the operation of a quantum-cascade intersubband laser (QCL) is used to investigate the energetic relaxation of injected electrons through phonon emission. The QCL emits at 3.8 μm and incorporates a strain-compensated active region with a large degree of internal strain. Energies of the relevant electron-phonon scatt...

The Hall coefficient R H of n-type CuInSe 2 single crystals is measured between 10 and 300 K in pulsed magnetic field up to 35 T. The threshold field B th , above which the magnetic freezeout starts to occur, varies linearly with temperature. From the analysis of the temperature dependence of electron concentration in the activation regime above 10...

We studied the behavior of middle IR GaAs/AlGaAs quantum cascade lasers (QCL) subjected to a strong magnetic field perpendicular to the 2D planes. We observed that both laser threshold and differential quantum efficiency are modulated by a magnetic field. The intersubband lifetime vs magnetic field is derived from the field dependence of QCL thresh...

In this paper we present a compact terahertz cyclotron resonance (CR) spectrometer based on a GaAs/AlGaAs quantum cascade laser. We demonstrate high reproducibility as well as high precision in order of ~1% in the position of CR absorption and ~10% in amplitude. The spectrometer is, finally, used for measurements of InAs x Sb 1-x alloys with As con...

We report on high-excitation photoluminescence (PL) measurements of an ensemble of InAs/GaAs self-assembled quantum dots with large inter-shell spacing in magnetic fields up to . The PL spectra show a complex picture of levels splitting and crossings. A simple two-band single-particle model provides a good approximation to explain the observed magn...

Intersubband magneto-phonon resonance in QWs appears as a resonant relaxation of the energy of carriers in excited subbands when a quantizing high magnetic field is applied along the growth axis. The carrier lifetime shows oscillations periodic with the reciprocal of the field. We recently evidenced this effect on the light intensity of GaAs/GaAlAs...

Microminiature Hall probes with sensitive area down to 33×115μm and based on n-InSb/i-GaAs optimized Sn-doped MBE-grown heterostructures are reported. The “metallurgical” thicknesses of the n-InSb epilayers lie in the range dm=1.1–10.5μm giving room-temperature mobilities of (9–15)×103cm2/Vs with carrier densities of (0.96–2.56)×1018cm−3. Character...

We review our recent work on the electron lifetime tuning by a quantizing magnetic field in mid-infrared GaAs/GaAlAs quantum cascade lasers (QCL). The observation of giant oscillations of light emission intensity in strong pulsed magnetic fields up to 60 T gives spectacular evidence of a progressive quenching of an optical phonon non-radiative rela...

By measuring the light emitted from a quantum cascade laser placed in a high magnetic field, we have investigated the energy relaxation of 0D magnetically confined electrons in the active quantum wells of the structure. The experiment consists of injecting electrons by tunnelling into one upper subband level and monitoring a resonant interaction wi...

An overview over past and present activities and future developments at the Toulouse pulsed magnetic field facility is given, both as far as technical developments of the infrastructure, as well as low temperature physics performed at the LNCMP are concerned.

The intersubband light emission of GaAs/GaAlAs quantum cascade lasers is measured under pulsed magnetic fields parallel to the current, up to 60 T. A giant modulation of the laser intensity is observed with complete suppression of the laser emission when the energy spacing between intersubband Landau quantized states matches the GaAs optical phonon...

Measurements of the light emission under strong magnetic field from quantum cascade lasers emitting at 9 and 11 μm are reported. The laser intensity shows strong oscillations as a function of the magnetic field. This effect is due to changes in the lifetime of the upper state of the laser transition, which is controlled by electron-optical phonon s...

Electron scattering with longitudinal-optical phonons is the main energy relaxation process between two-dimensional states in semiconductor heterostructures. This effect can be modified when the electron dispersion is broken into series of discrete states, similar to the energy spectrum of quantum boxes. This has been verified by applying a magneti...

We report on magnetotransport measurements of GaAs/GaAlAs quantum cascade structures in magnetic fields up to 62 T parallel to the current. We observe novel quantum oscillations series in tunneling current that are periodic in reciprocal magnetic field and have field positions independent of the applied bias. These oscillations are explained as int...

We have studied magnetotransport in GaAs/GaAlAs quantum cascade structures. These systems initially designed for intersubband laser emission are peculiar double barrier resonant tunneling structures. Under strong magnetic field applied parallel to the vertical current, we have observed marked quantum oscillations in the magnetoresistance that have...

A photovoltage was found across a silicon blocked impurity band detector when illuminated at low temperatures with photons of wavelengths up to about 30 μm. It appears as an open loop photovoltage, constant over a wide range of incident flux intensity, while the short circuit photocurrent changes linearly with photon flux. The device is a boron dop...

We report about the first time observing the logarithmic relaxation of the giant magnetoresistance (GMR) in Fe/SiO2-nanocomposites at relatively high temperatures with features characteristic for the glass-like behaviour. The model has been developed which describes the glass-like character of granular ferromagnetics and explains the quasi-threshol...

The REFIR (Radiation explorer in the far infrared) project is a study, funded by European Union, of feasibility of a novel space-borne instrument that will measure the atmospheric spectral radiance of the Earth in the broad spectral range 100-1100 cm-1 from space with sufficient spectral resolution (0.5 cm-1) and signal-to-noise ratio (SNR > 100)....

A short circuit photocurrent is measured across a silicon blocked impurity band (BIB) detector when the device is illuminated at low temperatures with photons of wavelength up to about 30 µm. The photocurrent changes linearly with photon flux over a wide range of flux intensity while the open loop photovoltage remains suprisingly constant. The devi...

The REFIR (Radiation explorer in the far infrared) project is a study, funded by European Union, of feasibility of a novel space-borne instrument that will measure the atmospheric spectral radiance of the Earth in the broad spectral range 100-1100 cm-1 from space with sufficient spectral resolution (0.5 cm-1) and signal-to-noise ratio (SNR > 100)....

The optical absorption spectra of magnetic quasi-2D Co island films and of hybrid Co/SiO2 multilayers in which island films are separated by SiO2 layers were studied. It was found that, when the Co film was masked by a thin SiO2 layer, the absorption considerably increased and exceeded 0.8. This was observed when the Co fraction was substantially l...

We have experimentally shown that percolating 2D electron systems based on Si-metal-nitride-oxide semiconductor structures with strong fluctuation potential reveal conductance quantization signatures up to room temperature, despite the sample sizes being in the micrometer range. The gate length of the structure was chosen to be comparable with the...

Experiments demonstrate that the magnetization of Fex(SiO2)1−x-nanocomposite at magnetic fields H⩽20T depends rather weakly on temperature T=4–300K. Thus, the Langevin model for the magnetization is invalid. We explain our results in the frame of a simple model taking into account distributions of non-spherical granules’ orientations and forms. Cal...

Pulsed field magnetotransport measurements up to 50 T were performed on GaAs/GaAlAs quantum cascades structures at liquid helium temperatures. Current–voltage measurements show a staircase profile enhanced dramatically by a constant magnetic field. This profile is tentatively explained by resonant tunnelling transport processes into the active well...

Up to six magnetophonon peaks are observed in the transverse magnetoresistance of high mobility samples of n-CdSe. After corrections are applied for the nonparabolicity of the band and the polaron effect, the 'bare' band edge masses are deduced to be 0.115 m for B perpendicular to c and 0.120 m for B//c. The corresponding low frequency masses are 0...

The magnetophonon effect in p-tellurium is extensively studied over the temperature range from 20 to 90K in magnetic fields of up to 300 kOe. High resolution of the peaks is achieved by means of a double differentiation technique. When the magnetic field is applied perpendicular to the c axis, the position of the magnetophonon peaks in the transver...

Up to eleven magnetophonon peaks are observed in the transverse magnetoresistance of high purity epitaxial films of n-type inp at temperatures between 77 and 300 k. The low frequency cyclotron effective mass of the electrons is found to be 0.0820 +or- 0.0010 m0 at 77 k and 0.0781 +or- 0.0010 m0 at 300 k.

The magnetophonon effect has been observed in the longitudinal and transverse magnetoresistance and the Hall voltage of n-InP under warm-electron conditions. Two distinct processes of electron energy relaxation are identified from the resonant structure: the first involves emission of a Gamma point LO phonon accompanied by the capture of the warm e...

The non-parabolicities of the transverse effective masses mperpendicular to * for the lowest conduction band minima are measured in silicon and germanium by means of cyclotron resonance at submillimeter wavelengths. For silicon a 2+or-1% increase in mperpendicular to * at 10 meV into the band is found, whereas for germanium an 8+or-4% increase at 5...

The exact form of the valence bands in III-V compounds has long been controversial and it is demonstrated that quantitative information concerning the valence band structure can be obtained from the magnetophonon effect. The valence band anisotropy deduced for InSb from the low-field peaks is comparable with that of Ge. For GaAs the heavy hole peak...

Cyclotron resonance of the holes in p-GaAs is reported at wavelengths of 2.2 mm and 337 mu m and at liquid nitrogen temperatures. The conditions under which hole cyclotron-resonance measurements can be interpreted as being dominated by classical light and heavy holes are investigated by means of complimentary cyclotron-resonance studies in p-Ge at...

The results of experimental studies of magnetic nanocomposites (granular metals) Fe/SiO2 with various metal-fraction concentrations in the close vicinity of the percolation transition are discussed. With the intent to shed light on the nature of unique properties of such structures, various measurements such as that of magnetoresistance, the Hall e...

Magnons, phonons and electronic excitations in the mixed crystal Fe1-xCoxCl2 have been studied by Raman scattering spectroscopy. Magnon-like excitations have been observed for T<TN in crystals with 0<or=x<0.03 and 0.9<X<or=1. The temperature dependences of the one-magnon peak position, linewidth and intensity have also been studied. For FeCl2 an in...

For pt.I see ibid., vol.16, p.3877, 1983. Using the known band structure of Cd3As2, and in particular the previously established fact that the effective masses are linear in energy over a wide energy range, the authors have shown by an analytic calculation that a 'cyclotron resonance' may in principle appear in the Voigt configuration, although it...

We report on unique electronic properties in Fe-SiO2 nanocomposite thin films in the vicinity of the percolation threshold. The electronic transport is dominated by quantum corrections to the metallic conduction of the Infinite Cluster (IC). At low temperature, mesoscopic effects revealed on the conductivity, Hall effect experiments and low frequen...

We present the results of the anomalous Hall effect investigations under the hopping transport regime. The Hall effect and magnetic measurements were performed in Fe/SiO2 nanocomposites at the insulator side of percolation transition. Unlike magnetic metals, in studied materials Hall effect is determined by non-direct electron tunneling between gra...

A new FIR photovoltaic effect, which does not depend on incident radiation intensity, is found at low temperatures in modulated unipolar boron-doped silicon structure. It is shown that the effect originates from an asymmetric ballistic hole transport across the low doped layer due to fast trapping process within the upper Hubbard impurity band of t...

Available from http://www3.interscience.wiley.com/cgi-bin/abstract/72507576/START

Des mesures électriques du coefficient de Hall et de mobilité électronique sont obtenues sur des échantillons de CuInSe2 type n lorsque la temp?rature varie de 4 à 300 K. L'étude des courbes de mobilité montre que dans le domaine des hautes températures, seules les diffusions des électrons par les impuretés ionisées, les phonons acoustiques et les...

It was established that the Hall effect in nanocomposite Fe/SiO2 under conditions of tunnel-activated conductivity is anomalous, that is the Hall resistivity ρH is proportional to the magnetization and results from the spin–orbit interaction. As this takes place, the parametric relation ρH between the Hall resistivity and the longitudinal (ρxx) one...

Available from http://www3.interscience.wiley.com/cgi-bin/abstract/70500210/START

We present far infrared transmission measurements of alpha'-NaV2O5 single crystals. This material is known to undergo a spin-Peierls like transition at T-SP=35K. Below the transition temperature we observed together with expected new sharp phonon lines a strong gap-like depression of absorption occurring in the low energy part of a continuum likely...

A new instrument named SAFIRE-A (Spectroscopy of the Atmosphere using Far-Infrared Emission/Airborne), which can operate on high-altitude platforms, has been developed for the study of the atmospheric composition through limb-scanning emission measurements. The instrument is a polarizing Fourier transform spectrometer that operates in the far infra...

A crossover from Efros-Shklovskii to Mott variable range hopping (VRH) has been observed in the electrical conductivity upon applying a high magnetic field B > 15 T on insulating compensated Si:(P,B). as has been found before in Ge:As. This crossover is deduced from the change of the exponent s of the temperature dependence of the VRH conductivity....

A new instrument named SAFIRE-A (Spectroscopy of the Atmosphere using Far-Infrared Emission/Airborne), which can operate on high-altitude platforms, has been developed for the study of the atmospheric composition through limb-scanning emission measurements. The instrument is a polarizing Fourier transform spectrometer that operates in the far infra...