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Time-resolved dynamics of GaN waveguide polaritons
Authors:
Loïc Méchin,
François Médard,
Joël Leymarie,
Sophie Bouchoule,
Blandine Alloing,
Jesús Zúñiga-Pérez,
Pierre Disseix
Abstract:
We implement a new experimental approach to directly measure the lifetime of guided polaritons arising from the strong-coupling of GaN excitons and the guided photonic modes of a slab waveguide. Using a Fourier imaging setup, combined with spatial filtering of the emission, the emission associated to polaritonic modes with well-defined propagation constants can be selectively analyzed in the tempo…
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We implement a new experimental approach to directly measure the lifetime of guided polaritons arising from the strong-coupling of GaN excitons and the guided photonic modes of a slab waveguide. Using a Fourier imaging setup, combined with spatial filtering of the emission, the emission associated to polaritonic modes with well-defined propagation constants can be selectively analyzed in the temporal domain. By directing it to the entrance slit of a streak camera, time-resolved photoluminescence (TRPL) measurements along the polariton dispersion branch were performed at 40 K, enabling to assess the time decay of polariton modes. By combining this information with the photonic/excitonic fraction corresponding to each polariton mode, extracted from a coupled-oscillators model that indicate a Rabi splitting of $Ω$ = 80 meV, we could extract the photon lifetime in the waveguide $τ_γ\, =\, 3\pm 1$ ps. This corresponds to a record $Q$-factor in the UV of 16 000. The excitonic reservoir lifetime, which contributes to polariton formation, was determined through TRPL measurements on excitonic luminescence. Finally, measurements conducted at lower temperature highlight secondary feeding mechanisms for the guided polaritonic mode, either via photon recycling from the AlGaN cladding layer or through resonant injection of photons from transitions below the band gap.
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Submitted 24 April, 2025;
originally announced April 2025.
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Effects of the built-in electric field on free and bound excitons in a polar GaN/AlGaN/GaN based heterostructure
Authors:
Loïc Méchin,
François Médard,
Joël Leymarie,
Sophie Bouchoule,
Blandine Alloing,
Jesùs Zuñiga-Pérez,
Pierre Disseix
Abstract:
Low-temperature luminescence spectra reveal the presence of two independant populations of GaN excitons within a $\mathrm{GaN/AlGaN/GaN/Al_2O_3}$ heterostructure in which a thick (1.5 $\mathrm{μm}$) AlGaN layer separates a thin (150 nm) top GaN layer and a thick (3.5 $\mathrm{μm}$) bottom GaN layer grown on sapphire. The presence of these two spectrally-distinct families of excitons in each GaN la…
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Low-temperature luminescence spectra reveal the presence of two independant populations of GaN excitons within a $\mathrm{GaN/AlGaN/GaN/Al_2O_3}$ heterostructure in which a thick (1.5 $\mathrm{μm}$) AlGaN layer separates a thin (150 nm) top GaN layer and a thick (3.5 $\mathrm{μm}$) bottom GaN layer grown on sapphire. The presence of these two spectrally-distinct families of excitons in each GaN layer of the heterostructure is demonstrated using three different experimental methods: (i) low-power $\mathrmμ$-photoluminescence ($\mathrm{μPL}$) using laser excitation sources with wavelengths above and below the AlGaN bandgap, (ii) $\mathrm{μPL}$ as a function of optically injected free carrier density, and (iii) quantitative numerical simulation of the $\mathrmμ$-Reflectivity ($\mathrm{μR}$). One major impact of the built-in electric field is the reduction of the excitonic lifetime in the GaN surface layer, which transitions from less than 10 ps in the presence of the built-in electric field to the bulk lifetime (90 ps) when the field is screened. This increase in the excitonic lifetime is related to the modification of the band structure in the presence of optically injected free carriers. The effect of these lifetime variations on the luminescence spectra is analyzed. Lastly, we provide an estimate of the Mott density in GaN as $n_{\mathrm{Mott}} = 4\times 10^{17}\, \mathrm{cm^{-3}}$ at 130 K, consistent with values reported in the literature and accounting for the free carrier density required to screen the electric field.
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Submitted 13 January, 2025;
originally announced January 2025.
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Simultaneous MOKE imaging and measurement of magneto-resistance with vector magnet: a low noise customized setup for low field magnetic devices and thin films characterization
Authors:
Imtiaz Noor Bhatti,
Ilyas Noor Bhatti,
L. G. Enger,
P. Victor,
B. Guillet,
M. Lam Chok Sing,
O. Rousseau,
V. Pierron,
S. Lebargy,
J. Camarero,
L. Mechin,
S. Flament
Abstract:
Here we report a custom design setup for the simultaneous measurement of magneto-resistance and MOKE imaging in longitudinal configuration for characterization of magnetic thin-films and sensors. The setup is designed so as to cope with a small signal to noise ratio of initial images and to allow sensitive magnetoresistance (MR) measurement at low field. An improved differential algorithm is used…
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Here we report a custom design setup for the simultaneous measurement of magneto-resistance and MOKE imaging in longitudinal configuration for characterization of magnetic thin-films and sensors. The setup is designed so as to cope with a small signal to noise ratio of initial images and to allow sensitive magnetoresistance (MR) measurement at low field. An improved differential algorithm is used to get a good enough contrast of the magnetic images and get rid of beam illumination or small camera gain fluctuations. Home made power supply and pre-amplifier stage were designed so as to reduce the low frequency noise as well as the thermal electrical noise. A vector magnet is used to produce rotational magnetic field so as to study the magnetic anisotropy and calculate the anisotropic constants in magnetic thin films. Magnetoresistive sensors patterned on epitaxial La$_{0.67}$Sr$_{0.33}$MnO$_3$ (LSMO) thin film have been characterized with this setup. The Images of the magnetization reversal process as well as the local magnetization loops deduced from these images provided evidence of a magnetic uniaxial anisotropy induced by the vicinal substrate. The magnetic anistropic constant of the films was then inferred from the MR measurements.
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Submitted 8 January, 2025;
originally announced January 2025.
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Experimental demonstration of a Two-Dimensional Hole Gas (2DHG) in a GaN/AlGaN/GaN based heterostructure by optical spectroscopy
Authors:
Loïc Méchin,
François Médard,
Joël Leymarie,
Sophie Bouchoule,
Jean-Yves Duboz,
Blandine Alloing,
Jesús Zuñiga-Pérez,
Pierre Disseix
Abstract:
The polarization discontinuity across interfaces in polar nitride-based heterostructures can lead to the formation of two-dimensional electron and hole gases. In the past, the observation of these electron and hole gases has been achieved through various experimental techniques, most often by electronic measurements but occasionally by optical means. However, the occurrence of a two-dimensional ho…
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The polarization discontinuity across interfaces in polar nitride-based heterostructures can lead to the formation of two-dimensional electron and hole gases. In the past, the observation of these electron and hole gases has been achieved through various experimental techniques, most often by electronic measurements but occasionally by optical means. However, the occurrence of a two-dimensional hole gas has never been demonstrated optically. The objective of this article is to demonstrate, thanks to the combination of various optical spectroscopy techniques coupled to numerical simulations, the presence of a two-dimensional hole gas in a GaN/AlGaN/GaN heterostructure. This is made possible thanks to a GaN/AlGaN/GaN heterostructure displaying a micrometer-thick AlGaN layer and a GaN cap thicker than in conventional GaN-based HEMTs structures. The band structure across the whole heterostructure was established by solving self-consistently the Schrödinger and Poisson equations and by taking into account the experimentally determined strain state of each layer. Continuous and quasi-continuos photoluminescence reveal the presence of a broad emission band at an energy around 50 meV below the exciton emission and whose energy blueshifts with increasing excitation power density, until it is completely quenched due to the complete screening of the internal electric field. Time-resolved measurements show that the emission arising from the two-dimensional hole gas can be assigned to the recombination of holes in the potential well with electrons located in the top GaN as well as electron from the bottom AlGaN, each of them displaying different decay times due to unequal electric fields. Besides the optical demonstration of a two-dimensional hole gas in a nitride-based heterostructure, our work highlights the optical recombination processes involved in the emission from such a hole gas.
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Submitted 20 December, 2023;
originally announced December 2023.
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Engineering Large Anisotropic Magnetoresistance in La0.7Sr0.3MnO3 Films at Room Temperature
Authors:
Paolo Perna,
Davide Maccariello,
Fernando Ajejas,
Ruben Guerrero,
Laurence Méchin,
Stephane Flament,
Jacobo Santamaria,
Rodolfo Miranda,
Julio Camarero
Abstract:
The magnetoresistance (MR) effect is widely employed in technologies that pervade our world from magnetic reading heads to sensors. Diverse contributions to MR, such as anisotropic, giant, tunnel, colossal, and spin-Hall, are revealed in materials depending on the specific system and measuring configuration. Half-metallic manganites hold promise for spintronic applications but the complexity of co…
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The magnetoresistance (MR) effect is widely employed in technologies that pervade our world from magnetic reading heads to sensors. Diverse contributions to MR, such as anisotropic, giant, tunnel, colossal, and spin-Hall, are revealed in materials depending on the specific system and measuring configuration. Half-metallic manganites hold promise for spintronic applications but the complexity of competing interactions has not permitted the understanding and control of their magnetotransport properties to enable the realization of their technological potential. Here we report on the ability to induce a dominant switchable magnetoresistance in La0.7Sr0.3MnO3 epitaxial films, at room temperature (RT). By engineering an extrinsic magnetic anisotropy, we show a large enhancement of anisotropic magnetoresistance (AMR) which leads to, at RT, signal changes much larger than the other contributions such as the colossal magnetoresistance (CMR). The dominant extrinsic AMR exhibits large variation in the resistance in low field region, showing high sensitivity to applied low magnetic fields. These findings have a strong impact on the real applications of manganite based devices for the high-resolution low field magnetic sensors or spintronics.
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Submitted 26 November, 2018;
originally announced November 2018.
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Room temperature biaxial magnetic anisotropy in La0.67Sr0.33MnO3 thin films on SrTiO3 buffered MgO (001) substrates for spintronic applications
Authors:
Sandeep Kumar Chaluvadi,
Fernando Ajejas,
Pasquale Orgiani,
Olivier Rousseau,
Giovanni Vinai,
Aleksandr Yu Petrov,
Piero Torelli,
Alain Pautrat,
Julio Camarero,
Paolo Perna,
Laurence Mechin
Abstract:
Spintronics exploits the magnetoresistance effects to store or sense the magnetic information. Since the magnetoresistance strictly depends on the magnetic anisotropy of the system, it is fundamental to set a defined anisotropy to the system. Here, we investigate by means of vectorial Magneto-Optical Kerr Magnetometry (v-MOKE), half-metallic La0.67Sr0.33MnO3 (LSMO) thin films that exhibit at room…
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Spintronics exploits the magnetoresistance effects to store or sense the magnetic information. Since the magnetoresistance strictly depends on the magnetic anisotropy of the system, it is fundamental to set a defined anisotropy to the system. Here, we investigate by means of vectorial Magneto-Optical Kerr Magnetometry (v-MOKE), half-metallic La0.67Sr0.33MnO3 (LSMO) thin films that exhibit at room temperature pure biaxial magnetic anisotropy if grown onto MgO (001) substrate with a thin SrTiO3 (STO) buffer. In this way, we can avoid unwanted uniaxial magnetic anisotropy contributions that may be detrimental for specific applications. The detailed study of the angular evolution of the magnetization reversal pathways, critical fields (coercivity and switching) allows for disclosing the origin of the magnetic anisotropy, which is magnetocrystalline in nature and shows four-fold symmetry at any temperature.
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Submitted 12 October, 2018;
originally announced October 2018.
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Ion irradiated YBa2Cu3O7 nano-meanders for superconducting single photon detectors
Authors:
P. Amari,
C. Feuillet-Palma,
A. Jouan,
F. Couedo,
N. Bourlet,
E. Géron,
M. Malnou,
L. Méchin,
A. Sharafiev,
J. Lesueur,
N. Bergeal
Abstract:
We report the fabrication of few hundred microns long, hundreds of nanometers wide and 30 nm thick meanders made from YBa2CU3O7. Thin films protected by a 8 nm-thick Ce02 cap layer have been patterned by high energy (a few tens of keV) oxygen ion irradiation through photoresist masks. DC and RF characterizations outline good superconducting properties of nano-meanders that could be used as Superco…
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We report the fabrication of few hundred microns long, hundreds of nanometers wide and 30 nm thick meanders made from YBa2CU3O7. Thin films protected by a 8 nm-thick Ce02 cap layer have been patterned by high energy (a few tens of keV) oxygen ion irradiation through photoresist masks. DC and RF characterizations outline good superconducting properties of nano-meanders that could be used as Superconducting Single Photon Detectors (SSPD). By mean of a resonant method, their inductance, which mainly sets the maximum speed of these devices, has been measured on a wide range of temperature. It compares favorably with expected values calculated from the geometry of the meanders and the known London penetration depth in YBa2CU3O7.
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Submitted 13 January, 2017; v1 submitted 22 December, 2016;
originally announced December 2016.
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Tailoring magnetic anisotropy in epitaxial half metallic La0.7Sr0.3MnO3 thin films
Authors:
P. Perna,
C. Rodrigo,
E. Jiménez,
F. J. Teran,
L. Méchin,
N. Mikuszeit,
J. Camarero,
R. Miranda
Abstract:
We present a detailed study on the magnetic properties, including anisotropy, reversal fields, and magnetization reversal processes, of well characterized half-metallic epitaxial La0.7Sr0.3MnO3 (LSMO) thin films grown onto SrTiO3 (STO) substrates with three different surface orientations, i.e. (001), (110) and (1-18). The latter shows step edges oriented parallel to the [110] (in-plane) crystallog…
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We present a detailed study on the magnetic properties, including anisotropy, reversal fields, and magnetization reversal processes, of well characterized half-metallic epitaxial La0.7Sr0.3MnO3 (LSMO) thin films grown onto SrTiO3 (STO) substrates with three different surface orientations, i.e. (001), (110) and (1-18). The latter shows step edges oriented parallel to the [110] (in-plane) crystallographic direction. Room temperature high resolution vectorial Kerr magnetometry measurements have been performed at different applied magnetic field directions in the whole angular range. In general, the magnetic properties of the LSMO films can be interpreted with just the uniaxial term with the anisotropy axis given by the film morphology, whereas the strength of this anisotropy depends on both structure and film thickness. In particular, LSMO films grown on nominally flat (110)-oriented STO substrates presents a well defined uniaxial anisotropy originated from the existence of elongated in-plane [001]-oriented structures, whereas LSMO films grown on nominally flat (001)-oriented STO substrates show a weak uniaxial magnetic anisotropy with the easy axis direction aligned parallel to residual substrate step edges. Elongated structures are also found for LSMO films grown on vicinal STO(001) substrates. These films present a well-defined uniaxial magnetic anisotropy with the easy axis lying along the step edges and its strength increases with the LSMO thickness. It is remarkable that this step-induced uniaxial anisotropy has been found for LSMO films up to 120 nm thickness. Our results are promising for engineering novel half-metallic magnetic devices that exploit tailored magnetic anisotropy.
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Submitted 9 March, 2011; v1 submitted 3 May, 2010;
originally announced May 2010.
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Mesoscopic electronic heterogeneities in the transport properties of V2O3 thin films
Authors:
C. Grygiel,
A. Pautrat,
W. C. Sheets,
W. Prellier,
B. Mercey,
L. Mechin
Abstract:
The spectacular metal-to-insulator transition of V2O3 can be progressively suppressed in thin film samples. Evidence for phase separation was observed using microbridges as a mesoscopic probe of transport properties where the same film possesses domains that exhibit a metal-to-insulator transition with clear first order features or remain metallic down to low temperatures. A simple model consist…
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The spectacular metal-to-insulator transition of V2O3 can be progressively suppressed in thin film samples. Evidence for phase separation was observed using microbridges as a mesoscopic probe of transport properties where the same film possesses domains that exhibit a metal-to-insulator transition with clear first order features or remain metallic down to low temperatures. A simple model consisting of two parallel resistors can be used to quantify a phase coexistence scenario explaining the measured macroscopic transport properties. The interaction between film and substrate is the most plausible candidate to explain this extended phase coexistence as shown by a correlation between the transport properties and the structural data.
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Submitted 23 October, 2008; v1 submitted 28 July, 2008;
originally announced July 2008.
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Nonresonant microwave absorption in epitaxial La-Sr-Mn-O films and its relation to colossal magnetoresistance
Authors:
M. Golosovsky,
P. Monod,
P. K. Muduli,
R. C. Budhani,
L. Mechin,
P. Perna
Abstract:
We study magnetic-field-dependent nonresonant microwave absorption and dispersion in thin La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ films and show that it originates from the colossal magnetoresistance. We develop the model for magnetoresistance of a thin ferromagnetic film in oblique magnetic field. The model accounts fairly well for our experimental findings, as well as for results of other researchers. W…
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We study magnetic-field-dependent nonresonant microwave absorption and dispersion in thin La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ films and show that it originates from the colossal magnetoresistance. We develop the model for magnetoresistance of a thin ferromagnetic film in oblique magnetic field. The model accounts fairly well for our experimental findings, as well as for results of other researchers. We demonstrate that nonresonant microwave absorption is a powerful technique that allows contactless measurement of magnetic properties of thin films, including magnetoresistance, anisotropy field and coercive field.
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Submitted 2 September, 2007;
originally announced September 2007.
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Resistive hystersis effects in perovskite oxide-based heterostructure junctions
Authors:
M. P. Singh,
L. Mechin,
W. Prellier,
M. Maglione
Abstract:
In this paper, we report the electrical and structural properties of the oxide-based metal/ferroelectric/metal (MFM) junctions. The heterostructures are composed of ultrathin layers of La0.7Ca0.3MnO3 (LCMO) as a metallic layer and, BaTiO3 (BTO) as a ferroelectric layer. Junction based devices, having the dimensions of 400 x 200 micom2, have been fabricated upon LCMO/BTO/LCMO heterostructures by…
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In this paper, we report the electrical and structural properties of the oxide-based metal/ferroelectric/metal (MFM) junctions. The heterostructures are composed of ultrathin layers of La0.7Ca0.3MnO3 (LCMO) as a metallic layer and, BaTiO3 (BTO) as a ferroelectric layer. Junction based devices, having the dimensions of 400 x 200 micom2, have been fabricated upon LCMO/BTO/LCMO heterostructures by photolithography and Ar-ion milling technique. The DC current-voltage (I-V) characteristics of the MFM junctions were carried out. At 300 K, the devices showed the linear (I-V) characteristics, whereas at 77 K, (I-V) curves exhibited some reproducible switching behaviours with well-defined remnant currents. The resulting resistance modulation is very different from what was already reported in ultrathin ferroelectric layers displaying resistive switching. A model is presented to explain the datas
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Submitted 6 October, 2006;
originally announced October 2006.
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Correlation between structure and properties in multiferroic La$_{0.7}$Ca$_{0.3}$MnO$_3$/BaTiO$_3$ superlattices
Authors:
M. P. Singh,
W. Prellier,
L. Mechin,
Ch. Simon,
B. Raveau
Abstract:
Superlattices composed of ferromagnetics, namely La$_{0.7}$Ca$_{0.3}$MnO$_3$ (LCMO), and ferroelectrics, namely, BaTiO$_3$(BTO) were grown on SrTiO$_3$ at 720$^o$C by pulsed laser deposition process. While the out-of-plane lattice parameters of the superlattices, as extracted from the X-ray diffraction studies, were found to be dependent on the BTO layer thickness, the in-plane lattice parameter…
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Superlattices composed of ferromagnetics, namely La$_{0.7}$Ca$_{0.3}$MnO$_3$ (LCMO), and ferroelectrics, namely, BaTiO$_3$(BTO) were grown on SrTiO$_3$ at 720$^o$C by pulsed laser deposition process. While the out-of-plane lattice parameters of the superlattices, as extracted from the X-ray diffraction studies, were found to be dependent on the BTO layer thickness, the in-plane lattice parameter is almost constant. The evolution of the strains, their nature, and their distribution in the samples, were examined by the conventional sin$^2ψ$ method. The effects of structural variation on the physical properties, as well as the possible role of the strain on inducing the multiferroism in the superlattices, have also been discussed.
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Submitted 7 December, 2005;
originally announced December 2005.
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Effect of ferroelectric layers on the magnetocapacitance properties of superlattices-based oxide multiferroics
Authors:
M. P. Singh,
W. Prellier,
L. Mechin,
W. Prellier
Abstract:
A series of superlattices composed of ferromagnetic La$_{0.7}$Ca$_{0.3}$MnO$_3$ (LCMO) and ferroelectric/paraelectric Ba$_{1-x}$Sr$_x$TiO$_3$ (0$\leq $x$\leq $1) were deposited on SrTiO$_3$ substrates using the pulsed laser deposition. Films of epitaxial nature comprised of spherical mounds having uniform size are obtained. Magnetotransport properties of the films reveal a ferromagnetic Curie te…
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A series of superlattices composed of ferromagnetic La$_{0.7}$Ca$_{0.3}$MnO$_3$ (LCMO) and ferroelectric/paraelectric Ba$_{1-x}$Sr$_x$TiO$_3$ (0$\leq $x$\leq $1) were deposited on SrTiO$_3$ substrates using the pulsed laser deposition. Films of epitaxial nature comprised of spherical mounds having uniform size are obtained. Magnetotransport properties of the films reveal a ferromagnetic Curie temperature in the range of 145-158 K and negative magnetoresistance as high as 30%, depending on the type of ferroelectric layers employed for their growth (\QTR{it}{i.e.} '\QTR{it}{x'} value). Ferroelectricity at temperatures ranging from 55 K to 105 K is also observed, depending on the barium content. More importantly, the multiferroic nature of the film is determined by the appearance of negative magnetocapacitance, which was found to be maximum around the ferroelectric transition temperature (3% per \QTR{it}{tesla}). These results are understood based on the role of the ferroelectric/paraelectric layers and strains in inducing the multiferroism.
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Submitted 18 November, 2005;
originally announced November 2005.
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Modulated optical reflectance measurements on La2/3Sr1/3MnO3 thin films
Authors:
Laurence Mechin,
Stephane Flament,
Andy Perry,
Darryl P. Almond,
Radoslav A. Chakalov
Abstract:
The modulated optical reflectance (MOR) measurement technique was applied to colossal magnetoresistive materials, in particular, La2/3Sr1/3MnO3 (LSMO) thin films. The contactless measurement scheme is prospective for many applications spanning from materials characterization to new devices like reading heads for magnetically recorded media. A contrasted room temperature surface scan of a 100 mic…
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The modulated optical reflectance (MOR) measurement technique was applied to colossal magnetoresistive materials, in particular, La2/3Sr1/3MnO3 (LSMO) thin films. The contactless measurement scheme is prospective for many applications spanning from materials characterization to new devices like reading heads for magnetically recorded media. A contrasted room temperature surface scan of a 100 microns wide 400 microns long bridge patterned into LSMO film provided preliminary information about the film homogeneity. Then the temperature was varied between 240 and 400 K, i.e. through the ferromagnetic to paramagnetic transition. A clear relation between the MOR signal measured as function of the temperature and the relative derivative of the resistivity up to the Curie temperature was observed. This relationship is fundamental for the MOR technique and its mechanism was explored in the particular case of LSMO. Analysis in the framework of the Drude model showed that, within certain conditions, the measured MOR signal changes are correlated to changes in the charge carrier concentration.
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Submitted 18 October, 2005;
originally announced October 2005.
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Uncooled bolometer response of a low noise La2/3Sr1/3MnO3 thin film
Authors:
Laurence Mechin,
Jean-Marc Routoure,
Bruno Guillet,
Fan Yang,
Stephane Flament,
Didier Robbes,
Radoslav A. Chakalov
Abstract:
We report measurements of the optical responses of a La2/3Sr1/3MnO3 (LSMO) sample at a wavelength of 533 nm in the 300-400 K range. The 200 nm thick film was grown by pulsed laser deposition on (100) SrTiO3 substrate and showed remarkably low noise. At 335 K the temperature coefficient of the resistance of a 100 micrometers wide 300 micrometers long LSMO line was 0.017 K-1 and the normalized Hoo…
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We report measurements of the optical responses of a La2/3Sr1/3MnO3 (LSMO) sample at a wavelength of 533 nm in the 300-400 K range. The 200 nm thick film was grown by pulsed laser deposition on (100) SrTiO3 substrate and showed remarkably low noise. At 335 K the temperature coefficient of the resistance of a 100 micrometers wide 300 micrometers long LSMO line was 0.017 K-1 and the normalized Hooge parameter was 9 e-30 m3, which is among the lowest reported values. We then measured an optical sensitivity at I = 5 mA of 10.4 V.W-1 and corresponding noise equivalent power (NEP) values of 8.1 e-10 W.Hz-1/2 and 3.3 e-10 W. Hz-1/2 at 30 Hz and above 1kHz, respectively. Simple considerations on bias current conditions and thermal conductance G are finally given for further sensitivity improvements using LSMO films. The performances were indeed demonstrated on bulk substrates with G of 10-3 W.K-1. One could expect a NEP reduction by three orders of magnitude if a membrane-type geometry was used, which makes this LSMO device competitive against commercially available uncooled bolometers.
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Submitted 7 October, 2005;
originally announced October 2005.
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Voltage noise and surface current fluctuations in the superconducting surface sheath
Authors:
J. Scola,
A. Pautrat,
C. Goupil,
L. Mechin,
V. Hardy,
Ch. Simon
Abstract:
We report the first measurements of the voltage noise in the surface superconductivity state of a type-II superconductor. We present strong evidences that surface vortices generates surface current fluctuations whose magnitude can be modified by the pinning ability of the surface. Simple two-stage mechanism governed by current conservation appears to describe the data. We conclude that large vol…
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We report the first measurements of the voltage noise in the surface superconductivity state of a type-II superconductor. We present strong evidences that surface vortices generates surface current fluctuations whose magnitude can be modified by the pinning ability of the surface. Simple two-stage mechanism governed by current conservation appears to describe the data. We conclude that large voltage fluctuations induced by surface vortices exist while the bulk is metallic. Furthermore, this experiment shows that sole surface current fluctuations can account for the noise observed even in the presence of vortices in the bulk.
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Submitted 31 May, 2005;
originally announced May 2005.
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Influence of pulsed laser deposition growth conditions on the thermoelectric properties of Ca3Co4O9 thin films
Authors:
H. Eng,
W. Prellier,
S. Hebert,
D. Grebille,
L. Mechin,
B. Mercey
Abstract:
Thin films of the misfit cobaltite Ca3Co4O9 were grown on (0001)-oriented (c-cut) sapphire substrates, using the pulsed-laser deposition techniques. The dependence of the thermoelectric/transport properties on the film growth conditions was investigated
Thin films of the misfit cobaltite Ca3Co4O9 were grown on (0001)-oriented (c-cut) sapphire substrates, using the pulsed-laser deposition techniques. The dependence of the thermoelectric/transport properties on the film growth conditions was investigated
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Submitted 7 October, 2004;
originally announced October 2004.
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Investigation of laser ablated ZnO thin films grown with Zn metal target: a structural study
Authors:
A. Fouchet,
W. Prellier,
B. Mercey,
L. Mechin,
V. N. Kulkarni,
T. Venkatesan
Abstract:
High quality ZnO thin films were gown using the pulsed laser deposition technique on (0001) Al$_2$O$_3$ substrates in an oxidizing atmosphere, using a Zn metallic target. We varied the growth conditions such as the deposition temperature and the oxygen pressure. First, using a battery of techniques such as x-rays diffraction, Rutherford Backscattering spectroscopy and atomic force microscopy, we…
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High quality ZnO thin films were gown using the pulsed laser deposition technique on (0001) Al$_2$O$_3$ substrates in an oxidizing atmosphere, using a Zn metallic target. We varied the growth conditions such as the deposition temperature and the oxygen pressure. First, using a battery of techniques such as x-rays diffraction, Rutherford Backscattering spectroscopy and atomic force microscopy, we evaluated the structural quality, the stress and the degree of epitaxy of the films. Second, the relations between the deposition conditions and the structural properties, that are directly related to the nature of the thin films, are discussed qualitatively. Finally, a number of issues on how to get good-quality ZnO films are addressed.
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Submitted 27 May, 2004;
originally announced May 2004.
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Quantitative analysis of the critical current due to vortex pinning by surface corrugation
Authors:
Alain Pautrat,
J. Scola,
C. Goupil,
Ch. Simon,
C. Villard,
B. Domenges,
Y. Simon,
Ch. Guilpin,
L. Mechin
Abstract:
The transport critical current of a Niobium (Nb) thick film has been measured for a large range of magnetic field. Its value and variation are quantitatively described in the framework of the pinning of vortices due to boundary conditions at the rough surface, with a contact angle well explained by the spectral analysis of the surface roughness. Increasing the surface roughness using a Focused I…
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The transport critical current of a Niobium (Nb) thick film has been measured for a large range of magnetic field. Its value and variation are quantitatively described in the framework of the pinning of vortices due to boundary conditions at the rough surface, with a contact angle well explained by the spectral analysis of the surface roughness. Increasing the surface roughness using a Focused Ion Beam results also in an increase of the superficial critical current.
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Submitted 14 April, 2004;
originally announced April 2004.
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High performance temperature controller: application to the excess noise measurements of YBCO thermometers in the transition region
Authors:
B. Guillet,
L. Mechin,
D. Robbes
Abstract:
Dedicated read-out electronics was developed for low impedance resistive thermometers. Using this high performance temperature controller, the temperature dependence of the excess noise of a YBa2Cu307-d (YBCO) sample in the superconducting transition was monitored as a function of the current bias. The noise could reach 3.10-8 K Hz-1/2 at 1 Hz, 5 mA bias and 90 K.
Dedicated read-out electronics was developed for low impedance resistive thermometers. Using this high performance temperature controller, the temperature dependence of the excess noise of a YBa2Cu307-d (YBCO) sample in the superconducting transition was monitored as a function of the current bias. The noise could reach 3.10-8 K Hz-1/2 at 1 Hz, 5 mA bias and 90 K.
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Submitted 26 May, 2003; v1 submitted 20 May, 2003;
originally announced May 2003.