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116
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Introduction
Skills and Expertise
Additional affiliations
January 2009 - present
"Institute of Light and Matter", UMR5306, CNRS,UCB Lyon 1
Position
- CNRS
January 2007 - present
Laboratoire Léon Brillouin, UMR12, CNRS, CEA
Position
- CNRS
January 2004 - December 2007
Publications
Publications (116)
Exploiting the structural complexity of crystals at the scale of their unit cell is a well-established strategy in the search for efficient materials for energy conversion, which aims at disentangling and separately engineering heat and charge transport. This route has resulted in the discovery of clathrates with exceptionally low lattice thermal c...
PECVD amorphous silicon nitride (a-SiNx) films are largely used into the dielectric stacks of integrated circuits, as passivation or capping layers, and are today an important alternative to silicon for integrated nonlinear optical applications, such as waveguides. In such applications, a-SiNx presents also the advantage of having a very low therma...
The impact of epitaxial strain on the structural, electronic, and thermoelectric properties of p-type transparent Sr-doped LaCrO3 thin films has been investigated. For this purpose, high-quality fully strained La0.75Sr0.25CrO3 (LSCO) epitaxial thin films were grown by molecular beam epitaxy on three different (pseudo)cubic (001)-oriented perovskite...
The low and weakly temperature-varying lattice thermal conductivity, κL(T), in crystals with a complex unit cell such as type-I clathrates is assumed to originate from a reduced momentum and energy space available for propagative lattice vibrations, which is caused by the occurrence of low-energy optical phonon modes. In the context of ab initio se...
Combining inelastic neutron and x-ray scattering with atomic scale simulation, we report on a comprehensive study of the lattice dynamics and its relationship with the low thermal conductivity of the o-Al13Co4 phase, a periodic approximant (about 100 atoms per cell) to a decagonal quasicrystal. The obtained experimental data, phonon lifetimes, and...
The reduction of dimensionality is an efficient pathway to boost the performances of thermo-electric materials, it leads to the quantum confinement of the carriers and thus to large Seebeck coefficients (S) and it also suppresses the thermal conductivity by increasing the phonon scattering processes. However, quantum confinement in superlattices is...
The reduction of dimensionality is an efficient pathway to boost the performances of thermoelectric materials, it leads to the quantum confinement of the carriers and thus to large Seebeck coefficients (S) and it also suppresses the thermal conductivity by increasing the phonon scattering processes. However, quantum confinement in superlattices is...
Engineering lattice thermal conductivity requires to control the heat carried by atomicvibration waves, the phonons. The key parameter for quantifying it is the phonon lifetime, limiting the travelling distance, whose determination is however at the limits of instrumentalcapabilities. Here, we show the achievement of a direct quantitative measureme...
Engineering lattice thermal conductivity requires to control the heat carried by atomicvibration waves, the phonons. The key parameter for quantifying it is the phonon lifetime, limiting the travelling distance, whose determination is however at the limits of instrumentalcapabilities. Here, we show the achievement of a direct quantitative measureme...
A particularly promising pathway to enhance the efficiency of thermoelectric materials lies in the use of resonant states, as suggested by experimentalists and theorists alike. In this paper, we go over the mechanisms used in the literature to explain how resonant levels affect the thermoelectric properties, and we suggest that the effects of hybri...
In the last years new composite materials made of a metallic glass matrix with embedded nanocrystals have arisen as a promising alternative to the metallic glasses, due to their higher hardness. Although the effects of a partial nano-crystallization onto mechanical and magnetic properties have been widely investigated, nothing is known about therma...
Thermoelectric materials are opening a promising pathway to address energy conversion issues governed by a competition between thermal and electronic transport. Improving the efficiency is a difficult task, a challenge that requires new strategies to unearth optimized compounds. We present a theory of thermoelectric transport in electron doped SrTi...
High-quality thermoelectric La0.2Sr0.8TiO3 (LSTO) films, with thicknesses ranging from 20 nm to 0.7 μm, have been epitaxially grown on SrTiO3(001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1°), and present very low electrical resistivity (<5...
High-quality thermoelectric LaxSr1-xTiO3 (LSTO) layers (here with x = 0.2), with thicknesses ranging from 20 nm to 700 nm, have been epitaxially grown on SrTiO3(001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1{\deg}), and present very low ele...
Thermoelectric materials are opening a promising pathway to address energy conversion issues governed by a competition between thermal and electronic transport. Improving the efficiency is a difficult task, a challenge that requires new strategies to unearth optimized compounds. We present a theory of thermoelectric transport in electron doped SrTi...
Stability studies by ab-initio calculations for the best-known binary Ba-Si clathrates reveal that Ba24Si100 is the most stable composition and that the latter can be stabilized in a relatively small energy range, of the order of a few kJ/mol.at. This suggested alternative synthesis routes, easier and cheaper to the commonly used high pressure-high...
High-throughput DFT calculations are used to predict the thermodynamic stability of ternary type I Si clathrates.
We use computational high-throughput techniques to study the thermodynamic stability of ternary type-I Si clathrates. Two strategies to stabilize the structures are investigated: through endohedral doping of the 2a and 6d Wyckoff positions (located at the center of the small and the large cages respectively), and by substituting the Si 6c positions...
We report an angle-resolved photoemission study of the charge stripe ordered
La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$ system. A comparative and quantitative line
shape analysis is presented as the system evolves from the overdoped regime
into the charge ordered phase. On the overdoped side ($x=0.20$), a normal state
anti-nodal spectral gap opens upon co...
We report on the magnetic properties of the B20 polycrystalline MnGe compound synthesized under high-temperature and high-pressure conditions. From isothermal ac susceptibility experiments, we found the presence of several different magnetic-field–induced phases presenting similarities with those in the isostructural compounds MnSi and FeGe but wit...
The ability of some materials with a perfectly ordered crystal structure to mimic the heat conduction of amorphous solids is a remarkable physical property that finds applications in numerous areas of materials science, for example, in the search for more efficient thermoelectric materials that enable to directly convert heat into electricity. Here...
An alternative approach for high-speed temperature measurement with micrometer-scale spatial resolution based on the luminescence of Ni-doped diamond micro-particles is described. Under picosecond pulsed laser excitation, these particles exhibit intense green luminescence; the lifetime of this luminescence decreases by several orders of magnitude u...
The strategy to react SnCl4 with M(OR)x provided a convenient and quantitative approach to new heterobimetallics with simple addition formula, [SnCl4M(OR)x(HOR)y] (M = Ti, Nb, Ta; R = Et, Pri, x = 4, 5; y = 0-2) or sometimes an oxo complex [SnCl3(O)Ti2(OPri)7(HOPri)2]. The alcoholysis reactions of these heterometallics afforded mixed alkoxo complex...
Perfectly crystalline solids are excellent heat conductors. Prominent counterexamples are intermetallic clathrates, guest-host systems with a high potential for thermoelectric applications due to their ultralow thermal conductivities. Our combined experimental and theoretical investigation of the lattice dynamics of a particularly simple binary rep...
Nodal angle resolved photoemission spectra taken on overdoped
La$_{1.77}$Sr$_{0.23}$CuO$_4$ are presented and analyzed. It is proven that the
low-energy excitations are true Landau Fermi-liquid quasiparticles. We show
that momentum and energy distribution curves can be analyzed self-consistently
without quantitative knowledge of the bare band dispe...
High-temperature superconductivity emerges from an un-conventional metallic state. This has stimulated strong efforts to understand exactly how Fermi liquids breakdown and evolve into an un-conventional metal. A fundamental question is how Fermi liquid quasiparticle excitations break down in momentum space. Here we show, using angle-resolved photoe...
We performed magnetic and ferroelectric measurements, associated with Landau
theory and symmetry analysis, in order to clarify the situation of the YMnO3
system, a classical example of type I multiferroics. We found that the only
magnetic group compatible with all experimental data (neutrons scattering,
magnetization,polarization, dielectric consta...
Complex Metallic Alloys (CMAs) are metallic solids of high structural complexity, consisting of large numbers of atoms in their unit cells. Consequences of this structural complexity are manifold and give rise to a variety of exciting physical properties. The impact that such structural complexity may have on the lattice dynamics will be discussed....
One of the key requirements for good thermoelectric materials is a low lattice thermal conductivity. Here we present a combined neutron scattering and theoretical investigation of the lattice dynamics in the type I clathrate system Ba-Ge-Ni, which fulfills this requirement. We observe a strong hybridization between phonons of the Ba guest atoms and...
One of the key requirements for good thermoelectric materials is a low
lattice thermal conductivity. Here we present a combined neutron scattering and
theoretical investigation of the lattice dynamics in the type I clathrate
system Ba-Ge-Ni, which fulfills this requirement. We observe a strong
hybridization between phonons of the Ba guest atoms and...
Aiming to shed light on the possible existence of hybrid phonon-magnon excitations in multiferroic manganites, neutron scattering
measurements have been undertaken at LLB and ILL on the particular case of hexagonal YMnO3. Our experiments focused on a transverse acoustic phonon mode polarized along the ferroelectric axis. The neutron data show
that...
Raman spectroscopy is a powerful tool to study the intrinsic vibrational characteristics of crystals, and, therefore, it is an adequate technique to explore phase transitions of carbon under pressure. However, the diamond-anvil cell, which is used in experiments to apply pressure, appears as a broad intense feature in the spectra. This feature lies...
Through a systematic structural search we found an allotrope of carbon with Cmmm symmetry which we predict to be more stable than graphite for pressures above 10 GPa. This material, which we refer to as Z-carbon, is formed by pure sp(3) bonds and it provides an explanation to several features in experimental x-ray diffraction and Raman spectra of g...
We performed magnetic and ferroelectric measurements, first principle
calculations and Landau theory analysis on hexagonal YMnO3. The polarization
and the AFM order parameter were found to present different temperature
dependence at TN. A linear coupling between these two order parameters is thus
forbidden in the Landau theory and P63cm cannot be t...
We have investigated how a magnetic field applied perpendicular to the CuO 2 planes of the near-optimally hole-doped high-temperature superconductor La 1.855Sr 0.145CuO 4 (T c ≈ 36 K) influences the low-energy magnetic excitation spectrum. Our detailed single-crystal neutron scattering experiments reveal that the gap to magnetic excitations falls o...
Recent ab initio studies have theoretically predicted room temperature ferromagnetism in several oxide materials of the type AO(2) in which the cation A(4+) is substituted by a non-magnetic element of the 1 A column. Our purpose is to address experimentally the possibility of magnetism in Ti(1-x)K(x)O(2) compounds. The samples have been synthesized...
A class of metal disilicides (of the form $X$Si${}_{2}$, where $X$ is a divalent metal) crystallizes in the EuGe${}_{2}$ structure, formed by hexagonal corrugated silicon planes intercalated with metal atoms. These compounds are superconducting like other layered superconductors, such as MgB${}_{2}$. Moreover, their properties can be easily tuned e...
In a recent letter, it has been predicted within first principle studies that Mn-doped ZrO 2 compounds could be good candidates for spintronics application because expected to exhibit ferromagnetism far beyond room temperature. Our purpose is to address this issue experimentally for Mn-doped tetragonal zirconia. We have prepared polycrystalline sam...
We present an angle-resolved photoelectron spectroscopy study of YBa2Cu3O7-δ films in situ grown by pulsed laser deposition. We have successfully produced underdoped surfaces with ordered oxygen vacancies within the CuO chains resulting in a clear ortho-II band folding of the Fermi surface. This indicates that order within the CuO chains affects th...
We present a joint experimental and theoretical study of the superconducting phase of the layered binary silicide BaSi(2). Compared with the AlB(2) structure of graphite or diboridelike superconductors, in the hexagonal structure of binary silicides the sp(3) arrangement of silicon atoms leads to corrugated sheets. Through a high-pressure synthesis...
As silicon is the basis of conventional electronics, so strontium titanate (SrTiO(3)) is the foundation of the emerging field of oxide electronics. SrTiO(3) is the preferred template for the creation of exotic, two-dimensional (2D) phases of electron matter at oxide interfaces that have metal-insulator transitions, superconductivity or large negati...
We present an angle-resolved photoelectron spectroscopy study of YBa2Cu3O7-delta films in situ grown by pulsed laser deposition. We have successfully produced underdoped surfaces with ordered oxygen vacancies within the CuO chains resulting in a clear ortho-II band folding of the Fermi surface. This indicates that order within the CuO chains affect...
A systematic angle-resolved photoemission study of the electronic structure of La2−xSrxCuO4 in a wide doping range is presented in this paper. In addition to the main energy band, we observed a weaker additional band, the (π, π) folded band, which shows unusual doping dependence. The appearance of the folded band suggests that a Fermi surface recon...
We have investigated the electronic states in quasi-one-dimensional CuO chains by microprobe angle resolved photoemission spectroscopy. We find that the quasiparticle Fermi surface consists of six disconnected segments, consistent with recent theoretical calculations that predict the formation of narrow, elongated Fermi surface pockets for coupled...
Ab initio studies have theoretically predicted room-temperature ferromagnetism in crystalline SnO2, ZrO2, and TiO2 doped with nonmagnetic element from the 1A column as K and Na. Our purpose is to address experimentally the possibility of magnetism in both Sn1−xKxO2 and Sn1−xCaxO2 compounds. The samples have been prepared using equilibrium methods o...
In this paper, we first give a concise overview of recent experimental and theoretical work dealing with “electronic liquid-crystal states” which spontaneously break different symmetries of the CuO2 layers of high-T
c cuprates, with an emphasis on evidence in the spin excitation spectrum. Then we describe the importance of using twin-free samples t...
In a recent letter, it has been predicted within first principle studies that Mn-doped ZrO2 compounds could be good candidate for spintronics application because expected to exhibit ferromagnetism far beyond room temperature. Our purpose is to address this issue experimentally for Mn-doped tetragonal zirconia. We have prepared polycrystalline sampl...
Similar to silicon that is the basis of conventional electronics, strontium titanate (SrTiO3) is the bedrock of the emerging field of oxide electronics. SrTiO3 is the preferred template to create exotic two-dimensional (2D) phases of electron matter at oxide interfaces, exhibiting metal-insulator transitions, superconductivity, or large negative ma...
In high-temperature copper oxide superconductors, a novel magnetic order associated with the pseudogap phase has been identified in two different cuprate families over a wide region of temperature and doping. We report here the observation below 120 K of a similar magnetic ordering in the archetypal cuprate La(2-x)Sr(x)CuO4 (LSCO) system for x=0.08...
In high-temperature copper oxide superconductors, a novel magnetic order associated with the pseudogap phase has been identified in two different cuprate families over a wide region of temperature and doping. We report here the observation below 120 K of a similar magnetic ordering in the archetypal cuprate La2-xSrxCuO4 (LSCO) system for x=0.085. I...
In high temperature copper oxides superconductors, a novel magnetic order associated with the pseudogap phase has been identified in two different cuprate families over a wide region of temperature and doping. We here report the observation below 120 K of a similar magnetic ordering in the archetypal cuprate ${\rm La_{2-x}Sr_xCuO_4}$ (LSCO) system...
Ab initio studies have theoretically predicted room temperature
ferromagnetism in crystalline SnO2, ZrO2 and TiO2 doped with non magnetic
element from the 1A column as K and Na. Our purpose is to address
experimentally the possibility of magnetism in both Sn1-xKxO2 and Sn1-xCaxO2
compounds. The samples have been prepared using equilibrium methods o...