Vincent Renard

Université Grenoble Alpes · Department of Physics

Metallic contamination was key to the discovery of semiconductor nanowires, but today it stands in the way of their adoption by the semiconductor industry. This is because many of the metallic catalysts required for nanowire growth are not compatible with standard CMOS (complementary metal oxide semiconductor) fabrication processes. Nanowire synthe...

We demonstrate that stacking layered materials allows a novel type of strain engineering where each layer is strained independently, which we call heterostrain. We combine detailed structural and spectroscopic measurements with tight-binding calculations to show that small uniaxial heterostrain suppresses Dirac cones and leads to the emergence of f...

Electronic band structures dictate the mechanical, optical and electrical properties of crystalline solids. Their experimental determination is therefore of crucial importance for technological applications. While the spectral distribution in energy bands is routinely measured by various techniques, it is more difficult to access the topological pr...

The study of moiré engineering started with the advent of van der Waals heterostructures in which stacking two‐dimensional layers with different lattice constants leads to a moiré pattern controlling their electronic properties. The field entered a new era when it was found that adjusting the twist between two graphene layers led to strongly‐correl...

The moiré of twisted graphene bilayers can generate flat bands in which charge carriers do not possess enough kinetic energy to escape Coulomb interactions with each other, leading to the formation of novel strongly correlated electronic states. This exceptionally rich physics relies on the precise arrangement between the layers. Here, we survey pu...

We investigate superconducting gallium in its $\alpha$ phase using scanning tunneling microscopy and spectroscopy at temperatures down to about 100 mK. High-resolution tunneling spectroscopies using both superconducting and normal tips show that superconducting $\alpha$-Ga is accurately described by Bardeen-Cooper-Schrieffer theory, with a gap $\De...

Two-dimensional and van der Waals ferromagnets are ideal platform to study low-dimensional magnetism and proximity effects in van der Waals heterostructures. Their ultimate two-dimensional character also offers the opportunity to easily adjust their magnetic properties using strain or electric fields. Among 2D ferromagnets, the Cr 1 + xTe2 compound...

Fractional charges are one of the wonders of the fractional quantum Hall effect. Such objects are also anticipated in two-dimensional hexagonal lattices under time reversal symmetry—emerging as bound states of a rotating bond texture called a Kekulé vortex. However, the physical mechanisms inducing such topological defects remain elusive, preventin...

Two‐dimensional (2D) materials, such as transition metal dichalcogenides (TMDs), are ideal platforms for spin‐charge conversion (SCC) as they possess strong spin‐orbit coupling (SOC), reduced dimensionality and crystal symmetries as well as tuneable band structure, compared to metallic structures. Moreover, SCC can be tuned with the number of layer...

The study of moir\'e engineering started with the advent of van der Waals heterostructures in which stacking two-dimensional layers with different lattice constants leads to a moir\'e pattern controlling their electronic properties. The field entered a new era when it was found that adjusting the twist between two graphene layers led to strongly-co...

Fractional charges are one of the wonders of the fractional quantum Hall effect, a liquid of strongly correlated electrons in a large magnetic field. Fractional excitations are also anticipated in two-dimensional crystals of non-interacting electrons under time-reversal symmetry, as bound states of a rotating bond order known as Kekulé vortex. Howe...

Achieving large-scale growth of two-dimensional (2D) ferromagnetic materials with high Curie temperature TC and perpendicular magnetic anisotropy (PMA) is highly desirable for the development of ultracompact magnetic sensors and magnetic memories. In this context, van der Waals (vdW) Cr2Te3 appears to be a promising candidate. Bulk Cr2Te3 exhibits...

Terahertz (THz) Spintronic emitters based on ferromagnetic/metal junctions have become an important technology for the THz range, offering powerful and ultra-large spectral bandwidths. These developments have driven recent investigations of two-dimensional (2D) materials for new THz spintronic concepts. 2D materials, such as transition metal dichal...

Achieving large-scale growth of two-dimensional (2D) ferromagnetic materials with high Curie temperature (TC) and perpendicular magnetic anisotropy (PMA) is highly desirable for the development of ultra-compact magnetic sensors and magnetic memories. In this context, van der Waals (vdW) Cr2Te3 appears as a promising candidate. Bulk Cr2Te3 exhibits...

Unlike conventional two-dimensional (2D) semiconductor superlattices, moiré patterns in 2D materials are flexible and their electronic, magnetic, optical, and mechanical properties depend on their topography. Within a continuous+atomistic theory treating 2D materials as crystalline elastic membranes, we abandon the flat-membrane scenario usually as...

The Berry phase of wave functions is a key quantity to understand various low-energy properties of matter, among which electric polarisation, orbital magnetism, as well as topological and ultra-relativistic phenomena. Standard approaches to probe the Berry phase in solids rely on the electron dynamics in response to electromagnetic forces. In graph...

The moir\'e of twisted graphene bilayers can generate flat bands in which charge carriers do not posses enough kinetic energy to escape Coulomb interactions with each other leading to the formation of novel strongly correlated electronic states. This exceptionally rich physics relies on the precise arrangement between the layers.We survey published...

We report on the fabrication of a clean, stable in room atmosphere and superconducting surface consisting of graphene on tantalum carbide (TaC) obtained by high-temperature an- nealing of a tantalum thin film on SiC. Low temperature scanning tunnelling spectroscopy reveals that the surface is superconducting with a superconducting order parameter u...

In crystal growth, surfactants are additive molecules used in dilute amount or as dense, permeable layers to control surface morphologies. Here, we investigate the properties of a strikingly different surfactant: a two-dimensional and covalent layer with close atomic packing, graphene. Using in situ, real time electron microscopy, scanning tunnelin...

Van der Waals heterojunctions composed of graphene and transition metal dichalcogenides have gain much attention because of the possibility to control and tailor band structure, promising applications in two-dimensional optoelectronics and electronics. In this report, we characterized the van der Waals heterojunction MoSe2/few-layer graphene with a...

Establishing good electrical contacts to nanoscale devices is a major issue for modern technology and contacting 2D materials is no exception to the rule. One-dimensional edge-contacts to graphene were recently shown to outperform surface contacts but the method remains difficult to scale up. We report a resist-free and scalable method to fabricate...

A method for manufacturing a graphite layer on an interstitial carbide layer, includes depositing a metal layer formed by one or more metals on a carbide substrate, the metal layer being able to form an interstitial carbide, the metal layer at least partially covering the carbide substrate; performing a heat treatment during which a temperature hig...

Valleytronics is rapidly emerging as an exciting area of basic and applied research. In two dimensional systems, valley polarisation can dramatically modify physical properties through electron-electron interactions as demonstrated by such phenomena as the fractional quantum Hall effect and the metal-insulator transition. Here, we address the elec-...

We demonstrate that spin polarization and valley polarization have quantitatively similar effects on the resistivity of a two-dimensional electron gas in a silicon-on-insulator quantum well. In-so-doing, we also examine the dependence on disorder, leading to a coarse but global phenomenology of how the resistivity depends on its key parameters: spi...

The invention relates to a method for fabricating silicon and/or germanium nanowires on a substrate, comprising a step of bringing a precursor comprising silicon and/or a precursor comprising germanium into contact with a compound comprising copper oxide present on the said substrate, by means of which growth of nanowires takes place.

This document contains the supplemental material on the analysis of Weak Localization magneto-conductance. In particular it contains the code used to fit the weak localization in presence of intervalley scattering.

The fundamental properties of valleys are recently attracting growing attention due to electrons in new and topical materials possessing this degree-of-freedom and recent proposals for valleytronics devices. In silicon MOSFETs, the interest has a longer history since the valley degree of freedom had been identified as a key parameter in the observa...

Metallic behaviour in SOI quantum well with strong intervalley scattering - Supplementary information

This image represents an electron tomogram of a Silicon nanowire. For more information see the video in the manuscript V.T. Renard et al. Nature Nanotech 4, 654 - 657 (2009)

This video shows en electron tomogram acquired from a silicon nanowire starting with a volume view. A series of vertical slices through the 3D volume are then displayed in sequence. In the isosurface representations, the first threshold used corresponds to the intensity of the Si, hence showing the outer surface (in blue). A second threshold is def...

We report a non-monotonic and strongly temperature dependent magneto-resistance observed in clean quantum point contacts. At the same time the conductance of the point contact varies linearly with temperature. This unexpected behavior may be related to electron-electron interactions.

We examine the temperature dependence of resistivity in a two-dimensional electron system formed in a silicon-on-insulator quantum well. The device allows us to tune the valley splitting continuously in addition to the electron density. Our data provide a global picture of how the resistivity and its temperature dependence change with valley polari...

Conductive Bridging RAM (CBRAM) is a promising candidate for future non-volatile memories. This technology is based on the change of the cell’s resistive state, due to formation and dissolution of a metallic filament through an insulating layer. In this work we study Cu/SiO2 cells fabricated using standard back-end-of-line (BEOL) processes, making...

Despite the promising potential of nanomaterials, their co-integration with CMOS, especially in interconnection levels, remains challenging because their fabrication has to be done within severe constrains. These nanomaterials can be grown by catalytic Chemical Vapor Deposition but the catalyst should be compatible with Back-End-Of-Line (BEOL) proc...

We investigate the growth of the recently demonstrated composite material composed of vertically aligned carbon nanotubes capped by few graphene layers. We show that the carbon nanotubes grow epitaxially under the few graphene layers. By using a catalyst and gaseous carbon precursor different from those used originally we establish that such unconv...

We investigate electron tunneling between two GaAs accumulation two-dimensional layers separated by an (AlGa)As barrier which is modulation-doped with donors. A Coulomb pseudogap suppresses electron tunneling at the Fermi level and is induced by a magnetic field applied perpendicular to the accumulation layers. By measuring the tunnel current as a...

The invention relates to a method for fabricating silicon and/or germanium nanowires on a substrate, comprising a step of bringing a precursor comprising silicon and/or a precursor comprising germanium into contact with a compound comprising copper oxide present on the said substrate, by means of which growth of nanowires takes place.

CMOS compatible nanowires provide an interesting opportunity to integrate logic functions in interconnects levels. We report here the development of a method to grow silicon nanowire using back-end-of-line compatible copper-based catalysts. Our approach is based on oxidation of copper prior to growth and allows reducing silicon nanowire synthesis t...

We examine the effect of an in-plane magnetic field on the resistance of a 2-dimensional electron system confined in a silicon quantum well when the Fermi energy is tuned through the upper valley-subband edge while the electrons are otherwise valley-polarized. In contrast to previous experiments on valley-degenerate systems which only showed positi...

The electron tunneling is experimentally studied between two-dimensional electron gases (2DEGs) formed in a single-doped-barrier heterostructure in the magnetic fields directed perpendicular to the 2DEGs planes. It is well known that the quantizing magnetic field induces the Coulomb pseudogap suppressing the electron tunneling at Fermi level. In th...

An unusual increase of the conductance with temperature is observed in clean quantum point contacts for conductances larger than 2(e2/h). At the same time, a positive magnetoresistance arises at high temperatures. A model accounting for electron-electron interactions mediated by boundaries (scattering on Friedel oscillations) qualitatively describe...

We report an unusual increase with temperature of the conductance of clean quantum point contact at large conductance and . Numerical simulation including electron–electrons interactions qualitatively explains this observation. Besides, a positive magneto-resistance that could also be related to electron–electron interactions is measured.

In the present work we have investigated the transport properties in a number of Si/SiGe samples with antidot lattices of different periods. In samples with the lattice periods 700 nm and 850 nm we have observed the conventional low-field commensurability magnetoresistance (MR) peaks consistent with the previous observations in GaAs/AlGaAs and Si/S...

In the present work we have investigated the transport properties in a number of Si/SiGe samples with square antidot lattices of different periods. In samples with lattice periods equal to 700 nm and 850 nm we have observed the conventional low-field commensurability magnetoresistance peaks consistent with the previous observations in GaAs/AlGaAs a...

The interaction effects in the transport and magnetransport of two-dimensional electrons in AlGaAs/GaAs and Si/SiGe heterojunctions, were studies. Silicon structure metal-insulator-semiconductor (MIS) with a 2D EG and a Si/SiGe heterojunction with a 2D Eg were similar in their electronic spectra, but differed in the structure of the scattering pote...

A joint scientific session of the Physical Science Division of the Russian Academy of Sciences and the Joint Physical Society of the Russian Federation was held on 26 October 2006 at the conference room of the Lebedev Physics Institute, RAS. The following reports were presented at the session.(1) Pudalov V M (Lebedev Physics Institute, RAS) "Metal...

Ce mémoire présente l'étude des corrections quantiques à la conductivité d'un gaz d'électron bidimensionnel. Les échantillons ont été choisis de façon à permettre une comparaison optimale avec les modèles théoriques disponibles à l'heure actuelle. La première partie de l'étude expérimentale porte sur des gaz d'électrons de haute densité et de faibl...

We report an experimental study of quantum conductivity corrections in a low mobility, high density two-dimensional electron gas in an AlGaAs/GaAs/AlGaAs quantum well in a wide temperature range (1.5-110 K). This temperature range covers both the diffusive and the ballistic interaction regimes for our samples. It has been therefore possible to stud...

The work is devoted to interaction-induced magnetoresistance in a two-dimensional electron gas in a Si/SiGe heterostructure. Several types of magnetoresistance behavior are discussed including a magnetoresistance that changes sign with temperature. The data is analyzed using the recent theory of interaction-induced magnetoresistance for arbitrary t...

We report on the study of the quantum interference transport properties of a high density two dimensional electron gas in a AlGaN/GaN heterostructure. We show that the data are qualitatively well described by the theory of quantum correction to conductivity and scattering by phonons.

We studied the negative temperature-independent magnetoresistance in a high-density, two-dimensional electron gas in Alx Ga1-x N/GaN heterostructure. This magnetoresistance is attributed to the classical percolation of electrons in a random array of strong scatterers (interface roughness) on the background of the smooth impurity potential. The rati...

We present the study of the magnetoresitance (MR) in a two dimensional electron gas in a Si/SiGe heterostructure. We show that the sign of this MR can change with temperature depending on the sample. We analyze the observed magnetoresistance in terms of the recent theory of interaction induced MR (Phys. Rev. B, 69, 045313 (2003)).

In the present work we study the electron transport properties of small (≈ 100 nm) ring interferometers fabricated by the local anodic oxidation of a AlGaAs/GaAs heterostructures containing 2D electron gas. Owing to the small size of the rings the Aharonov-Bohm (AB) oscillations in them can be observed at temperatures as high as 9 K. It has been fo...

We have observed a large positive quasiclassical magnetoresistance (MR) in a high mobility two-dimensional electron gas in an AlGaAs∕GaAs heterostructure. The magnetoresistance is nonsaturating and increases with magnetic field as Δρxx∼Bα (α=0.9−1.2). In antidot lattices a nonmonotonic MR is observed. We show that in both cases this MR can be quali...

We report the first observation of the metal–insulator transition (MIT) in a two-dimensional electron gas (2DEG) in a Si/SiGe heterostructure at zero field. We have performed an analysis of the temperature dependence of conductivity and magnetoresistance of our sample on the metallic side of the transition using recent theories.

We observed a giant positive quasi-classical magnetoresistance (MR) of high mobility 2D electron gas in AlGaAs/GaAs heterostructure. The MR is non-saturating and increases with the magnetic field as rhoxx~Balpha (alpha=0.9-1.2). In antidot lattice a non-monotonic behavior is observed. We show that the MR in both cases is well described by the recen...

We experimentally study the parabolic negative magneto-resistance (NMR) in high density (Ns>1012cm−2) and low mobility (μ

Commensurability peaks in new kind of two-dimensional (2D) systems with artificial scatterers—2D electron gas in the array of diffusive and thermalizing scatterers (it was AuGeNi alloy dots)—was studied experimentally. It is shown that the position and the amplitude of these peaks are completely described by the model of pin-ball electron trajector...

We report magnetotransport properties ofelectrons in a new kind oftwo-dimensional electron system (2DES)—a narrow single quantum well with electron density so large that the electrons splash out ofthe well. We show that the system is a two-component 2D electron gas consisting ofvery low mobility (10^3 cm^2/Vs) main part ofthe electrons and very sma...

An experimental study of the two-, three-, and four-terminal resistance of a ballistic wire is carried out. The wire is fabricated on the basis of high-mobility 2D electron gas in an AlGaAs/GaAs heterojunction. Different behavior of mesoscopic fluctuations of multiterminal resistances is observed depending on the gate voltage and magnetic field. At...

We have studied the strain state, film and surface morphology of SiGe virtual substrates (Ge concentrations in-between 20% and 55%) grown by reduced pressure – chemical vapor deposition. The macroscopic degree of strain relaxation of those virtual substrates is equal to 97.2 ± 1.5%. The misfit dislocations generated to relax the lattice mismatch be...

In the present work we study the electron transport properties of small (≈ 100 nm) ring interferometers fabricated by the local anodic oxidation of a AlGaAs/GaAs heterostructures containing 2D electron gas. Owing to the small size of the rings the Aharonov-Bohm (AB) oscillations in them can be observed at temperatures as high as 9 K. It has been...

We have studied the strain state, film and surface morphology of SiGe virtual substrates grown by reduced pressure chemical vapour deposition (RP-CVD). The macroscopic strain relaxation and the Ge composition of those virtual substrates have been estimated in high resolution x-ray diffraction, using Omega-2Theta scans around the (004) and (224) ord...

We report the observation of a metal-insulator transition (MIT) in a two-dimensional electron gas (2DEG) in a Si/SiGe heterostructure at zero magnetic field. On going through the MIT we observe the corresponding evolution of the magnetic field induced transition between the insulating phase and the quantum Hall (QH) liquid state in the QH regime. S...