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The HYBRID group gathers condensed matter physicists exploring quantum states hosted by two-dimensional materials (graphene and transition metal dichalcogenides for instance). We focus on quantum states involving different kinds of excitations, electronic, phononic or magnonic, possibly related to strong interaction effects, and seek ways to tune these interactions. This is done via, e.g., electromagnetic fields, mechanical deformations, the proximity to magnetic or superconducting materials, or by controlling structural parameters such as the twist angle between two stacked 2D materials.
The group’s research currently deals with four class of effects, respectively relevant in (i) quantum optoelectronics, (ii) quantum engineering, (iii) optothermics and (iv) 2D ordering phenomena. We operate various equipments to probe these effects: low-temperature magnetotransport setups, optical spectroscopy measurement lines, and a comprehensive platform (2Dfab) for the fabrication of artificial 2D heterostacks. Besides, we have direct access to various growth, advanced nanocharacterizations, and nanofabrication facilities.
Vibrational properties of optoelectronics devices
Quantum engineering
Thermal properties of 2D systems
Surface physics with 2D materials
Optical phonons couple to electrons in most of the materials we investigate. Thus by studing optical phonons using spatially resolved Raman spectroscopy , we access their structure and electronic properties. Moreover, by combinig such a technique with photoluminescence / cathodoluminescence experiments, local probe measurements, and first principles calculations, we can address most of their physical properties . This analysis can be further enriched with Kelvin probe microscopy (coll. SyMMES) high magnetic field optical spectroscopy (col . LNCMI), or our-wave mixing spectroscopy ( coll. NPSC).
For example, we have addressed the prototypical dichalcogenide MoS2 (poorly understood due to strong disorder), developed encapsulation on strategies to eliminate this disorder and access the intrinsic excitonic properties, and thus understand better charge/energy transfers on others 2D materials.
We also study the optical gating of 1D and 2D materials using adsorbed chromophore molecules (coll. DCM) in order to address charge transfer down to the single electron tunneling at low temperature, and energy transfers related to excitonic effects.
Finally, electron-phonon coupling in some of the 1d and 2D Materials has a strong influence on their electronic and excitonic properties. Thus, we investigate the mechanism which enhances the phonon response and specially the role of the excitons localization in 1D systems. By probing the interplay between phonons and Fermi electrons we will be able to detect weak light signals at low temperature. This approach is generalized to VDW stacks of 2D materials with direct bandgaps.
The role of electron-phonon coupling in Charge density waves TaS2 family is also a part of our activity on 2D Materials. Some outstanding questions related to the coexistence of such an order with superconductivity at low dimensionality are one of challenging issues that we want to address. To reach this goal we use electronic transport and Raman spectroscopy which show strong signatures of the transitions.
We couple two dimensional materials to confined electromagnetic fields in order to study interacting quantum systems in different regimes.
In superconducting circuits, working with microwave photons, we integrate graphene in order to add gate tunability in such devices. More specifically, we have recently demonstrated a gate tunable Josephson parametric amplifier that operates at the quantum limit [1]. We are currently developing gate tunable superconducting Qubits, also based on a graphene Josephson junction.
In the optical domain, we integrate 2D transition metal dichalcogenides (TMDC) with microcavities. We focus on the interaction between excitations (i.e. excitons) which is peculiar in TMDC in order to demonstrate non-classical sources of photons [2].
Contact: julien.renard@neel.cnrs.fr
[1] G. Butseraen et al Nature Nanotechnology 17, 1147 (2022)
[2] P. Stepanov et al Phys. Rev. Lett. 126, 167401 (2021)
A monolayer transition metal dichalcogenides inserted in an optical microcavity
A graphene based Josephson junction can be inserted in a microwave cavity to allow gate tunability
Graphene exhibit an outstanding thermal transport properties. However, the mechanism of heat propagation is still lively discussed. Usually, the Fourier law is invoked to rationalize the observed properties, which assumes that the mean free path of heat carrier is much smaller that the sample size. Recent theoretical works show that this assumption is not correct in 2D materials.
We address the thermal properties of 2D membranes via versatile, non-invasive optical techniques, especially Raman spectroscopy in which intensity and energy of the Raman modes is temperature dependent. The originality of our approach is to use two lasers beams, one as a heater and the other one as a probe which allows us to spatially map the local temperature, doping and strain. The theory developed by our collaborator at IMPMC in Paris predicts signature pf ballistic transport at room temperature in Graphene. We are currently testing experimentally such prediction and work on phonon engineering using patterned 2D materials from C2N. collaborator.
We study the structure of 2D materials such as graphene, oxides, transition metal dichalcogenides, which we grow ourselves. This includes the study of moirés in epitaxial systems, of mechanical deformations, and the exploration of defects. These are key questions to understand the microscopic and macroscopic properties (optical, electronic, magnetic) of the materials (the defects’ response sometimes dominates in the material’s properties), to optimise the structural quality of the materials, and on a more fundamental perspective, to try and understand the very peculiar nature of structural order in 2D.
We often exploit interface effects in hybrid systems that combine the 2D material with, for instance, a metallic substrate. The latter can be magnetic, superconducting, electro-donor/acceptor, etc. These interface effects produce original magnetic, electronic, vibrational, and even optical properties, which can be tuned for instance by exploiting the phenomenon of intercalation between the 2D material and its substrate.
A few recent publications:
– A. Purbawati et al., “In-plane magnetic domains and Néel-like domain walls in thin flakes of the room temperature CrTe2 van der Waals ferromagnet”, ACS Appl. Mater. Interfaces 12, 30702 (2020)
– R. Sant et al., “Decoupling molybdenum disulfide from its substrate by cesium intercalation”, J. Phys. Chem. C 124, 12397 (2020)
– K. Omambac et al., “Temperature-controlled rotational epitaxy of graphene”, Nano Lett. 19, 4594 (2019)
Contact Johann Coraux (johann.coraux@neel.cnrs.fr) and visit this website for more information
We devote significant efforts to the controlled elaboration of 2D materials, hybrid systems (with molecules, metallic clusters or thin films) based on these materials, and van der Waals heterostructures. For that purpose we use CVD and MBE UHV reactors, some equipped with in situ STM and electron diffraction apparatuses (in collaboration with the EpiCM technological group of the lab) deterministic micro-transfer setup (in air and inside a glove box, collaboration with Experimental Engineering and Automation groups), chemical functionalisation. Device fabrication based on these materials is done in the Nanofab cleanroom using state of the art lithography techniques.
Position type: Master 2 internships and theses
Contact: Coraux / Johann - +33 4 7688 1289 | Faugeras / Clément -
The objective is to explore the means to manipulate magnetism in 2D materials, to understand the magnetic properties, the link between magnons and phonons, and the coupling between these excitations. The project will be carried out in two laboratories that are implanted on the same geographical site, Néel Institute, where sample fabrication is mastered and advanced magnetic characterisations (imaging, magnetometry) will be performed, and the High Magnetic Field National Laboratory (LNCMI), where spectroscopy will be performed under extreme conditions.
Position type: Master 2 internships and theses
Contact: Coraux / Johann - 04 76 88 12 89 | Faugeras / Clément -
L’objectif est d’explorer les façons de manipuler le magnétisme dans des matériaux 2D, et d’étudier le couplage entre des excitations magnoniques et phononiques. Le travail se déroulera entre deux laboratoires installés sur le même site géographique, l’Institut Néel, où est maitrisée la fabrication des échantillons et leur caractérisation magnétique avancée (imagerie, magnétométries), et le Laboratoire National des Champs Magnétiques Intenses, où des mesures spectroscopiques en conditions extrêmes seront conduites.
Person in charge: Laetitia MARTY
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