Large efforts have been made in the past decades to develop new types of cryogenic sensors for various applications, ranging from material analysis for the industry to astroparticles detection. Future spatial programs involve detectors working around 50 mK, while their readout electronics (eg preamplifiers), still working at much higher temperature, frequently prevent extracting the best performance from these detectors. In this wide and competitive context, mesoscopic devices provide attractive solutions for these problems. In this project, we propose to implement a mesoscopic charge amplifier for the readout of ionisation detectors, used for particles detection in many domains. Importantly, our device could improve by an order of magnitude the detection threshold of the EDELWEISS experiment for dark matter search, to which the CSNSM participates. The course of this research will go through developments, both fundamental and instrumental, based on the mesoscopic physics of quantum superconducting circuits. The aim of the present application is to provide with the funds necessary to initiate this new activity, consecutive to the hiring of the project's principal investigator at the CNRS (CSNSM). This project takes place within a broader framework aimed at developing a front-end mesoscopic cryoelectronics, to catch up with the latest developments in cryogenic detectors.

Neutrinoless Double Beta Decay (0v-DBD) is in a central position for the study of elementary particles and fundamental interactions. It has strong implications on topics of cosmological character as well. After the discovery of neutrino flavor oscillations, crucial issues remain open, such as the absolute neutrino mass scale and the mass hierarchy, together with the quest of the neutrino nature: Dirac or Majorana fermion? The purpose of this project, named LUMINEU, is to set the bases for the realization of a next-generation 0v-DBD experiment with unprecedented sensitivity. To succeed, LUMINEU proposes to reduce the residual background due to alpha particles owing to the simultaneous measurement of the light and the heat generated in a nuclear event. This double read-out approach will allow rejecting interactions due to alpha particles with efficiency close to 1. If the scintillating bolometers contain a candidate to 0v-DBD with transition energy higher than the natural gamma radioactivity end-point (2.6 MeV), the rejection of alpha particles enables a virtually zero-background experiment for the exposures required to scrutinize the inverted hierarchy region of the neutrino mass pattern. LUMINEU envisages the study of large ZnMoO4 scintillating crystals, containing the excellent candidate 100Mo, which is featured by a Q-value around 3 MeV. The ZnMoO4 crystals will be grown with an advanced technique which warrants excellent crystal quality, extreme purity and negligible waste of the starting material. A mass of 400 g for the single module is foreseen. The rejection of alpha particles is correlated to the quality of the light measurement. A special effort will be dedicated to the optimization of the scintillation light detectors in terms of energy threshold, size, reproducibility and time response. Reducing this time would be the key in case of ultimate background due to the pile-up of standard DBD with neutrino, particularly relevant in the case of 100Mo. As a consequence, beside the production of standard semiconductor sensors (NTD) by nuclear transmutation, new sensors will be studied: high impedance superconductive films and metallic paramagnetic thermometers. The coupling of such sensors to massif crystals without loss in their nominal performances would be a strong innovation. This result would have an impact on astroparticle physics beyond the 0v-DBD. This may lead to important advancements in dark matter direct detection in EDELWEISS-3 and EURECA. The progress in thermal sensors and their coupling, will lead to the improvement of the energy resolution and threshold of the heat channel and to a better sensitivity to WIMPs in particular at low masses. LUMINEU will take advantage of contributions from both communities. In the same time, both field of research will take benefit of LUMINEU’s developments. The results on the scintillating crystals and on the light detectors will enable a 0v-DBD pilot experiment performed in an underground environment and containing a considerable amount of enriched molybdenum (about 1 kg). After the conclusion of LUMINEU, the realization of a large-scale experiment looking at the 20 meV region for the effective neutrino mass will be just a matter of political will and fund availability.

Fifty years of dramatic advances in microelectronics have reshaped the way we communicate and work, but progress on silicon-based technologies could well be reaching their limits. This calls for fresh research on new materials for the electronic industry. In this context, fabrication of high quality oxide heterostructures (HS) lies at the heart of the emerging field of oxide electronics. Indeed, Ohtomo and Hwang (2004) have shown that a two dimensional electron gas (2DEG) can be formed in HS based on the wide-gap band insulator SrTiO3 (STO). This is appealing, as STO is a member of the transition metal oxides (TMOs). These materials present unique properties, such as high temperature superconductivity in cuprates, colossal magnetoresistance in manganites, multiferroic behaviour in bismuth ferrites. Owing to their similar perovskite structure, one can combine them into a large variety of HS, hoping for novel emerging properties at their interfaces. A recent breakthrough due to the Coordinator and several members on this project may open a new way to create and study 2DEGs in TMOs: we found that a 2DEG can be obtained at the bare surface of insulating STO by simply fracturing a crystalline sample in vacuum. An exciting perspective, which is at the core of the present proposal, is that the underpinning mechanism of such a 2DEG may be generic to other perovskites, and that the ensuing 2DEGs might inherit some of the properties of their host compounds, which are often correlated electron systems. Thus, we will aim at the creation and engineering of novel 2D electronic states at the surface of TMOs endowed with technologically promising functionalities. Materials to be investigated include the ferroelectric BaTiO3 (BTO), as well as manganites and multiferroics, which could present strongly spin-polarized 2DEGs allowing the creation of electrically controllable spintronic devices. Furthermore, very recent results from our consortium suggest original routes to craft non-trivial topological states in oxide surfaces. In this project, we will explore the realization of new topological 2DEGs at the surface of TMOs. Moreover, in order to search for optimal or new functionalities, we will tailor in-situ their microscopic properties, like carrier density, spin-orbit or spin-spin interactions, and directly follow the evolution of their electronic structure. At the core of our strategy, we will use a combination of state-of-the-art in-situ preparation and characterization techniques and photoemission spectroscopy. Understanding such surface metallic states requires detailed studies of the role of oxygen vacancies created during the fracturing process. Key issues to be addressed include identifying the mechanisms that can form, stabilize and allow an engineering of the oxygen vacancies at the surface of TMOs. Furthermore, we will find ways to protect the surface 2DEGs to render them usable for transport measurements and for applications. This project is a re-submission of our project “LACUNES”. We have taken into account the remarks made by the Evaluation Committee, and made sure to allay their concerns. Outcomes of this project can open new avenues for the development of electronics based on TMOs. The consortium combines the necessary skills to meet the challenges of the present proposal, as our recent experimental/theoretical collaboration shows. Our discovery and recent preliminary results, described below, demonstrate the feasibility and potential of our approach to create novel 2DEGs in several TMOs.

A recent article in the French scientific review “La Recherche” is dedicated to “ultraheavy atoms”. This shows once more that one of the major challenges of modern Nuclear Physics is to investigate the limits of nuclear existence. One simple and yet fundamental question is: what is the maximum number of protons a nucleus can sustain? To answer such a question, the synthesis of new elements with an ever increasing number of protons (Z=114 to 122) is carried out and motivated by the theoretical prediction of a new island of stability. Furthermore, superheavy nuclei provide a unique laboratory within which nuclear structure and dynamics under very intense Coulomb forces can be studied. While cross-sections to synthesize the heaviest elements are extremely low, the production rate of superheavy nuclei with proton numbers ranging from Z=100 to Z=106 is high enough to obtain significant information on their nuclear structure. Detailed internal-conversion-electron and gamma-ray spectroscopy of nuclei in this region of the nuclear chart is the prime motivation of the Franco-Russian GABRIELA (Gamma Alpha Beta Recoil Investigation with the Electromagnetic Analyzer VASSILISSA) project launched in 2003. The combination of high beam intensities and the availability of actinide targets makes GABRIELA@VASSILISSA a very unique experimental set-up, complementary to the S3 (Super Separator Spectrometer) project of heavy element spectroscopy with ultra-intense beams at SPIRAL2. The upgrade of the VASSILISSA separator, funded by the ANR within the SHELS (Separator for Heavy Element Spectroscopy, ANR-06-BLAN-0034) project, will allow the collaboration to access new and unexplored nuclei. The purpose of this new call is dedicated to transforming the photon-detection system at the focal plane of the VASSILISSA separator into a state-of-the-art array of Compton-suppressed Germanium detectors. This task will be done in collaboration with physicists from the Flerov Laboratory of Nuclear Reactions. In particular, recent experimental results have shown that the coincidence detection efficiency is crucial to disentangle the complex decay schemes of high-K isomers, whose existence is favored in this mass region. This is why we wish to upgrade the GABRIELA detector array with a dedicated array of coaxial Germanium detectors and a Clover detector in close and compact geometry, all equipped with new Compton suppression shields to maximize the efficiency of the array as well as the signal to noise ratio. Our Franco-Russian collaboration (between FLNR-JINR and IN2P3) started 7 years ago within the GABRIELA project. It has, therefore, stood the test of time and has proven to be very fruitful. Finally, the above-mentioned gamma detection system will be shared with the S3 project when it comes online in 2015-2016.