The MoQuaS project pioneers the new field of Molecular Quantum Spintronics in which molecular spins, embedded in electronic circuits, are used to fabricate hybrid spintronic devices working in quantum regime. The final goal is to design, fabricate and test concept-devices at the molecular scale with radically new functionalities that can be used for processing quantum information. MoQuaS focused on two classes of molecular building blocks: mono and di-nuclear Ln(Tb) phthalocyanines as prototype of molecular spin centres and Graphene Nano-Ribbons (GNR) as template for charge transport. We have thus synthesized new bi-nuclear phthalocyanines, namely the complexes PcLn1PcLn2Pc which comprise two lanthanides working as spin centers (J.Mater.Chem. C, 2015, 3, 9794). For GNR, we had two major goals: the first one was to control the band gap by essentially tailoring the size of the nanoribbons and the second one was to develop suitable methods to embed these carbon-based units within electrodes. We have synthesized different types of GNRs through polymerization of suitable precursors (Nature 531, 489, 2016, ACS Nano 8, 11622, 2014, JACS 137, 4022, 2015). GNRs with varying structures have been also achieved by the CVD method and transferred onto suitable substrates for the device studies (manuscripts submitted). Further GNRs deposition methods on insulating substrate (e.g., by electro-spray, Carbon 104, 21740, 2016) as well as experiments for the device integrations have been performed (JACS doi: 10.1021/ja512897m). Overall these results pave the way for the exploitation of chemically synthesized GNR in electronic devices.
Molecular scale electrodes, based on gold or graphene, have been massively fabricated and widely tested. Metal junctions are routinely obtained by electromigration and we developed an electro-burning technique to obtain nm-size junctions in different type of graphene (Beilstein J. Nanotech., 2015, 6, 711). An extensive collection of statistical data on different steps of the fabrication process and relative success yield is reported on the White Book (Download the pdf).
With these molecular building blocks and nano-platforms (electrodes), prototypical devices such as molecular spin valves and molecular spin transistors have been fabricated and tested. Mechanisms underlying the functioning of these devices have been carefully studied in key experiments at very low temperature. Overall results of our experiments reveal genuine quantum features of our devices and possibility to read out and manipulate single molecular spin. More specifically, with experiments at mK and fast sweeping magnetic field, the CNRS team has demonstrated to be able to read out the electronic and nuclear spin state of a single TbPc2 molecule by using an electronic circuit. Since the lifetime of the Tb nuclear states exceed ms, their manipulation was feasible. The CNRS team thus used an oscillating electric field to effectively manipulate the nuclear spin of Tb and observe Ramsey interference fringes (Science, 2014, 344, 1135) demonstrating the capability to coherently manipulate the spin state of a single molecule. Based on this background, the Tb spin states could be prepared and manipulated at wish. In this way, a protocol including spin initialization and pulse sequence have been successfully encoded to our prototypical TbPc2 molecular spin transistor thus demonstrating that the Grover’s search algorithm can be implemented with our single molecule device (manuscript in preparation).
Making use of our molecular templates, more complex devices, including multi-gate/multi-bits gates, ferromagnetic electrodes have been also designed and they are currently under development. Other complementary experiments have been performed in order to understand the mechanism underlying our devices. Notably we have performed an extensive study of X-ray absorption and dichroism on isolated TbPc2 in order to evaluate the magnetic coupling between the Tb centre and the organic (carbon) layer. Results have been interpreted with the help of DFT calculations that evidence the role of the f-d orbitals of Ln and that of the radical in organic ligands in transmitting magnetic interactions (Scientific Report 2016, 6, 21740; ACS Nano, 2016, DOI: 10.1021/acsnano.6b04107). Complementary experiments, such as microSQUID (ACS Nano, 2015, 9, 4458–64), EPR, specific heat (manuscript in preparation) further evidence the key role of radical in determining the double-dot behaviour of TbPc2.
MoQuaS comprised three complementary groups of Physicists (the Italian CNR-Nano in Modena, the French CNRS-Néel in Grenoble, the German JGU in Mainz) and teams with different skills in synthetic chemistry (KIT in Karlsruhe and MPIP in Mainz). A consortium agreement was signed at the beginning of the projects by the five partners. This web page contains clips and a collection of images produced by the partners to spread the results to general public (outreach).
Overall, the activities of MoQuaS led to more than 70 articles published on international Journals, among which 1 article in Science, 1 in Nature, 3 in Nature Communications, 7 in JACS, 4 in ACS Nano and others in prestigious Journals like Scientific Report, Adv. Mat., Chemistry Eur J., etc. Four of these publications led to cover pages of the respective journal’s issues. 5 chapters in themed books have been published and more than 10 manuscripts are now in preparation or just submitted.
All partners actively contribute to the diffusion of results with invited talks at numerous international conferences (WP8): we can count more than 100 oral contributions (including several invited talks) at International Conferences by MoQuaS researchers.
As concerns the organization of scientific events: Prof. M. Ruben (KIT) organized the symposium “Molecular materials – towards quantum properties” at EMRS conference (Lille, F, May 2014). Prof. M. Kläui organized MAINZ Summer School on Organic Transport Charge and Spin Transport in Non-Metallic Systems and Confined Geometries August 24-29, 2014 in Mainz (Germany). Prof. Affronte co-organised a joint symposium on “Atom and Molecular based systems and devices” at the EMRS Fall Meeting in Warsaw (PL) (September 2016). Achievements obtained with MoQuaS significantly contribute to design the role of molecular spins for Quantum Technology road map.
Involvement of young researchers, project meetings, exchange visits during the first year and equal opportunities issues are reported in details in annual deliverables D7 and D8. More specifically MoQuaS has contributed to train 9 PhD students (see D8.2) who worked full time on the project.
All the main targets of the project have been successfully achieved and complementary activities also led to further results (not initially planned in the DoW).
Besides the main scientific objectives, the MoQuaS project has significantly contributed to the development of 4 enabling technologies:
– Development of table top dilution cryostat (D4.2)
– Development of processes for fabrication of molecular electrodes and devices (D2.2, D3.2)
– Development of HTC superconducting planar resonators and MW technology related to spin-photon coupling (D4.2)
– Synthesis of nano-structured graphene and its artificial control. (D1.2)