Quantum Nano-Electro-Mechanical Systems (QNEMS)

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Quantum Nano-Electro-Mechanical Systems (QNEMS) We aim to understand simultaneously the mechanical and electronic capabilities of quantum nano-electro-mechanical systems (QNEMS). To do so, we leverage our unique instrumentation (strain and quantum transport at ultra-low temperatures), and nanodevices (suspended low-disorder 2D and 1D crystals). We will pursue three groups of experiments in QNEMS: (1) Strain-engineering of mesoscopic transport: ballistic transport, many-body phases, and valleytronics, (2) Opto-NEMS (NOEMS): interplays of mechanical resonances, photon absorption, and thermal transport, and (3) Tunable Molecular-scale NEMS. A first cluster of objectives is the strain engineering of transport in 2D materials. Monolayer and bilayer graphene are ideal systems to bridge the gap between the presently limited experiments and advanced theories in strain-engineering of 2D quantum transport. We will apply uniaxial strains up to a few percent to ultra-clean suspended graphene transistors to demonstrate high on/off ratio transistors in pristine (bulk) graphene for applications in flexible electronics. We will also use uniaxial strain in magic-angle bilayer graphene (two graphene crystal stamped on one another with a one degree rotation) to tune its band structure and explore its superconducting phase diagram. We will develop the capability to apply tri-axial strain to graphene to create tunable pseudo-magnetic fields, and achieve valley-polarized currents. A second axis will explore photon absorption and heat transport in graphene opto-electronic heterostructures (NOEMS). Large (several microns) suspended devices will be created by stamping 2D crystals above trenches in boron nitride. When adding aluminum reflectors below the suspended 2D materials, the devices will host opto-electro-mechanical cavities. Using them, we will engineer the enhancement of optical absorption in 2D materials. Another set of experiments will be to measure simultaneously the lattice (phonon) and electron (carrier) heat conductivities of 2D materials such as graphene, and bilayer graphene to quantity the energy flow between the charge carriers and phonons. A third set of objectives is aimed at exploring highly-tunable near-molecular scale (~10-nm) NEMS, consisting of suspended quantum dots (QDs) in single-wall carbon nanotubes (SWCNTs) and graphene. We propose to bridge the gap in the understanding of NEMS between the single-molecule scale and 100-nm scale. We will test the scaling-limit of the mechanical performance of QNEMS, with possible applications as mass sensors and RF mixers. We will study many-body quantum effects taking place in single-molecule electronics such as polaron physics in SWCNT-QDs. Another fascinating prospect is using 10-nm scale SWCNT QDs to make hybrid S-N-S Josephson junction. This will enable us to study the physics of Kondo, Andreev bound states, Shiba states, and their phase diagrams.