Under standard conditions, the electrostatic field-effect is negligible in conventional metals and was expected to be completely ineffective also in superconducting metals. This common belief was recently put under question by a family of experiments that displayed full gate-voltage-induced suppression of critical current in superconducting all-metallic gated nanotransistors. To date, the microscopic origin of this phenomenon is under debate, and trivial explanations based on heating effects given by the negligible electron leakage from the gates should be excluded. In this paper, Francesco Giazotto’s superconductivity group at NEST demonstrates the control of the supercurrent in fully suspended superconducting nanobridges. Their advanced nanofabrication methods allows to build suspended superconducting Ti-based supercurrent transistors which show ambipolar and monotonic full suppression of the critical current for gate voltages of VGC ≃ 18 V and for temperatures up to ∼80% of the critical temperature. The suspended device architecture minimizes the electron–phonon interaction between the superconducting nanobridge and the substrate, and therefore, it rules out any possible contribution stemming from charge injection into the insulating substrate. Besides, the finite element method simulations of vacuum electron tunneling from the gate to the bridge and thermal considerations rule out the cold-electron field emission as a possible driving mechanism for the observed phenomenology. Their findings promise a better understanding of the field effect in superconducting metals.
More detail on the ACS NANO publication HERE