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SUMMARY:Supercurrent and Josephson field-effect transistors go metal - Dr.
  Francesco Giazotto\, NEST Istituto Nanoscienze-CNR and Scuola Normale Sup
 eriore\, Pisa\, Italy
DTSTART:20190508T130000Z
DTEND:20190508T140000Z
UID:TALK124438@talks.cam.ac.uk
CONTACT:Dr Kaveh Delfanazari
DESCRIPTION:In their original formulation of superconductivity\, the Londo
 n brothers predicted more than eighty years ago the exponential suppressio
 n of an electrostatic field inside a superconductor over the so-called Lon
 don penetration depth\, λL\, in analogy to the Meissner-Ochsenfeld effect
 . Despite a few experiments indicating hints of perturbation induced by el
 ectrostatic fields\, no clue has been provided so far on the possibility t
 o manipulate conventional superconductors via field-effect. In this talk\,
  I will report the evidence of full field-effect control of the supercurre
 nt in\nall-metallic transistors made of different BCS superconducting thin
  films [1]. At low temperature\, our field-effect transistors (FETs) show 
 a monotonic decay of the critical current under increasing electrostatic f
 ield up to total quenching for gate voltage values as large as ±40V in ti
 tanium-based devices. This bipolar field effect persists up to ∼85% of t
 he critical temperature (∼ 0.41K)\, and in the presence of sizable magne
 tic fields. A similar behavior\, though less pronounced\, was observed in 
 aluminum thin film FETs [1]. A phenomenological theory accounts for our ob
 servations\, and provides a description compatible with an electric field-
 induced non-local perturbation propagating deeply inside the superconducti
 ng film. In our interpretation\, this affects the pairing potential\, and 
 quenches the supercurrent.\nMoreover\, I will show the experimental realiz
 ation of Ti-based Dayem bridge field-effect transistors (DB − FETs) [2\,
  3] able to control the Josephson critical current (IC) of the superconduc
 ting channel. Our easy fabrication process DB− FETs show symmetric full 
 suppression of IC for an applied critical gate voltage as low as VGC  
 ±8V at temperatures\nreaching about the 85% of the record critical temper
 ature 550mK for titanium. Our devices show extremely high values of transc
 onductance (up to 15μA/V) and variations of Josephson kinetic inductance 
 with gate voltage of two orders of magnitude.\nFinally\, I will show the b
 ehavior of mesoscopic superconductor-normal metal-superconductor (SNS) Jos
 ephson field-effect transistors which will reveal as well the impact of in
 tense electrostatic fields even on proximity metals. All this seems to sug
 gest that the field effect is universal\, i.e.\, it can affect either genu
 ine or proximity fully-metallic\nsuperconductors.\nBesides shedding light 
 on a key issue in physics\, these results represent a groundbreaking asset
  for the realization of an all-metallic superconducting field-effect elect
 ronics and leading edge quantum information architectures based on Josephs
 on FETs. Possible electronic and circuital schemes based on this all-metal
 lic technology will be furthermore discussed.\nReferences\n[1] G. De Simon
 i\, F. Paolucci\, P. Solinas\, E. Strambini\, and F. Giazotto\, Nat. Nanot
 echnol. 13\, 802 (2018).\n[2] F. Paolucci\, G. De Simoni\, E. Strambini\, 
 P. Solinas\, and F. Giazotto\, Nano Lett. 18\, 4195 (2018).\n[3] F. Paoluc
 ci\, G. De Simoni\, P. Solinas\, E. Strambini\, N. Ligato\, P. Virtanen\, 
 A. Braggio\, and F. Giazotto\, arXiv:1808.00353\, to appear in Phys.\nRev.
  Appl. (2019).
LOCATION:Mott Seminar Room (531)\, Cavendish Laboratory\, Department of Ph
 ysics
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