Fig. 1: Hybrid superconducting PtSiGe–Ge/SiGe device.
From: A quantum dot in germanium proximitized by a superconductor
a, False-coloured scanning electron micrograph of a nominally identical device. The device comprises three lithographically defined metallic layers, separated by a dielectric of Al2O3 grown using atomic layer deposition. A plunger gate PG (orange) controls the electrochemical potential of the QD. The coupling of the QD to the PtSiGe SCs (S and D) is controlled by two barrier gates, LB and RB (yellow). A cut-off gate CO prevents accumulation beneath the gate fan-out of PG, and a helper gate HG provides further control of the QD confinement. b, Heterostructure and gate stack schematic corresponding to the cross-section indicated by the black dashed line in a. c, Energy schematic depicting the physical system in a. Here, Δ is the SC gap energy, U is the charging energy of the QD, ΓS is the hybridization energy of the SC and QD and ϵ0 is the electrochemical potential of the QD with respect to the SC Fermi energy. The inset axis depicts energy (E) versus space (x) along the line-cut in a. d, Source–drain current ISD as a function of barrier gates VLB and VRB at bias voltage VSD = 300 μV, VPG = −2.22 V and VHG = −1.00V. The square, circle and triangle correspond to the indicated gate voltage setting in e, f and g. Horizontal features likely correspond to charge instabilities in the environment surrounding the QD. e–g, Bias spectroscopy for the three gate voltages indicated in d, with high, moderate and low coupling of the QD to the SCs, respectively, showing a transition between strongly coupled lead (e) and weakly coupled lead (g). Negative differential conductance observed may indicate Coulomb diamonds of odd occupancy64.
