ИСТИНА

Superconducting quantum interference devices (SQUIDs) are the widely used and most sensitive magnetic field sensors which can approach sensitivity up to detect a single electron spin-flip. SQUIDs have depressed sensitivity at millikelvin temperatures due to a hysteresis of current-voltage (I-V) characteristics. A widely known approach to solve this problem is to add a resistive shunt in parallel to Josephson junctions, but it takes an additional space on a chip and decreases a SQUID signal modulation by magnetic flux. In this research, we propose a new bilayer material (Al/Pt) and a planar Al/Pt SQUID based on nanojunctions (Dayem bridges). The platinum layer reduces the heat concentration near Josephson junctions and reduces overheat by Joule heating, which is considered to cause hysteresis in different models. Compared to the pure aluminium SQUID of the same geometry, the bilayer Al/Pt SQUID has no hysteresis over the whole range of working temperatures, from millikelvin temperatures up to T_C. It also exhibited an order of magnitude lower critical current I_C due to the proximity effect, which leads to decrement the screening parameter β_L=2πLI_C/Φ_0 and, thus, to the increased SQUID sensitivity. Thus, we propose a way to widen a SQUID temperature range without any additional unwished effects, like lowered sensitivity or increased measurement time. This, combined with a decreased noise due to millikelvin temperatures, paves the way towards achieving a SQUID sensitivity approaching one Bohr magneton.