Table 1 Sample parameters and literature values for thermal boundary resistance.

Here, A is the area of a tunnel junction, d is the diameter of the subchip, RA = RTA is the characteristic junction resistance, and RT is the junction resistance. Thermal resistance prefactors (α) are the values obtained from the fits of Fig. 2, whereas αAMM and αDMM correspond to theoretical RPTB (35).

SampleA
μm2
d
μm
RA = RTA
Ωμm2
α
K4/μW
αAMM
K4/μW
αDMM
K4/μW
Max cooling
%
Max cooling
mK
S12.0/137*3005384.515 (@ 140 mK)22 (@ 166 mK)
S27.510004765.66.58.840 (@ 170 mK)83 (@ 244 mK)
S33.2300194529162129 (@ 173 mK)56 (@ 220 mK)

*Sample S1 had silicon oxide between leads and subchip, and therefore, the effective area of the phononic heat contact, 137 μm2, is larger than the junction area 2.0 μm2.