Low temperature spin relaxation length exceeding 3 μm in highly conductive copper channels

Abstract

Despite extensive studies of spin transport in metallic structures, it remains a challenge to achieve spin relaxation length well above 1 μm in metals even at low temperatures. We explore nonlocal spin transport in Cu channels with a cross section of 0.5 × 0.5 μm2, which exhibit superior values of electrical conductivity and residual resistivity ratio (RRR). Based on structures fabricated in a single batch, we found an average spin relaxation length of λCu=3.2±0.7μm and an average spin relaxation time of τs = 120 ± 50 ps at 30 K. Substantial variations of λCu, RRR, and resistivity ρCu are found among the structures and the three quantities correlate well to one another. The most conductive Cu channel in the batch yields λCu=5.3±0.8μm and τs=250±80ps. These superior values exceed expectations for metals and can be attributed to reduced spin relaxation from grain boundaries and surfaces.