Clear Reduction in Spin Susceptibility and Superconducting Spin Rotation for \(H\parallel a\) in the Early-Stage Sample of Spin-Triplet Superconductor UTe2

We report the re-measurement of the $a$-axis spin susceptibility component in\nan early-stage sample of the spin-triplet superconductor UTe$_2$ with the\ntransition temperature of $T_{\\rm SC}$ = 1.6 K. Using Knight-shift measurements\nalong the $b$ axis and at a 10-degree tilt from the $b$ axis towards the $a$\naxis, we accurately determined the $a$-axis component without directly\nmeasuring the $a$-axis Knight shift. Our results reveal a decrease of\napproximately 3\\% in the $a$-axis spin susceptibility in the superconducting\nstate under $a$-axis magnetic field $\\mu_0 H_a \\sim 0.1$ T, indicating that the\nspin susceptibility decreases similarly in both early-stage and ultraclean\nsamples with $T_{\\rm SC}$ = 2.1 K. The previously reported absence of the\nreduction in Knight shift is attributed to the missing of signal from the\nsuperconducting region and to the detection of residual signals from the\nnon-superconducting region instead. We also found that the decrease in the\n$a$-axis spin susceptibility is immediately suppressed with increasing the\n$a$-axis magnetic field and is estimated to be completely suppressed at around\n1.5 T due to superconducting spin rotation.\n