We investigated the local density of states (LDOS) of a normal metal (N) in good electrical contact with a superconductor (S) as a function of the distance $x$ to the NS interface. The sample consists of a pattern of alternate $L=1$ $\mu$m wide strips of Au and Nb made by UV lithography. We used a low temperature scanning tunneling microscope and a lock-in detection technique to record simultaneously $\mathrm{d}I/\mathrm{d}V(V,x)$ curves and the topographic profile $z(x)$ at $1.5$ K. We scanned along lines perpendicular to the strips. All the spectra show a dip near the Fermi energy, which spectral extension decreases from the superconducting gap $\Delta$ at the NS interface to zero at distances $x\gg\xi_{\mathrm{N}}$ where $\xi_{\mathrm{N}}\simeq\sqrt{\hbar D_{\mathrm{N}}/2\Delta}\simeq53$ nm is the coherence length in the normal metal. Our measurements are correctly described in the framework of the quasi-classical Green's function formalism. We numerically solved the $\mathrm{1D}$ Usadel equation and extracted a decoherence time in gold of $4$ ps. We also investigated the LDOS of small ridges of Au deposited on the top of the Nb lines. In this case, $L\leqslant \xi_{\mathrm{N}}$ and the spatial variations of the spectra depend on the exact shape of the Au ridge. However, our results are consistent with a predicted minigap related to the Thouless energy.

RT Journal
T1 Scanning tunneling spectroscopy on superconducting proximity nanostructures
A1 Chapelier,C.
A1 Vinet,M.
A1 Lefloch,F.
PB Успехи физических наук
PY 2001
FD 10 Sup, 2001
JF Успехи физических наук
JO Усп. физ. наук
VO 171
IS 13
SP 71-74
DO 10.1070/1063-7869/44/10S/S15
LK https://ufn.ru/ru/articles/2001/13/o/