Interaction of both charge density waves in $\mathrm{NbSe_3}$ from interlayer tunneling experiments

Interlayer tunneling technique has been used for spectroscopy of charge density wave (CDW) energy gaps, $\Delta_{1,2}$, in $\mathrm{NbSe_3}$ subsequently opened at the Fermi surface on decreasing temperature at $T_{p1}=145$ K (CDW1) and at $T_{p2}=60$ K (CDW2). We found that the CDW2 formation is accompanied by an increase of the CDW1 gap below $T_{p2}$. The maximum enhancement of $\Delta_1$, $\delta\Delta_1$, is about 10%. The effect observed has been predicted theoretically as resulting from the joint phase locking of both CDWs with the underlying crystalline lattice below $T_{p2}$.