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Gap like structure in a nonsuperconducting layered oxycarbonate Bi$_{2+x}$Sr$_{4-x}$Cu$_2$CO$_3$O$_{8+δ}$ single crystal

The magnetic field and temperature dependence of the in-plane tunneling conductance $dI/dV(V)$ in high-quality nonsuperconducting (down to 10 mK) layered oxycarbonate Bi$_{2+x}$Sr$_{4-x}$Cu$_2$CO$_3$O$_{8+δ}$ single crystals has been investigated using break junctions. Combining measurements of the in-plane magnetoresistivity $ρ_{ab}(T,H)$ and the magnetotunneling, we present evidence for the existence of a small "pseudogap" in a nonsuperconducting cuprate, without local incoherent pairs or any correlation phenomena associated with superconductivity. We are unable to distinguish if such a "pseudogap" is totally unrelated to superconductivity or if its existence is a necessary condition for the subsequent occurrence of superconductivity with increasing carrier density in the sample.