Indication for the coexistence of closed orbit and quantum interferometer with the same cross section in the organic metal (ET)4(H3O)[Fe(C2O4)3].C6H4Cl2: Persistence of SdH oscillations above 30 K

Shubnikov-de Haas (SdH) and de Haas-van Alphen (dHvA) oscillations spectra of the quasi-two dimensional charge transfer salt $\beta$"-(ET)${}_4$(H${}_3$O)[Fe(C${}_2$O${}_4$)${}_3$]$\cdot$C${}_6$H${}_4$Cl${}_2$ have been investigated in pulsed magnetic fields up to 54 T. The data reveal three basic frequencies F${}_a$, F${}_b$ and F${}_{b-a}$, which can be interpreted on the basis of three compensated closed orbits at low temperature. However a very weak thermal damping of the Fourier component F${}_b$, with the highest amplitude, is evidenced for SdH spectra above about 6 K. As a result, magnetoresistance oscillations are observed at temperatures higher than 30 K. This feature, which is not observed for dHvA oscillations, is in line with quantum interference, pointing to a Fermi surface reconstruction in this compound.