Superconductivity above 30 K in alkali-metal-doped hydrocarbon

Abstract

The recent discovery of superconductivity with a transition temperature (T(c)) at 18 K in K(x)picene has extended the possibility of high-T(c) superconductors in organic materials. Previous experience based on similar hydrocarbons, like alkali-metal doped phenanthrene, suggested that even higher transition temperatures might be achieved in alkali-metals or alkali-earth-metals doped such polycyclic-aromatic-hydrocarbons (PAHs), a large family of molecules composed of fused benzene rings. Here we report the discovery of high-T(c) superconductivity at 33 K in K-doped 1,2:8,9-dibenzopentacene (C(30)H(18)). To our best knowledge, it is higher than any T(c) reported previously for an organic superconductor under ambient pressure. This finding provides an indication that superconductivity at much higher temperature may be possible in such PAHs system and is worthy of further exploration.

Figure 1. Magnetization data for K_3.17dibenzopentacene.

(a) χ versus T plots for K_3.17dibenzopentacene with T_c^onset = 28.2 K at H = 10 Oe (main panel). The left inset shows the ac susceptibility at H = 5 Oe, and the right inset shows the molecular structure of dibenzopentacene; unfortunately, to our knowledge, no report on the crystal structure of 1,2:8,9-dibenzopentacene has been published. (b) χ versus T plots for the sample in the ZFC measurements under different magnetic field H. The solid lines indicate the determination of the transition temperature as described in the text. (c) The H versus T_c plot. (d) Field dependence of the magnetization isotherm for the sample measured at 4.5 K. The solid line gives the linear fit to the low field M(H) curve.

Figure 2. Temperature dependence of magnetization for K_3.45dibenzopentacene and K₃dibenzopentacene.

(a) χ versus T plots for superconducting K_3.45dibenzopentacene at H = 10 Oe (main panel). The ZFC curve indicates the presence of three different superconducting phases. The left inset shows on an expanded scale, the region around T_c, revealing a critical temperature of 33.1 K. The right inset shows χ versus T plots for the sample K_3.45dibenzopentacene in the ZFC measurements under different magnetic field H. It clearly shows that all the three superconducting transitions are suppressed slowly by applying the magnetic fields. (b) χ versus T plots for the twice annealed K₃dibenzopentacene sample with T_C = 7.4 K at H = 10 Oe.

Figure 3. Dependence of the superconducting transition temperature on the number of benzene rings.

T_c increases from 5 K for K_xphenanthrene with three benzene rings to 18 K for K_xpicene with five benzene rings, and up to 33.1 K for K_xdibenzopentacene with seven benzene rings, shows linear relativity to the number of benzene rings.