Large Magnetoresistance at Room Temperature in Organic Molecular Tunnel Junctions with Nonmagnetic Electrodes

We report room-temperature resistance changes of up to 30% under weak magnetic fields (0.1 T) for molecular tunnel junctions composed of oligophenylene thiol molecules, 1–2 nm in length, sandwiched between gold contacts. The magneto­resistance (MR) is independent of field orientation and the length of the molecule; it appears to be an interface effect. Theoretical analysis suggests that the source of the MR is a two-carrier (two-hole) interaction at the interface, resulting in spin coupling between the tunneling hole and a localized hole at the Au/molecule contact. Such coupling leads to significantly different singlet and triplet transmission barriers at the interface. Even weak magnetic fields impede spin relaxation processes and thus modify the ratio of holes tunneling <i>via</i> the singlet state versus the triplet state, which leads to the large MR. Overall, the experiments and analysis suggest significant opportunities to explore large MR effects in molecular tunnel junctions based on widely available molecules

High-Mobility Transistors Based on Single Crystals of Isotopically Substituted Rubrene‑<i>d</i>₂₈

We have performed a comprehensive study of chemical synthesis, crystal growth, crystal quality, and electrical transport properties of isotopically substituted rubrene-<i>d</i>₂₈ single crystals (D-rubrene, C₄₂D₂₈). Using a modified synthetic route for protonated-rubrene (H-rubrene, C₄₂H₂₈), we have obtained multigram quantities of rubrene with deuterium incorporation approaching 100%. We found that the vapor-grown D-rubrene single crystals, whose high qualities were confirmed by X-ray diffraction and atomic force microscopy, maintained the remarkable transport properties originally manifested by H-rubrene crystals. Specifically, field-effect hole mobility above 10 cm² V^–1 s^–1 was consistently achieved in the vacuum-gap transistor architecture at room temperature, with an intrinsic band-like transport behavior observed over a broad temperature range; maximum hole mobility reached 45 cm² V^–1 s^–1 near 100 K. Theoretical analysis provided estimates of the density and characteristic energy of shallow and deep traps presented in D-rubrene crystals. Overall, the successful synthesis and characterization of rubrene-<i>d</i>₂₈ paves an important pathway for future spin-transport experiments in which the H/D isotope effect on spin lifetime can be examined in the testbed of rubrene