  Charge transport in Rubrene single crystals under uniaxial mechanical strain
is systematically investigated in the crystal's two in-plane transport
directions both under tensile and compressive strain applied parallel or
perpendicular to the current direction. The density of trap states remains
unchanged. The field-effect mobility as a benchmark figures for intermolecular
transport is found to increase with compressive strain and vice versa with a
magnitude of -1.5 cm2/Vs per percent of strain independently of tranport
direction. A very remarkable result is the mobility change when the crystal is
strained perpendicular to the transport direction. While this enhancement could
be quantitatively explained from an improved wave-function overlap, mobility in
the perpendicular direction improves even more, contrary to simple geometric
considerations based od later expansion and usual Poisson ratios. This result
emphasises the central role of the stress induced variations of the dynamics
wave function overlap in organic molecular crystals.
