Potential for spin-based information processing in a thin-film molecular semiconductor

Organic semiconductors are studied intensively for applications in electronics and optics, and even spin-based information technology, or spintronics. Fundamental quantities in spintronics are the population relaxation time ($T_{1})$ and the phase memory time ($T_{2})$: $T_{1}$ measures the lifetime of a classical bit, in this case embodied by a spin oriented either parallel or antiparallel to an external magnetic field, and $T_{2}$ measures the corresponding lifetime of a quantum bit, encoded in the phase of the quantum state. Here we establish that these times are surprisingly long for a common, low-cost and chemically modifiable organic semiconductor, the blue pigment copper phthalocyanine, in easily processed thin-film form of the type used for device fabrication. At 5 K, a temperature reachable using inexpensive closed-cycle refrigerators, $T_{1}$ and $T_{2}$ are respectively 59 ms and 2.6 ms, and at 80 K, which is just above the boiling point of liquid nitrogen, they are respectively 10 ms and 1 ms, demonstrating that the performance of thin-film copper phthalocyanine is superior to that of single-molecule magnets over the same temperature range.