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

Organic semiconductors are studied intensively for applications in electronics and optics(1), and even spin-based information technology, or spintronics(2). 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(3), 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 mu s, 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(4). T-2 is more than two orders of magnitude greater than the duration of the spin manipulation pulses, which suggests that copper phthalocyanine holds promise for quantum information processing, and the long T-1 indicates possibilities for medium-term storage of classical bits in all-organic devices on plastic substrates.