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

Abstract

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 (T1) and the phase memory time (T2): T1 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 T2 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, T1 and T2 are respectively 59 ms and 2.6 μs, and at 80 K, which is just above the boiling point of liquid nitrogen, they are respectively 10 μs and 1 μs, demonstrating that the performance of thin-film copper phthalocyanine is superior to that of single-molecule magnets over the same temperature range. T2 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 T1 indicates possibilities for medium-term storage of classical bits in all-organic devices on plastic substrates.

Exchange interaction between the triplet exciton and the localized spin in copper-phthalocyanine

“…Especially, the spin-bearing MPcs are of great interest. They can have very long spin-lattice relaxation times [11], which may pave the way towards robust electron-spin qubit. Moreover, as organic semiconductors, due to their plasticity, they can be prepared in different forms such as bulk crystalline, thin films [2,8], and nanowires [3].…”

“…The metal-phthalocyanine (MPc), in which a metallic ion is centred at a conjugated Pc ring, has attracted much attention recently due to its fascinating physical properties [1][2][3][4][5][6][7][8][9][10][11]. Especially, the spin-bearing MPcs are of great interest.…”

“…Moreover, as organic semiconductors, due to their plasticity, they can be prepared in different forms such as bulk crystalline, thin films [2,8], and nanowires [3]. In conjugation with their magnetic tunability realised by the state-of-the-art molecular growth techniques [2,8], these advanced materials properties are highly promising in the applications including quantum information processing (QIP) [11] and organic spintronics [12].…”

Spintronic detection of interfacial magnetic switching in a paramagnetic thin film of tris(8-hydroxyquinoline)iron(III)

“…In contrast to organic spintronics, 'molecular spintronics' utilizes the chemical versatility of molecules; in particular those that have paramagnetic metal ions, for manipulating the spin states [20][21][22][23][24][25][26][27][28]. One particularly promising class of building blocks for molecular spintronics devices is the metalloporphyrins, which exhibit an intrinsic remnant magnetization when in contact with a FM metallic electrode [23], similar to single molecule magnets [29].…”

“…Recently, metallophthalocyanines (e.g. CuPc [27], MnPc [30]) also have been intensely studied due to their potential highly spin polarized surface spins ('spinterface') that can act as a spin filter. However, the spin orientation of the molecular ensemble, which is crucial to the ability of spin filtering, was only investigated in the limit of monolayer using a variety of surface science techniques [23][24][25][26][27][28][29][30][31].…”