A curious response of graphene to light and heat may be useful for optoelectronic applications. A conventional thermocouple consists of two different metal wires placed in contact with each other. When the junction is heated and the free ends are kept cold, a voltage can be measured across the two free ends. If the metals are the same, then no voltage should appear. On page 648 of this issue, Gabor et al. (1) report a thermo couple effect that contradicts this conventional expectation. Upon heating a junction made of a single graphene sheet by shining laser light on it, they found that a voltage does develop across the junction. The observed photothermoelectric effect could be potentially exploited in novel optoelectronic devices.
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