Near-Field Radiative Nanothermal Imaging of Nonuniform Joule Heating in Narrow Metal Wires.

Probing spatial variation of temperature at the nanoscale provides key information for exploring diverse areas of modern science and technology. Despite significant progress in the development of contact thermometers with high spatial resolution, one inherent disadvantage is that the quantitative analysis of temperature can be complicated by the direct thermal contact. On the other hand, noncontact infrared radiation thermometer is free from such contact-induced disturbance, but suffers from insufficient spatial resolution stemming from diffraction-limit in the micrometer range. Combining a home-built sensitive infrared microscope with a noncontact scattering probe, we detected fluctuating electromagnetic evanescent fields on locally heated material surface, and thereby mapped temperature distribution in subwavelength scales. We visualize nanoscale Joule heating on current-carrying metal wires and find localized "hot-spots" developing along sharp corners of bended wires in the temperature mapping. Simulation calculations give quantitative account of the nanoscale temperature distribution, definitely indicating that the observed effect is caused by the nonuniform energy dissipation due to the current-crowding effect. The equipment in this work is a near-field version of infrared radiation thermometer with a spatial resolution far below the detection wavelength (<100 nm, or λ/140) in which local temperature distribution of operating nanoscale devices can be noninvasively mapped with a temperature resolution ∼2 K at room-temperature.

Magnetization plateau of two-dimensional antiferromagnetic solid 3He on a triangular lattice.

3He film adsorbed on a graphite surface offers an ideal two-dimensional antiferromagnetic S=1/2 quantum spin system on a triangular lattice. In addition, competition between various multiple spin exchange interactions makes it strongly frustrated. The ground state in such a frustrated quantum spin system is one of the most interesting issues in condensed matter physics. Recent experiments on the antiferromagnetic solid 3He in the second layer indicate the ground state is a spin liquid, whereas there still exists a controversy on whether or not the spin gap is finite. Here we report the first precise magnetization measurement below 1 mK over the wide magnetic field range up to 11 T. The magnetization curve is found to show a plateau at half of the saturation magnetization, being followed by the full saturation at the unexpectedly high field of around 10 T.