Thermal transport in individual atomic junctions and chains is of great fundamental interest because of the distinctive quantum effects expected to arise in them. By using novel, custom-fabricated, picowatt-resolution calorimetric scanning probes, we measured the thermal conductance of gold and platinum metallic wires down to singleatom junctions. Our work reveals that the thermal conductance of gold single-atom junctions is quantized at room temperature and shows that the Wiedemann-Franz law relating thermal and electrical conductance is satisfied even in single-atom contacts. Furthermore, we quantitatively explain our experimental results within the Landauer framework for quantum thermal transport. The experimental techniques reported here will enable thermal transport studies in atomic and molecular chains, which will be key to investigating numerous fundamental issues that thus far have remained experimentally inaccessible.T he study of thermal transport at the nanoscale is of critical importance for the development of novel nanoelectronic devices and holds promise to unravel quantum phenomena that have no classical analogs (1-3). In the context of nanoscale devices, metallic atomic-size contacts (4) and single-molecule junctions (5) represent the ultimate limit of miniaturization and have emerged as paradigmatic systems revealing previously unknown quantum effects related to charge and energy transport. For instance, transport properties of atomic-scale systems-such as electrical conductance (6), shot noise (7, 8), thermopower (9-11), and Joule heating (12)-are completely dominated by quantum effects, even at room temperature. Therefore, they drastically differ from those of macroscale devices. Unfortunately, the experimental study of thermal transport in these systems constitutes a formidable challenge and has remained elusive to date, in spite of its fundamental interest (13).Probing thermal transport in junctions of atomic dimensions is crucial for understanding the ultimate quantum limits of energy transport. These limits have been explored in a variety of microdevices (14-18), where it has been shown that, irrespective of the nature of the carriers (phonons, photons, or electrons), heat is ultimately transported via discrete channels. The maximum contribution per channel to the thermal conductance is equal to the universal thermal conduct-T/3h, where k B is the Boltzmann constant, T is the absolute temperature, and h is the Planck's constant. However, observations of quantum thermal transport in microscale devices have only been possible at sub-Kelvin temperatures, and other attempts at higher-temperature regimes have yielded inconclusive results (19).The energy-level spacing in metallic contacts of atomic size is of the order of electron volts (i.e., much larger than thermal energy); therefore, these junctions offer an opportunity to explore whether thermal transport can still be quantized at room temperature. However, probing thermal transport in atomic junctions is challenging because of the technic...

Many experiments have shown that the conductance histograms of metallic atomic-sized contacts exhibit a peak structure, which is characteristic of the corresponding material. The origin of these peaks still remains as an open problem. In order to shed some light on this issue, we present a theoretical analysis of the conductance histograms of Au atomic contacts. We have combined classical molecular dynamics simulations of the breaking of nanocontacts with conductance calculations based on a tight-binding model. This combination gives us access to crucial information such as contact geometries, forces, minimum cross-section, total conductance and transmission coefficients of the individual conduction channels. The ensemble of our results suggests that the low temperature Au conductance histograms are a consequence of a subtle interplay between mechanical and electrical properties of these nanocontacts. At variance with other suggestions in the literature, our results indicate that the peaks in the Au conductance histograms are not a simple consequence of conductance quantization or the existence of exceptionally stable radii. We show that the main peak in the histogram close to one quantum of conductance is due to the formation of single-atom contacts and chains of gold atoms. Moreover, we present a detailed comparison with experimental results on Au atomic contacts where the individual channel transmissions have been determined.

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Using Monte-Carlo simulation and mean field calculations, we study the liquid-vapour phase diagram of a square well binary fluid mixture as a function of a parameter δ measuring the relative strength of interactions between particles of dissimilar and similar species. The results reveal a rich variety of liquid-vapour coexistence behaviour as δ is tuned. Specifically, we uncover critical end point behaviour, a triple point involving a vapour and two liquids of different density, and tricritical behaviour. For a certain range of δ, the mean field calculations also predict a 'hidden' (metastable) liquid-vapour binodal.