Heating and cooling mechanisms in single-molecule junctions

Abstract

In this work we analyze the role played by molecular resonances on the thermal behavior of single molecule junction. We consider a fullerene molecule on a Cu͑110͒ substrate when current is driven across using an scanning tunnel microscope tip. Calculations based on density-functional theory and nonequilibrium Green's functions have predicted a lowering of molecular temperature whenever a resonance gets close to the injection window. This behavior, due on the interplay of emission and absorption phonon processes, can take place ͑at T 0 =0 K͒ for bias E L − ប Ͻ V Ͻ E L + ប where E L and ប are the lowest unoccupied molecular orbital ͑LUMO͒ and phonon energy, respectively. We further show that the decay channel into electron-hole excitations is very effective in keeping the molecule stable, whereas the direct decay of the vibron into contact phonons gives only a marginal correction. Furthermore, we have investigated the possibility to cool the molecule below the environment temperature. We found that this phenomena is favorite for modes with energy ប Ͻ k b T 0 and ប Ͻ E L − E F .

First-principles quantum transport with electron-vibration interactions: A maximally localized Wannier functions approach

“…We have also observed that nonequilibrium vibrational occupations for high-energy modes can be cooled down in an intermediate bias regime, which may be understood in terms of a resonant state in the device region. This observation agrees well with resonant cooling reported in other first-principle calculations 63 .…”

“…One can hint at a qualitative explanation for this cooling behavior examining the local density of states in the device region, as recently reported in Ref. 63 . As observed in Fig.14-(a), there is one resonant peak located at a energy higher than µ eq , which is the common Fermi level before the bias is applied.…”

Effect of broadening in the weak-coupling limit of vibrationally coupled electron transport through molecular junctions and the analogy to quantum dot circuit QED systems

“…Photons can be localized inside a cavity [4][5][6]. In both cases, the bosonic degrees of freedom can be driven into highly excited nonequilibrium states [7][8][9][10][11][12][13][14]. It is challenging to understand these states, because they cannot be described via a Bose-Einstein distribution function.…”

“…Nevertheless, these states determine the functionality and efficiency of many devices that may be used for nanoelectronic applications [8][9][10][15][16][17][18][19][20][21][22][23], quantum information processing [16,[24][25][26], solar energy conversion [27][28][29][30] or the control of chemical processes [31][32][33][34][35].…”

Single molecular shuttle-junction: Shot noise and decoherence

“…The measurement correction can be better than the zero-point-motion uncertainty. In addition, vibrational junctions have abundant physical applications such as heat transfer and cooling based on nonequilibrium hot electron transport [13,14], subresonance inelastic electronic transport that is analogous to atomic laser-induced cooling [14,15] and tip-induced cooling [16]. The effective temperature of the molecular island is defined as the internal energy stored in the vibrational degrees of freedom.…”