Mixed, charge and heat noises in thermoelectric nanosystems

Mixed, charge and heat current fluctuations as well as thermoelectric differential conductances are considered for non-interacting nanosystems connected to reservoirs. Using the Landauer-Buttiker formalism, we derive general expressions for these quantities and consider their possible relationships in the entire ranges of temperature, voltage and coupling to the environment or reservoirs. We introduce a dimensionless quantity given by the ratio between the product of mixed noises and the product of charge and heat noises, distinguishing between the auto-ratio defined in the same reservoir and the cross-ratio between distinct reservoirs. From the linear response regime to the high-voltage regime, we further specify the analytical expressions of differential conductances, noises and ratios of noises, and examine their behavior in two concrete nanosystems: a quantum point contact in an ohmic environment and a single energy level quantum dot connected to reservoirs. In the linear response regime, we find that these ratios are equal to each other and are simply related to the figure of merit. They can be expressed in terms of differential conductances with the help of the fluctuation-dissipation theorem. In the non-linear regime, these ratios radically distinguish between themselves as the auto-ratio remains bounded by one, while the cross-ratio exhibits rich and complex behaviors. In the quantum dot nanosystem, we moreover demonstrate that the thermoelectric efficiency can be expressed as a ratio of noises in the non-linear Schottky regime. In the intermediate voltage regime, the cross-ratio changes sign and diverges, which evidences a change of sign in the heat cross-noise.Comment: 13 pages, 9 figures, 4 table

Planning Curricular Proposals on Sound and Music with Prospective Secondary-School Teachers

Sound is a preferred context to build foundations on wave phenomena, one of the most important disciplinary referents in physics. It is also one of the best-set frameworks to achieve transversality, overcoming scholastic level and activating emotional aspects which are naturally connected with every day life, as well as with music and perception. Looking at sound and music by a transversal perspective - a border-line approach between science and art, is the adopted statement for a teaching proposal using meta-cognition as a strategy in scientific education. This work analyzes curricular proposals on musical acoustics, planned by prospective secondary-school teachers in the framework of a Formative Intervention Module answering the expectation of making more effective teaching scientific subjects by improving creative capabilities, as well as leading to build logical and scientific categorizations able to consciously discipline artistic activity in music students. With this aim, a particular emphasis is given to those concepts - like sound parameters and structural elements of a musical piece, which are best fitted to be addressed on a transversal perspective, involving simultaneously physics, psychophysics and music.Comment: 12 pages with 5 figures. Submitted for publication in Physics Curriculum Design, Development and Validation - GIREP 2008 book of selected papers, 200

Heat-charge mixed noise and thermoelectric efficiency fluctuations

The close relationship between the noise and the thermoelectric conversion is studied in a quantum dot using a quantum approach based on the non-equilibrium Green function technique. We show that both the figure of merit and the efficiency can be written in term of noise and we highlight the central role played by the correlator between the charge current and the heat current that we call the mixed noise. After giving the expression of this quantity as an integral over energy, we calculate it, first in the linear response regime, next in the limit of small transmission through the barriers (Schottky regime) and finally in the intermediate regime. We discuss the notion of efficiency fluctuations and we also see here that the mixed noise comes into play.Comment: Proceeding of the UPON 2015 conferenc

Getting information from the mixed electrical-heat noise

We give a classification of the different types of noise in a quantum dot, for variable temperature, voltage and frequency. It allows us first to show which kind of information can be extracted from the electrical noise, such as the ac-conductance or the Fano factor. And next, to classify the mixed electrical-heat noise, and to identify in which regimes information on the Seebeck coefficient, on the thermoelectric figure of merit, or on the thermoelectric efficiency can be obtained.Comment: Proceeding of the ICNF 2017 conference, IEEE, International Conference on Noise and Fluctuations (2017

Entropy production in photovoltaic-thermoelectric nanodevices from the non-equilibrium Green's function formalism

We derive the expressions of photon energy and particle currents inside an open nanosystem interacting with light using non-equilibrium Green's functions. The model allows different temperatures for the electron reservoirs, which basically defines a photovoltaic-thermoelectric hybrid. Thanks to these expressions, we formulate the steady-state entropy production rate to assess the efficiency of reversible photovoltaic-thermoelectric nanodevices. Next, quantum dot based nanojunctions are closely examined. We show that entropy production is always positive when one considers spontaneous emission of photons with a specific energy, while in general the emission spectrum is broadened, notably for strong coupling to reservoirs. In this latter case, when the emission is integrated over all the energies of the spectrum, we find that entropy production can reach negative values. This result provides matter to question the second law of thermodynamics for interacting nanosystems beyond the assumption of weak coupling.Comment: 12 pages, 4 figure

Correlations between charge and heat currents in an interacting quantum dot

We consider an interacting quantum dot connected to two reservoirs driven at distinct voltage/temperature and we study the correlations between charge and heat currents first as a function of the applied voltage bias, and second as a function of the temperature gradient between the two reservoirs. The Coulomb interactions in the quantum dot are treated using the Hartree approximation and the dot occupation number is determined self-consistently. The correlators exhibit structures in their voltage dependency which are highly non-linear when the coupling between the dot and the reservoirs is weak, and their behavior with temperature is non-monotonous. Moreover the sign of heat cross-correlator can change contrary to what happens with the charge cross-correlator which is always negative. The presence of Coulomb interactions enlarges the domain of voltage in which the heat cross-correlator is negative.Comment: Proceeding of the SCES 2014 conferenc