Methodologies 

Elaboration of theoretical and numerical frameworks 

One important expertise of the NQS group lies in the elaboration of theoretical and numerical frameworks to address realistic device functioning and to decipher the underlying mechanisms that may boost device performances.

This group expertise is developed along three directions:

  • taking into account electron-boson interaction including accelerated numerical protocols [Y. Lee, M. Lannoo, N. Cavassilas, M. Luisier, and M. Bescond, Phys. Rev. B 93, 205411 (2016) http://dx.doi.org/10.1103/PhysRevB.93.205411]

  • using NEGF-based modeling and simulations for completing thermodynamics in the quantum regime [F. Michelini, A. Crépieux and K. Beltako, Journal of Physics : Condensed Matter 29, 175301 (2017) https://doi.org/10.1088/1361-648X/aa62e4]

  • providing derivations, simulations and interpretations within time-dependent regimes.

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Example

As an example of our results, NQS group has investigated the time-dependent regime including electron-electron correlations at the Hartree-Fock level

[K. Beltako, N. Cavassilas, M. Lannoo, F. Michelini, J. Phys. Chem. C 123, 30885-30892 (2019) https://doi.org/10.1021/acs.jpcc.9b10911].

 

In close relationship with thermodynamics, a formal framework was also derived to address time-dependent energy transport inside quantum networks. The approach permits to investigate how energy converted from a femtosecond laser pulse is stored and released in a molecular donor-acceptor junction, comparing fork and loop circuit configurations presented Fig 1A). Time-resolved analysis reveals that a long-lasting energy flow may emerge from asymmetry as shown Fig. 1B), which explains the global energy transfer enhancement inside the loop architecture

[F. Michelini and K. Beltako, Phys. Rev. B100,024308 (2019) https://doi.org/10.1103/PhysRevB.100.024308].

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Fig. 1. A) Direct energy current (in Arb. Unit) flowing between sites D1, D2, A and B for the loop (solid lines) and the fork (dashed lines) circuits, as a function of D2 − A coupling.  B) Time-resolved energy current between D1 and A in the driven and relaxation regimes for four different D2 − A coupling values, βD2−A = 0.042 (purple), 0.060 (sky blue), 0. (yellow, fork circuit) and 0.05 eV (red, symmetric loop circuit). Both short and long-time responses are represented in different figures for convenience.

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