324 research outputs found
Tuning the thermal conductance of molecular junctions with interference effects
We present an \emph{ab initio} study of the role of interference effects in
the thermal conductance of single-molecule junctions. To be precise, using a
first-principles transport method based on density functional theory, we
analyze the coherent phonon transport in single-molecule junctions based on
several benzene and oligo-phenylene-ethynylene derivatives. We show that the
thermal conductance of these junctions can be tuned via the inclusion of
substituents, which induces destructive interference effects and results in a
decrease of the thermal conductance with respect to the unmodified molecules.
In particular, we demonstrate that these interference effects manifest as
antiresonances in the phonon transmission, whose energy positions can be
controlled by varying the mass of the substituents. Our work provides clear
strategies for the heat management in molecular junctions and more generally in
nanostructured metal-organic hybrid systems, which are important to determine,
how these systems can function as efficient energy-conversion devices such as
thermoelectric generators and refrigerators
Spectral properties of one-dimensional Fermi systems after an interaction quench
We show that the single-particle spectral properties of gapless
one-dimensional Fermi systems in the Luttinger liquid state reached at
intermediate times after an abrupt quench of the two-particle interaction are
highly indicative of the unusual nonequilibrium nature of this state. The line
shapes of the momentum integrated and resolved spectral functions strongly
differ from their ground state as well as finite temperature equilibrium
counterparts. Using an energy resolution improved version of radio-frequency
spectroscopy of quasi one-dimensional cold Fermi gases it should be possible to
experimentally identify this nonequilibrium state by its pronounced spectral
signatures.Comment: 5 pages, 3 figure
Thermal conductance of metallic atomic-size contacts: Phonon transport and Wiedemann-Franz law
Motivated by recent experiments [Science 355, 6330 (2017); Nat. Nanotechnol.
12, 430 (2017)], we present here an extensive theoretical analysis of the
thermal conductance of atomic-size contacts made of three different metals,
namely gold (Au), platinum (Pt) and aluminum (Al)
Pro-environmental behavior as a signal of cooperativeness: Evidence from a social dilemma experiment
Review of recent developments of the functional renormalization group for systems out of equilibrium
We recapitulate recent developments of the functional renormalization group (FRG) approach to the steady state of systems out of thermal equilibrium. In particular, we discuss second-order truncation schemes which account for the frequency-dependence of the two particle vertex and which incorporate inelastic processes. Our focus is on two different types of one-dimensional fermion chains: (i) infinite, open systems which feature a translation symmetry, and (ii) finite systems coupled to left and right reservoirs. In addition to giving a detailed and unified review of the technical derivation of the FRG schemes, we briefly summarize some of the key physical results. In particular, we compute the non-equilibrium phase diagram and analyze the fate of the Berezinskii–Kosterlitz–Thouless transition in the infinite, open system
Integral Equation Methods for the Morse-Ingard Equations
We present two (a decoupled and a coupled) integral-equation-based methods
for the Morse-Ingard equations subject to Neumann boundary conditions on the
exterior domain. Both methods are based on second-kind integral equation (SKIE)
formulations. The coupled method is well-conditioned and can achieve high
accuracy. The decoupled method has lower computational cost and more
flexibility in dealing with the boundary layer; however, it is prone to the
ill-conditioning of the decoupling transform and cannot achieve as high
accuracy as the coupled method. We show numerical examples using a Nystr\"om
method based on quadrature-by-expansion (QBX) with fast-multipole acceleration.
We demonstrate the accuracy and efficiency of the solvers in both two and three
dimensions with complex geometry
Transmission eigenchannels for coherent phonon transport
We present a procedure to determine transmission eigenchannels for coherent
phonon transport in nanoscale devices using the framework of nonequilibrium
Green's functions. We illustrate our procedure by analyzing a one-dimensional
chain, where all steps can be carried out analytically. More importantly, we
show how the procedure can be combined with ab initio calculations to provide a
better understanding of phonon heat transport in realistic atomic-scale
junctions. In particular, we study the phonon eigenchannels in a gold metallic
atomic-size contact and different single-molecule junctions based on molecules
such as an alkane chain, C, and a brominated benzene-diamine, where in
this latter case destructive phonon interference effects take place
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