Speaker
Felix Ritort
(Universitat de Barcelona)
Description
Temperature is a well-defined quantity for systems in
equilibrium. For glassy systems, it has been extended to the
non-equilibrium regime, showing up as an effective quantity
in a modified version of the fluctuation–dissipation
theorem. However, experimental evidence supporting this
definition remains scarce. Here, we present the first direct
experimental demonstration of the effective temperature by
measuring correlations and responses in single molecules in
non-equilibrium steady states generated under external
random forces. We combine experiment, analytical theory and
simulations for systems with different levels of complexity,
ranging from a single bead in an optical trap to two-state
and multiple-state DNA hairpins. From these data, we extract
a unifying picture for the existence of an effective
temperature based on the relative order of various
timescales characterizing intrinsic relaxation and external
driving. Our study thus introduces driven small systems as a
fertile ground to address fundamental concepts in
statistical physics, condensed-matter physics and biophysics.
Ref: Nature Physics (2015) doi:10.1038/nphys3435