Cristiano Nisoli, Alan. R. Bishop
We show that a filament in thermal equilibrium subjected to torque $\tau$ and a large enough tension undergoes a phase transition of infinite order when the torque is twice the temperature $T$: for very large values of the ratio $\tau/T$, the polymer's average supercoiling responds linearly to the applied torque, but it tends to zero exponentially fast as the ratio reaches the critical value $\tau/T=1/2$. When approaching the transition from below, correlation lengths tend exponentially to infinity, which suggests an essentially topological nature. At room temperature, this transition happens at a torque $\sim$ 2 pN$\times$nm, and it should be detectable in carefully performed single molecule manipulation experiments.
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http://arxiv.org/abs/1304.2710
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