How heat propagates in `non-Fermi liquid' 3^3He

In Landau's Fermi liquid, transport is governed by scattering between quasi-particles. The normal liquid $^3$He conforms to this picture, but only when T$< 0.02$ T$_F$. Here, we observe that the deviation from the standard behavior is concomitant with the fermion-fermion scattering time falling below the Planckian time, $\frac{\hbar}{k_BT}$. The thermal diffusivity of this quantum liquid is bounded by a minimum set by fundamental physical constants and earlier observed in classical liquids. This implies that collective excitations of the liquid (a sound mode) are carrying heat. We argue that if heat is carried by 2k$_F$ hydrodynamic sound mode, both the amplitude and the hitherto unexplained $T^{1/2}$ temperature dependence of thermal conductivity find an explanation with no other adjustable parameter.Comment: 7 pages, 4 figures and a supplemen

Quantum dissipation in a scalar field theory with gapped momentum states

Understanding quantum dissipation is important from both theoretical perspective and applications. Here, we show how to describe dissipation in a scalar field theory. We treat dissipation non-perturbatively, represent it by a bilinear term in the Lagrangian and quantize the theory. We find that dissipation promotes a gap in momentum space and reduces the particle energy. As a result, particle mass becomes dressed by dissipation due to self-interaction. The underlying mechanism is similar to that governing the propagation of transverse collective modes in liquids. We discuss the interplay between the dissipative and mass terms, the associated different regimes of field dynamics and the emergence of ultraviolet and infrared cutoffs due to dissipation

Slow dynamics and stress relaxation in a liquid as an elastic medium

We propose a new framework to discuss the transition from exponential relaxation in a liquid to the regime of slow dynamics. For the purposes of stress relaxation, we show that a liquid can be treated as an elastic medium. We discuss that, on lowering the temperature, the feed-forward interaction mechanism between local relaxation events becomes operative, and results in slow relaxation.Comment: changed conten

Compressibility, kinetics, and phase transition in pressurized amorphous silica

We model the process of densification of silica glass using molecular dynamics simulation in order to resolve the current controversy regarding the existence of the first-order phase transition in this material. We propose the picture in which the structural changes start to take place in the pressure window between 3 and 5 GPa, after which significant modifications take place with the structural breakdown in the medium range. We also study microscopic processes behind temperature-induced volume decrease of pressurized glass, seen experimentally. We simulate this process and observe similar negative thermal swelling, accompanied by considerable rebonding and relaxations processes. Global nature of rebonding, resulting from the extended character of floppy modes present in silica glass, yields a large value of temperature-induced densification. The densified structure shows broadening of the rings distribution, and we identify the microscopical changes that lead to the breakdown of the medium-range structure. The interesting observation from the long annealing of pressuried glass is the large-amplitude cooperative flow of atoms, which takes place as the structure relaxes through continuous rebonding and relaxation events