Near-Equilibrium Approach to Transport in Complex Sachdev-Ye-Kitaev Models

TL;DR

This paper analyzes the non-equilibrium transport properties of a complex Sachdev-Ye-Kitaev chain, revealing diffusive behavior, Einstein relations, and bounds related to quantum chaos, providing a tractable approach to strongly interacting systems.

Contribution

It introduces a method to compute transport coefficients in a complex SYK chain, linking diffusion, chaos, and thermoelectric properties in a strongly coupled quantum system.

Findings

Diffusivity matrix simplifies in various limits.

Recovered the Wiedemann-Franz ratio at low temperatures.

Diffusivity eigenvalues are bounded by chaos propagation rates.

Abstract

We study the non-equilibrium dynamics of a one-dimensional complex Sachdev-Ye-Kitaev chain by directly solving for the steady state Green's functions in terms of small perturbations around their equilibrium values. The model exhibits strange metal behavior without quasiparticles and features diffusive propagation of both energy and charge. We explore the thermoelectric transport properties of this system by imposing uniform temperature and chemical potential gradients. We then expand the conserved charges and their associated currents to leading order in these gradients, which we can compute numerically and analytically for different parameter regimes. This allows us to extract the full temperature and chemical potential dependence of the transport coefficients. In particular, we uncover that the diffusivity matrix takes on a simple form in various limits and leads to simplified Einstein relations. At low temperatures, we also recover a previously known result for the Wiedemann-Franz ratio. Furthermore, we establish a relationship between diffusion and quantum chaos by showing that the diffusivity eigenvalues are upper bounded by the chaos propagation rate at all temperatures. Our work showcases an important example of an analytically tractable calculation of transport properties in a strongly interacting quantum system and reveals a more general purpose method for addressing strongly coupled transport.