On Hydrodynamic Correlations in Low-Dimensional Interacting Systems

TL;DR

This paper critiques the limitations of Bosonization in describing long-range correlations in low-dimensional quantum systems and develops a hydrodynamic approach to improve theoretical modeling and predictions.

Contribution

It introduces a hydrodynamic framework to address Bosonization's failure in capturing long-range correlators in one-dimensional systems.

Findings

Bosonization fails for large disturbances in correlators.

Hydrodynamic description successfully models long-range correlations.

Asymptotic analysis of EFP in XY model relates to criticality.

Abstract

Low-dimensional systems are an important field of current theoretical and experimental research. Recent technological developments provide many possible realizations of effectively one-dimensional systems. These devices promise to give us access to a new range of phenomena. It is therefore very interesting to develop theoretical methods specific for such systems to model their behavior and calculate the correlators of the resulting theory. Incidentally, one such method exists and is known as Bosonization. It can be applied to one-dimensional systems and effectively describes low energy excitations in a universal way. We use the example of a correlator known as the Emptiness Formation Probability to show that Bosonization fails to describe some long range correlators corresponding to large disturbances (the EFP measures the probability for the ground state of the system to develop a region without particles). We trace this failure to the fact that Bosonization is constructed as a linear approximation of the full theory and we set up to develop a collective description with the required non-linearity. The resulting scheme is essentially a Hydrodynamic paradigm for quantum systems. We show how to construct such a hydrodynamic description for a variety of exactly integrable models and illustrate how it can be used to make new predictions. For the special case of the spin-1/2 XY model we take advantage of the structure of the model to express the EFP as a determinant of a very special type of matrix, known as Toeplitz Matrix. We use the theory of Toeplitz determinants to calculate the asymptotic behavior of the EFP in the XY model and discuss its relation with the criticality of the theory.