# Measuring the imaginary time dynamics of quantum materials

## TL;DR

This paper presents a method to compute imaginary-time correlation functions directly from real-time response data, aiding the analysis of quantum materials' dynamics and comparison with theoretical models.

## Contribution

It introduces a novel approach to derive imaginary-time correlators from real-time response functions, facilitating experimental-theoretical comparisons and identifying quantum critical behavior.

## Key findings

- Applied to Raman spectroscopy data on iron-based superconductors
- Identified potential quantum critical contributions in the nematic response
- Provided a new method for analyzing long-time relaxational dynamics

## Abstract

Theoretical analysis typically involves imaginary-time correlation functions. Inferring real-time dynamical response functions from this information is notoriously difficult. However, as we articulate here, it is straightforward to compute imaginary-time correlators from the measured frequency dependence of (real-time) response functions. In addition to facilitating comparison between theory and experiment, the proposed approach can be useful in extracting certain aspects of the (long-time relaxational) dynamics from a complex data set. We illustrate this with an analysis of the nematic response inferred from Raman scattering spectroscopy on the iron-based superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, which includes a new method for identifying a putative quantum critical contribution to that response.