Pseudogap phase and fractionalization: Predictions for Josephson junction setup

TL;DR

This paper proposes experimental signatures in Josephson junctions that can distinguish between a pair density wave (PDW) and coexisting orders as explanations for the pseudogap phase in underdoped cuprates, aiding in understanding this enigmatic phenomenon.

Contribution

It introduces specific testable predictions for Josephson junction experiments that differentiate a fractionalized PDW from coexisting charge order and superconductivity.

Findings

AC Josephson current exhibits beat-like structure in PDW scenario

Additional frequencies appear at half-odd integer multiples of the Josephson frequency

Sharp Shapiro steps break down in the PDW case

Abstract

The pseudogap regime of the underdoped cuprates arguably remains one of the most enigmatic phenomena of correlated quantum matter. Recent theoretical ideas suggest that a pair density wave (PDW) or a "fractionalized PDW" could be a key ingredient for the understanding of the pseudogap physics. These ideas are to be contrasted to the scenario where charge density wave order and superconductivity coexist at low temperatures. In this paper, we present a few tests to compare the two scenarios in a Josephson junction setup. For a PDW scenario, we observe a beat-like structure of AC Josephson current. The additional frequencies for the AC Josephson current appear at the half-odd integer multiple of the standard Josephson frequency. We can extract the modulation wavevector of the PDW state by studying the average Josephson current. Furthermore, the usual sharp Shapiro steps break down. In contrast, these signatures are absent for the simple coexistence of orders. Any detection of such signatures in a similar experimental setup will strongly support the PDW scenario for the pseudogap phase.