Charge density wave and Weyl Semimetal phase in Y$_2$Ir$_2$O$_7$

TL;DR

This paper reports the discovery of a charge density wave phase in Y$_2$Ir$_2$O$_7$ below 10 K and its transition to a Weyl semimetal phase at higher temperatures, with phase control via crystallite size reduction.

Contribution

It demonstrates the coexistence and temperature-driven transition between CDW and WSM phases in Y$_2$Ir$_2$O$_7$, revealing phase tunability through crystallite size.

Findings

CDW phase observed below 10 K with nonlinear conductivity

Transition to Weyl semimetal phase at higher temperatures

Crystallite size reduction suppresses CDW, restoring WSM phase

Abstract

The subtle interplay of band topology and symmetry broken phase, induced by electron correlations, has immense contemporary relevance and potentially offers novel physical insights. Here, we demonstrate charge density wave (CDW) in bulk Y$_2$Ir$_2$O$_7$ for T < 10 K, and its transition to the Weyl semimetal (WSM) phase at higher temperatures. The CDW phase is evidenced by a) current induced nonlinear conductivity with negative differential resistance at low temperature, b) low frequency Debye like dielectric relaxation at low temperature with a large dielectric constant, and c) an anomaly in the temperature dependence of the thermal expansion coefficient. The WSM phase at higher temperature is confirmed by the DC and AC transport measurements which show an inductive response at low frequencies. More interestingly, we show that by reducing the crystallite size, the low temperature CDW phase can be eliminated leading to the restoration of the WSM phase.