Electric field induced permanent superconductivity in layered metal nitride chloride MNCl(M: Hf and Zr)

TL;DR

This study demonstrates that applying a proper gate voltage in an electric double-layer transistor can induce permanent superconductivity in layered metal nitride chlorides HfNCl and ZrNCl, revealing a new electrochemical approach to tuning 2D electronic states.

Contribution

It introduces a method to achieve permanent superconductivity in layered nitrides via electrochemical gating, bridging chemical synthesis and electrochemical mechanisms.

Findings

Permanent superconductivity with Tc of 24 K in HfNCl and 15 K in ZrNCl.

Reversible switching between insulating and superconducting states at low temperature.

Irreversible superconductivity induced by high-temperature gating causing Cl deintercalation.

Abstract

The device of electric double-layer transistor (EDLT) with ionic liquid has been employed as an effective way to dope carriers over a wide range, which can induce metallic state, magnetic reconstruction and superconducting transition. However, the induced electronic state can hardly survive in the materials after releasing the gate voltage, strongly restricting the experimental study for discovery of physics. Here, we show that a permanent superconductivity with transition temperature $T_c$ of 24 and 15 K is realized in single crystals and polycrystalline samples of HfNCl and ZrNCl upon applying proper gate voltage $V_{\rm G}$, respectively. Reversible change between insulating and superconducting state can be obtained through applying positive and negative $V_{\rm G}$ at low temperature such as 220 K, whereas $V_{\rm G}$ applied at high temperatures ($\geq$ 250 K) could induce partial deintercalation of Cl ions and result in irreversible superconducting transition. The present results clarify a connection between traditional chemical synthesis and the electrochemical mechanism of the EDLT induced superconductivity. Such a technique shows a great potential to systematically tune the bulk electronic state in the similar two-dimensional (2D) systems.