Chin. Phys. Lett.  2018, Vol.35 Issue (9): 097401  DOI:10.1088/0256-307X/35/9/097401
Electric Field Induced Permanent Superconductivity in Layered Metal Nitride Chlorides HfNCl and ZrNCl
1Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing 1001902School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 1000493School of Physics and Electronics, Shandong Normal University, Jinan 2500144Collaborative Innovation Center of Quantum Matter, Beijing 100190>

### Abstract

Devices of electric double-layer transistors (EDLTs) with ionic liquid have been employed as an effective way to dope carriers over a wide range. However, the induced electronic states can hardly survive in the materials after releasing the gate voltage $V_{\rm G}$ at temperatures higher than the melting point of the selected ionic liquid. Here we show that a permanent superconductivity with transition temperature $T_{\rm c}$ of 24 and 15 K is realized in single crystals and polycrystalline samples of HfNCl and ZrNCl upon applying proper $V_{\rm G}$'s at different temperatures. Reversible change between insulating and superconducting states can be obtained by applying positive and negative $V_{\rm G}$ at low temperature such as 220 K, whereas $V_{\rm G}$'s applied at 250 K induce the irreversible superconducting transition. The upper critical field $H_{\rm c2}$ of the superconducting states obtained at different gating temperatures shows similar temperature dependence. We propose a reasonable scenario that partial vacancy of Cl ions could be caused by applying proper $V_{\rm G}$'s at slightly higher processing temperatures, which consequently results in a permanent electron doping in the system. Such a technique shows great potential to systematically tune the bulk electronic state in the similar two-dimensional systems.

### 基金资助

Supported by the National Natural Science Foundation of China under Grant No 11704403, the National Key Research Program of China under Grant No 2016YFA0401000 and 2016YFA0300604, and the Strategic Priority Research Program (B) of Chinese Academy of Sciences under Grant No XDB07020100.

### 引用本文

[英文]
Shuai Zhang, Mo-Ran Gao, Huan-Yan Fu, Xin-Min Wang, Zhi-An Ren, Gen-Fu Chen. Electric Field Induced Permanent Superconductivity in Layered Metal Nitride Chlorides HfNCl and ZrNCl[J]. CPL, 2018, 35(9): 097401.

PACS