Metallization of Quantum Material GaTa4Se8 at High Pressure - Drs. Hongshan Deng and Yang Ding

JUNE 15, 2021

A team of HPSTAR scientists led by Dr. Yang Ding and Dr. Hongshan Deng has solved a thirty-year mystery regarding the insulator-to-metal transition in the quantum molecular compound GaTa₄Se₈(GTS), a material that could revolutionize computer memory as a resistive RAM. Using new methods integrating electrical resistance with Raman spectroscopy at high pressure, they observed an extraordinary range of material phases in  GaTa₄Se₈ at previously unattainable pressures above 50 GPa. "Metallization of Quantum Material GaTa₄Se₈ at High Pressure" is published in the latest edition of the Journal of Physical Chemistry Letters as a supplementary journal cover.

GTS is considered a candidate for both resistive switching materials and memory devices. It exhibits successive transitions from a Mott insulator to a metal and a metal to a superconductor at high pressure. In addition to its unique magnetic and transport properties at ambient conditions, potential material phases include intriguing topological superconductivity, spin-freezing superconductivity, and a multipolar magnetic phase. However, these vast, exciting possibilities remain largely unexplored, especially in the high-pressure regime until now.

Upon compression, the HPSTAR team revealed that GTS exhibits an unprecedented number of phases, showing vastly different electronic and magnetic properties. Remarkably, all phases sustained a superconducting state. The most interesting discovery using the group’s new techniques was that the band closing and the insulator-metal transition is actually driven by structural changes. Thus, the insulator-to-metal transitions in  GaTa₄Se₈ is a Peierls-like transition rather than a Mott transition. This observation defies three decades’ worth of belief that the insulator-to-metal transition is always a Mott-type.   

The observation of  GaTa₄Se₈'s unique variety of phases is unprecedented in published literature to date. This breakthrough research will undoubtedly stimulate more interest in understanding the unusually rich phase diagram of  GaTa₄Se₈, which has a potential impact for materials science and applications.

Caption: Resistive switching materials  GaTa₄Se₈ experience insulator to metal and superconductivity transition accompany cubic to monoclinic structure transition under high pressure. Discovery the band gap and structure distortion linear correlation. using the new techniques integrating electrical resistance with Raman spectroscopy measurement.

量子材料GaTa₄Se₈不仅是一种电阻开关和储存介质材料,它还展现出了多种奇异有趣的物理性质如绝缘体到金属相变、Jeff量子态以及拓扑超导等，所以近来备受关注。然而此材料中最为核心的绝缘体基态性质以及其金属相变机制却一直存在争论。最近北京高压科学研究中心的丁阳研究员带领的研究团队通过综合利用高压及同步辐射X射线衍射、吸收光谱、Raman光谱，以及电阻测量等多种实验方法，并结合第一性原理计算，对 GaTa₄Se₈中高压诱导的金属化相变进行了深入的研究，发现其能隙减小与结构畸变存在一个不易被观察到的相关性，从而确定了 GaTa₄Se₈的金属化相变实际上是Peierls-Mott型，而非几十年一直认为的纯Mott型相变。这一结论对深入理解和调控 GaTa₄Se₈的各种相关物理性质极为关键。相关成果最近以封面文章的形式发表在 Journal of Physical Chemistry Letters（DOI 10.1021/acs.jpclett.1c01069 ）杂志上。