Abstract
Lacunar spinel GaTa4Se8 is a unique example of spin–orbit coupled Mott insulator described by molecular jeff = 3/2 states. It becomes superconducting at Tc = 5.8 K under pressure without doping. In this work, we show, this pressure-induced superconductivity is a realization of a new type topological phase characterized by spin-2 Cooper pairs. Starting from first-principles density functional calculations and random phase approximation, we construct the microscopic model and perform the detailed analysis. Applying pressure is found to trigger the virtual interband tunneling processes assisted by strong Hund coupling, thereby stabilizing a particular d-wave quintet channel. Furthermore, we show that its Bogoliubov quasiparticles and their surface states exhibit novel topological nature. To verify our theory, we propose unique experimental signatures that can be measured by Josephson junction transport and scanning tunneling microscope. Our findings open up new directions searching for exotic superconductivity in spin–orbit coupled materials.
Highlights
The confluence of spin–orbit coupling (SOC) and strong electron correlation provides a new paradigm of solid-state quantum phenomena[1,2,3,4,5,6]
In order to facilitate its confirmation, we propose the concrete experimental setups and the signatures to be identified in Josephson junction transport and scanning tunneling microscopy (STM)
Among the possible superconducting order parameter configurations with t2g most favorable state, syhmψTmT e!γtrψyi, we find that the 1⁄4 ð1; 0; 0Þ-state wenheerrgeeti!cγal1⁄4ly ðγ[1]; γ2; γ3Þ represents quintet pairing with t2g symmetry, is characterized by gapless nodal lines as shown in Fig. 2a; see Supplementary Information 4 for more details of our calculation
Summary
The confluence of spin–orbit coupling (SOC) and strong electron correlation provides a new paradigm of solid-state quantum phenomena[1,2,3,4,5,6]. Applying pressure induces the phase transition from a spin–orbit coupled Mott insulator to a metal and eventually to a superconductor[22,30,31,32]. The characteristics of this superconductivity are quite intriguing in many regards. Due to the intriguing interplay of multi-band jeff = 3/2 character and interband correlation, novel d-wave quintet superconductivity with spin-2 Cooper pairs is stabilized. In order to facilitate its confirmation, we propose the concrete experimental setups and the signatures to be identified in Josephson junction transport and scanning tunneling microscopy (STM)
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