High pressure sequence of Ba_3NiSb_2O_9 structural phases: new $S = 1$ quantum spin-liquids based on Ni^{2+}

TL;DR

This study reports the synthesis of two new S=1 quantum spin liquid candidates in Ba3NiSb2O9 under high pressure, exhibiting gapless behavior and Fermi-liquid-like properties despite being insulating.

Contribution

It introduces two novel S=1 quantum spin liquids with distinct lattice structures, expanding the understanding of gapless QSLs in 3D and triangular lattices.

Findings

Both phases show no magnetic order down to 0.35 K.

The 6H-B phase exhibits Fermi-liquid-like behavior with a large Wilson ratio.

The 3C phase displays a T^2 specific heat, indicating a 3D QSL ground state.

Abstract

By using a high pressure, high temperature (HPHT) technique, the antiferromagnetically ordered ($T_N$ = 13.5 K) 6H-A phase of Ba$_3$NiSb$_2$O$_9$ was transformed into two new gapless quantum spin liquid(QSL) candidates with S=1 (Ni$^{2+}$) moments: the 6H-B phase with a Ni$^{2+}$-triangular lattice and the 3C-phase with a Ni$^{2+}$-three-dimensional (3D) edge-shared tetrahedral lattice. Both compounds show no magnetic order down to 0.35 K despite Curie-Weiss temperatures $\theta_{CW}$ of -75.5 K (6H-B) and -182.5 K (3C), respectively. Below $\sim 25$ K the magnetic susceptibility of the 6H-B phase saturates to a constant value $\chi_0 = 0.013 $ emu/mol which is followed below 7 K, by a linear-temperature dependent magnetic specific heat ($C_M$) displaying a giant coefficient $\gamma$ = 168 mJ/mol-K$^2$. Both observations suggest the development of a Fermi-liquid like ground state characterized by a Wilson ratio of 5.6 in this insulating material. For the 3C phase, the $C_M \propto T^2$ behavior indicates a unique S=1, 3D QSL ground-state.