Magnetic field induced quantum spin liquid in the two coupled trillium lattices of K$_2$Ni$_2$(SO$_4$)$_3$

Abstract

Quantum spin liquids are exotic states of matter which form when strongly frustrated magnetic interactions induce a highly entangled quantum paramagnet far below the energy scale of the magnetic interactions. Three-dimensional cases are especially challenging due to the significant reduction of the influence of quantum fluctuations. Here, we report the magnetic characterization of K 2 Ni 2 (SO 4 ) 3 forming a three dimensional network of Ni 2+ spins. Using density functional theory calculations we show that this network consists of two interconnected spin-1 trillium lattices.In the absence of a magnetic field, magnetization, specific heat, neutron scattering and muon spin relaxation experiments demonstrate a highly correlated and dynamic state, coexisting with a peculiar, very small static component exhibiting a strongly renormalized moment. A magnetic field B 4 T diminishes the ordered component and drives the system in a pure quantum spin liquid state. This shows that a system of interconnected S = 1 trillium lattices exhibit a significantly elevated level of geometrical frustration.Strongly correlated systems are at the forefront of condensed matter research, exhibiting exotic phases and nourishing novel theoretical concepts. In magnetism, one of the most sought-after strongly correlated phase is a quantum spin liquid (QSL), a state in which spins avoid long-range order (LRO) and are considered entangled on all spatial scales [1-3]. To realize a QSL, geometrical frustration and reduced dimensionality of the magnetic subsystem have been considered vital. 1D Heisenberg chains exhibit QSL behavior even without frustration [4,5] while 3D cases are rare due to the significant reduction of quantum fluctuations. Nevertheless, it has been found that 3D lattices like pyrochlore [6-8] and hyperhyperkagome [9, 10] support QSL behavior.In this Letter we provide extensive experimental and computational evidence that K 2 Ni 2 (SO 4 ) 3 exhibits QSL behavior, based on a novel arrangement of spins forming two interconnected trillium lattices. Previous work on compounds featuring a single trillium lattice was mainly driven by a pressure-induced quantum phase transition (QPT) discovered in the itinerant helimagnet MnSi [11] and evidence of non-Fermi liquid behavior above a critical pressure [12]. Later theoretical works [13,14] showed some degree of geometrical frustration in the trillium lattice, nevertheless insufficient to prevent the onset of LRO. From that perspective, K 2 Ni 2 (SO 4 ) 3 and other members of the langbeinite family K 2 M 2 (SO 4 ) 3 (M =