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Physical review. B./Physical review. B

Quasi-two-dimensional frustrated spin-1 triangular lattice antiferromagnet C a 3 NiN b 2 O 9 : A proximate spin liquid

Sonia Deswal, Deepu Kumar, Dibyata Rout, Surjeet Singh, Pradeep Kumar

Published Jul 25, 2024• 5 citations
Publisher

Abstract

The spin-1 triangular lattice Heisenberg antiferromagnet $\mathrm{C}{\mathrm{a}}_{3}\mathrm{NiN}{\mathrm{b}}_{2}{\mathrm{O}}_{9}$ and its sister compounds are conjectured to promote the formation of many-body quantum entangled states such as a quantum spin liquid (QSL), an exotic phase which features fractionalized quasiparticle excitations and emergent gauges. We probe the single crystal of $\mathrm{C}{\mathrm{a}}_{3}\mathrm{NiN}{\mathrm{b}}_{2}{\mathrm{O}}_{9}$ using an in-depth Raman spectroscopic technique. Our measurements provide evidence for the fractionalized excitations, suggesting that the current system is in close proximity to the QSL phase. This is also in line with the proposed higher-order fractional magnetization plateau in this system, as these plateaus have an intricate relationship with the spin entanglement. We observed unconventional underlying scattering as a broad continuum with an intensity that shows fermionic statistics. Additionally, phonon modes show Fano asymmetry, also conjectured as a fingerprint of the spin-liquid phase, and above a critical Raman shift also show fermionic statistics in their intensity evolution.

DOI
10.1103/physrevb.110.024430

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The spin-1 triangular lattice Heisenberg antiferromagnet Ca3NiNb2O9\mathrm{C}{\mathrm{a}}_{3}\mathrm{NiN}{\mathrm{b}}_{2}{\mathrm{O}}_{9}Ca3​NiNb2​O9​ and its sister compounds are conjectured to promote the formation of many-body quantum entangled states such as a quantum spin liquid (QSL), an exotic phase which features fractionalized quasiparticle excitations and emergent gauges. We probe the single crystal of Ca3NiNb2O9\mathrm{C}{\mathrm{a}}_{3}\mathrm{NiN}{\mathrm{b}}_{2}{\mathrm{O}}_{9}Ca3​NiNb2​O9​ using an in-depth Raman spectroscopic technique. Our measurements provide evidence for the fractionalized excitations, suggesting that the current system is in close proximity to the QSL phase. This is also in line with the proposed higher-order fractional magnetization plateau in this system, as these plateaus have an intricate relationship with the spin entanglement. We observed unconventional underlying scattering as a broad continuum with an intensity that shows fermionic statistics. Additionally, phonon modes show Fano asymmetry, also conjectured as a fingerprint of the spin-liquid phase, and above a critical Raman shift also show fermionic statistics in their intensity evolution.
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The search for unconventional phases of matter, such as quantum spin liquids (QSL), is one of the fundamental and most debated issues in condensed matter physics. While gapped spin liquids have been widely studied and are now accepted to exist in nature, the existence and stability of gapless spin liquids is more controversial. The authors present their analysis of the frustrated antiferromagnetic spin model on a triangular lattice, which has been suggested very recently as a platform to host QSLs. They use a combination of several numerical techniques to show that a gapless spin liquid, which can be described via emergent interacting Dirac fermions, proves to be an excellent candidate ground state to describe the frustrated regime for the spin model.
Magnetically frustrated spin systems compose a significant proportion of topological quantum spin liquid candidates. Evidence for spin liquids in these materials comes largely from the detection of fractionalised spin-1/2 quasiparticles, known as spinons. However, the one-dimensional Heisenberg chain, which is topologically trivial, also hosts spinons. Thus, observing spinons does not necessarily signify long-range entanglement. Here, we show that spinons arising from one-dimensional physics leave a clear fingerprint in magnetic Raman scattering. We achieve this by calculating the magnetic Raman intensity of coupled Heisenberg chains. Our findings are in excellent agreement with the magnetic Raman scattering measurements on the anisotropic triangular antiferromagnet Ca3_33​ReO5_55​Cl2_22​.
Dynamics and stability of U(1) spin liquids beyond mean-field theory: Triangular-lattice J1J_1J1​-J2J_2J2​ Heisenberg model
Quantum spin liquids (QSLs) are long-range entangled phases of frustrated magnets exhibiting fractionalised spin excitations. In two dimensions, there is limited analytical understanding of their excitation spectra beyond parton mean-field theories, which fail to capture many features of the finite frequency dynamical response. We use a self-consistent mean-field theory combined with the random phase approximation (RPA) for the J1J_1J1​-J2J_2J2​ Heisenberg model on the triangular lattice to describe the strong spinon-spinon interactions of the U(1) Dirac QSL. We obtain quantitative results for the dynamical spin structure factor and phase diagram compatible with comprehensive numerical efforts. We show the continuum response at the Brillouin zone corners is described by a spinon-exciton hybridised with monopole gauge excitations. We further show that the transition from the QSL to 120-degree coplanar order is in the QED3_33​ O(3)-GN universality class. We extend the method to chiral QSLs and XXZ anisotropy, and discuss its broad range of applicability to other models and for describing inelastic neutron scattering experiments in KYbSe2_22​.
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Quantum antiferromagnets on geometrically frustrated lattices have long attracted interest for the formation of quantum disordered states and the possible emergence of quantum spin liquid (QSL) ground states. Here we turn to the nearest-neighbor spin-1/21/21/2 Heisenberg antiferromagnet on the maple-leaf lattice, which is known to relieve frustration by the formation of canted ${120}^{\ensuremath{\circ}}$ magnetic order or valence bond crystal order when varying the bond anisotropy. Employing a pseudofermion functional renormalization group approach to assess its ground state phase diagram in detail, we present evidence for a QSL regime sandwiched between these two limiting phases. The formation of such a QSL might signal proximity to a possible deconfined quantum critical point from which it emerges, and that is potentially accessible by tuning the exchange couplings. Our conclusions are based on large-scale simulations involving a careful finite-size scaling analysis of the behavior of magnetic susceptibility and spin-spin correlation functions under renormalization group flow.