Quantum spin liquid ground state with the evidence of roton-like excitations at elevated temperatures in the triangular-lattice delafossite YbCuSe${}_2$

Abstract

We present a comprehensive experimental investigation of the temperature evolution of magnetic states in triangular-lattice delafossite YbCuSe${}_2$. Magnetization measurements on high-quality single crystals reveal easy-plane anisotropy. Specific heat, magnetization, and muon spin relaxation ($\mu$SR) establish the absence of magnetic order or spin freezing down to 0.03 K ($\le J_{\mathrm{avg}}/250$), demonstrating a dynamically fluctuating quantum spin liquid (QSL) ground state. Thermodynamic measurements uncover multiple characteristic energy scales at $T_H\approx 4.5$ K, $T_L\approx 1.8$ K, and $T^{\ast }\approx 0.7$ K. Below $T^{\ast }$, $\mu$SR detects a dynamical phase separation in which the majority of the spins are forming a QSL state whereas the remaining spins form a sporadic, disorder-induced state decoupled from the dominant QSL component. Remarkably, the unconventional temperature dependence of the $\mu$SR relaxation rate indicates roton-like excitations emerging between $T_H$ and $T_L$, a feature not previously observed in any QSL system, preceding the stabilization of the low-temperature QSL at 0.3 K. These findings identify YbCuSe${}_2$ as a unique QSL platform, providing valuable insights for further experimental and theoretical exploration.

8 pages, 4 figures

References in corpus (37)

• Mantid - Data Analysis and Visualization Package for Neutron Scattering and $\mu SR$ Experiments
• Projected wavefunction study of Spin-1/2 Heisenberg model on the Kagome lattice
• Spin liquid phase of the $S=\frac{1}{2}$ $J_1-J_2$ Heisenberg model on the triangular lattice
• Unusual ordered phases of highly frustrated magnets: a review
• Fractional excitations in the square-lattice quantum antiferromagnet
• $\mu$SR evidence for the U(1) quantum spin liquid ground state in the triangular antiferromagnet YbMgGaO${}_4$
• Anisotropic field-induced ordering in the triangular-lattice quantum spin liquid NaYbSe${}_2$
• Excitation spectra of the spin-1/2 triangular-lattice Heisenberg antiferromagnet
• Field-induced instability of the quantum-spin-liquid ground state in the $J_{\mathrm{eff}}=\frac{1}{2}$ triangular-lattice compound NaYbO${}_2$
• Quantum spin liquid ground state in the disorder free triangular lattice NaYbS${}_2$
• Quantum spin liquid in the Ising triangular-lattice antiferromagnet neodymium heptatantalate
• Witnessing quantum criticality and entanglement in the triangular antiferromagnet KYbSe${}_2$
• Field-induced magnetic transition and spin fluctuation in quantum spin liquid candidate CsYbSe${}_2$
• The phase diagram of the antiferromagnetic XXZ model on the triangular lattice
• Microscopic Model Calculations for the Magnetization Process of Layered Triangular-Lattice Quantum Antiferromagnets
• Spin excitations in the frustrated triangular lattice antiferromagnet NaYbO${}_2$
• Crystalline Electric-Field Excitations in Quantum Spin Liquids Candidate $NaYbS{e}_2$
• Magnetic field induced quantum spin liquid in the two coupled trillium lattices of K${}_2$Ni${}_2$(SO${}_4$)${}_3$
• Avoided quasiparticle decay and enhanced excitation continuum in the spin-1/2 near-Heisenberg triangular antiferromagnet Ba3CoSb2O9
• Field-Induced Spin Excitations in the Spin-1/2 Triangular-Lattice Antiferromagnet CsYbSe${}_2$
• Complete field-induced spectral response of the spin-1/2 triangular-lattice antiferromagnet CsYbSe${}_2$
• Spectral function of the $J_1-J_2$ Heisenberg model on the triangular lattice
• Evidence of Dirac Quantum Spin Liquid in YbZn2GaO5
• Finite-temperature properties of the Kitaev-Heisenberg models on kagome and triangular lattices studied by improved finite-temperature Lanczos methods
• Gapless quantum spin liquid in the triangular system Sr${}_3$CuSb${}_2$O${}_9$
• Synthesis and Anisotropic Magnetism in Quantum Spin Liquid Candidates $A$YbSe${}_2$ ($A$ = K and Rb)
• Continuum excitations in a spin-supersolid on a triangular lattice
• Schwinger boson mean field study of the $J_1$-$J_2$ Heisenberg quantum antiferromagnet on the triangular lattice
• Magnetic field effects on the quantum spin liquid behaviors of NaYbS${}_2$
• Double Magnon-Roton Excitations in the Triangular-Lattice Spin Supersolid
• Phase Diagram of the Easy-Axis Triangular-Lattice $J_1-J_2$ Model
• Quantum Spin Dynamics Due to Strong Kitaev Interactions in the Triangular-Lattice Antiferromagnet CsCeSe${}_2$
• Stripe antiferromagnetic ground state of ideal triangular lattice KErSe${}_2$
• Magnetic, thermodynamic, and magnetotransport properties of CeGaGe and PrGaGe single crystals
• Evidence of quantum spin liquid state in a Cu${}^{2+}$-based $S=1/2$ triangular lattice antiferromagnet
• Origin of the hidden energy scale and the $f$-ratio in geometrically frustrated magnets
• Dominant Kitaev interaction and field-induced quantum phase transitions in triangular-lattice KCeSe2