Evidence of quantum spin liquid state in a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow><mml:mi>Cu</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:math>-based <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>S</mml:mi><mml:mo>=</mml:mo><mml:mfrac><mml:mn>1</mml:mn><mml:mn>2</mml:mn></mml:mfrac></mml:mrow></mml:math> triangular lattice antiferromagnet
K. Bhattacharya, S. Mohanty, A. D. Hillier, Mark T. F. Telling, R. Nath, M. Majumder
Abstract
The layered triangular lattice owing to $1:2$ order of $B$ and ${B}^{\ensuremath{'}}$ sites in the triple perovskite ${A}_{3}B{B}_{2}^{\ensuremath{'}}{\mathrm{O}}_{9}$ family provides an enticing domain for exploring the complex phenomena of quantum spin liquids (QSLs). We report a comprehensive investigation of the ground-state properties of ${\mathrm{Sr}}_{3}{\mathrm{CuTa}}_{2}{\mathrm{O}}_{9}$ that belongs to the above family by employing magnetization, specific heat, and muon spin relaxation $(\ensuremath{\mu}\mathrm{SR})$ experiments down to the lowest temperature of 0.1 K. Analysis of the magnetic susceptibility indicates that the spin lattice is a nearly isotropic $S=1/2$ triangular lattice. We illustrate the observation of a gapless QSL in which conventional spin ordering or freezing effects are absent, even at temperatures more than two orders of magnitude smaller than the exchange energy $({J}_{\mathrm{CW}}/{k}_{\mathrm{B}}\ensuremath{\simeq}\ensuremath{-}5.04 \mathrm{K})$. Magnetic specific heat in zero field follows a power law, ${C}_{\mathrm{m}}\ensuremath{\sim}{T}^{\ensuremath{\eta}}$, below 1.2 K with $\ensuremath{\eta}\ensuremath{\approx}2/3$, which is consistent with a theoretical proposal of the presence of a spinon Fermi surface. Below 1.2 K, the $\ensuremath{\mu}\mathrm{SR}$ relaxation rate shows no temperature dependence, suggesting persistent spin dynamics, as expected for a QSL state. Delving deeper, we also analyze longitudinal field $\ensuremath{\mu}\mathrm{SR}$ spectra, revealing strong dynamical correlations in the spin-disordered ground state. All of these highlight the characteristics of spin entanglement in the QSL state.