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Register a new userSpin-orbit-coupled triangular-lattice spin liquid in rare-earth chalcogenides
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Spin-orbit coupling is an important ingredient in many spin liquid candidate materials, especially among the rare-earth magnets and Kitaev materials. We explore the rare-earth chalcogenides NaYbS$_2$ where the Yb$^{3+}$ ions form a perfect triangular lattice. Unlike its isostructural counterpart YbMgGaO$_4$ and the kagom{e} lattice herbertsmithite, this material does not have any site disorders both in magnetic and non-magnetic sites. We carried out the thermodynamic and inelastic neutron scattering measurements. The magnetic dynamics could be observed with a broad gapless excitation band up to 1.0 meV at 50 mK and 0 T, no static long-range magnetic ordering is detected down to 50 mK. We discuss the possibility of Dirac spin liquid for NaYbS$_2$. We identify the experimental signatures of field-induced transitions from the disordered spin liquid to an ordered antiferromagnet with an excitation gap at finite magnetic fields and discuss this result with our Monte Carlo calculation of the proposed spin model. Our findings could inspire further interests in the spin-orbit-coupled spin liquids and the magnetic ordering transition from them.
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Frustrated quantum magnets are expected to host many exotic quantum spin states like quantum spin liquid (QSL), and have attracted numerous interest in modern condensed matter physics. The discovery of the triangular lattice spin liquid candidate YbMgGaO$_4$ stimulated an increasing attention on the rare-earth-based frustrated magnets with strong spin-orbit coupling. Here we report the synthesis and characterization of a large family of rare-earth chalcogenides AReCh$_2$ (A = alkali or monovalent ions, Re = rare earth, Ch = O, S, Se). The family compounds share the same structure (R$bar{3}$m) as YbMgGaO$_4$, and antiferromagnetically coupled rare-earth ions form perfect triangular layers that are well separated along the $c$-axis. Specific heat and magnetic susceptibility measurements on NaYbO$_2$, NaYbS$_2$ and NaYbSe$_2$ single crystals and polycrystals, reveal no structural or magnetic transition down to 50mK. The family, having the simplest structure and chemical formula among the known QSL candidates, removes the issue on possible exchange disorders in YbMgGaO$_4$. More excitingly, the rich diversity of the family members allows tunable charge gaps, variable exchange coupling, and many other advantages. This makes the family an ideal platform for fundamental research of QSLs and its promising applications.
YbMgGaO$_{4}$, a structurally perfect two-dimensional triangular lattice with odd number of electrons per unit cell and spin-orbit entangled effective spin-1/2 local moments of Yb$^{3+}$ ions, is likely to experimentally realize the quantum spin liquid ground state. We report the first experimental characterization of single crystal YbMgGaO$_{4}$ samples. Due to the spin-orbit entanglement, the interaction between the neighboring Yb$^{3+}$ moments depends on the bond orientations and is highly anisotropic in the spin space. We carry out the thermodynamic and the electron spin resonance measurements to confirm the anisotropic nature of the spin interaction as well as to quantitatively determine the couplings. Our result is a first step towards the theoretical understanding of the possible quantum spin liquid ground state in this system and sheds new lights on the search of quantum spin liquids in strong spin-orbit coupled insulators.
Ba3IrTi2O9 crystallizes in a hexagonal structure consisting of a layered triangular arrangement of Ir4+ (Jeff=1/2). Magnetic susceptibility and heat capacity data show no magnetic ordering down to 0.35K inspite of a strong magnetic coupling as evidenced by a large Curie-Weiss temperature=-130K. The magnetic heat capacity follows a power law at low temperature. Our measurements suggest that Ba3IrTi2O9 is a 5d, Ir-based (Jeff=1/2), quantum spin liquid on a 2D triangular lattice.
We study the spin-$1/2$ Heisenberg model on the triangular lattice with the antiferromagnetic first ($J_1$) and second ($J_2$) nearest-neighbor interactions using density matrix renormalization group. By studying the spin correlation function, we find a $120^{circ}$ magnetic order phase for $J_2 lesssim 0.07 J_1$ and a stripe antiferromagnetic phase for $J_2 gtrsim 0.15 J_1$. Between these two phases, we identify a spin liquid region characterized by the exponential decaying spin and dimer correlations, as well as the large spin singlet and triplet excitation gaps on finite-size systems. We find two near degenerating ground states with distinct properties in two sectors, which indicates more than one spin liquid candidates in this region. While the sector with spinon is found to respect the time reversal symmetry, the even sector without a spinon breaks such a symmetry for finite-size systems. Furthermore, we detect the signature of the fractionalization by following the evolution of different ground states with inserting spin flux into the cylinder system. Moreover, by tuning the anisotropic bond coupling, we explore the nature of the spin liquid phase and find the optimal parameter region for the gapped $Z_2$ spin liquid.
Broad interest in quantum spin liquid (QSL) phases was triggered by the notion that they can be viewed as insulating phases with preexisting electron-pairs, such that upon light doping they might automatically yield superconductivity. Yet despite intense efforts, definitive evidence is lacking. We address the problem of a lightly doped QSL through a large-scale density-matrix renormalization group study of the $t$-$J$ model on the triangular lattice with a small but non-zero concentration of doped holes. The ground state is consistent with a Luther-Emery liquid with power-law superconducting and charge-density-wave correlations associated with partially-filled charge stripes. In particular, the superconducting correlations are dominant on both four-leg and six-leg cylinders at all hole doping concentrations. Our results provide direct evidences that doping a QSL can naturally lead to robust superconductivity.
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