By direct calculations of the spin gap in the frustrated Heisenberg model on the square lattice, with nearest- ($J_1$) and next-nearest-neighbor ($J_2$) super-exchange couplings, we provide a solid evidence that the spin-liquid phase in the frustrated regime $0.45 \lesssim J_2/J_1 \lesssim 0.6$ is gapless. Our numerical method is based on a variational wave function that is {\it systematically} improved by the application of few Lanczos steps and allows us to obtain reliable extrapolations in the thermodynamic limit. The peculiar nature of the non-magnetic state is unveiled by the existence of S=1 gapless excitations at $k=(π,0)$ and $(0,π)$. The magnetic transition can be described and interpreted by a variational state that is built from Abrikosov fermions having a $Z_2$ gauge structure and four Dirac points in the spinon spectrum.
Gapless Magnetic and Quasiparticle Excitations due to the Coexistence of Antiferromagnetism and Superconductivity in CeRhIn$_5$ : A study of $^{115}$In-NQR under Pressure
Possibility of Gapless Spin Liquid State by One-dimensionalization
基于对$κ$ -（BEDT-TTF）$_2$ Cu $_2$（CN）$_3$中无带隙自旋液态的观察，我们在共振价键平均场近似下分析了各向异性三角晶格$S=1/2$ Heisenberg模型.注意到小准一维各向异性的材料，我们采取的方法从一维（1D）链加上令人沮丧的锯齿键。通过计算改变各向异性参数$J'/J$的单粒子激发谱，从一维链到各向同性三角晶格，我们发现在很宽的一维极限范围内几乎没有带隙的激发.这种一维阻挫被认为是一个候选的无隙自旋液体状态的机制。
Quantum chiral phases in frustrated easy-plane spin chains
本文用场论方法研究了具有XY型各向异性和次近邻相互作用受挫的反铁磁自旋S链在大整数S极限下的相图。结果表明，在最近的数值研究中发现的无间隙和有间隙手性相的存在[M.Kaburagi et al.，日本物理学会第68卷，3185（1999），T.Hikihara等人，日本物理学会vol.69，259（2000）]不是S=1的特定特征，而是一般的大S特征。估计相应的过渡边界，并提出了一个草图的典型相图。它还表明，挫折稳定的Halcoxin相对各向异性的变化。
Dynamical Spectral Function of the Kagome Quantum Spin Liquid
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）；California Institute of Technology（加州理工学院）；Paul Scherrer Institute（保罗谢勒研究所）
