Leibniz Institute for Solid State and Materials Research IFW Dresden, Germany.
Phys Rev Lett. 2011 Jul 1;107(1):017203. doi: 10.1103/PhysRevLett.107.017203. Epub 2011 Jun 30.
We report a comparative study of (63)Cu nuclear magnetic resonance spin lattice relaxation rates T(1)(-1) on undoped SrCuO(2) and Ca-doped Sr(0.9)Ca(0.1)CuO(2) spin chain compounds. A temperature independent T(1)(-1) is observed for SrCuO(2) as expected for an S=1/2 Heisenberg chain. Surprisingly, we observe an exponential decrease of T(1)(-1) for T<90 K in the Ca-doped sample evidencing the opening of a spin gap. The data analysis within the J(1)-J(2) Heisenberg model employing density-matrix renormalization group calculations suggests an impurity driven small alternation of the J(2)-exchange coupling as a possible cause of the spin gap.
我们报告了（63）Cu 核磁共振自旋晶格弛豫率 T(1)(-1)在未掺杂 SrCuO(2)和 Ca 掺杂 Sr(0.9)Ca(0.1)CuO(2)自旋链化合物中的比较研究。正如预期的那样，对于 S=1/2 Heisenberg 链，SrCuO(2)表现出温度独立的 T(1)(-1)。令人惊讶的是，我们在 Ca 掺杂样品中观察到 T<90 K 时 T(1)(-1)的指数下降，这表明出现了自旋能隙。在使用密度矩阵重整化群计算的 J(1)-J(2)Heisenberg 模型的数据分析中，提出杂质驱动的 J(2)交换耦合的微小交替可能是自旋能隙的原因。
