Exact Dimer Ground State and Quantized Magnetization Plateaus in the Two-Dimensional Spin System<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>SrCu</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msub><mml:mrow><mml:mi>BO</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mo>)</mml:mo><mml:mrow><mml:msub><mml:mrow><mml:mi/></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Abstract

Magnetic susceptibility, Cu NQR, and high-filed magnetization have been measured in polycrystalline $\mathrm{SrCu}{}_{2}(\mathrm{BO}{}_{3}{)}_{2}$ having a two-dimensional (2D) orthogonal network of Cu dimers. This cuprate provides a new class of 2D spin-gap system $(\ensuremath{\Delta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}30\mathrm{K})$ in which the ground state can be solved ``exactly.'' Furthermore, in the magnetization, two plateaus corresponding to $\frac{1}{4}$ and $\frac{1}{8}$ of the full Cu moment were first observed for 2D quantum spin systems.