标题： V$_6$O$_{13}$ 中超高磁场下分子轨道的坍缩 显示英文标题

标题： Collapse of molecular orbital by ultrahigh magnetic fields in V$_6$O$_{13}$

摘要： V$_6$O$_{13}$在钒-钒（V-V）二聚体形成过程中表现出金属-绝缘体转变（MIT）。 在本工作中，沿晶体学$b$-轴测量了 V$_6$O$_{13}$在多个温度下的超高压磁场（高达186 T）下的磁致伸缩。 在转变温度以下，观察到最大达$\Delta L / L \sim10^{-3}$的负磁致伸缩。 基于实验结果和V$_6$O$_{13}$的物理性质，可以得出结论，观察到的大负磁致伸缩对应于V-V二聚体分子轨道（MO）的坍塌。 这是首次直接观察到来自钒氧化物中磁场所诱导的V-V二聚体MO坍塌引起的晶格变化的情况。 此外，$B$-$T$相图和磁致伸缩的大小表明，V-V二聚体MO的坍塌可能伴随着绝缘体到金属的转变。 观察到了一个大于50 T的较大滞后，这可能是由于电荷、自旋和晶格等自由度的非平衡交叉相关性引起的。 与VO$_2$的情况相比，表明绝缘相中剩余顺磁自旋的磁熵可能在V$_6$O$_{13}$的MIT中起重要作用。 显示英文摘要

摘要： V$_6$O$_{13}$ exhibits the metal-insulator transition (MIT) with vanadium-vanadium (V-V) dimer formation. The magnetostriction of V$_6$O$_{13}$ along the crystallographic $b$-axis has been measured in ultrahigh magnetic fields up to 186 T at several temperatures in this work. The large negative magnetostriction as large as $\Delta L / L \sim10^{-3}$ was observed above 110 T below the transition temperature. Discussion based on experimental results and the physical property of V$_6$O$_{13}$ suggests that the observed large negative magnetostriction corresponds to the collapse of V-V dimer molecular orbital (MO). This is the first case for direct observation of lattice change originating from the magnetic field-induced collapse of V-V dimer MO in vanadium oxides. In addition, the $B$-$T$ phase diagram and the magnitude of magnetostriction indicate that the collapse of V-V dimer MO probably accompanies the insulator-to-metal transition. A large hysteresis that is larger than 50 T was observed, which probably arises from the non-equilibrated cross-correlation of such degrees of freedom as the charge, spin, and lattice. Comparison with the VO$_2$ case suggests the magnetic entropy of the remanent paramagnetic spins in the insulating phase may play an important role for the MIT in V$_6$O$_{13}$.