Spectral densities of disordered quantum magnets

无序在凝聚态物理学中是不可避免的，并且被认为是有趣的新物理学的来源，例如它可以改变量子临界性甚至破坏量子相变。同时，从理论上处理无序是典型的困难，对于动力学相关函数尤其如此。后者是期望的量，因为有意掺杂的材料的高分辨率光谱学正在成为实验的焦点。在这个项目中，我们应用在微扰连续么正变换的框架下的白图展开来处理无序量子磁体的带隙相位。无序平均采取大型有限系统或直接在热力学极限，所以一个有效的准粒子图片推导出远远超出平均场方法的带隙量子相位。

Disorder is inevitable in condensed matter physics and is known to be the source of interesting novel physics, e.g. it can change quantum criticality or even destroy quantum phase transitions. At the same time it is typically hard to treat disorder theoretically which is especially true for dynamical correlation functions. The latter are desired quantities, since high-resolution spectroscopy on materials with intentional doping are becoming a focus experimentally. In this project we apply white-graph expansions in the framework of perturbative continuous unitary transformations to treat gapped phases of disordered quantum magnets. Disorder averages are taken either for large finite systems or directly in the thermodynamic limit, so an effective quasi-particle picture is derived which goes well beyond mean-field approaches for gapped quantum phases.