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arXiv 2407.15919cond-mat.str-elhep-th
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金属量子相变讲义

Lectures on the quantum phase transitions of metals

Subir Sachdev

AI总结:

本讲义将金属量子相变分为三类,介绍了第三类无对称破缺的FL*-FL相变在不同模型中的实现及对铜氧化物的应用,分析了纯净与哈里斯无序下的临界行为及普适描述模型。

摘要:

金属的量子相变涉及费米面的变化,可分为三类。前两类涉及对称性破缺,会导致费米面发生形变或重构。第三类涉及费米面所包围的体积发生变化,但不存在任何对称性破缺:其中一相是具有常规卢廷格体积的费米液体(Fermi liquid, FL),另一相是“分数化费米液体”(fractionalized Fermi liquid, FL*),它具有非卢廷格体积的费米面,同时伴随带有分数化激发的自旋液体。在近藤晶格模型中实现FL*-FL相变是相对简单的事。不过,FL*-FL相变也可以存在于单带哈伯德类模型中:这一现象可通过“辅助比特(ancilla)”方法有效描述,该方法表明这种相变是一种“翻转的”近藤晶格相变。研究认为这种单带FL*-FL相变适用于空穴掺杂铜氧化物的金属态。在纯净极限下,三类量子相变的临界性质各不相同,但都会在量子临界区域产生完美金属输运。由杂质诱导的“哈里斯无序(Harris disorder)”——即量子临界点的局域位置存在空间涨落——是对纯净临界点的一种相关微扰。在存在哈里斯无序的情况下,所有三类相变都表现出奇异金属行为,这种行为可通过一个普适的二维Yukawa-Sachdev-Ye-Kitaev模型来描述。

英文摘要:

Quantum phase transitions of metals involve changes in the Fermi surface, and can be divided into three categories. The first two categories involve symmetry breaking, and lead to a deformation or reconstruction of the Fermi surface. The third category involves a change in the volume enclosed by the Fermi surface without any symmetry breaking: one phase is a Fermi liquid (FL) with the conventional Luttinger volume, while the other phase is a `fractionalized Fermi liquid' (FL*), which has a non-Luttinger volume Fermi surface accompanied by a spin liquid with fractionalized excitations. It is a relatively simple matter to obtain a FL*-FL transition in Kondo lattice models. However, the FL*-FL transition can also be present in single-band Hubbard-like models: this is efficiently described by the `ancilla' method, which shows that the transition is a `flipped' Kondo lattice transition. This single-band FL*-FL transition is argued to apply to the metallic states of the hole-doped cuprates. In the clean limit, the critical properties of the quantum transitions in the three categories are distinct, but all lead to perfect metal transport in the quantum-critical regime. Impurity-induced `Harris disorder', with spatial fluctuations in the local position of the quantum critical point, is a relevant perturbation to the clean critical points. In the presence of Harris disorder, all three categories exhibit strange metal behavior, which can be described by a universal two-dimensional Yukawa-Sachdev-Ye-Kitaev model.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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