论文标题
电荷密度波超出2D系统的Pauli顺磁极限
Charge Density Waves beyond the Pauli paramagnetic limit in 2D systems
论文作者
论文摘要
二维材料是表现出顺磁性限制行为的宿主电荷密度波（CDW）的理想候选者，类似于已知的超导体案例。在这里，我们研究了二维系统中的CDW如何通过在Zeeman田地下开发广义的CDW均值理论，包括不可固定性，不完美的嵌套和温度效应，以及竞争性或共存的旋转密度波（SDW）阶的可能性，如何在Pauli限制范围内生存。我们的数值计算产生了丰富的相图，在Pauli限制场之上，具有不同的高场相。对于完美嵌套的相称的CDW，这是一个$ Q $调制的CDW相，与超导fulde-ferrell-larkin-ovchinnikov（FFLO）相完全类似，出现在高场面。在更常见的嵌套不完美的情况下，相同的CDW地面晶体经历了一系列磁场诱导的相转换，首先是相应的CDW和SDW共存的相位，然后转到CDW和SDW的另一个阶段，但是，CDW和SDW从纯Fflo cdw阶段获得了$ Q $调节。与Pauli极限相当但在其上方生存的田地发生了相称的CDW+SDW阶段。因此，该阶段为CDW提供了一种合理的机制，可以在高场上生存，而无需形成更脆弱的FFLO相。我们建议最近发现的2D材料（例如过渡金属二进制基因源）为观察这种外来场诱导的CDW现象提供了有前途的平台。
Two-dimensional materials are ideal candidates to host Charge density waves (CDWs) that exhibit paramagnetic limiting behavior, similarly to the well known case of superconductors. Here we study how CDWs in two-dimensional systems can survive beyond the Pauli limit when they are subjected to a strong magnetic field by developing a generalized mean-field theory of CDWs under Zeeman fields that includes incommensurability, imperfect nesting and temperature effects and the possibility of a competing or coexisting Spin density wave (SDW) order. Our numerical calculations yield rich phase diagrams with distinct high-field phases above the Pauli limiting field. For perfectly nested commensurate CDWs, a $q$-modulated CDW phase that is completely analogous to the superconducting Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase appears at high-fields. In the more common case of imperfect nesting, the commensurate CDW groundstate undergoes a series of magnetic-field-induced phase transitions first into a phase where commensurate CDW and SDW coexist and subsequently into another phase where CDW and SDW acquire a $q$-modulation that is however distinct from the pure FFLO CDW phase. The commensurate CDW+SDW phase occurs for fields comparable to but less than the Pauli limit and survives above it. Thus this phase provides a plausible mechanism for the CDW to survive at high fields without the need of forming the more fragile FFLO phase. We suggest that the recently discovered 2D materials like the transition metal dichalcogenides offer a promising platform for observing such exotic field induced CDW phenomena.
