Karmakar Madhuparna
Indian Institute of Technology, Madras, Chennai-600036, India.
J Phys Condens Matter. 2020 Jul 3;32(40). doi: 10.1088/1361-648X/ab926a.
We report a quantum phase transition in Pauli limited d-wave superconductors and give the mean field estimates of the associated quantum critical point. For a population imbalanced d-wave superconductor a stable ground state phase viz quantum breached pair phase has been identified which comprises of spatial coexistence of gapless superconductivity and nonzero magnetization. Based on the thermodynamic and quasiparticle indicators we for the first time analyze this phase, discuss the thermal behavior of Pauli limited d-wave superconductor, give accurate estimates of the thermal scales associated with such systems and map out the pseudogap regime. Our work shows that while the Pauli limited superconductors are known to exhibit exotic modulated superconducting phase at large imbalance of fermion populations; in the regime of weak imbalance an intriguing phase of competing orders is realized. We have established that rather than the superconducting pairing field, it is the average magnetization of the system that quantifies this quantum phase transition. Given that the existing Pauli limited superconductors possess unconventional pairing state symmetry of the superconducting order, our work promises to open up new avenues in the experimental research of these materials. We have also demonstrated an alternate scenario wherein the quantum breached pair phase is a natural outcome for a d-wave superconductor with unequal effective masses of the fermion species.
我们报道了泡利极限d波超导体中的量子相变，并给出了相关量子临界点的平均场估计。对于粒子数不平衡的d波超导体，已确定了一种稳定的基态相，即量子破缺对相，它由无隙超导性和非零磁化强度的空间共存组成。基于热力学和准粒子指标，我们首次分析了这一相，讨论了泡利极限d波超导体的热行为，给出了与此类系统相关的热尺度的精确估计，并描绘出赝能隙区域。我们的工作表明，虽然已知泡利极限超导体在费米子粒子数严重不平衡时会表现出奇异的调制超导相；但在弱不平衡区域会实现一种有趣的竞争序相。我们已经确定，量化这种量子相变的不是超导配对场，而是系统的平均磁化强度。鉴于现有的泡利极限超导体具有超导序的非常规配对态对称性，我们的工作有望为这些材料的实验研究开辟新途径。我们还展示了另一种情况，即对于费米子种类有效质量不相等的d波超导体，量子破缺对相是一种自然结果。
