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arXiv 1906.02709cond-mat.mes-hallcond-mat.supr-con
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自旋极化费米子的高阶拓扑超导电性

Higher-Order Topological Superconductivity of Spin-Polarized Fermions

Junyeong Ahn, Bohm-Jung Yang

备注：
6+13 pages, 2+1 figures; accepted version
发表信息：
Phys. Rev. Research 2, 012060 (2020)
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摘要：

研究了中心对称铁磁金属中自旋极化电子的超导电性。由于电子的自旋极化和费米统计，超导配对函数自然具有奇宇称。根据Fu、Berg和Sato提出的宇称公式，当正常金属具有奇数个费米面时，奇宇称配对导致常规的一阶拓扑超导性。在这里，我们推导出表征中心对称超导体高阶拓扑结构的拓扑不变量的广义宇称公式。在此基础上，我们系统地分类了铁磁金属所有可能的能带结构，这些能带结构可以诱导出反转保护的高阶拓扑超导电性。其中，掺杂铁磁结半金属被认为是最有希望的高阶拓扑超导正常态平台。在二维空间中，我们证明了掺杂狄拉克半金属的奇宇称配对诱导出二阶拓扑超导体。在三维空间中，掺杂节线半金属的奇宇称配对产生了一个带负电荷的节线拓扑超导体。另一方面，掺杂半导体结线半金属的奇宇称配对诱导出三维三阶拓扑超导体。我们的理论表明，超导性和铁磁结半金属的组合开辟了一个新的途径，未来的拓扑量子计算使用马约拉纳零模式。

英文摘要：

We study the superconductivity of spin-polarized electrons in centrosymmetric ferromagnetic metals. Due to the spin-polarization and the Fermi statistics of electrons, the superconducting pairing function naturally has odd parity. According to the parity formula proposed by Fu, Berg, and Sato, odd-parity pairing leads to conventional first-order topological superconductivity when a normal metal has an odd number of Fermi surfaces. Here, we derive generalized parity formulae for the topological invariants characterizing higher-order topology of centrosymmetric superconductors. Based on the formulae, we systematically classify all possible band structures of ferromagnetic metals that can induce inversion-protected higher-order topological superconductivity. Among them, doped ferromagnetic nodal semimetals are identified as the most promising normal state platform for higher-order topological superconductivity. In two dimensions, we show that odd-parity pairing of doped Dirac semimetals induces a second-order topological superconductor. In three dimensions, odd-parity pairing of doped nodal line semimetals generates a nodal line topological superconductor with monopole charges. On the other hand, odd-parity pairing of doped monopole nodal line semimetals induces a three-dimensional third-order topological superconductor. Our theory shows that the combination of superconductivity and ferromagnetic nodal semimetals opens up a new avenue for future topological quantum computations using Majorana zero modes.

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