Multipole Superconductivity in Nonsymmorphic Sr2IrO4

Abstract

Discoveries of marked similarities to high-T_{c} cuprate superconductors point to the realization of superconductivity in the doped J_{eff}=1/2 Mott insulator Sr_{2}IrO_{4}. Contrary to the mother compound of cuprate superconductors, several stacking patterns of in-plane canted antiferromagnetic moments have been reported, which are distinguished by the ferromagnetic components as -++-, ++++, and -+-+. In this paper, we clarify unconventional features of the superconductivity coexisting with -++- and -+-+ structures. Combining the group theoretical analysis and numerical calculations for an effective J_{eff}=1/2 model, we show unusual superconducting gap structures in the -++- state protected by nonsymmorphic magnetic space group symmetry. Furthermore, our calculation shows that the Fulde-Ferrell-Larkin-Ovchinnikov superconductivity is inevitably stabilized in the -+-+ state since the odd-parity magnetic -+-+ order makes the band structure asymmetric by cooperating with spin-orbit coupling. These unusual superconducting properties are signatures of magnetic multipole order in nonsymmorphic crystal.

Insulator-Metal Transition and Topological Superconductivity in UTe2 from a First-Principles Calculation

“…Although we can speculate gap structures from the order parameter, it is desirable to use the classification of gap structures in terms of symmetry and topology [18][19][20][21][31][32][33][34][35][36][37] because symmetry-protected gap nodes are precisely obtained. Detailed results of the topological classification are shown in the Supplemental Material [26].…”

Group-theoretical classification of multipole order: Emergent responses and candidate materials

“…Recent studies shed light on odd-parity multipole order, where the inversion symmetry is spontaneously broken, although the studies of atomic multipole physics were restricted to even-parity order. In addition to the electric dipole order, which has been well-known as ferroelectric order, electric octupole [25,26], magnetic monopole [27][28][29], magnetic quadrupole [27,[30][31][32][33], magnetic toroidal dipole [34][35][36][37][38][39][40][41][42], and magnetic hexadecapole order [43] have been investigated.…”

Odd-parity multipole fluctuation and unconventional superconductivity in locally noncentrosymmetric crystal

“…In this section, we introduce a two-dimensional twosublattice Hubbard model which was adopted for Sr 2 IrO 4 [39]. We consider a two-dimensional IrO 2 plane of quasitwo-dimensional Sr 2 IrO 4 .…”

“…Another topic of recent interest in locally NCS crystals is an odd-parity electromagnetic multipole order [25,28,[32][33][34][35][36][37][38][39][40][41][42][43], which spontaneously breaks global inversion symmetry through an anisotropic spin and charge distribution. Although previous studies provided a profound understanding of evenparity multipole order in strongly correlated electron systems [44][45][46][47], it has been recently recognized that odd-parity electromagnetic multipole order is ubiquitous in materials.…”