Reconstruction of Band Structure Induced by Electronic Nematicity in an FeSe Superconductor

Abstract

We have performed high-resolution angle-resolved photoemission spectroscopy on an FeSe superconductor (T_{c}∼8 K), which exhibits a tetragonal-to-orthorhombic structural transition at T_{s}∼90 K. At low temperature, we found splitting of the energy bands as large as 50 meV at the M point in the Brillouin zone, likely caused by the formation of electronically driven nematic states. This band splitting persists up to T∼110 K, slightly above T_{s}, suggesting that the structural transition is triggered by the electronic nematicity. We have also revealed that at low temperature the band splitting gives rise to a van Hove singularity within 5 meV of the Fermi energy. The present result strongly suggests that this unusual electronic state is responsible for the unconventional superconductivity in FeSe.

Broken rotational symmetry on the Fermi surface of a high-Tc superconductor

“…We have also established that although the CDW in the cuprates is relatively weak and disordered compared to more traditional CDW metals, 60 its symmetry and wavevector directly determine Fermi surface properties. This is similar to the iron pnictide superconductors, where the nematic state is directly observable on the Fermi surface, 14 and suggests that the physics underlying both the superconductivity and the quantum criticality in these two classes of materials share a similar origin. Our Fermi surface model predicts that for tetragonal HgBa 2 CuO 4 , where both short-range CDW order and a small Fermi surface have been observed, 61,62 sufficient uniaxial strain should favour anisotropic CDW formation and give rise to anisotropic AMR similar to what we have observed in YBa 2 Cu 3 O 6.58 .…”

“…12,13 In the iron-based superconductors broken C 4 symmetry is observed directly on the Fermi surface, 14 and has been taken as an indication that this broken symmetry drives the high T c . 15 The question of whether the same type of symmetry breaking is relevant in the copper-oxide high-T c superconductors 16 has been left open because it has never been observed on the Fermi surface.…”

Anomalous Fermi surface in FeSe seen by Shubnikov–de Haas oscillation measurements

“…Although the nature of the transition at T s in FeSe is not yet clear, angle-resolved photoemission spectroscopy (ARPES) measurements on FeSe have found a splitting of the d xz and d yz bands at the corner of the Brillouin zone below ∼110 K, [5][6][7] similar to one found in BaFe 2 As 2 , 8 suggesting orbital order. 9 Secondly, the onset temperature of superconductivity can be enhanced up to ∼37 K by application of pressure.…”

Possible nematic spin liquid in spin-1 antiferromagnetic system on the square lattice: Implications for the nematic paramagnetic state of FeSe

“…Besides, FeSe possesses an electronic nematic order after a tetragonal-to-orthorhombic structural transition at T s 90K [19][20][21][22] . Although the primary origin of this nematic order is still unclear [23][24][25][26][27][28][29][30][31][32][33][34] , neutron scattering measurements indicate the important role of spin degree of freedom 24,25 .…”