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

Ruixing Liang,K. A. Modic,N. Harrison,W. N. Hardy,P. A. Goddard,B. J. Ramshaw,D. A. Bonn,S. E. Sebastian,S. Ghannadzadeh

doi:10.1038/s41535-017-0013-z

Abstract

Broken fourfold rotational (C4) symmetry is observed in the experimental properties of several classes of unconventional superconductors. It has been proposed that this symmetry breaking is important for superconducting pairing in these materials, but in the high-Tc cuprates this broken symmetry has never been observed on the Fermi surface. Here we report a pronounced anisotropy in the angle dependence of the interlayer magnetoresistance of the underdoped high transition temperature (high-Tc) superconductor YBa2Cu3O6.58, directly revealing broken C4 symmetry on the Fermi surface. Moreover, we demonstrate that this Fermi surface has C2 symmetry of the type produced by a uniaxial or anisotropic density-wave phase. This establishes the central role of C4 symmetry breaking in the Fermi surface reconstruction of YBa2Cu3O6+δ, and suggests a striking degree of universality among unconventional superconductors.

Highlights

Broken C4 symmetry is observed in a number of experiments on unconventional superconductors, including transport,[1,2,3,4] nuclear magnetic resonance (NMR),[5, 6] neutron scattering,[7, 8] X-ray scattering[9,10,11] and scanning tunneling microscopy.[12, 13]
In the underdoped high-Tc cuprates it is well established that a charge-density wave (CDW) competes with superconductivity, but a direct experimental connection is still missing between the CDW and the Fermi surface
Since the 1930s it has been known that a change in resistance with an applied magnetic field—magnetoresistance—provides geometric information about a metallic Fermi surface,[28] and early magnetoresistance experiments were instrumental in developing the modern quantum theory of metals.[29]

Summary

INTRODUCTION

Broken C4 symmetry is observed in a number of experiments on unconventional superconductors, including transport,[1,2,3,4] nuclear magnetic resonance (NMR),[5, 6] neutron scattering,[7, 8] X-ray scattering[9,10,11] and scanning tunneling microscopy.[12, 13] In the iron-based superconductors broken C4 symmetry is observed directly on the Fermi surface,[14] and has been taken as an indication that this broken symmetry drives the high Tc.[15]. A precise determination of Fermi surface geometry, provides information about symmetry-breaking states of matter that feed back into the electronic structure. QO (quantum oscillation) measurements, performed in the high-field state, have been instrumental in determining the presence of a small electron Fermi surface in the underdoped side of the phase diagram.[17, 19,20,21,22] While QOs provide precise information about the area of the Fermi surface, they are relatively insensitive to its overall shape in two-dimensional (2D) metals We present the results of a complementary technique, angle-dependent magnetoresistance (AMR), that determines the geometry and symmetry of the Fermi surface. We identify the shape of the Fermi surface as consistent with certain proposed CDW reconstruction scenarios,[17, 23,24,25,26,27] and we find that this reconstruction is anisotropic in nature

RESULTS

DISCUSSION

METHODS