Visualizing magnetic field-induced rotational electronic symmetry breaking in a spinel oxide superconductor

TL;DR

This study reveals magnetic field-induced rotational symmetry breaking of the Fermi surface in LiTi2O4, leading to unique vortex structures and quasiparticle behavior, highlighting novel physics in spinel oxide superconductors.

Contribution

It demonstrates magnetic field-driven electronic symmetry breaking and vortex imaging in LiTi2O4, a novel observation in spinel oxide superconductors.

Findings

Triangular Abrikosov vortices observed deviating from expected symmetry

Magnetic field induces rotational symmetry breaking of the Fermi surface

Josephson vortices form along domain boundaries due to symmetry breaking

Abstract

The spinel oxide superconductor LiTi2O4 (LTO) is an intriguing material platform where the electronic structure near the Fermi energy (EF) is derived from 3d elections on the geometrically frustrated Ti pyrochlore network. A recent angle-resolved photoemission spectroscopy (ARPES) study has revealed the existence of an exotic quasiparticle state arising from the competition between instability towards orbital ordering and geometrical frustration below 150 K. An intriguing remaining challenge is the imaging of Abrikosov vortices, which generally inherits the symmetry of the Fermi surface at k_z=0. Here, we observe surprising triangular-shaped Abrikosov vortices on an LTO(111) film, deviating from the conventional expectations of the six-fold symmetric Fermi surface at k_z=0. In combination with the experimentally observed isotropic pairing, we propose magnetic field-driven rotational electronic symmetry breaking of the underlying Fermi surface. Consequently, we observe Josephson vortices along the crystalline domain boundary, across which quasiparticle hopping is suppressed due to the symmetry-broken Fermi surface in each domain. Our discoveries point to the existence of unique physics of magnetic field-induced electronic rotational symmetry breaking in the spinel oxide superconductor LTO. This picture is in stark contrast to the other exotic superconductors with partial gap opening or long-range ordering with broken symmetry above the superconducting critical temperature at zero magnetic field.