Discovery of an intermediate nematic state in a bilayer kagome metal ScV₆Sn₆.

Abstract

Nematicity, spontaneous breaking of rotational symmetry, is a ubiquitous phenomenon in correlated quantum matter. Here we show a phase transition in high-quality ScV₆Sn₆ bilayer kagome metal at a temperature <math xmlns="http://www.w3.org/1998/Math/MathML"> <msup><mrow><mi>T</mi></mrow> <mrow><mo>*</mo></mrow> </msup> </math> , occurring seven Kelvins below the charge density wave transition at <math xmlns="http://www.w3.org/1998/Math/MathML"> <msub><mrow><mi>T</mi></mrow> <mrow><mi>C</mi> <mi>D</mi> <mi>W</mi></mrow> </msub> </math> , as indicated by thermodynamic, transport, and optical measurements. This emerging intermediate phase does not exhibit spontaneous time-reversal-symmetry breaking, as evidenced by zero-field Sagnac interferometry. However, it displays a strong, spontaneous in-plane anisotropy between <math xmlns="http://www.w3.org/1998/Math/MathML"> <msup><mrow><mi>T</mi></mrow> <mrow><mo>*</mo></mrow> </msup> </math> and <math xmlns="http://www.w3.org/1998/Math/MathML"> <msub><mrow><mi>T</mi></mrow> <mrow><mi>C</mi> <mi>D</mi> <mi>W</mi></mrow> </msub> </math> , revealed by transport and optical polarization rotation measurements. A pronounced depolarization effect detected by the Sagnac interferometer further confirms its nematic nature. Unlike AV₃Sb₅, this phase, alongside the recently discovered intra-unit cell nematic order at lower temperatures, presents a diverse landscape of nematicities at multiple length and temperature scales. Our findings highlight ScV₆Sn₆ as a prime candidate for realizing symmetry-breaking phases driven by charge density competition, kagome physics, and Van Hove singularities.