Competing charge-density wave instabilities in the kagome metal ScV6Sn6

Abstract

Abstract Owing to its unique geometry, the kagome lattice hosts various many-body quantum states including frustrated magnetism, superconductivity, and charge-density waves (CDWs). In this work, using inelastic X-ray scattering, we discover a dynamic short-range $$\sqrt{3}\times \sqrt{3}\times 2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msqrt> <mml:mo>×</mml:mo> <mml:msqrt> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msqrt> <mml:mo>×</mml:mo> <mml:mn>2</mml:mn> </mml:math> CDW that is dominant in the kagome metal ScV 6 Sn 6 above T CDW ≈ 91 K, competing with the $$\sqrt{3}\times \sqrt{3}\times 3$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msqrt> <mml:mo>×</mml:mo> <mml:msqrt> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msqrt> <mml:mo>×</mml:mo> <mml:mn>3</mml:mn> </mml:math> CDW that orders below T CDW . The competing CDW instabilities lead to an unusual CDW formation process, with the most pronounced phonon softening and the static CDW occurring at different wavevectors. First-principles calculations indicate that the $$\sqrt{3}\times \sqrt{3}\times 2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msqrt> <mml:mo>×</mml:mo> <mml:msqrt> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msqrt> <mml:mo>×</mml:mo> <mml:mn>2</mml:mn> </mml:math> CDW is energetically favored, while a wavevector-dependent electron-phonon coupling (EPC) promotes the $$\sqrt{3}\times \sqrt{3}\times 3$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msqrt> <mml:mo>×</mml:mo> <mml:msqrt> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msqrt> <mml:mo>×</mml:mo> <mml:mn>3</mml:mn> </mml:math> CDW as the ground state, and leads to enhanced electron scattering above T CDW . These findings underscore EPC-driven correlated many-body physics in ScV 6 Sn 6 and motivate studies of emergent quantum phases in the strong EPC regime.