Gap collapse and flat band induced by uniaxial strain in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>1</mml:mn><mml:mi>T</mml:mi><mml:mtext>−</mml:mtext><mml:msub><mml:mi>TaS</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>

Abstract

Interlayer coupling is strongly implicated in the complex electronic properties of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mn>1</a:mn><a:mi>T</a:mi></a:mrow><a:mo>−</a:mo><a:msub><a:mi>TaS</a:mi><a:mn>2</a:mn></a:msub></a:math>. Uniaxial strain engineering offers a route to modify this coupling in order to elucidate its interplay with the electronic structure and electronic correlations. Here, we employ angle-resolved photoemission spectroscopy (ARPES) to reveal the effect of uniaxial strain on the electronic structure in <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:mn>1</b:mn><b:mi>T</b:mi></b:mrow><b:mo>−</b:mo><b:msub><b:mi>TaS</b:mi><b:mn>2</b:mn></b:msub></b:math>. The gap of the normally insulating ground state is significantly reduced, with a correlated flat band appearing close to the Fermi level. Temperature-dependent ARPES measurements reveal that the flat band only develops below the commensurate charge density wave (CCDW) transition, where interlayer dimerization produces a band insulator in unstrained samples. Electronic structure calculations suggest that the correlated flat band is stabilized by a modified interlayer coupling of the Ta <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:msub><c:mi>d</c:mi><c:msup><c:mi>z</c:mi><c:mn>2</c:mn></c:msup></c:msub></c:math> electrons. Further hints of a strain-induced structural modification of the interlayer order are obtained from x-ray diffraction. Our combined approach provides critical input for understanding the complex phase diagram of this platform material for correlated physics. Published by the American Physical Society 2024