Charge-density wave associated with higher-order Fermi-surface nesting in monolayer VS2
Tappei Kawakami, K. Sugawara, Hirofumi Oka, K. Nakayama, Ken Yaegashi, S. Souma, Takashi Takahashi, Tomoteru Fukumura, T. Sato
Abstract
Abstract Fermi-surface (FS) nesting originating from Peierls’ idea of electronic instabilities in one-dimensional materials is a key concept to stabilize charge-density wave (CDW), whereas its applicability to two-dimensional (2D) materials is under intensive debate. Here we report unusual CDW associated with the higher-order FS nesting in monolayer 2D VS2. Angle-resolved photoemission spectroscopy and scanning tunneling microscopy uncovered stripe CDW with $$\sqrt {21} R10.9^\circ \times \sqrt 3 R30^\circ$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msqrt> <mml:mrow> <mml:mn>21</mml:mn> </mml:mrow> </mml:msqrt> <mml:mi>R</mml:mi> <mml:mn>10</mml:mn> <mml:mo>.</mml:mo> <mml:msup> <mml:mrow> <mml:mn>9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>∘</mml:mo> </mml:mrow> </mml:msup> <mml:mo>×</mml:mo> <mml:msqrt> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msqrt> <mml:mi>R</mml:mi> <mml:mn>3</mml:mn> <mml:msup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>∘</mml:mo> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> periodicity together with an energy-gap opening on the entire FS. We suggest that this CDW involves the higher-order FS-nesting vector 2 q twice larger than that of the normal one ( q ), as supported by the anomalies in the calculated phonon dispersion and electronic susceptibility. The present results suggest that the cooperation of q and 2 q nesting leads to the fully gapped CDW state unlike the case of conventional single q nesting which produces a partial gap, pointing to an intriguing mechanism of CDW transition.