Dresden 2020 – scientific programme

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O: Fachverband Oberflächenphysik

O 11: 2D Materials I: Electronic Structure, Excitations, etc. (joint session O/CPP/HL)

O 11.6: Talk

Monday, March 16, 2020, 12:00–12:15, WIL C107

Melting the low temperature gap in monolayer VSe₂, in time resolved ARPES — •Deepnarayan Biswas^1,2, Alfred Jones¹, Paulina Majchrzak^1,3, Klara Volckaert¹, Charlotte Sanders^1,3, Igor Marković², Federico Andreatta¹, Akhil Rajan², Yu Zhang³, Gabriel Karras³, Tsung-Han Lee⁴, Chang-Jong Kang⁴, Byoung Ki Choi⁵, Richard Chapman³, Adam Waytt³, Emma Springate³, Jill Miwa¹, Philip Hofmann¹, Phil D. C. King², Young Jun Chang⁵, Nikola Lanata¹, and Søren Ulstrup¹ — ¹Aarhus University, Denmark — ²University of St Andrews, UK — ³Central Laser Facility, UK — ⁴Rutgers University, USA — ⁵University of Seoul, Republic of Korea

The group V transition metal dichalcogenide VSe₂ shows a charge density wave (CDW) transition at 110 K with (4×4×3) charge ordering in its bulk form. In contrast, recent experiments on monolayer (ML) VSe₂ have shown an enhanced transition at ∼ 140 K with very different charge ordering. Moreover, this transition is accompanied by a full gapping of the Fermi surface. Here, we have used time and angle resolved photoelectron spectroscopy (TR-ARPES) to understand the electron dynamics in ML VSe₂ above and below the transition temperature. We have also modelled the ARPES intensity using a modified BCS self energy and density functional theory calculated bare bands. We find the gapped phase vanishes upon pumping and takes unusually long time to recover (more than 10 ps). This behaviour points toward a hot electron relaxation bottleneck coupled with an electronic phase transition in this sample.