An Alternative Route out of Equilibrium: Probing Uniaxial Strain Effects in TMDs with ARPES

PC Department Online Seminar
Date: May 17, 2021
Time: 11:00 AM (Local Time Germany)
Speaker: Christopher Nicholson
University of Fribourg
Host: Laurenz Rettig

The fascinating properties of emergent phases in condensed matter systems can give usconsiderable insight into the physical mechanisms underpinning them. A central scientific goalof recent decades has been to employ external perturbations such as doping, pressure,magnetic fields and intense laser pulses in order to push materials away from their equilibriumconfigurations, revealing further insights into the mechanisms relevant to stabilising thesephases.

Within this context uniaxial strain has recently emerged as a powerful approach to influence the properties of solids [1] and offers a path to tailor both physical properties and device functionalities from the nano to macro scale. However, there are significant challenges when combining strain with powerful probes of the electronic structure, such as angle-resolved
photoemission spectroscopy (ARPES).
In this seminar, I will present our recent work combining uniaxial strain with ARPES, with a particular focus on the transition metal dichalcogenide IrTe . This quasi-2D material is predicted as a type-II bulk Dirac semimetal with a Dirac point slightly above the Fermi level. It displays a number of coexisting structural phases below 180 K, severely hindering spectroscopic access to the ground state. By applying a modest uniaxial strain (e ~ 0.1%), we demonstrate the selective stabilization of a single structural phase with domain sizes four orders of magnitude larger than in unstrained samples [2]. We find that strain initiates a charge transfer into Te anti-bonding states already at room temperature, thereby removing the phase degeneracy in favour of a single phase at low temperatures. This energetic bias allows unprecedented spectroscopic access both to the previously unobserved bulk Dirac-like states – which become the dominant inter-layer transport channel – and to new quasi one-dimensional states that appear to be intermediate between Mott insulator and Luttinger liquid phases [3]. Time allowing I will briefly discuss our ongoing work and give an outlook for using strain to influence phase transitions, bonding and topology in 2D materials.
[1] Hicks, C. W., et al. Science 344, 283–285 (2014); Kim, H. H. et al. Science 362, 1040–1044
(2018); Riccò, S. et al. Nat. Commun. 9, 4535 (2018)
[2] Nicholson, C.W., et al. Commun. Mater. 2, 25 (2021)
[3] Nicholson, C.W., et al. in preparation

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