A Perspective on the Application of Spatially Resolved ARPES for 2D Materials

Abstract

In this paper, a perspective on the application of Spatially- and Angle-Resolved PhotoEmission Spectroscopy (ARPES) for the study of two-dimensional (2D) materials is presented. ARPES allows the direct measurement of the electronic band structure of materials generating extremely useful insights into their electronic properties. The possibility to apply this technique to 2D materials is of paramount importance because these ultrathin layers are considered fundamental for future electronic, photonic and spintronic devices. In this review an overview of the technical aspects of spatially localized ARPES is given along with a description of the most advanced setups for laboratory and synchrotron-based equipment. This technique is sensitive to the lateral dimensions of the sample. Therefore, a discussion on the preparation methods of 2D material is presented. Some of the most interesting results obtained by ARPES are reported in three sections including: graphene, transition metal dichalcogenides (TMDCs) and 2D heterostructures. Graphene has played a key role in ARPES studies because it inspired the use of this technique with other 2D materials. TMDCs are presented for their peculiar transport, optical and spin properties. Finally, the section featuring heterostructures highlights a future direction for research into 2D material structures.

Revealing the single electron pocket of FeSe in a single orthorhombic domain

“…In a wider context, nano-ARPES is a novel and fastimproving technique that has already had a significant impact in the field of two-dimensional materials, especially in heterostructures and devices [45][46][47]. However, thus far it has seen relatively few applications in traditional correlated electron systems [28,29], at least partially because the lower energy scales involved require a high energy resolution, which is challenging to combine with a micron-scale spatial resolution.…”

Charge order from structured coupling in VSe$_2$

“…Angle-resolved photo-emission spectroscopy (ARPES) studies, for example, do not show clear gaps in the spectral function at low temperatures, such that the CDW gap structure remains unclear [25][26][27][28][29]. This is in stark contrast to other transition metal dichalcogenides (TMDC) with CDW instabilities, such as 2H-NbSe 2 , 2H-TaSe 2 and 1T -TaS 2 [30,31].…”

“…Two practical issues contributing to its elusiveness are the small gap size (2∆ ≈ 24 meV[17]) and the three-dimensional nature of the electron dispersion, which necessitate experiments with high energy and k z -resolution. Some low-temperature ARPES measurements are suggestive of a gap around k z ≈ 0.5c *[25,[27][28][29]. The reported gap size of 80-100 meV in Ref [25],.…”

“…however, refers to a shift in peak positions of energy dispersion curves, while the CDW gap is more closely related to the leading edge shift[46]. Ref [27][28][29],. on the other hand, show spectral weight suppression in Fermi pockets around the L-point even above T c , while Ref [26].…”

Magneto-Optical Tools to Study Effects in Dirac and Weyl Semimetals

“…ARPES is a powerful experimental technique that provides information regarding the energy and momentum of the electronic state. However, besides high-resolution ARPES images in the case of spin-and time-resolved images, this technique is usually limited to large or epitaxial samples [31].…”