Skip to main content

Vertical Transport and Photoresponse in van der Waals hybrid structures

Periodic Reporting for period 1 - TranspvdW (Vertical Transport and Photoresponse in van der Waals hybrid structures)

Reporting period: 2016-10-01 to 2018-09-30

Two-dimensional materials have emerged in recent years as a new class of materials, with great promise for technological applications. Besides displaying extraordinary mechanical, electronic and optical properties, due to the (quasi) all surface nature of these materials, their properties can be easily tuned by external parameters – an essential requirement for technological applications.

Two-dimensional materials can also be combined to form layered structures, referred to as van der Waals (vdW) structures, which can combine properties from different materials, and display new ones, which are not manifested by the isolated layers. This opens up novel ways to engineer systems with new electronic and optical properties, which can be used in applications. However, the understanding and simulation of these materials poses significant difficulties.

The overall objectives of TranspvdW are to:

(i) Develop methods to model layered structures and use them to study the spectral and electronic transport properties of layered structures
(ii) Study the iteration of light with two-dimensional and layered materials.

It was concluded that the electronic transport properties of layered structures depend drastically on the way different layers are aligned. It was also concluded that the structure of the electrons wavefunction plays an important role in the highly non-linear current that is generated in two-dimensional materials, when these are illuminated by very intense light.
The results achieved during the project have been disseminated in several scientific articles. The new methods developed to model multilayered van der Waals structures were published in:

• B. Amorim, Eduardo V. Castro, arXiv:1807.11909 (2018) (submitted to PRB)
• B. Amorim, Phys. Rev. B 97, 165414 (2018)

These methods were used to model experimental angle-resolved photoemission experiments in:

• Y.-R. Lin, N. Samiseresht, M. Franke, S. Parhizkar, S. Soubatch, B. Amorim, T.-L. Lee, C. Kumpf,F.S. Tautz, F.C. Bocquet, arXiv:1809.07958 (2018) (submitted to PRL)

The possibility of the emergence of a Hall conductivity, in the absence of magnetic fields, in a class of semiconducting two-dimensional materials, due to electron-electron interactions, was investigated in:

• João E. H. Braz, B. Amorim, Eduardo V. Castro, Phys. Rev. B 98, 161406 (2018)

The possibility of modifying a nanoparticle polarizability due to the presence of a two-dimensional materials was studied in:

• B. Amorim, P. A. D. Gonçalves, M. I. Vasilevskiy, N. M. R. Peres, Appl. Sci., 7(11), 1158 (2017).

Finally, the effect of electronic wavefunction structure and topology in the generation of high-harmonic photocurrent in two-dimensional materials was investigated in:

• R.E.F. Silva, Á. Jiménez-Galán, B. Amorim, O. Smirnova, M. Ivanov, arXiv:1806.11232 (2018) (submitted to Nature Photonics)

Two further papers are currently being prepared which study the electronic transport properties of bilayer and trilayer van der Waals structures and how these are affected by the alignment of the different layers.

The fellow also disseminated his research via talks in several international conferences, including the APS March Meeting and the DPG Spring Meeting, and in research institutions and universities, including the York University and the Jülich Research Centre.

The work on modelling of bilayer vdW structures also result in the publication of a book chapter:

• Twisted bilayer graphene: Low-energy physics, electronic and optical properties Gonçalo Catarina, Bruno Amorim, Eduardo V. Castro, João M. V. P. Lopes, Nuno Peres. To appear as Chapter 6 of Handbook of Graphene, Volume 3: Graphene-Like 2D Materials, WILEY-Scrivener (forthcoming)
During the action, the fellow developed a new, numerically efficient, method to model incommensurate multilayered van der Waals structures. Previous methods were restricted to the case of bilayer structures and effectively relied on approximating the bilayer by a periodic structure, which is not always true. The new methods developed in this action went beyond the state of the art, by allowing the modelling of structures with more than two layers and not requiring approximating the vdW structure by a periodic one. The developed method enabled the theoretical modelling of the electronic spectral and transport properties of bilayer and trilayer vdW structures. The new developed method also allows to study the effect of interlayer coupling in the electronic transport beyond previous perturbative methods.

The fellow also contributed to the developed a theory describing highly non-linear photocurrent generation in two-dimensional materials. This theory goes beyond previous approaches by correctly taking into account the electronic wavefunction structure (via de Berry curvature). This shows that the high-harmonic spectrum of the photocurrent encodes information regarding the electrons wavefunction and the topology of the electronic band structure.

Two-dimensional materials are currently considered crucial for European Union's Technological Innovation and Competitiveness. The methods developed in this action will be used by the fellow in the future to continue studying electronic transport and photocurrent generation in two-dimensional materials and van der Waals structures, with the goal of modelling vdW structure based transistors and photodetectors, which have potential technological applications.