Matthew Watson

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Matthew Watson is a Beamline Scientist at I05.

Email: matthew.watson@diamond.ac.uk

Keywords

ARPES, nano-ARPES, DFT

correlated electron systems, superconductivity, charge density waves, transition metal dichalcogenides, 2D materials, monolayers

FeSe, Fe-based superconductors, TiSe2, CrGeTe3, Ta2NiSe5

  1. Research Interests
  2. Publications
  3. Biography
Research Interests -

I use the technique of Angle-Resolved Photoemission Spectroscopy (ARPES) to investigate the electronic structure of quantum materials. At I05 at Diamond, I am particularly involved with the push towards ever smaller beam size at the nano-ARPES endstation, as the demand increases for ARPES measurements from inside small domains, on thin flakes, and even from in-operando devices.

One of my research interests is correlated electron systems, with a particular focus on the Fe-based superconductors such as FeSe. I have performed and analysed a number of ARPES experiments with extremely high energy resolution in order to probe both the temperature-dependent electronic structure and the superconducting gap. As part of this, I also performed ARPES measurements of samples under mechanical strain to overcome issues with domains.  

More recently, I have been working on understanding phase transitions in a number of layered or quasi-2D materials, including transition-metal dichalcogenides, for example taking a fresh look at the well-known charge density wave in TiSe2 in both bulk and monolayer forms.    

Another ongoing research project is on van der Waals ferromagnets (e.g. CrGeTe3), and how ARPES can shed light on the superexchange mechanism in this family of materials. 

I do my own DFT calculations to support the experimental work and take an interest in tight-binding-based approaches to modelling electronic structure. I also maintain an interest in transport measurements and soft x-ray techniques such as XMCD, where these are complementary to the ARPES studies. 

I have a wide network of collaborators past and present, particularly Phil King , Amalia Coldea, Amir A. HaghighiradLuke Rhodes , and Timur Kim . 

Publications - +

Please visit my researchgate profile to view my latest publications. Particular highlights include:

Phys. Rev. Lett. 122, 076404 (2019)

Orbital- and kz-selective hybridisation of Se 4p and Ti 3d states in the charge density wave phase of TiSe2

M. D. Watson, O. J. Clark, F. Mazzola, I. Marković, V. Sunko, T. K. Kim, K. Rossnagel, P. D. C. King

TiSe2 has been well-studied with photoemission for decades, but the dispersion of bands in the kz-direction had been often neglected. In this paper, we showed that the band hybridisations occur in a kz-selective manner, and also identified an orbital-selective hybridisation. These effects combined lead to a ground state that contains both strongly hybridized and essentially unhybridized states – with the latter being most relevant for the low energy properties. This leads to the unexpected result that the total band gap is smaller in the low-temperature phase.

Phys. Rev. B 98, 180503(R) (2018)  [Editor’s suggestion]

Scaling of the superconducting gap with orbital character in FeSe                

L. C. Rhodes, M. D. Watson, A. A. Haghighirad, D. I. Evtushinsky, M. Eschrig, and T. K. Kim

My extensive research on FeSe with collaborators at the I05 beamline culminated in us taking on the challenge of measuring the anisotropy of the superconducting gap. This paper contains some of the highest resolution data ever measured by synchrotron-based ARPES, which we used to directly demonstrate a link between the orbital character of the bands and the gap structure. In combination with calculations, we argued that this is direct evidence for a spin-fluctuation pairing mechanism.

Phys. Rev. Lett. 118, 097002 (2017)

Multiband One-Dimensional Electronic Structure and Spectroscopic Signature of Tomonaga-Luttinger Liquid Behavior in K2Cr3As3

M. D. Watson, Y. Feng, C. W. Nicholson, C. Monney, J. M. Riley, H. Iwasawa, K. Refson, V. Sacksteder, D. T. Adroja, J. Zhao, and M. Hoesch

This paper remains the only reported ARPES study of the quasi-1D superconductor K2Cr3As3, due to the extreme air-sensitivity of the samples combined with challenging sample morphology and short lifetime in UHV. With careful preparation and transport of the samples, we overcame these experimental challenges to report the experimental electronic structure and found an unusual depletion of spectral weight of the bands approaching the Fermi level, which was interpreted as a signature of Tomonoga-Luttinger liquid behaviour.

Phys. Rev. B 91, 155106 (2015) [Editor’s Suggestion] (200+ citations)

Emergence of the nematic electronic state in FeSe

M. D. Watson, T. K. Kim, A. A. Haghighirad, N. R. Davies, A McCollam, A. Narayanan, S. F. Blake, Y. L. Chen, S. Ghannadzadeh, A. J. Schofield, M. Hoesch, C. Meingast, T. Wolf, and A I. Coldea

This paper was the amongst the first to discuss the anisotropic electronic state of FeSe at low temperatures, and showed that the ARPES and quantum oscillations were mostly in agreement. This paper was my first to include ARPES data, represents a good fraction of my PhD thesis, and has been highly cited as it was one of the papers which set the stage for several years of highly debated research on FeSe.  

Biography - +

Matthew performed both his undergraduate and postgraduate studies at the nearby University of Oxford. From 2015 to 2017, he worked as a postdoc on the I05 beamline at Diamond, before moving to the University of St Andrews to join the King group. In October 2019 he returned to Diamond to take up his current role as a Beamline Scientist at I05.  

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