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Dr Joel Barker

I completed my M.Phys. at Warwick in 2012, and continued on to a joint Warwick/ISIS funded Ph.D. project investigating unconventional superconductivity, supervised by Prof. Don Paul and Dr Adrian Hillier (ISIS).

My research focused on studies of superconducting systems using the muon spin rotation and relaxation (μSR) facilities at the ISIS neutron and muon spallation source. I studied a wide variety of materials, however my primary focuswas superconductors which lack inversion symmetry, and multiband systems.

Thesis: Muon Studies of Unconventional Superconductors

Non-centrosymmetric superconductors

Systems which lack a centre of inversion symmetry in their crystal structure have a non-uniform lattice potential - this leads to a splitting of the Fermi surface into spin up and spin down components. In a superconducting material, this means that the ground state can be an admixture of spin-singlet and spin-triplet paired electrons. Using μSR, it is possible to detect the tiny spontaneous magnetization that can arise in the superconduting state if a spin-triplet channel is stabilized and to study the relationship between the spin-orbit coupling and the spin-triplet pairing state. Spin-triplet superconductors are expected to exhibit a rich variety of different physical phenomena, such as Majorana bound states.

Current Role

Instrument Scientist with special responsibility for the GPS muon instrument in LMU - the Laboratory for Muon Spin Spectroscopy, part of PSI, Villigen, Switzerland.

Publications

[1] - Probing the superconducting ground state of the noncentrosymmetric superconductors CaTSi3 (T = Ir, Pt) using muon-spin relaxation and rotation,
R. P. Singh, A. D. Hillier, D. Chowdhury, J. A. T. Barker, D. McK. Paul, M. R. Lees, and G. Balakrishnan,
Phys. Rev. B 90, 104504 (2014). – Published 9 September 2014 (link)

[2] - Superconducting properties of Sn1-xInxTe (x = 0.38-0.45) studied using muon-spin spectroscopy,
M. Saghir, J. A. T. Barker, G. Balakrishnan, A. D. Hillier, and M. R. Lees,
Phys. Rev. B 90, 064508 (2014). – Published 15 August 2014 (link)

[3] - Unconventional Superconductivity in La7Ir3 Revealed by Muon Spin Relaxation: Introducing a New Family of Noncentrosymmetric Superconductor That Breaks Time-Reversal Symmetry,
J. A. T. Barker, D. Singh, A. Thamizhavel, A. D. Hillier, M. R. Lees, G. Balakrishnan, D. M. Paul, and R. P. Singh,
Phys. Rev. Lett. 115, 267001 (2015). - Published 30 December 2015 (link)

Presentations

[a] - ISIS Student Meeting 2014 (slides)
[b] - Frontiers in Unconventional Superconductivity and Magnetism 2015 (slides)

Courses Taken

MPAGS

EX3 - Crystallography (November 2012)
EX4 - Magnetism in Condensed Matter Systems (February 2013)
EX8 - Introduction to solid-state devices (January 2013)

Training Schools

ISIS Muon Training School 2014
ISIS Neutron Training School 2015

Teaching

I taught in the 3rd year MPhys laboratory and the first year electronics workshop. I also tutored A level physics, maths and further maths.

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Contact Details


E-Mail joel dot barker at psi dot ch