Tuning many body states in TiSe2 by ionic liquid gating

Unconventional superconductivity nearly always arises in the vicinity of another ordered state and the role of interactions with a second fluctuating order parameter is currently a very active topic of research. 1T-TiSe2 is a layered semimetal with weakly overlapping valence and conduction bands. Under ambient conditions the material does not exhibit superconductivity at any temperature but a charge density wave state develops for T<200K. It has, however, been demonstrated that the CDW can be suppressed in bulk samples by Cu intercalation [1] or by the application of hydrostatic pressure [2], giving rise to a characteristic superconducting ‘dome’ at high compositions/pressures. Recent work has shown that superconductivity can also be induced in few-layer 1T-TiSe2 flakes with an ionic gel gate [3]. Magnetoresistance oscillations in the superconducting state of these samples have been interpreted in terms of spatial texturing of the superconducting order parameter supported by an inhomogenous matrix of CDW states. Moreover, STM and transient reflectivity measurements claim to show that CDWs have a chiral character in 1T-TiSe2, stimulating theoretical work in trilayer samples which predicts unconventional superconductivity and a possible chiral pairing state that breaks time-reversal symmetry [4].

Within this PhD project you will fabricate few-layer 1T-TiSe2 field effect transistors and investigate the use of ionic liquid gating to suppress the CDW transition and induce superconductivity. The superconducting/CDW phase diagram will be established as a function of temperature and applied magnetic field, and compared with that of reference [3] using an ionic gel. Samples composed of different numbers of 1T-TiSe2 layers will also be systematically investigated to search for the predicted unconventional pairing states.

Your project will be based in the Centre for Nanoscience and Nanotechnology at the University of Bath which provides a supportive environment for training and other career development opportunities. Your work will make extensive use of nanopatterning, deposition and etching tools in the University’s Nanofabrication Facility as well as low temperature measurement systems in Bath. You will have your own project, but will interact strongly with other PhD students and postdocs working on related projects. You will also have the opportunity to present your work at leading international conferences and publish in high-quality peer-reviewed journals.

Applications: Applicants should have a strong interest in pursuing experimental condensed matter research and have or expect to gain a First or good Upper Second Class UK Honours degree in physics. Applications from equivalently qualified non-UK students are also welcome.

Contact Prof. Simon Bending ([Email Address Removed]) with informal enquiries.
Group web site: http://www.bath.ac.uk/physics/contacts/academics/simon_bending/
Nanofabrication Facilities: http://bath.ac.uk/facilities/nanofab/