An unusual spin excitation mode observed by neutron scattering has inspired numerous theoretical studies of the interplay between charged quasiparticles and collective spin excitations in the copper oxide high-temperature superconductors. The mode has, thus far, only been observed in materials with crystal structures consisting of copper oxide bilayers, and it is absent in the single-layer compound La 2− x Sr x CuO 4+δ . Neutron-scattering data now show that the mode is present in Tl 2 Ba 2 CuO 6+δ , a single-layer compound with a superconducting transition temperature of ∼90 kelvin, demonstrating that it is a generic feature of the copper oxide superconductors, independent of the layer sequence. This restricts the theoretical models for the origin of the resonant mode and its role in the mechanism of high-temperature superconductivity.

This is an author produced version of a paper subsequently published in 2D Mater. Tonndorf et al, Single-photon emitters in GaSe (2017) 4 021010, https://doi.org/10. 1088/2053-1583/aa525b eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request.

Integration of quasi-two-dimensional (2D) films of metal–chalcogenides in optical microcavities permits new photonic applications of these materials. Here we present tunable microcavities with monolayer MoS2 or few monolayer GaSe films. We observe significant modification of spectral and temporal properties of photoluminescence (PL): PL is emitted in spectrally narrow and wavelength-tunable cavity modes with quality factors up to 7400; a 10-fold PL lifetime shortening is achieved, a consequence of Purcell enhancement of the spontaneous emission rate.

We report on a study of the infrared properties of Bi 2 Sr 2 CaCu 2 O 81d , Bi 1.66 Pb 0.34 Sr 2 CaCu 2 O 81d , and Tl 2 Ba 2 CuO 61d crystals at doping levels from underdoped to strongly overdoped. We calculate the frequency-dependent scattering rate 1͞t͑v, T ͒ and study its doping dependence. While we observe a normal-state gaplike depression in 1͞t͑v, T͒ in the underdoped regime, it is not observed in the overdoped regime. While the high-frequency 1͞t͑v, T ͒ is temperature independent in the underdoped regime, it scales with temperature in the overdoped regime.

Gallium chalcogenides are promising building blocks for novel van der Waals heterostructures. We report on the low-temperature micro-photoluminescence (PL) of GaTe and GaSe films with thicknesses ranging from 200 nm to a single unit cell. In both materials, PL shows a dramatic decrease by 10 4 -10 5 when film thickness is reduced from 200 to 10 nm. Based on evidence from continuouswave (cw) and time-resolved PL, we propose a model explaining the PL decrease as a result of nonradiative carrier escape via surface states. Our results emphasize the need for special passivation of two-dimensional films for optoelectronic applications.