Nematicity and structure in LaFe1-xCoxAsO

Abstract We present thermal expansion studies on single-crystalline LaFe 1 - x Co x AsO with doping levels of x = 0, 0.026, and 0.034, and on BaFe 2 As 2 . Anomalies in the thermal expansion coefficient α enable reading off the structural and magnetic transition temperatures T S and T N . The evolution of the orthorhombic distortion at T S is illustrated by length changes of the a - and b -axes and the experimentally determined orthorhombicity δ . The results are compared to BaFe 2 As 2 . Finally, the electronic phase diagram is discussed.