Abstract
Bragg coherent diffraction imaging (BCDI) experiments have been carried out at the Advanced Photon Source using a new cryostat system developed to achieve high mechanical stability and low vibrations. We measured the (012)LTO Bragg peak which is unique to the low-temperature orthorhombic (LTO) phase of micron-sized crystals of the high-temperature superconductor La2−xBaxCuO4 (LBCO) to study the formation of structural domains. Each time the sample was cooled into the orthorhombic phase, the diffraction pattern of domains was different. This confirms the interpretation of pinning of the lower-temperature charge density Wave domains observed in coherent resonant X-ray speckle correlation analysis experiments.
Highlights
Bragg coherent diffraction imaging (BCDI) experiments have been carried out at the Advanced Photon Source using a new cryostat system developed to achieve high mechanical stability and low vibrations
The charge density wave (CDW) formation temperature is roughly coincident with TLTT and it is speculated that the longer range order seen in LBCO is connected somehow with the special feature of LBCO having this additional LowTemperature Tetragonal” (LTT) phase, as this produces rows of oxygen atoms all displaced below the plane, which form potential pinning features for the CDW
It was found firstly that the speckles were static over long periods [13], that the domain texture does not fluctuate, and secondly that the speckle positions were stable in temperature, even as the material was thermally cycled above the TLTT phase transition where the CDWs melt and the diffraction signal disappears [15]
Summary
La2−xBaxCuO4 (LBCO) is a complex oxide, which was the first high-temperature superconductor (HTS) material, reported by Bednorz and Muller in 1985 [1] At room temperature, it has a layered high-temperature tetragonal (HTT) structure where the Cu–O square layers, which are usually assumed to be the hosts of the superconductivity, form flat planes. LBCO has the longest CDW correlation length of ~ 20 nm [4] discovered so far at zero magnetic field and applied strain. How this CDW state forms is still not fully understood and is the subject of ongoing investigations [5,6,7,8,9,10,11]. The CDW formation temperature is roughly coincident with TLTT and it is speculated that the longer range order seen in LBCO is connected somehow with the special feature of LBCO having this additional LTT phase, as this produces rows of oxygen atoms all displaced below the plane, which form potential pinning features for the CDW
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