Bragg glass signatures in the disordered charge density wave material PdxErTe3 from X-ray diffraction data using unsupervised machine learning*

Vestigial nematic and Bragg glass are new phases that emerge when an incommensurate long-range ordered charge density wave (CDW) gets suppressed by a quenched disorder. Pd intercalated rare earth tritelluride (PdxRTe3) has emerged as a promising model system to systematically investigate these emergent phases when the bi-directional orthogonal CDW order of RTe3 interacts with a controlled amount of disorder (Pd intercalation). Using X-ray diffraction Temperature Clustering (X-TEC), an unsupervised and interpretable machine learning technique introduced in Ref. [1], we extract signatures of  Bragg glass and vestigial nematic phases in PdxErTe3 from a large volume of X-ray temperature series data spanning 20000 Brillouin zones, collected using the Pilatus 2M CdTe detector on Sector 6-ID-D at the Advanced Photon Source. In addition to identifying the two order parameters from the CDW peak intensities, X-TEC probes the temperature dependence of the CDW peak widths and the disorder induced asymmetry in the diffuse scattering. X-TEC-enabled extraction of these otherwise subtle signatures from the data helps us arrive at a phase diagram. Our results suggest that  Pd intercalation turns the long-range ordered CDW into the Bragg glass phase, providing first X-ray based detection of the Bragg glass phase.  

 

 

[1] Venderley et al, https://arxiv.org/abs/2008.03275