Is There Any Hidden Symmetry in the Stripe Structure of Perovskite High-Temperature Superconductors?

Gavrichkov, Vladimir A.; Shan'ko, Yury; Zamkova, Natalia G.; Bianconi, Antonio Source: JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 10 (8):1840-1844; 10.1021/acs.jpclett.9b00513 APR 18 2019

Local and fast structural probes using synchrotron radiation have shown nanoscale striped puddles and nanoscale phase separation in doped perovskites. It is known that the striped phases in doped perovskites are due to competing interactions involving charge, spin, and lattice degrees of freedom. In this work, we show that two different stripes can be represented as a superposition of a pair of stripes, Un) or Dn), characterized by perovskite tilts where one of the pair is rotated in relation to the other partner by an angle Δθn = π/2. The spatial distribution of the U and D stripes is reduced to all possible maps in the well-known mathematical four-color theorem. Both the periodic striped puddles and random structures can be represented by using planar graphs with a chromatic number χ ≤ 4. To observe the colors in mapping experiments, it is necessary to recover variously oriented tilting effects from the replica. It is established that there is an interplay between the annihilation/creation of new stripes and ordering/disordering tilts in relation to the θn angle in the CuO2 plane, where the characteristic shape of the stripes coincides with the tilting-ordered regions.