Experimental Evidence for Field-Induced Emergent Clock Anisotropies in the XY Pyrochlore Er2Ti2O7
Jonathan Gaudet, A. M. Hallas, J. Thibault, Nicholas Butch, H. A. Dabkowska, B. D. Gaulin
The XY pyrochlore antiferromagnet Er2Ti2O7 exhibits a rare case of Z6 discrete symmetry breaking in its ψ2 magnetic ground state. The Ising model, with Z2 symmetry breaking, is known to capture the salient physics of many magnetic materials and a wealth of other physical systems. Despite being well-studied theoretically, systems with higher discrete symmetry breakings are uncommon in nature. Thus, Er2Ti2O7 provides a remarkable experimental playground for the study of broken Zn symmetry, for n>2. In particular, recent theoretical work probed Zeeman coupling on a pyrochlore lattice with broken Z6 symmetry and applied it to Er^2^Ti2O7. Multiple domain transitions are predicted to occur, depending on the crystallographic orientation of the magnetic field, inducing rich and controllable magnetothermodynamic behavior. In this work, we perform neutron scattering measurements on Er2Ti2O7 with a magnetic field applied along the  and  directions, providing the first experimental observation of these exotic domain transitions. In a  field, a ψ2 to ψ3 transition is observed at a critical field of 0.18 ± 0.05 T. We are thus able to extend the concept of the spin-flop transition, which have long been observed in Ising systems, to higher discrete ZN symmetry systems. In a  field, we observe a series of successive domain-based phase transitions for fields of 0.15 ± 0.03 T. We show that these field-induced transitions are consistent with the emergence of two-fold, three-fold and possibly six-fold Zeeman terms. Considering all the possible ψ2 and ψ3 domains, these Zeeman terms can be mapped onto a conventional clock - exemplifying a literal clock anisotropy. Lastly, characterizing the domain selection in Erd2^Ti2O7 provides a pathway for determining the strength of order-by-disorder as the ground state selection mechanism.
, Hallas, A.
, Thibault, J.
, Butch, N.
, Dabkowska, H.
and Gaulin, B.
Experimental Evidence for Field-Induced Emergent Clock Anisotropies in the XY Pyrochlore Er<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub>, Physical Review B, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=922730
(Accessed December 5, 2023)