Revealing the emergence of altermagnetism and density wave order in Ti-doped Ca₃Ru₂O₇

The n=2 Ruddlesden-Popper ruthenate Ca₃Ru₂O₇ is reported to be an antiferromagnetic metal at low temperatures. With dilute Ti doping, the ground state evolves to an insulator, which is followed by a magnetic structure change [1]. Previous studies on Ca₃Ru₂O₇ and its doped variants have identified the crystalline symmetry as Bb2₁m, which remains unchanged across the multiple magnetic and electronic transitions induced by temperature, doping and magnetic field. However, recent DFT calculations suggest an emergent symmetry lowering to Pn2₁a for the parent compound [2], rendering the antiferromagnetic ground state an altermagnet [3]. Our temperature dependent polarized Raman spectroscopy, supported by DFT, identify that this symmetry lowering can also be induced through Ti doping, thereby opening up a pathway of controlling altermagnetic order though chemical substitution. In addition, symmetry resolved electronic Raman scattering reveal signatures of density wave ordering. The strong coupling between the spin, charge, lattice and orbital degrees of freedom in this system makes it an interesting platform for exploring the coupling of density wave and altermagnetic order, paving way for tunable electronic functionalities. 

[1] Peng et al. Phys. Rev. B. 87, 085125 (2013) 

[2] Puggioni et al. Phys. Rev. Res. 2, 023141 (2020)

[3] Zhao et al. Phys. Rev. B. 112, 165127 (2025)