A phase transition driven by subtle distortion without broken symmetry on spin, charge and lattice in Layered LnCu4-{\delta}P2(Ln=Eu, Sr)

TL;DR

This paper reports a rare phase transition in layered LnCu4-{ extdelta}P2 materials around 120-140 K driven by subtle structural distortion without breaking symmetry, challenging traditional Landau theory expectations.

Contribution

It reveals a thermodynamic phase transition caused by minimal lattice distortion without symmetry breaking, expanding understanding of phase transitions in condensed matter.

Findings

Detected a phase transition at ~120-140 K via heat capacity anomalies.

Observed minimal lattice parameter changes (~0.013-0.062%) during transition.

Confirmed the transition occurs without symmetry breaking in charge, spin, or lattice.

Abstract

In the scenario of Landau phase transition theory in condensed matter physics, any thermal dynamic phase transition must be subject to some kind of broken symmetries, that are relative to its spin, charge, orbital and lattice. Here we report a rare phase transition at Tp ~120 K or 140 K in layered materials LnCu4-{\delta}P2 (Ln=Eu, Sr) driven by a subtle structural-distortion without any broken symmetry on charge, spin and lattice. The variations of the lattice parameters, ({\Delta}Lc/Lc) ~ 0.013% or 0.062%, verified by thermal expansion, is much less than that for a typical crystalline phase transition (~0.5-1%), but the significant anomaly in heat capacity provides clear evidence of its intrinsic nature of thermodynamic transition.