【Molecular Systems and Materials Chemistry】Unraveling Structural Fluctuations in Polar Metals - Shallow Energy Landscapes Driven by Conduction Electrons and Emergent Dynamics -

For decades, physicists held that polarity and metallicity could never coexist. Electrons roaming freely through a metal were thought to neutralize any internal electric polarization ― much like a crowd instantly filling every gap in a room. The discovery of so-called polar metals challenged that assumption. But a deeper question remained: how exactly do conduction electrons shape the stability of polar structures, and what governs their behavior across a phase transition?
A joint international research team, led by doctoral student Kantaro Murayama, Associate Professor Hiroshi Takatsu, and Professor Hiroshi Kageyama of the Graduate School of Engineering, Kyoto University, together with Professor Ryotaro Arita of the Graduate School of Science, The University of Tokyo, has now answered that question in lithium rhenate (LiReO3). The team confirmed a structural phase transition between polar and nonpolar states ― and made a more striking finding: even below the transition temperature (Ts), the structure never fully settles in polar metals. Fluctuations persist.
The reason, they found, is that conduction electrons induce a shallow potential energy landscape, leaving the material perpetually poised between two states ― like a ball resting at the bottom of an almost imperceptibly gentle valley. This delicate balance produces anomalous physical behavior: an unusually broad thermal hysteresis and a reverberant resonant absorption of ultrasound that lingers well after the signal has passed.
The broader implication is a conceptual shift. What was once dismissed as noise is recast here as an intrinsic physical signature of shallow energy landscapes ― something not to be suppressed but understood and engineered. This work offers a new design principle for functional materials, with promising applications in energy harvesting and low-power devices.

The findings were published online in Science Advances on April 3, 2026 (2:00 p.m. Eastern Time).

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Solid State Chemistry