Tuning Incommensurate Charge Order in Ba1-xSrxAl4 and Ba1-yEuyAl4

Published

July 20, 2025

Author(s)

Prathum Saraf, Eleanor M. Clements, Danila Sokratov, Shanta Saha, Peter Zavalij, Thomas Heitmann, Jeffrey Lynn, Camille Bernal-Chobin, Dipanjan Chaudhuri, Caitlin Kengle, Yue Su, Simon Bettler, Nathan Manning, Peter Abbamonte, Sananda Biswas, Roser Valenti, Johnpierre Paglione

Abstract

The BaAl4-type structure family is home to a vast landscape of interesting and exotic properties, with descendant crystal structures hosting a variety of electronic ground states including magnetic, superconducting and strongly correlated electron phenomena. BaAl4 itself has recently been shown to host a non-trivial topological band structure, but is otherwise a paramagnetic metal. However, the other members of the AAl4 family (A= alkali earth), including SrAl4 and EuAl4, exhibit symmetry-breaking ground states including charge density wave (CDW) and magnetic orders. Here we investigate the properties of the solid solution series Ba1−xSrxAl4 and Ba1−yEuyAl4 using transport, thermodynamic and scattering experiments to study the evolution of the charge-ordered state as it is suppressed with Ba substitution to zero near 50% substitution in both systems. Neutron and x-ray diffraction measurements reveal a nearly commensurate CDW state in SrAl4 with c-axis-oriented ordering vector (0, 0, 0.097) that evolves with Ba substitution toward a longer wavelength. A similar progression is observed in the Ba1−yEuyAl4 series that also scales with the ordering temperature, revealing a universal correlation between charge-order transition temperature and ordering vector that points to a critical wavevector that stabilizes CDW order in both systems. We study the evolution of the phonon band structure in the Ba1−xSrxAl4 system, revealing the suppression of the CDW phase matches the suppression of a phonon instability at precisely the same momentum as observed in experiments, confirming the electron-phonon origin of charge order in this system.

Citation

Physical Review B

Volume

112

Issue

3

Pub Type

Journals

Download Paper

https://doi.org/10.1103/d8yy-1w3l

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Keywords

Topological semimetal, Charge Density Wave, neutron diffraction, SrAl4, Ba doping.

Citation

Saraf, P. , Clements, E. , Sokratov, D. , Saha, S. , Zavalij, P. , Heitmann, T. , Lynn, J. , Bernal-Chobin, C. , Chaudhuri, D. , Kengle, C. , Su, Y. , Bettler, S. , Manning, N. , Abbamonte, P. , Biswas, S. , Valenti, R. and Paglione, J. (2025), Tuning Incommensurate Charge Order in Ba1-xSrxAl4 and Ba1-yEuyAl4, Physical Review B, [online], https://doi.org/10.1103/d8yy-1w3l, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=959914 (Accessed October 27, 2025)