Dresden 2026 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 81: Correlated Electrons: Other Materials
TT 81.7: Vortrag
Donnerstag, 12. März 2026, 16:45–17:00, HSZ/0101
Tuning through a tetragonal collapse in Ca1−xSrxCo2As2 single crystals investigated by thermal expansion — •Sven Graus1, Adrian Valadkhani2, N. S. Sangeetha1, Markus Garst3, Roser Valentí2, Andreas Kreyssig1, and Anna E. Böhmer1 — 1Experimental Physics IV, Ruhr University Bochum, Bochum, Germany — 2Institute for Theoretical Physics, Goethe University Frankfurt, Frankfurt am Main, Germany — 3Institute of Theoretical Solid State Physics, Karlsruhe Institute of Technology, Karlsruhe, Germany
Ca1−xSrxCo2As2 crystallizes in the tetragonal ThCr2Si2-type structure and undergoes a rare substitution-driven crossover from a collapsed tetragonal to an uncollapsed tetragonal structure. The resulting rich magnetic and electronic phase diagram provides an interesting platform to investigate the complex interplay between lattice, magnetic and electronic degrees of freedom.
High-resolution thermal-expansion measurements reveal strong anisotropy between in-plane and out-of-plane directions and identify a critical region near x≈0.48 , where the thermal expansion coefficients αa/T and αc/T diverge at low temperatures. Analysis of the temperature dependence of the c/a ratio shows an accumulation of entropy in this region. The thermal-expansion behavior is well captured by a simple model of a pressure-tuned Van Hove singularity which is supported by density-functional theory calculations.
We acknowledge support from the Deutsche Forschungsgemeinschaft (DFG) under CRC/TRR 288 (Project A02).
Keywords: capacitance dilatometry; thermal expansion; Van Hove singularity; antiferromagnetism