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  Charge fluctuations across the pressure-induced quantum phase transition in EuCu2(Ge1-xSix)2

Ahmida, M. A., Forthaus, M. K., Geibel, C., Hossain, Z., Hearne, G. R., Kagti, J., et al. (2020). Charge fluctuations across the pressure-induced quantum phase transition in EuCu2(Ge1-xSix)2. Physical Review B, 101(20): 205127, pp. 1-10. doi:10.1103/PhysRevB.101.205127.

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 Creators:
Ahmida, Mahmoud A.1, Author
Forthaus, Martin K.1, Author
Geibel, Christoph2, Author              
Hossain, Zakir1, Author
Hearne, Giovanni R.1, Author
Kagti, Jirka1, Author
Prchal, Jiri1, Author
Sechovsky, Vladimir1, Author
Abd-Elmeguid, Mohsen M.1, Author
Affiliations:
1External Organizations, ou_persistent22              
2Christoph Geibel, Physics of Quantum Materials, Max Planck Institute for Chemical Physics of Solids, Max Planck Society, ou_1863465              

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 Abstract: Pressurizing strategically selected compositions of the EuCu2(Ge1-xSix)(2) series affords an opportunity for gaining microscopic insight into the ground-state properties and interplay between magnetism and valence fluctuations across a quantum critical point. This is investigated by way of systematic Eu-151 Mossbauer spectroscopy measurements on x = 0 and x = 0.5 compositions in the series, pressurized up to 7 GPa including variable temperature scans in the range 300-4.2 K. In EuCu2Ge2 the temperature and pressure dependences of the hyperfine interaction parameters indicate that both the magnetic and divalent state, Eu nu+ where nu = 2, are stable up to 6-7 GPa, thus serving as a useful reference. Whereas in the x = 0.5 composition which initially involves Eu2+, collapse of the magnetically ordered state is onset at similar to 1.3 GPa and there is emergence of a nonmagnetic intermediate valence state coexisting with the magnetically ordered state. This regime of mixed states is a precursor of a quantum phase transition to a nonmagnetic homogeneous intermediate valence state nu similar to 2.45, across a quantum critical point at 3.6 GPa, suggesting a first-order phase transition. X-ray-diffraction pressure studies at 300 K up to 6 GPa of the x = 0.5 composition indicate there is no change in lattice symmetry from the tetragonal ThCr2Si2-type structure. There are also no obvious discontinuities in pressure dependences of the lattice parameters upon evolving through the quantum critical point at 3.6 GPa. Increasing pressure changes the starting Eu2+ valence monotonically, until the mean valence attains its largest value nu similar to 2.45 indicative of enhanced charge fluctuations at the quantum critical point and plateaus thereafter. High-pressure resistance measurements at low temperatures down to 40 mK near the quantum critical point reveal no evidence for superconductivity.

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Language(s): eng - English
 Dates: 2020-05-182020-05-18
 Publication Status: Published in print
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Title: Physical Review B
  Abbreviation : Phys. Rev. B
Source Genre: Journal
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Publ. Info: Woodbury, NY : American Physical Society
Pages: - Volume / Issue: 101 (20) Sequence Number: 205127 Start / End Page: 1 - 10 Identifier: ISSN: 1098-0121
CoNE: https://pure.mpg.de/cone/journals/resource/954925225008