Structure of the normal state and origin of the Schottky anomaly in the correlated heavy-fermion superconductor $\mathrm{U}{\mathrm{Te}}_{2}$

Structure of the normal state and origin of the Schottky anomaly in the correlated heavy-fermion superconductor $U {Te}_{2}$

S. Khmelevskyi, L. V. Pourovskii, and E. A. Tereshina-Chitrova

Phys. Rev. B 107, 214501 – Published 5 June 2023

Abstract

The recently discovered $U {Te}_{2}$ superconductor is regarded as a heavy-fermion mixed-valence system with very peculiar properties within the normal and superconducting (SC) states. It shows no signs of magnetic order, but has a strong anisotropy of magnetic susceptibility and SC critical field. In addition to a heavy-fermion-like behavior in the normal state, it exhibits a distinctive Schottky-type anomaly at $\sim 12$ K and a characteristic excitations gap $\sim 35 - 40$ K. Here, we show, by virtue of dynamical mean-field theory calculations with a quasiatomic treatment of electron correlations, that ab initio-derived crystal-field splitting of the $5 f^{2}$ ionic configuration yields agreement with these experimental observations. A close analogy of the normal paramagnetic state of $U {Te}_{2}$ to that of $U {Ru}_{2} {Si}_{2}$ in the Kondo arrest scenario is revealed. We consider the impact of anisotropic superexchange interactions within the U-U structural dimer on magnetization and development of strong orbital and magnetic moment fluctuations in $U {Te}_{2}$ .

Received 15 September 2022
Revised 24 April 2023
Accepted 22 May 2023

DOI:https://doi.org/10.1103/PhysRevB.107.214501

Physics Subject Headings (PhySH)

Heavy-fermion systems Strongly correlated systems Unconventional superconductors

Dynamical mean field theory

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

S. Khmelevskyi ^1,*, L. V. Pourovskii ^2,3, and E. A. Tereshina-Chitrova ⁴

¹Research Center for Computational Materials Science and Engineering, Technical University of Vienna, Karlsplatz 13, A-1040 Vienna, Austria
²CPHT, CNRS, École polytechnique, Institut Polytechnique de Paris, 91120 Palaiseau, France
³Collège de France, 11 place Marcelin Berthelot, 75005 Paris, France
⁴Institute of Physics, Czech Academy of Sciences, 18121 Prague, Czech Republic

^*sk@cms.tuwien.ac.at

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Vol. 107, Iss. 21 — 1 June 2023

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Figure 1
Calculated spectral density of $U {Te}_{2}$ in the density functional theory (DFT) + Hubbard $I$ approximation with the localized $5 f^{2}$ configuration. The upper panel shows the total spectral function as a color map in a logarithmic intensity scale to clearly highlight the band dispersions. The lower panel shows partial U $5 f$ spectral function as a color map in the same range but in a linear intensity scale to resolve the magnitude of the U $5 f$ contribution to different bands. A set of flat bands above the Fermi energy $(E_{F})$ is the $5 f$ upper Hubbard band due to the transition from the $^{3} H_{4}$ multiplet of the U $5 f^{2}$ configuration to the $5 f^{3}$ states. Metallic bands crossing the Fermi level are the $p$ bands of Te hybridized with the U $5 f$ states. Small discontinuities seen in some band dispersions arise due to different treatment of the Kohn-Sham (KS) states within and outside the projection window range, with the self-energy correction applied only to the KS bands within this window (see text for details).
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Figure 2
The calculated energy level splitting of the $^{3} H_{4}$ ground-state multiplet of the $5 f^{2}$ configuration in $U {Te}_{2}$ . The lower-energy wave functions are given in the text in the $| J M 〉$ basis representation.
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Figure 3
Comparison of the temperature dependences of the calculated single-ion contribution to specific heat of $U {Te}_{2}$ and available experimental estimations. The black curve is a theoretical curve based on the ab initio derived splitting from Fig. 2. Green and blue dots are the experimental data from Refs. [12, 13], respectively. The difference between the two experimental curves is due to uncertainties in the subtraction of the phonon and heavy fermionic part of the electronic specific heat related to the conduction band (see text).
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Figure 4
(Upper panel) Magnetization as a function of applied field at 1.8 K calculated (lines) for the three crystallographic axes and the experimental data (hollow symbols) adapted from Ran et al. [2]. (Lower panel) Comparison of the calculated and experimental (from Ref. [11]) temperature dependences of magnetization for the field $μ_{0} H = 1$ T applied along the three crystallographic axes.
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Figure 5
Temperature dependence of the specific heat of $U {Te}_{2}$ . The experimental curves are the same as in Fig. 3, but the theoretical curves are now calculated considering the superexchange interactions within the U-U structural dimer.
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Figure 6
Calculated magnetization curves after considering anisotropic superexchange interactions within the structural U-U dimer. (Upper panel) Magnetization as a function of applied field at 1.8 K calculated (lines) for the three crystallographic axes and the experimental data (hollow symbols) adapted from Ran et al. [2]. (Lower panel) Comparison of the calculated and experimental (from Ref. [11]) temperature dependences of magnetization for the field $μ_{0} H = 1$ T applied along the three crystallographic axes.
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Physical Review B

covering condensed matter and materials physics

Structure of the normal state and origin of the Schottky anomaly in the correlated heavy-fermion superconductor $U {Te}_{2}$

S. Khmelevskyi, L. V. Pourovskii, and E. A. Tereshina-Chitrova

Phys. Rev. B 107, 214501 – Published 5 June 2023

Abstract

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Physical Review B

covering condensed matter and materials physics

Structure of the normal state and origin of the Schottky anomaly in the correlated heavy-fermion superconductor UTe2

S. Khmelevskyi, L. V. Pourovskii, and E. A. Tereshina-Chitrova

Phys. Rev. B 107, 214501 – Published 5 June 2023

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Structure of the normal state and origin of the Schottky anomaly in the correlated heavy-fermion superconductor $U {Te}_{2}$