Insight into the temperature dependent properties of the ferromagnetic Kondo lattice YbNiSn

A. Generalov, D. A. Sokolov, A. Chikina, Yu. Kucherenko, V. N. Antonov, L. V. Bekenov, S. Patil, A. D. Huxley, J. W. Allen, K. Matho, K. Kummer, D. V. Vyalikh, and C. Laubschat

Phys. Rev. B 95, 184433 – Published 30 May 2017

Abstract

Analyzing temperature dependent photoemission (PE) data of the ferromagnetic Kondo-lattice (KL) system YbNiSn in the light of the periodic Anderson model (PAM) we show that the KL behavior is not limited to temperatures below a temperature ${\bar{T}}_{K}$ , defined empirically from resistivity and specific heat measurements. As characteristic for weakly hybridized Ce and Yb systems, the PE spectra reveal a $4 f$ -derived Fermi level peak, which reflects contributions from the Kondo resonance and its crystal electric field (CEF) satellites. In YbNiSn this peak has an unusual temperature dependence: With decreasing temperature a steady linear increase of intensity is observed which extends over a large interval ranging from 100 K down to 1 K without showing any peculiarities in the region of ${\bar{T}}_{K} \sim T_{C} = 5.6$ K. In the light of the single-impurity Anderson model (SIAM) this intensity variation reflects a linear increase of $4 f$ occupancy with decreasing temperature, indicating an onset of Kondo screening at temperatures above 100 K. Within the PAM this phenomenon could be described by a non-Fermi-liquid-like $T$ - linear damping of the self-energy which accounts phenomenologically for the feedback from the closely spaced CEF states.

Received 23 February 2017

DOI:https://doi.org/10.1103/PhysRevB.95.184433

Physics Subject Headings (PhySH)

Kondo effect Quantum criticality

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

A. Generalov¹, D. A. Sokolov^2,3, A. Chikina⁴, Yu. Kucherenko⁵, V. N. Antonov⁵, L. V. Bekenov⁵, S. Patil⁶, A. D. Huxley², J. W. Allen⁷, K. Matho⁸, K. Kummer⁹, D. V. Vyalikh^10,11,12,*, and C. Laubschat⁴

¹MAX IV Laboratory, Lund University, Box 118, 22100 Lund, Sweden
²School of Physics and CSEC, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom
³Max-Planck-Institut für Chemische Physik fester Stoffe, D-01187 Dresden, Germany
⁴Institut für Festkörperphysik, Technische Universität Dresden, D-01062 Dresden, Germany
⁵Institute for Metal Physics, National Academy of Science of Ukraine, UA-03142 Kiev, Ukraine
⁶Department of Physics, Indian Institute of Technology, Banaras Hindu University, Varanasi-225001, India
⁷Randall Laboratory, University of Michigan, 450 Church St., Ann Arbor, Michigan 48109-1040, USA
⁸Institut Néel, C.N.R.S. and Université Grenoble Alpes, BP 166, 38042 Grenoble cedex 9, France
⁹European Synchrotron Radiation Facility, 71 Avenue des Martyrs, Grenoble, France
¹⁰Saint Petersburg State University, Physics Department, Saint Petersburg 198504, Russia
¹¹Donostia International Physics Center (DIPC), Departamento de Fisica de Materiales and CFM-MPC UPV/EHU, 20080 San Sebastian, Spain
¹²IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain

^*Corresponding author: Denis.Vyalikh@dipc.org

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Vol. 95, Iss. 18 — 1 May 2017

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Images

Figure 1
(a) Schematic representation of the YbNiSn crystal structure. Note that the origin is shifted with respect to its symmetry group position to put the Yb atoms in the vertices of the unit cell for better visualization. (b) The unit cell projected on the $y z$ plane. The coordinate system is slightly rotated around the $y$ axis in order to show all atoms in the layer. (c) The unit cell projected on the $x z$ plane. The bonds of the Yb atom within the $x z$ atomic layer are shown.
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Figure 2
Bulk properties of YbNiSn (magnetic field $H = 0$ ): (a) $T$ dependence of the electrical resistivity along the $a$ axis. The rise below 150 K signals the Kondo screening of a $J = 7 / 2$ multiplet. The broad feature at $\sim 70$ K corresponds to the freezing out of the lowest CEF excitation. The KL formation sets in below the maximum at $\sim 10$ K (arrow). The resistivity drop is accentuated by the suppression of spin disorder scattering in the FM phase. (b) $T$ dependence of the specific heat $C / T$ and the entropy $S (T)$ . The large, lambdalike anomaly at $T_{C} = 5.6$ K marks the FM transition. The arrow points to the fact that only half the entropy of a two level system, $S = \frac{1}{2} R ln 2$ , is recovered at $T_{C}$ . The red dot indicates the zone of intense competition between FM order and KL formation.
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Figure 3
PE spectrum of the YbNiSn taken at $h ν = 110 eV$ and $T = 19 K$ (upper panel) and its simulation by means of the SIAM with hybridization strength $Δ = 0.201 eV$ (lower panel).
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Figure 4
(a) PE peak near $E_{F}$ , corresponding to the $4 f_{7 / 2}^{13}$ final-state configuration, measured from 97 K to 19 K. (b) $T$ dependence of the integrated weight for two series of measurements. Inset: $T$ dependence of the Yb valence, obtained from the SIAM simulations based on the BESSY (blue circles) and SLS (red triangles) experiments.
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Figure 5
Fine structure around $E_{F}$ , as simulated by the toy model. The half width of the bare VB is $W = 1$ eV. The effective KL scale is $k_{B} {\bar{T}}_{K}^{(8)} = 5.3$ meV. (a) $k$ -resolved $f$ intensity at $T = 0$ , showing a QP band and a less renormalized bonding band, both of finite width, repelling each other at the renormalized $f$ level $ε_{f}^{*}$ (continuous line). The crossing points (arrows) lie on the large FS. (b) Partial DOS $ρ_{f} (ε)$ (green line) and $ρ_{c} (ε)$ (red line), at $T = 0$ K and 100 K. The $f$ -DOS dominates in an interval of $\pm 10$ meV around $E_{F}$ and again around the top of the bonding band. Simulated $T$ dependences: (c) Weight of $ρ_{f} (ε)$ (integrated over $\pm 0.1$ eV) as a percentage of the Pauli weight and (d) maximum of $ρ_{f}$ .
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