Kondo-Induced Giant Isotropic Negative Thermal Expansion

Abstract

Negative thermal expansion is an unusual phenomenon appearing in only a handful of materials, but pursuit and mastery of the phenomenon holds great promise for applications across disciplines and industries. Here we report use of X-ray spectroscopy and diffraction to investigate the 4felectronic properties in Y-doped SmS and employ the Kondo volume collapse model to interpret the results. Our measurements reveal an unparalleled decrease of the bulk Sm valence by over 20% at low temperatures in the mixed-valent golden phase, which we show is caused by a strong coupling between an emergent Kondo lattice state and a large isotropic volume change. The amplitude and temperature range of the negative thermal expansion appear strongly dependent on the Y concentration and the associated chemical disorder, providing control over the observed effect. This finding opens avenues for the design of Kondo lattice materials with tunable, giant and isotropic negative thermal expansion.

Pressure and Temperature Evolution of Sm Mean-Valence in Golden SmS

“…Normalized Intensity (arb. units) In contrast to the black-SmS in which the Sm mean-valence is almost independent of temperature [13], as the temperature is decreased, the Sm mean-valence decreases, followed by flattening tendency below about 40 K. Interestingly, this is qualitatively (but not quantitatively) compatible with a theoretical prediction [9]. Note that a similar feature was observed in SmB 6 [14,15].…”

Soliton Generation in Negative Thermal Expansion Materials

“…There is much interest in systems which exhibit this remarkable material behavior, particularly because strong NTE has been observed in the vicinity of low-temperature phase transitions. For example, insulating perovskite ScF 3 appears to have an incipient structural instability (Handunkanda et al, 2015;Wendt et al, 2019;Bird et al, 2020) while semiconducting Sm 1−x Y x S (Takenaka et al, 2019;Mazzone et al, 2020) shows an unusual magnetic transition at low temperature. Experiments of the type proposed here are nondestructive and sensitive to other lattice-related materials properties and may benefit NTE research in certain contexts.…”

“…Specific candidates of opaque NTE films include metallic perovskite ReO 3 (Chatterji et al, 2009a;Chatterji et al, 2009b;Rodriguez et al, 2009), semiconducting Sm 0.8 Y 0.2 S (Takenaka et al, 2019;Mazzone et al, 2020), and insulating Si (Shah and Straumanis, 1972) or CdTe (Greenough and Palmer, 1973;Jovanovic et al, 2014) at low temperature at pump photon energies exceeding their band gap (1 and 1.51 eV at 300 K respectively (Bludau et al, 1974;Jovanovic et al, 2014)). Given recent advances in high-harmonic generation of laser sources, any NTE material could be considered if the photon energy exceeds the candidate material band gap.…”

Pressure-induced valence transition in the mixed-valence (Sm1/3Ca2/3)2.75C60 fulleride

“…The need to use more than one Voigt function to satisfactorily reproduce each white peak originates from the crystal-field splitting of the Sm 5d band. 24,29 A similar fitting strategy was used for the Sm 3+ spectral contribution except that it was found necessary to include only two Voigt functions to describe the corresponding main peak. In the lower pressure range of the experiments, an additional Voigt function was included in order to account for the small spectral uplift above 6730 eV (underlying baseline in Fig.…”

“…are recently drawing much attention in order to bring the insulator-to-metal transition to ambient pressure and utilize the huge NTE that accompanies the valence transition by tuning its operational temperature range. [22][23][24] In the process, it is of particular importance to clarify the differences on the valence transition between controlling size (chemical or physical pressure) and doping (electronic structure).…”