TY - JOUR
T1 - Electronic properties across metal-insulator transition in β -pyrochlore-type CsW2 O6 epitaxial films
AU - Soma, Takuto
AU - Yoshimatsu, Kohei
AU - Horiba, Koji
AU - Kumigashira, Hiroshi
AU - Ohtomo, Akira
N1 - Funding Information:
This work was partly supported by MEXT Elements Strategy Initiative to Form Core Research Center and a Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for Scientific Research (No. 16H05983, No. 18H03925, and No. 18J10171). The work at KEK-PF was done under the approval of the Program Advisory Committee (Proposals No. 2017G596 and No. 2015S2-005) at the Institute of Materials Structure Science, KEK. T. S. acknowledges the financial support from a JSPS Research Fellowship for Young Scientists.
Publisher Copyright:
© 2018 American Physical Society.
PY - 2018/11/27
Y1 - 2018/11/27
N2 - In CsW2O6, which undergoes a metal-insulator transition (MIT) at 213 K, the emergence of exotic properties associated with rattling motion of Cs is expected owing to its characteristic β-pyrochlore-type structure. However, a hurdle for crystal growth hampers elucidation of detailed properties and mechanisms of the MIT. Here we report on the epitaxial growth of β-pyrochlore-type CsW2O6 films and their electronic properties across the MIT. Using pulsed-laser deposition technique, we grew single-crystalline CsW2O6 films exhibiting remarkably lower resistivity compared with a polycrystalline bulk and sharp MIT around 200 K. Negative magnetoresistance and a positive Hall coefficient were found, which became pronounced below 200 K. The valence-band and core-level photoemission spectra indicated the drastic changes across the MIT. In the valence-band photoemission spectrum, the finite density of states was observed at the Fermi level in the metallic phase. In contrast, an energy gap appeared in the insulating phase. The split of W4f core-level spectrum suggested the charge disproportionation of W5+ and W6+ in the insulating phase. The change of spectral shape in the Cs4d core levels reflected the rattling motion of Cs+ cations. These results strongly suggest that CsW2O6 is an exotic material in which MIT is driven by the charge disproportionation associated with the rattling motion.
AB - In CsW2O6, which undergoes a metal-insulator transition (MIT) at 213 K, the emergence of exotic properties associated with rattling motion of Cs is expected owing to its characteristic β-pyrochlore-type structure. However, a hurdle for crystal growth hampers elucidation of detailed properties and mechanisms of the MIT. Here we report on the epitaxial growth of β-pyrochlore-type CsW2O6 films and their electronic properties across the MIT. Using pulsed-laser deposition technique, we grew single-crystalline CsW2O6 films exhibiting remarkably lower resistivity compared with a polycrystalline bulk and sharp MIT around 200 K. Negative magnetoresistance and a positive Hall coefficient were found, which became pronounced below 200 K. The valence-band and core-level photoemission spectra indicated the drastic changes across the MIT. In the valence-band photoemission spectrum, the finite density of states was observed at the Fermi level in the metallic phase. In contrast, an energy gap appeared in the insulating phase. The split of W4f core-level spectrum suggested the charge disproportionation of W5+ and W6+ in the insulating phase. The change of spectral shape in the Cs4d core levels reflected the rattling motion of Cs+ cations. These results strongly suggest that CsW2O6 is an exotic material in which MIT is driven by the charge disproportionation associated with the rattling motion.
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U2 - 10.1103/PhysRevMaterials.2.115003
DO - 10.1103/PhysRevMaterials.2.115003
M3 - Article
AN - SCOPUS:85060587485
VL - 2
JO - Physical Review Materials
JF - Physical Review Materials
SN - 2475-9953
IS - 11
M1 - 115003
ER -