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SUMMARY:Mott-insulating state of alkali-metal clusters in sodalite studied
  by $\\mu$SR
DTSTART;VALUE=DATE-TIME:20220901T164000Z
DTEND;VALUE=DATE-TIME:20220901T170000Z
DTSTAMP;VALUE=DATE-TIME:20220826T122313Z
UID:indico-contribution-3754@indico.stfc.ac.uk
DESCRIPTION:Speakers: Takehito Nakano (Ibaraki University)\nIn Mott insula
 tors\, band electrons are localized due to strong electron-electron intera
 ctions. Although the s-electrons of alkali metals are very delocalized\, b
 y confining them in the periodic nanospace of zeolite crystals and making 
 them moderately localized\, such a strongly correlated electron system can
  be created.$^1$ In sodalite\, $\\beta$-cages with an inner diameter of 0.
 7 nm are arranged in a bcc structure. By loading alkali atoms\, an $A_4^{3
 +}$ cluster ($A$: alkali atom) is formed in the cage. The cluster has one 
 unpaired s-electron. Antiferromagnetic order of Mott insulating state has 
 been identified in $A =$ Na\, K\, and K-Rb alloy clusters.$^2$ $T_N$ syste
 matically increases from 50 K (Na) to 90 K (K-Rb alloy). In ZF-$\\mu^+$SR\
 , a uniform local field is observed below $T_N$\, and its value is higher 
 for clusters with heavier chemical compositions.$^2$\nTo clarify the mecha
 nism of the systematic change in the local field and its relation with the
  Mott-insulating state of this system\, we investigate the muon Knight shi
 ft by high TF-$\\mu^+$SR using NuTime at TRIUMF. We successfully obtained 
 the hyperfine coupling constants between $\\mu^+$ and the s-electron above
  $T_N$ from the $K-\\chi$ plot. By combining the ZF-$\\mu^+$SR local field
 \,$^2$ we determined the size of the ordered moments\, which systematicall
 y decreases from $\\simeq$ 0.5 $\\mu_B$ (Na) to $\\simeq$ 0.3 $\\mu_B$ (K-
 Rb alloy). It correlates perfectly with the increase in $T_N$\, namely\, t
 he decrease in the electron correlation $U/t$ in the Mott-Hubbard model. F
 rom DFT calculations\, we found that $\\mu^+$ is in a hydride (Mu−) stat
 e at the cage center. This also explains that the systematic increase in t
 he local field corresponds to the decrease in $U/t$ due to the shallower p
 otential of the heavier alkali atoms.\n$^1$T. Nakano and Y. Nozue\, Adv. P
 hys.: X **2**\, 254-280 (2017). \n$^2$T. Nakano *et al*.\, J. Phys. Soc. J
 pn. **79**\, 073707-1-4 (2010).\n\nhttps://indico.stfc.ac.uk/event/53/cont
 ributions/3754/
LOCATION:Science and Technology Campus\, University of Parma
URL:https://indico.stfc.ac.uk/event/53/contributions/3754/
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