Field-induced metal-insulator transition in partially deuterated<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>κ</mml:mi><mml:mtext>−</mml:mtext><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mi>BEDT</mml:mi><mml:mtext>−</mml:mtext><mml:mi>TTF</mml:mi><mml:mo>)</mml:mo></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:mi mathvariant="normal">Cu</mml:mi><mml:mrow><mml:mo>[</mml:mo><mml:mi mathvariant="normal">N</mml:mi><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mi mathvariant="normal">C</mml:mi><mml:mi mathvariant="normal">N</mml:mi><mml:mo>)</mml:mo></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:mo>]</mml:mo></mml:mrow><mml:mi mathvariant="normal">Br</mml:mi></mml:mrow></mml:math>

Atsushi Kawamoto, Masato Yamasita, Ken-ichi Kumagai

doi:10.1103/physrevb.70.212506

A $^{13}\mathrm{C}$-NMR study on nondeuterated and partially deuterated $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}\mathrm{Cu}[\mathrm{N}{(\mathrm{C}\mathrm{N})}_{2}]\mathrm{Br}$ is reported, where BEDT-TTF is bis(ethylenedithio)tetra-thiafulvalene. By using a BEDT-TTF molecule with $^{13}\mathrm{C}$ as one of its central carbons, we could estimate the density of states from the Knight shift and the spin-lattice relaxation rate. Although the reduced mass effect predicted from the specific-heat measurement was not observed in the $^{13}\mathrm{C}$-NMR spectrum, a metal-to-antiferromagnetic phase transition was observed with a phase separation at around $18\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ on the half-deuterated $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}\mathrm{Cu}[\mathrm{N}{(\mathrm{C}\mathrm{N})}_{2}]\mathrm{Br}$ under a high magnetic field. No such transition occurred in the half-deuterated salt under a zero or low field. These results point to a first-order field-induced metal-insulator transition. These findings can explain the complex phenomena observed near the phase boundary under a high magnetic field.

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