True First-Order Surface Phase Transition without Nanoscale Phase Separation

초록

Nanoscale phase separation is common in many materialsrangingfrom correlated electron systems to semiconductor surfaces undergoingphase transitions. On solid surfaces, nanoscale phase separationsare known to occur over an extended temperature range during temperature-drivenfirst-order surface phase transitions, precluding the true first-ordertransitions in thermodynamics. Here, we report the case of a surfacephase transition very close to a true first-order transition. An arrayof indium wires on Si(111) undergoes a first-order charge-density-wave(CDW) transition with surprisingly little or no phase separation whenprepared free of indium adatom impurities. The lack of phase separationwas attributed to the small difference in strain with the substratebetween the two competing normal and CDW phases. Indium adatom impuritiescause phase separation and blur the transition, making it gradualand incomplete. These experimental observations provide insight intothe surface phase transition at the nanoscale level.

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