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Metal-insulator transition induced by oxygen isotope exchange in the magnetoresistive perovskite manganites

机译：磁阻钙钛矿锰矿中氧同位素交换诱导的金属-绝缘体转变

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Perovskite manganites derived from LaMnO_3 have recently become the subject of intensive study following the discovery of 'colossal' magnetoresistance (a magnetically induced change in electrical resistance of up to several orders of magnitude) in several members of this family of compounds. The manganites exhibit a broad range of electronic and magnetic phases, ranging from low-resistance ferromagnetic metals to high-resistance insulators, which are extremely sensitive to variation of composition, temperature and pressure. A recent study showed that such sensitivity also extends to oxygen isotope exchange: replacing ~(16)O with ~(18)O in La_(0.8)Ca_(0.2)MnO_3 produces an unusually large change in the magnetic properties (a 21-kelvin decrease in the Curie temperature). The magnitude of this isotope shift is evidence for the essential role played by electron-phonon coupling in determining the transport properties of these materials. Here we show that this sensitivity to oxygen isotope exchange can be even more extreme. In its normal state, the compound La_(0.175)Pr_(0.525)Ca_(0.3)MnO_3 undergoes an insulator-to-metal transition as it is cooled below ～95 K. But we find that, after substituting ~(18)O for ~(16)O, the compound remains an insulator down to 4.2 K, so providing a vivid demonstration of the importance of lattice vibrations in these materials.
机译：在该化合物家族的一些成员中发现了“巨大的”磁阻（磁感应电阻变化高达几个数量级）之后，源自LaMnO_3的钙钛矿锰矿最近成为了深入研究的主题。锰具有广泛的电子和磁性相，从低电阻铁磁金属到高电阻绝缘体，对成分，温度和压力的变化极为敏感。最近的一项研究表明，这种敏感性还扩展到氧同位素交换：用La_（0.8）Ca_（0.2）MnO_3中的〜（18）O代替〜（16）O会引起磁性能异常大的变化（21开尔文降低居里温度）。同位素位移的大小证明了电子-声子耦合在确定这些材料的传输特性中所起的重要作用。在这里，我们证明了这种对氧同位素交换的敏感性甚至更高。在正常状态下，化合物La_（0.175）Pr_（0.525）Ca_（0.3）MnO_3在冷却至约95 K以下时经历了从绝缘体到金属的转变。但是我们发现，用〜（18）O代替〜（16）O时，该化合物仍保持低至4.2 K的绝缘体，因此生动地证明了这些材料中晶格振动的重要性。

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