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首页> 外文OA文献 >Spin-polarized tunneling spectroscopic studies of the intrinsic heterogeneity and pseudogap phenomena in colossal magnetoresistive manganite La_{0.7}Ca_{0.3}MnO_{3}
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Spin-polarized tunneling spectroscopic studies of the intrinsic heterogeneity and pseudogap phenomena in colossal magnetoresistive manganite La_{0.7}Ca_{0.3}MnO_{3}

机译：内禀的自旋极化隧道谱研究   巨磁阻红锰矿中的非均质性和赝能隙现象   了La_ {0.7} {Ca_ 0.3} mnO_ {3}

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摘要

Spatially resolved tunneling spectroscopic studies of colossalmagnetoresistive (CMR) manganite $\rm La_{0.7}Ca_{0.3}MnO_3$ (LCMO) epitaxialfilms on $\rm (LaAlO_3)_{0.3}(Sr_2AlTaO_6)_{0.7}$ substrate are investigated asfunctions of temperature, magnetic field and spin polarization by means ofscanning tunneling spectroscopy. Systematic surveys of the tunneling spectrataken with Pt/Ir tips reveal spatial variations on the length scale of a fewhundred nanometers in the ferromagnetic state, which may be attributed to theintrinsic heterogeneity of the manganites due to their tendency towards phaseseparation. The electronic heterogeneity is found to decrease either withincreasing field at low temperatures or at temperatures above all magneticordering temperatures. On the other hand, spectra taken with Cr-coated tips areconsistent with convoluted electronic properties of both LCMO and Cr. Inparticular, for temperatures below the magnetic ordering temperatures of bothCr and LCMO, the magnetic-field dependent tunneling spectra may bequantitatively explained by the scenario of spin-polarized tunneling in aspin-valve configuration. Moreover, a low-energy insulating energy gap $\sim0.6$ eV commonly found in the tunneling conductance spectra of bulk metallicLCMO at $T \to 0$ may be attributed to a surface ferromagnetic insulating (FI)phase, as evidenced by its spin filtering effect at low temperatures andvanishing gap value above the Curie temperature. Additionally, temperatureindependent pseudogap (PG) phenomena existing primarily along the boundaries ofmagnetic domains are observed in the zero-field tunneling spectra. The PGbecomes strongly suppressed by applied magnetic fields at low temperatures whenthe tunneling spectra of LCMO become highly homogeneous. These findings suggestthat the occurrence PG is associated with the electronic heterogeneity of themanganites.
机译：研究了在$ \ rm（LaAlO_3）_ {0.3}（Sr_2AlTaO_6）_ {0.7} $衬底上的大磁阻（CMR）锰矿$ \ rm La_ {0.7} Ca_ {0.3} MnO_3 $（LCMO）外延膜的空间分辨隧穿光谱研究扫描隧道光谱法研究温度，磁场和自旋极化的函数用Pt / Ir尖端对隧道光谱进行的系统调查显示，在铁磁状态下数百纳米的长度尺度上存在空间变化，这可能归因于锰铁矿的内在非均质性，因为它们趋于相分离。发现电子异质性在低温下或在高于所有磁序温度的温度下在增加的磁场内减小。另一方面，用Cr涂层尖端获得的光谱与LCMO和Cr的复杂的电子特性一致。特别地，对于低于Cr和LCMO两者的磁性有序温度的温度，可以通过在阿斯旺-阀构造中的自旋极化隧穿的情形来定量地解释与磁场有关的隧穿谱。此外，通常在块状金属LCMO的隧穿电导谱中在$ T \至0 $处发现的低能绝缘能隙$ \ sim0.6 $ eV可能归因于表面铁磁绝缘（FI）相，如其低温下的自旋过滤效果和高于居里温度的间隙值消失。另外，在零场隧穿光谱中观察到主要沿着磁畴的边界存在的与温度无关的伪间隙（PG）现象。当LCMO的隧道光谱变得高度均匀时，PG在低温下会受到磁场的强烈抑制。这些发现表明，PG的出现与锰矿的电子异质性有关。

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