![]() Moreover, the power law fit of phase-coherent length versus temperature further confirms the WL effect of our ultrathin films is within a two-dimensional (2D) localization theory. This leads to the solid conclusion that the low-temperature resistivity minima in single-crystal manganites are the result of QIEs from the combination of e-e interaction and WL effect. In particular, the sharp cusps around zero magnetic field in MR measurements is evidenced as the typical WL effect. The T 1/2 dependent resistivity under high magnetic field is evidenced as e-e interaction. We give direct experimental evidences of e-e interaction and WL effect. The films are deposited by laser molecular beam epitaxy (LMBE) on SrTiO 3 (STO) substrates. In this work, the low-temperature resistivity minima and transport properties of LSMO ultrathin films are investigated. Thus, the conclusion that low-temperature resistivity minima are attributed to QIEs with the combination of e-e interaction and WL effect requires the further direct experimental evidence. Although vast phenomenological analyses have been fitted to prove the existence of the WL effect 2, 11, 12, the typical WL effect in magnetoresistance (MR) measurements, i.e., the sharp cusps around zero magnetic field at low temperatures, has not been observed. However, to date the evidence of WL effect has still remained insufficient in manganites. 7 investigated the behavior of the resistivity minima with various magnetic fields and they found that the WL effect was suppressed by a high field ( H > 1 T) and the electrical resistivity only followed the T 1/2 dependence with the characteristics of enhanced e-e interaction. The T 1/2 dependent resistivity under high magnetic fields has been evidenced as e-e interaction. 12 studied the resistivity minimum of LSMO films integrated with nonmagnetic ZrO 2 particles as a second phase to tune the contribution of an enhanced three dimensional WL effect. 2 investigated the low-temperature transport properties of La 0.7Sr 0.3MnO 3 (LSMO) films as a function of the sample thickness and interpreted their results as an interplay of e-e interaction and WL effect. 14 investigated the temperature and field dependence of the conductivity of a La 1.2Sr 1.8Mn 2O 7 single crystal in terms of QIEs. Both contributions lead to an enhancement of resistivity as the temperature decreases. Generally, QIEs lead to correction to the resistivity from two different sources 5: (i) electron-electron (e-e) interaction and subsequent modification of the density of states at the Fermi energy (ii) weak localization (WL) effect arising from the self-interference of the wave pockets as they are backscattered coherently by the impurities or other defects. Recently, QIEs in manganites have been intensively investigated to interpret the low-temperature resistivity minima 2, 6, 9, 11, 12, 13, 14. While Kondo effect dominates in intrinsically disordered samples 9, 10. In polycrystalline samples, the resistivity minima at low temperatures shift towards the lower temperatures upon applying a magnetic field and disappear at certain critical fields, which is interpreted in terms of the spin-polarized tunneling via grain boundaries 1, 6, 7, 8. In the past few years, people have attributed the resistivity minima to different mechanisms, such as spin-polarized tunneling through grain boundaries 1, 3, Kondo-like effect due to spin disorder 4, as well as quantum interference effects (QIEs) 5. Although great efforts were devoted to explaining the resistivity minima behavior in manganites, no convincing conclusions have yet been reached up to now. The appearance of a low-temperature resistivity minimum has been observed in polycrystalline and single-crystalline colossal magnetoresistance (CMR) manganites 1, 2. Moreover, the temperature-dependent phase-coherence length corroborates the WL effect of LSMO ultrathin films is within a two-dimensional localization theory. This convincingly leads to the solid conclusion that the resistivity minima at low temperatures in single-crystal manganites are attributed to both the e-e interaction and the WL effect. The sharp cusps around zero magnetic field in magnetoresistance measurements is unambiguously observed, which corresponds to the WL effect. Here we report on the direct experimental evidence of WL in QIEs observed in the single-crystal La 0.7Sr 0.3MnO 3 (LSMO) ultrathin films deposited by laser molecular beam epitaxy. However, the evidence of the other source of QIEs, weak localization (WL), still remains insufficient in manganites. The T 1/2 dependent resistivity under high magnetic field has been evidenced as electron-electron (e-e) interaction. Quantum interference effects (QIEs) dominate the appearance of low-temperature resistivity minimum in colossal magnetoresistance manganites. ![]()
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