1,721,059 research outputs found
Evolution of electronic band reconstruction in thickness-controlled perovskite SrRuO3 thin films
No full textTransition metal perovskite oxides display a variety of emergent phenomena which are tunable by tailoring the oxygen octahedral rotation. SrRuO3, a ferromagnetic perovskite oxide, is well known to have various atomic structures and octahedral rotations when grown as thin films. However, how the electronic structure changes with the film thickness has been hardly studied. Here, using angle-resolved photoemission spectroscopy and electron diffraction techniques, we study the electronic structure of SrRuO3 thin films as a function of the film thickness. Different reconstructed electronic structures and spectral weights are observed for films with various thicknesses. We suggest that octahedral rotations on the surface can be qualitatively estimated via comparison of intensities of different bands. Our observation and methodology shed light on how structural variation and transition may be understood in terms of photoemission spectroscopy data.11Nsciescopuskc
Growth and characterization of superconductor-ferromagnet thin film heterostructure la1.85sr0.15cuo4/srruo3
No full text© 2021, Korea Institute of Applied Superconductivity and Cryogenics. All rights reserved.Superconductor-ferromagnet thin film heterostructure is an ideal system for studying the interplay between superconductivity and ferromagnetism. These two antagonistic properties combined in thin film heterostructure create interesting proximity effects such as spin-triplet superconductivity. Thin film heterostructure of optimally doped La2-xSrxCuO4(LSCO) cuprate superconductor and SrRuO3(SRO) ruthenate ferromagnet has been grown by pulsed laser deposition. Its temperature-dependent resistivity and Hall effect measurements show that our LSCO/SRO heterostructure has both superconductivity and ferromagnetism. In the Hall effect measurement results, we find additional hump-like structures appear in the anomalous Hall effect signal in the vicinity of superconducting transition. We conclude that giant magnetoresistance of the LSCO layer distorts the AHE signal, which results in a hump-like structure.11Nscopuskc
Determination of the band parameters of bulk 2H-MX2 (M = Mo, W; X = S, Se) by angle-resolved photoemission spectroscopy
Full text linkMonolayer MX2 (M = Mo, W; X = S, Se) has recently been drawn much attention due to their application possibility as well as the novel valley physics. On the other hand, it is also important to understand the electronic structures of bulk MX2 for material applications since it is very challenging to grow large size uniform and sustainable monolayer MX2. We performed angle-resolved photoemission spectroscopy and tight binding calculations to investigate the electronic structures of bulk 2H-MX2. We could extract all the important electronic band parameters for bulk 2H-MX2, including the band gap, direct band gap size at K (-K) point and spin splitting size. Upon comparing the parameters for bulk 2H-MX2 (our work) with mono- and multi-layer MX2 (published), we found that stacked layers, substrates for thin films, and carrier concentration significantly affect the parameters, especially the band gap size. The origin of such effect is discussed in terms of the screening effect. © The Author(s) 20161341sciescopu
Magnetic field detwinning in feTe
No full text© 2019, Korea Institute of Applied Superconductivity and Cryogenics. All rights reserved.Iron-based superconductors (IBSs) possess nematic phases in which rotational symmetry of the electronic structure is spontaneously broken. This novel phase has attracted much attention as it is believed to be closely linked to the superconductivity. However, observation of the symmetry broken phase by using a macroscopic experimental tool is a hard task because of naturally formed twin domains. Here, we report on a novel detwinning method by using a magnetic field on FeTe single crystal. Detwinning effect was measured by resistivity anisotropy using the Montgomery method. Our results show that FeTe was detwinned at 2T, which is a relatively weak field compared to the previously reported result. Furthermore, detwinning effect is retained even when the field is turned off after field cooling, making it an external stimulation-free detwinning metho
Challenges in identifying chiral spin textures via the topological Hall effect
Full text linkChiral spin textures such as skyrmions are of interest to the field of spintronics for their potential use in future computing devices. Hall effect measurements are a simple and powerful method to probe the electronic and magnetic properties of materials. The topological Hall effect, which appears as anomalies in Hall resistance versus magnetic field measurements compared to magnetic measurements, has frequently been used to establish the occurrence of chiral spin textures. However, in addition to experimental issues, intrinsic electronic mechanisms combined with inhomogeneity in materials and at interfaces can lead to an inhomogeneous anomalous Hall effect which could be mistaken for a topological Hall signal. This review covers recent research using Hall effect measurements to probe chiral spin textures, focusing on SrRuO3 as a model system. The ambiguity between Hall effects due to topological sources has led to disagreement in the interpretation of experimental results and casts doubts on the effectiveness of these techniques for investigating chiral spin textures
Ferromagnetic insulating substrate for magnetic proximity studies: LaCoO3 thin film
No full textFerromagnetic insulators (FMIs) are intriguing not only due to their rare nature, but also due to their potential applications in spintronics and various electronic devices. One of its key promising applications is based on an FMI-induced magnetic proximity effect, which can impose an effective time-reversal symmetry breaking on the target ultrathin layer to realize novel emergent phenomena. Here, we conduct systematic studies on thin film LaCoO3, an insulator known to be ferromagnet under tensile strain, with varying thicknesses, to establish it as an FMI platform to be integrated in heterostructures. The optimal thickness of the LaCoO3 layer, providing a smooth surface and robust ferromagnetism with large remanence, is determined. A heterostructure consisting of an ultrathin target layer (2 uc SrRuO3), the LaCoO3 FMI layer, and the La0.5Sr0.5CoO3 conducting layer has been fabricated and the angle-resolved photoemission spectroscopy measurement on the multi-layer system demonstrates a sharp Fermi edge and a well-defined Fermi surface without the charging effect. This demonstrates the feasibility of the proposed heterostructure using LaCoO3 thin film as the FMI layer, and further lays a groundwork to investigate the magnetic proximity induced phases in quantum materials.11Nsciescopu
Possible electric field induced indirect to direct band gap transition in MoSe2
Full text linkDirect band-gap semiconductors play the central role in optoelectronics. In this regard, monolayer (ML) MX2 (M = Mo, W; X = S, Se) has drawn increasing attention due to its novel optoelectronic properties stemming from the direct band-gap and valley degeneracy. Unfortunately, the more practically usable bulk and multilayer MX2 have indirect-gaps. It is thus highly desired to turn bulk and multilayer MX2 into direct band-gap semiconductors by controlling external parameters. Here, we report angle-resolved photoemission spectroscopy (ARPES) results from Rb dosed MoSe2 that suggest possibility for electric field induced indirect to direct band-gap transition in bulk MoSe2. The Rb concentration dependent data show detailed evolution of the band-gap, approaching a direct band-gap state. As ionized Rb layer on the surface provides a strong electric field perpendicular to the surface within a few surface layers of MoSe2, our data suggest that direct band-gap in MoSe2 can be achieved if a strong electric field is applied, which is a step towards optoelectronic application of bulk materials. © 2017 The Author(s)1
Line-shape analysis of the raman-spectrum from b1g bond buckling phonon in Bi2Sr2CaCu2O8+x
No full text© 2019, Korea Institute of Applied Superconductivity and Cryogenics. All rights reserved.We performed Raman spectroscopy on two different over-doped Bi2Sr2CaCu2O8+x (BSCCO), of which superconducting transition temperatures are 89 K and 77 K. Line-shape analysis of the Raman-spectrum was done, focused on B1g bond buckling mode which have drawn a lot of attention, since photoemission studies showed an evidence for strong coupling between the mode and electron. The line-shapes show asymmetry and are well fitted by the Fano line-shape formula. Remarkably, we found that the peak line-widths from B1g bond buckling mode in BSCCO show much broader than those in YBa2Cu3O7−x. The broad line width can be attributed to the superstructure modulation of BSCCO. Our results imply that B1g bond buckling mode may have close relation to the origin of superconductivity or to boosting the superconducting transition temperature in BSCC
Strong One-Dimensional Characteristics of Hole-Carriers in ReS 2 and ReSe 2
Full text linkEach plane of layered ReS 2 and ReSe 2 materials has 1D chain structure, from which intriguing properties such as 1D character of the exciton states and linearly polarized photoluminescence originate. However, systematic studies on the 1D character of charge carriers have not been done yet. Here, we report on systematic and comparative studies on the energy-momentum dispersion relationships of layered transition metal dichalcogenides ReS 2 and ReSe 2 by angle resolved photoemission. We found that the valence band maximum or the minimum energy for holes is located at the high symmetric Z-point for both materials. However, the out-of-plane (k z ) dispersion for ReSe 2 (20 meV) is found to be much smaller than that of ReS 2 (150 meV). We observe that the effective mass of the hole carriers along the direction perpendicular to the chain is about 4 times larger than that along the chain direction for both ReS 2 and ReSe 2 . Remarkably, the experimentally measured hole effective mass is about twice heavier than that from first principles calculation for ReS 2 although the in-plane anisotropy values from the experiment and calculations are comparable. These observation indicate that bulk ReS 2 and ReSe 2 are unique semiconducting transition metal dichalcogenides having strong one-dimensional characters. © 2019, The Author(s
Out-of-plane Magnetic Anisotropy in Cleaved and Uncleaved CoS2
No full textMagnetic anisotropy is an important phenomenon driven by a strong electron correlation. It is defined as the magnetization tendency of magnetic material in a particular crystallographic direction. In this paper, we investigated the magnetic anisotropy of CoS2 single crystal. Here, torque magnetometry was used to determine the magnetocrystalline anisotropy of the crystal. The angle dependence of torque τ (Θ) for CoS2 was measured at several temperatures above and below the ferromagnetic order transition Tc. To verify the effect of surface morphology on magnetic properties, we compared the τ (Θ) of uncleaved and cleaved pure CoS2. Results show that two-fold symmetry was equally dominant in both. Furthermore, we compared higher orders of magnetic anisotropy to track the intrinsic and shape anisotropies. All amplitudes showed the same behavior for cleaved and uncleaved samples, but the higher orders were more dominatant in the cleaved sample.11Nscopuskc
- …
