Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session M41: Spin Phenomena in Nonmagnetic 2D Materials II |
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Sponsoring Units: GMAG DMP FIAP DCOMP Chair: Wei Yuan, University of California, Riverside Room: 707 |
Wednesday, March 4, 2020 11:15AM - 11:27AM |
M41.00001: The Electronic Properties of Quasi-One-Dimensional TiS3 and ZrS3 Simeon Gilbert, Andrew J. Yost, Mingxing Li, Hemian Yi, Alexey Lipatov, Takashi Komesu, José Avila, Alexander Sinitskii, Jian Wang, Maria Asensio, Peter A Dowben The transition metal trichalcogenides (TMTs) are an emerging class of 2D materials in which 2D sheets are formed by the van der Waals-like bonding of quasi-1D chains. Here we present our work on the electronic properties of two TMTs, TiS3 and ZrS3, including the experimental band structure from nanospot angle resolved photoemission spectroscopy (nanoARPES). The band structures of both TMTs exhibit strong in-plane anisotropy due to their quasi-1D structure. The extracted effective hole mass for both materials is doubled along the chain direction, giving rise to a preferential charge transport direction. Additionally, high resolution nanoARPES measurements show a spin-orbit coupling splitting at the top of the valence band in TiS3. This spin-orbit coupling splitting is expected to increase for heavier TMTs such as ZrS3 and could be utilized to produce a spin polarized surface current. |
Wednesday, March 4, 2020 11:27AM - 11:39AM |
M41.00002: Origin of Magnetism in undoped and Ta doped anatase TiO2 free-standing films Sonu Devi, Thirumalai Venkatesan Thin films of anatase titanium dioxide (TiO2) are semiconducting and exhibit signs of room temperature ferromagnetism. However, the role of the surface, substrate and interface in the observed magnetism are controversial. Here, the magnetic properties of two systems, Ta-doped anatase and undoped-anatase have been studied in detail. To avoid the effects from the substrate as well as interface we have fabricated free-standing films using an epitaxial, water-soluble Sr3Al2O6 sacrificial buffer layer. We have found a strong linear correlation between the observed magnetism and Ta-doping, in addition to an intrinsic contribution. The magnetization exhibits a minimum as a function of the oxygen pressure present during film deposition and the result are consistent with a model where Ti interstitials and oxygen vacancies may be responsible for the magnetism at low oxygen pressure while at the high oxygen pressures, Ti vacancies dominate. This study proves that magnetism in anatase TiO2 system is intrinsic and cannot be arising from either the interface or the substrate. |
Wednesday, March 4, 2020 11:39AM - 11:51AM |
M41.00003: Efficient intrinsic spin-to-charge current conversion in an all-epitaxial single-crystal perovskite-oxide heterostructure of La0.67Sr0.33MnO3/LaAlO3/SrTiO3 Shinobu Ohya, Daisei Araki, Le Duc Anh, Shingo Kaneta, Munetoshi Seki, Hitoshi Tabata, Masaaki Tanaka The two-dimensional electron gas formed at the interface between insulating perovskite oxides LaAlO3 (LAO) and SrTiO3 (STO) is promising for efficient spin-charge conversion, so-called the (inverse) Edelstein effect (EE). A giant (inverse) EE has been observed in multilayer structures composed of a polycrystalline ferromagnetic layer and LAO/STO; however, the reported temperature dependences of the (inverse) EE are significantly different from each other, and unified understanding of its real mechanism is still lacking. Here, we demonstrate efficient intrinsic spin-to-charge current conversion in an all-epitaxial single-crystal heterostructure of La0.67Sr0.33MnO3/LAO/STO, which can suppress spin scattering and give us an ideal environment to investigate intrinsic spin-charge conversion. With decreasing temperature to 20 K, the spin-to-charge current conversion efficiency is drastically enhanced to +6.7 nm, which is the largest value among those reported for LAO/STO. Our band-structure calculation well reproduces this behavior and predicts further enhancement by controlling the Fermi level position [1]. |
Wednesday, March 4, 2020 11:51AM - 12:03PM |
M41.00004: Magnetic proximity effects in vdW heterostructures of layered materials Jacob Gobbo, Ryan Muzzio, Igor Pinchuk, Jyoti Katoch, Simranjeet Singh The van der Waals (vdW) based heterostructures of different layered materials have emerged as a modular solid-sate platform to engineer tunable properties in novel quantum systems. The vdW superlattices offer unprecedented flexibility to tune the interfacial interactions at the atomic scale to engineer spin related phenomena in two-dimensional (2D) materials. In this talk, we will present our preliminary results in the direction of probing magnetic proximity effects in vdW based heterostructures of 2D-magnetic systems and transition metal dichalcogenides (TMDs). We will discuss the preparation of high-quality vdW interfaces of 2D-magnets and TMDs in controlled environment. The proximity induced magnetic correlations in otherwise non-magnetic TMDs are probed through variable temperature magneto-transport measurements and will be discussed in this talk. |
Wednesday, March 4, 2020 12:03PM - 12:15PM |
M41.00005: Magnetic proximity in a van der Waals heterostructure of magnetic insulator and graphene. Bogdan Karpiak, Aron Cummings, Klaus Zollner, Marc Vila, Dmitrii Khokhriakov, Md Anamul Hoque, André Dankert, Peter Svedlindh, Jaroslav Fabian, Stephan Roche, Saroj Dash By investigating the the van der Waals heterostructures of the ferromagnetic insulator Cr2Ge2Te6 and graphene, we observe an out-of-plane proximity-induced ferromagnetic exchange interaction in graphene1. The perpendicular magnetic anisotropy of Cr2Ge2Te6 results in significant modification of the spin transport and precession in graphene, which can be ascribed to the proximity-induced exchange interaction. Furthermore, the observation of a larger lifetime for perpendicular spins in comparison to the in-plane counterpart suggests the creation of a proximity-induced anisotropic spin texture in graphene. Our experimental results and density functional theory calculations open up opportunities for the realization of proximity-induced magnetic interactions and spin filters in 2D material heterostructures and can form the basic building blocks for future spintronic and topological quantum devices. |
Wednesday, March 4, 2020 12:15PM - 12:27PM |
M41.00006: Novel Exciton Condensation and Lorenz Number in Graphene Sang-Boo Nam We present a novel condensation of boson (exciton = electron + hole) in 2 dimension at the temperature Tc = (6/π2 )½ TF (fermi temperature). At Tc, the condensed bosons are to become fermions, electrons to holes, and vice versa. We found the Lorenz number peak value (LNPV) in the case of the elastic scatterings, L(b)/L(0) - 1 = 2bg/3, L(0) = (9/4) ζ(3)/ln2 = 3.895 = 1.183 (π2/3) in the unit of (kB/e)2 , where b = boson/fermion = 2gp/n, g and n are the fermion degeneracy and density, respectively, p the optimum density for the condensation, with the temperature full width (the intrinsic nature) for the half LNPV, Tw = 2(1 - w) Tc, w = [(1 + b)/(2 + b)]½ . Calculated LNPV and Tw for g = 4, account very well, without any parameter, for the data in graphene by Crossno et al, Science 351, 1058 (2016). We found the optimum 2bg/3 = 64/3, p = 4 x 109 /cm2 , vF = 1.03 x 108 cm/s , Tc = 45 K, and Tw = 4.5 K for graphene. We predict the Hall resistance (Rh) peak value and the plasmon frequency square (Ws) dip value, |
Wednesday, March 4, 2020 12:27PM - 12:39PM |
M41.00007: Giant spin-layer locking in novel two-dimensional X2Bi2 (X=Si, Ge, or Sn) Seungjun Lee, Young-Kyun Kwon In contrast to the general view in spin-orbit interaction, it was reported that even in materials with centrosymmetry may have Rashba spin-orbit coupling (the R-2 effect) resulting in spatial spin splitting. However, not only its underlying fundamental physics been still unclear, but the search for materials emerging the R-2 interaction has also been very limited. Here, we propose novel two-dimensional materials X2Bi2 (X=Si, Ge, or Sn), which exhibit spin-layer locking with giant Rashba parameter value (α_R≤12.3 eV nm). Our first principles calculations show the top and bottom atomic sublayers in X2Bi2 produce opposite out-of-plane dipole moments leading to the spin-layer locking phenomenon for in-plane spin moment. We also find that the local orbital angular momentum (OAM) plays a crucial role in determining the R-2 spin splitting. We further suggest possible manipulation strategies for securing the R-2 spin splitting: 1) Strain reinforces the R-2 effect via changing OAM distribution, and 2) layer stacking ensures further spatial spin splitting. |
Wednesday, March 4, 2020 12:39PM - 12:51PM |
M41.00008: Edgetronic and spintronic applications of carbon phosphide nanoribbon liemao cao, Yee Sin Ang, Qingyun Wu, Lay Kee Ang Carbon phosphide (CP) monolayer, a hybrid of graphene and phosphorene that simultaneously preserves their high electrical mobility, finite band gap and air stability, has been successfully synthesized in recent experiment. In this work, we study the electronic and transport properties of CP nanoribbons in α-phase with different edge configurations using first-principle density functional theory simulation. We found that Zα-CPNRs can mimic the behaviors of graphene and phosphorene nanoribbon depending on the edge configurations Intriguingly, when the external electric field exceeds a critical value, the charge transport channel becomes strongly localized to only one edge, and the edge localization can be tuned by an external electric field, thus opening up a new device concept of edgetronics. Our findings reveal the potential of CP nanoribbon as a spintronic materials that fuses the strengths of both graphene and phosphorene. |
Wednesday, March 4, 2020 12:51PM - 1:03PM |
M41.00009: Rashba spin splitting and perpendicular magnetic anisotropy of Gd-adsorbed zigzag graphene nanoribbon modulated by edge states under external electric fields Zhenzhen Qin, Guangzhao Qin, Bin Shao, Xu Zuo The one-dimensional (1D) Rashba effect has become much important due to its key role in basic science to realize exotic electronic phenomena, such as Majorana bound states. Similar to the 2D or 3D systems, the modulation of Rashba effect in 1D matrix is the kernel of spintronics for manipulating electron spin. Herein, by investigating the effects of transverse and vertical external electric field (EEF) on the Rashba spin splitting and magnetic anisotropy energy (MAE) of Gd-adsorbed zigzag graphene nanoribbons from first principles, we found that the Rashba spin splitting in such 1D system can be effectively regulated by the transverse EEF. Moreover, perpendicular magnetic anisotropy holds with either transverse or vertical EEF applied, despite obvious modulation of the MAE contributions in k-space as well as the Rashba spin splitting. It is found the modulation of Gd-5dx2-y2, dxy by C-pz orbitals of edge states is the key to manipulating the magnetic anisotropy, which even plays a decisive role on modifying the Rashba spin splitting in such 1D nanoribbon system. Our study introduces a new strategy to manipulate Rashba spin splitting by edge states and provides new insight into the magnetic anisotropy in 1D Rashba system. |
Wednesday, March 4, 2020 1:03PM - 1:15PM |
M41.00010: Observation of Giant Optical Linear Dichroism and Pseudo Critical Slowing Down in van der Waals Zigzag Antiferromagnets Kyle Hwangbo, Qi Zhang, Qianni Jiang, Di Xiao, Jiun-Haw Chu, Xiaodong Xu Two-dimensional antiferromagnetism (AFM) has been a topic of great interest due to its intertwined relationship with various correlated phenomena like unconventional superconductivity and its potential applicability in novel spintronic devices. In contrast to its ferromagnetic counterpart, direct optical probing and study of AFM order is challenging due to the absence of net magnetization and the resulting weak magneto-optical coupling. Here, we report an optical study of an atomically thin zigzag antiferromagnet, FePS3. We observed a large optical linear dichroism associated with the zigzag AFM order. By performing time-resolved polarimetry measurements, we further examined the critical fluctuations of the AFM order parameter, which exhibit a prominent pseudo-critical slowing down behavior near the Néel temperature. Our findings point to a new optical approach to identify zigzag AFM order and study its non-equilibrium dynamics in strongly correlated systems. |
Wednesday, March 4, 2020 1:15PM - 1:27PM |
M41.00011: Ferromagnetism in multilayered graphite nanostructures doped with nitrogen Aram Manukyan, Harutyun Gyulasaryan, Eduard Sharoyan, Paul Oyala, Oscar Bernal, Armen Kocharian Carbon microspheres consisting of multilayered nanographite structures are prepared using solid-phase pyrolysis of metal-free phthalocyanine H2(C32N8H16). The mean diameter d=3±0.2μm of carbon microspheres have been obtained at pyrolysis Tpyr =670oC, and tpyr =30min. Morphology and structure of prepared samples at two temperatures Tpyr were investigated by HRTEM, X-ray diffractometry, Raman and XPS spectroscopy. Magnetic properties of samples were investigated using vibrational magnetometer and magnetic fields up to 80 kOe, as well as X-band ESR spectrometer in range of temperature, T=5-300K. We found that the temperature dependences of saturation magnetization closely follow the behavior of integrated magnetic resonance intensity. Parameters of ESR spectrum are following g-factor 2.0031, intensity ~5×1019 spin/g and narrow linewidth of 0.8Oe due to strong exchange. Maximum values of saturation magnetization Ms≈0.03emu/g and coercive force Hc=400Oe have been obtained at 25K. The results suggest that observed ferromagnetism in multilayer graphene can be attributed to nitrogen atoms and zigzag edges. |
Wednesday, March 4, 2020 1:27PM - 1:39PM |
M41.00012: Modulating electronic and magnetic properties of ferromagnetic Hf2MnC2O2 MXenes Edirisuriya Siriwardane, Pragalv Karki, Yen Lee Loh, Deniz Cakir In this work, density functional theory calculations were carried out to evaluate the electronic and magnetic properties of the uniaxial and biaxial strains applied, and surface defects introduced Hf2MnC2O2 ferromagnetic MXene. The bare Hf2MnC2O2 monolayer is an indirect bandgap semiconductor with a 0.282 eV bandgap. Our calculations show that the semiconductor-to-half-metal phase transition occurs at 7%, and 9% under uniaxial tensile strain in zig-zag and armchair directions, respectively. The same phase transition can be seen at 8% biaxial tensile strain. This ferromagnetic semiconductor can become a metal under small uniaxial and biaxial compressive strains. We are also able to show that the bare Hf2MnC2O2 monolayer contains an easy-plane anisotropy. The anisotropy of the monolayer transforms into an enhanced, easy-axis anisotropy when the O vacancies and the H adatoms are introduced. |
Wednesday, March 4, 2020 1:39PM - 1:51PM |
M41.00013: Raman signatures on a van der Waals antiferromagnet Yujin Cho, Subhajit Ghosh, Zhangji Zhao, Chaowei Hu, Jin Ho Kang, Fariborz Kargar, Ni Ni, Alexander Balandin, Chee Wei Wong Mixing other exotic properties, such as magnetism or superconductivity, into a topological material has been drawing a lot of researchers’ attention due to its potential as quantum computation and realizing topological phenomena. MnBi2Te4 has been demonstrated to be the first intrinsic antiferromagnetic (AFM) topological insulator (TI) [1]. It consists of Bi2Te3 and Mn-Te bilayer. So far, most studies focused on magnetic properties or electronic structure of the bulk material via magnetic susceptibility, angle-resolved photo-emission spectroscopy, and magnetotransport [2]. When the material comes down to 2D limits, optical Raman spectroscopy becomes advantageous due to its sensitivity and strong layer-dependent characteristic in 2D materials. Raman peaks can also reflect spin interactions that are related to magnetic ordering [3], as well as in-plane magnetic anisotropy. In this project, we will correlate the optical Raman spectrum on MnBi2Te4 with its magnetic transition temperature (~25K) and the in-plane magnetic anisotropy. |
Wednesday, March 4, 2020 1:51PM - 2:03PM |
M41.00014: Detection of Spin Canting Using Magnetic Field Modulated Microwave Spectroscopy. Alex Hojem, James Wampler, Ivan K. Schuller Magnetic field modulated microwave spectroscopy (MFMMS) is the most sensitive technique for detecting superconducting transitions[1]. While superconducting transitions exhibit a reproducible peak behavior, magnetic transitions can have a range of responses including: slopes, steps and local minima in the temperature dependent MFMMS measurements. Other work has shown that a magnetic response in a similar microwave spectroscopy technique can be caused by spin canting[2]. One system of materials that provides an interesting test case for this is the Ruthenocuprates[3]. These compounds have a ferromagnetic response due to spin canting, above the onset of superconductivity. Here, we show that the temperature and field dependence of spin canting of the Ru-1212 system (RuSr2GdCu2O8) can be determined by comparing the MFMMS to magnetometry and resistance measurements. |
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