Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session V35: 2D Materials -Magnetism and Magnetotransport IFocus
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Sponsoring Units: DMP GMAG Chair: Elizabeth McCormick, Ohio State Univ - Columbus Room: LACC 409B |
Thursday, March 8, 2018 2:30PM - 2:42PM |
V35.00001: Spin-Orbit Interaction and Magnetic Order in (111) Oriented (La0.3Sr0.7)(Al0.65Ta0.35)/SrTiO3 Heterostructures Varada Bal, Venkat Chandrasekhar, Zhen Huang, Kun Han, Ariando Ariando, Thirumalai Venkatesan The 2-dimensional carrier gas in (111) oriented SrTiO3 (STO) based heterostructures has attracted a lot of attention due to its complex Fermi surface and the possibility of exotic topological physics. We present magnetoresistance (MR) studies on (111) oriented (La0.3Sr0.7)(Al0.65Ta0.35)/SrTiO3 (LSAT/STO), which is less strained as compared to the better studied LaAlO3/STO. We find that at high positive values of the applied gate voltage Vg, transport is dominated by high mobility electron-like carriers with a tendency towards weak localization. As Vg is lowered, carrier mobility is reduced, hole-like carriers start becoming important and weak anti-localization effects become pronounced. This indicates that spin-orbit interaction (SOI) is stronger in this regime, in contrast to what has been observed in (100) STO based structures. We have earlier reported on hysteretic MR that develops at millikelvin temperatures at low Vg,1 signifying that low mobility carriers with strong SOI may play a role in supporting a ferromagnetic phase in this system. We believe these results can shed light on how the interplay between crystal orientation and strain can affect the properties of STO based carrier gases. [1] Bal et al, Appl. Phys. Lett. 111, 081604 (2017) |
Thursday, March 8, 2018 2:42PM - 2:54PM |
V35.00002: Compressibility and Spin/Valley Susceptibility of Electron Gas in Doped Two-Dimensional Semiconductors Shiyuan Gao, Giovanni Vignale, Li Yang Due to the exchange interaction, the two-dimensional electron gas (2DEG) can have negative electronic compressibility and undergo a ferromagnetic transition below a critical density, which depends on the screening environment. In a uniform dielectric, the screening is simply characterized by the dielectric constant, which renormalizes the energy and electron density scale. However, in a 2D material or its heterostructure, the screening is characterized by a quasi-2D form with a intrinsic length scale called the 2D polarizability, resulting in different compressibility and spin/valley susceptibility for the 2DEG in doped 2D materials. With input from first-principles calculation, we calculate the total energy of the electron gas in such doped 2D semiconductor as a function of the carrier density and spin/valley polarization within the random-phase approximation. We find negative electronic compressibility and enhanced spin/valley susceptibility at low carrier density, which appear stronger in material with lower 2D polarizability and effective mass. |
Thursday, March 8, 2018 2:54PM - 3:06PM |
V35.00003: Multiple Dirac cones and spontaneous quantum anomalous Hall state in monolayer transition metal trichalcogenides Yusuke Sugita, Takashi Miyake, Yukitoshi Motome Atomically-thin magnets have attracted much attention for potential application to next-generation devices. Among many van der Waals materials, the transition metal trichalcogenides (TMTs) have gained great interest since the discovery of ferromagnetism in the few-layer forms. Although the interplay between electron correlations and the spin-orbit coupling (SOC) in TMTs would play a key role to realize the exotic phase of matters in the purely 2D systems, their potentials have not been fully explored. Here, using the ab initio calculations, we investigate the electronic properties of the group 10 TMTs in the monolayer form [1]. We find that eg-orbital bands possess multiple Dirac cones near the Fermi level. The origin of the multiple Dirac cones is ascribed to a honeycomb superstructure composed of the third-neighbor hopping enhanced by the spatial symmetry of orbitals and crystal structure of the monolayer TMTs. We also clarify that the SOC gaps out these Dirac cones and the mass gap as well as the valley structure can be tuned by the trigonal distortion. Furthermore, we elucidate that electron correlations and the SOC may turn the multiple-Dirac semimetal to a quantum anomalous Hall insulator with a high Chern number. [1] Y. Sugita, T. Miyake, and Y. Motome, arXiv:1704.00318. |
Thursday, March 8, 2018 3:06PM - 3:18PM |
V35.00004: Giant magnetoresistance by Pauli blockade in hydrogenated graphene Nicholas Hemsworth, Jonathan Guillemette, Alexandr Vlasov, Jeffrey Kirman, Farzaneh Mahvash, Pierre Levesque, Mohamed Siaj, Richard Martel, Guillaume Gervais, Sergei Studenikin, Andy Sachrajda, Thomas Szkopek Giant magnetoresistance is a manifestation of spin dependent charge transport that encompasses a wide range of phenomena. The strength of the giant magnetoresistive effect has led to its application in the sensing of magnetic fields, most importantly in high density magnetic information storage. To date, in-plane magnetoresistive effects in atomically thin 2D electron systems have been found to be comparatively small [1]. |
Thursday, March 8, 2018 3:18PM - 3:30PM |
V35.00005: Long Range Intrinsic Magnetic Order in Bulk Semiconducting MoTe2 and MoSe2 Alexander Kerelsky, Zurab Guguchia, Drew Edelberg, Soham Banerjee, Fabian Rohr, Declan Scullion, Mathias Augustin, Daniel Rhodes, Zurab Shermadini, Hubertus Luetkens, Alexander Shengelaya, Christopher Baines, Elvezio Morenzoni, Alex Amato, Rustem Khasanov, James Hone, Simon J Billinge, Elton Santos, Yasutomo Uemura, Abhay Pasupathy The search for semiconducting materials with intrinsic dilute magnetism has been an ongoing challenge for many years. The semiconducting transition metal dichalcogenides have drawn great interest due to a wide array of electrical and optical applications. In this work, we report the direct observation of long-range magnetic order below TM=40K and TM=100K in bulk 2H-MoTe2 and 2H-MoSe2 respectively by muon spin relaxation/rotation (µSR). To investigate the origin of the long-range magnetic order, we perform scanning tunneling microscopy (STM) which reveals a uniform density of intrinsic defects in the materials. Atomic-resolution STM reveals that the primary defects are substitutions of chalcogen atoms, likely by molybdenum. Hubbard density functional theory (DFT) simulations predict that these molybdenum substitutional defects induce magnetic moments at defect sites with long range interaction. Scanning tunneling spectroscopy taken at defect sites is also in confirmation with the L-DOS calculated via the DFT simulations . Thus, we conclude that the long range magnetic order observed via µSR is native to the materials, due to interacting intrinsic magnetic defects. |
Thursday, March 8, 2018 3:30PM - 4:06PM |
V35.00006: Magnetism in Cleavable Transition Metal Halides Invited Speaker: Michael McGuire There is great interest in identifying cleavable magnetic materials to complement the variety of optical and electronic monolayer components currently available for van der Waals heterostructures. The layered compound CrI3 was recently proposed as a promising candidate, and subsequently demonstrated as a monolayer ferromagnet with interesting layer-number dependent properties, and incorporated into van der Waals heterostructures with other 2D materials. These developments have brought increased attention to transition metal halide materials for the study of 2D physics and functional heterostructures. This large family of layered materials displays a wide variety of magnetic phenomena, including strong frustration, spin-liquid behavior, ferromagnetism, antiferromagnetism, and multiferroicity. Recent developments with CrI3 monolayers, and other related transition metal halides will be presented, including antiferromagnetic CrCl3 and the 4d transition metal analog MoCl3, in which magnetism only appears well above room temperature. |
Thursday, March 8, 2018 4:06PM - 4:18PM |
V35.00007: Magnetic Proximity Effects in Transition-Metal Dichalcogenides: Converting Excitons Benedikt Scharf, Gaofeng Xu, Alex Matos Abiague, Igor Zutic The two-dimensional character and reduced screening in monolayer transition-metal dichalcogenides (TMDs) lead to the ubiquitous formation of robust excitons with binding energies orders of magnitude larger than in bulk semiconductors. Focusing on neutral excitons, bound electron-hole pairs, that dominate the optical response in TMDs, it is shown that they can provide fingerprints for magnetic proximity effects in magnetic heterostructures [1]. These proximity effects cannot be described by the widely used single-particle description, but instead reveal the possibility of a conversion between optically inactive and active excitons by rotating the magnetization of the magnetic substrate. With recent breakthroughs in fabricating Mo- and W-based magnetic TMD heterostructures, this emergent optical response can be directly tested experimentally. |
Thursday, March 8, 2018 4:18PM - 4:30PM |
V35.00008: Magneto Photoluminescence Measurements in Transition Metal Dichalcogenides on a Magnetic Substrate, YIG Jungryeol Seo, Mumtaz Murat Arik, Alok Mukherjee, Chuan Zhao, Hao Zeng, Benedikt Scharf, Igor Zutic, John Cerne It is theoretically predicted that the valley degeneracy in transition metal dichalcogenides (TMDs) can be removed using relatively small magnetic fields if the film is on a magnetic substrate [1], [2]. Recent experiments demonstrate the proximity-induced exchange splitting in monolayer TMDs on magnetic substrates such as EuS [3] and CrI3 [4]. We report systematic magneto-optical measurements on a TMD film that is grown on the magnetic substrate YIG (yttrium iron garnet). We perform photoluminescence (PL) measurements using a visible laser (Epump = 2.33 eV) as a function of magnetic fields up to 7T at 10K. We observe an enhanced magnetic field dependence of the PL peak splitting of 0.42 meV/T for the charged exciton, compared to a smaller splitting with SiO2 substrates of 0.1~0.2 meV/T. We observe a linear magnetic field dependence of the PL polarization and PL peak positions of the neutral exciton, charged exciton and local states. |
Thursday, March 8, 2018 4:30PM - 4:42PM |
V35.00009: Magnetic properties of ultrathin layered chromium di-telluride Bheema Lingam Chittari, Jeil Jung Based on ab initio calculations we have studied the magnetic properties of two dimensional chromium di-telluride CrTe2 in the few layers limit and the bulk. We find that for both trigonal (H) and octahedral (T) structures the CrTe2 multilayers exhibit intralayer ferromagnetism and layer thickness dependent interlayer magnetic coupling. The layer anti-ferromagnetism (L-AFM) is stabilized in bi- and tri- layer systems, but we find a transition to the layer ferromagnetic (L-FM) phase for a tetralayer. The magnetic anisotropy calculations reveals that single layers are in-plane magnets for both H-CrTe2 and T-CrTe2 systems while in the bulk they have respectively out-of-plane and in-plane magnetizations. For T-CrTe2 the easy axis orientation is found to align with increasing anisotropy energy towards the out-of-plane direction for the bi-, tri- and tetra layers, in contrast to the magnetisation behavior in the bulk. We explore the anisotropy energy increase with layer number in connection with the atomic structural distortions present in ultrathin multilayers. |
Thursday, March 8, 2018 4:42PM - 4:54PM |
V35.00010: Large Magnetic Anisotropy Energy and Valley Splitting Energy of Single Transition Metal Adatoms on Monolayer WS2 Pengju Zuo, Hui Wang, Ruqian Wu
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Thursday, March 8, 2018 4:54PM - 5:06PM |
V35.00011: Raman studies of the antiferromagnetic phase transition in atomically thin NiPS3 Kangwon Kim, Soo Yeon Lim, Jae-Ung Lee, Sung Min Lee, Tae Yun Kim, Ji Hoon Ryoo, Pilkwang Kim, Cheol Hwan Park, Je-Guen Park, Hyeonsik Cheong NiPS3 is one of the new class of layered magnetic materials, which can be exfoliated atomically thin films due to weak van der Waals bonding along the c-axis. It shows antiferromagnetic phase transition at the Néel temperature (TN) of 155 K. For few-layer, as the dimension of the materials is changed from 3- to 2-dimension (2D), magnetic ordering can be affected. Raman spectroscopy is a powerful tool for studying 2D magnetic materials, as it can investigate phonon scattering as well as magnetic scattering. Below the TN, the Raman spectrum of NiPS3 shows anomalous features: 2-magnon scattering and a Breit-Wigner-Fano type signal. It also shows temperature dependent low-energy excitation due to spin fluctuations. Since these originate from the magnetic properties, the TN of NiPS3 can be estimated by using temperature dependence of these features. We prepared few-layer NiPS3 samples by mechanically exfoliation. By conducting temperature dependent Raman measurement, we found the signatures of antiferromagnetic phase transitions in few-layer NiPS3. |
Thursday, March 8, 2018 5:06PM - 5:18PM |
V35.00012: Layer dependent magneto-optical properties of ferromagnetic chromium triiodide: An ab initio study Vijay Kumar Gudelli, Guang-Yu Guo Two-dimensional materials (TDM) have attracted enormous attention because of their fascinating properties for next-generation device applications. TDM of graphene and beyond-graphene materials such as transition metal dichalcogenides, are receiving increasing interests because of their excellent applications on electronic and optoelectronics. Ferromagnetism and half-metallicity have been predicted recently in TDM, which promise exciting potentials for semiconductor spintronics. This unveils the importance of the magnetism and magneto-optical (MO) properties of TDM for a better understanding of magnetism in these materials. In the present work, we perform a systematic ab initio density functional study on the MO Kerr and Faraday effects of bulk and monolayer (ML) ferromagnetic (FM) CrI3. We report the electronic structure and optical conductivity of semiconductor CrI3 for both bulk and ML. Furthermore, we also study the MO properties of the FM CrI3, and find that for bulk and ML MO Kerr and Faraday effects to be high compared to the traditional MO materials. Thin film ML of CrI3 with SiO2 as a substrate, the MO Kerr rotation is found to be in good agreement with the recent experimental work, which shows that FM CrI3 is an excellent family of TDM for MO and spintronic nanodevices. |
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