Search query: magnet CrI3 raman

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abstract: Significance The two dimensional (2D) magnetic semiconductor CrI3 hosts a variety of strong and tunable magneto optical effects and allows for the development of novel magneto optical devices. While the elastic magneto optical effects in CrI3 are well understood, its recently discovered inelastic magneto Raman effect remains to have case specific interpretations varying upon the thickness of CrI3. We perform comprehensive Raman measurements on 2D CrI3 with polarization, temperature, layer number, and magnetic field dependence. We resolve a Davydov split induced N fold multiplet in N layer CrI3 and reveal the distinct magneto Raman behaviors of individual phonons within the multiplet. Our results discover a layered magnetism coupled phonon scattering mechanism that explains the rich magneto Raman effect in CrI3 of arbitrary thickness and elucidates the spin phonon coupling physics in layered magnets. We used a combination of polarized Raman spectroscopy experiment and model magnetism phonon coupling calculations to study the rich magneto Raman effect in the two dimensional (2D) magnet CrI3. We reveal a layered magnetism assisted phonon scattering mechanism below the magnetic onset temperature, whose Raman excitation breaks time reversal symmetry, has an antisymmetric Raman tensor, and follows the magnetic phase transitions across critical magnetic fields, on top of the presence of the conventional phonon scattering with symmetric Raman tensors in N layer CrI3. We resolve in data and by calculations that the first order Ag phonon of the monolayer splits into an N fold multiplet in N layer CrI3 due to the interlayer coupling (N>=2) and that the phonons within the multiplet show distinct magnetic field dependence because of their different layered magnetism phonon coupling. We further find that such a layered magnetism phonon coupled Raman scattering mechanism extends beyond first order to higher order multiphonon scattering processes. Our results on the magneto Raman effect of the first order phonons in the multiplet and the higher order multiphonons in N layer CrI3 demonstrate the rich and strong behavior of emergent magneto optical effects in 2D magnets and underline the unique opportunities of spin phonon physics in van der Waals layered magnets.
author_names: Wencan Jin

Zhipeng Ye

Xiangpeng Luo

Bowen Yang

Gaihua Ye

Fangzhou Yin

Hyun Ho Kim

Laura Rojas

Shangjie Tian

Yang Fu

Shaohua Yan

Hechang Lei

Kai Sun

Adam W Tsen

Rui He

Liuyan Zhao
title: Tunable layered magnetism assisted magneto Raman effect in a two dimensional magnet CrI3
venue: Proceedings of the National Academy of Sciences
year: 2020

abstract: The recent discovery of 2D magnets has revealed various intriguing phenomena due to the coupling between spin and other degree of freedoms (such as helical photoluminescence, nonreciprocal SHG) Previous research on the spin phonon coupling effect mainly focuses on the renormalization of phonon frequency. Here we demonstrate that the Raman polarization selection rules of optical phonons can be greatly modified by the magnetic ordering in 2D magnet CrI3. For monolayer samples, the dominant A1g peak shows abnormally high intensity in the cross polarization channel at low temperature, which is forbidden by the selection rule based on the lattice symmetry. While for bilayer, this peak is absent in the cross polarization channel for the layered antiferromagnetic (AFM) state and reappears when it is tuned to the ferromagnetic (FM) state by an external magnetic field. Our findings shed light on exploring the emergent magneto optical effects in 2D magnets.
author_names: Yujun Zhang

Xiaohua Wu

Bing-Kuan Lyu

Minghui Wu

Shixuan Zhao

Junyang Chen

Mengyuan Jia

Chusheng Zhang

Le Wang

Xinwei Wang

Yuanzhen Chen

Jia Wei Mei

Takashi Taniguchi

Kenji Watanabe

Hugen Yan

Qihang Liu

Li Mei Huang

Yuer Zhao

Mingyuan Huang
title: Magnetic order induced polarization anomaly of Raman scattering in 2D magnet CrI3.
venue: Nano letters
year: 2019

abstract: The coupling between spin and charge degrees of freedom in a crystal gives rise to magneto optical effects with applications in the sensitive detection of local magnetic order, optical modulation and data storage. In two dimensional magnets these effects manifest themselves in the large magneto optical Kerr effect1,2, spontaneous helical light emission3,4 from ferromagnetic (FM) monolayers and electric field induced Kerr rotation5 7 and giant second order non reciprocal optical effects8 in antiferromagnetic (AFM) bilayers. Here we demonstrate the tuning of inelastically scattered light through symmetry control in atomically thin chromium triiodide (CrI3) In monolayers, we found an extraordinarily large magneto optical Raman effect from an A1g phonon mode due to the emergence of FM order. The linearly polarized, inelastically scattered light rotates by ~40deg, more than two orders of magnitude larger than the rotation from the magneto optical Kerr effect under the same experimental conditions. In CrI3 bilayers, the same phonon mode becomes Davydov split into two modes of opposite parity, which exhibit divergent selection rules that depend on inversion symmetry and the underlying magnetic order. We demonstrate the magneto electrical control over these selection rules by activating or suppressing Raman activity for the odd parity phonon mode and the magneto optical rotation of scattered light from the even parity phonon mode. Our work underlines the unique opportunities provided by two dimensional magnets to control the combined time reversal and inversion symmetries to manipulate Raman optical selection rules and for exploring emergent magneto optical effects and spin phonon coupled physics.Symmetry control in atomically thin chromium triiodide enables the observation of tunable magneto optical Raman effects in the 2D limit.
author_names: Bevin Huang

John Cenker

Xiaoou Zhang

Essance L Ray

Tiancheng Song

Takashi Taniguchi

Kenji Watanabe

Michael A McGuire

Di Xiao

Xiaodong Xu
title: Tuning inelastic light scattering via symmetry control in the two dimensional magnet CrI3
venue: Nature Nanotechnology
year: 2020

abstract: Exciton dynamics can be strongly affected by lattice vibrations through electron phonon coupling. This is rarely explored in two dimensional magnetic semiconductors. Focusing on bilayer CrI3, we first show the presence of strong electron phonon coupling through temperature dependent photoluminescence and absorption spectroscopy. We then report the observation of periodic broad modes up to the 8th order in Raman spectra, attributed to the polaronic character of excitons. We establish that this polaronic character is dominated by the coupling between the charge transfer exciton at 1.96 eV and a longitudinal optical phonon at 120.6 cm 1. We further show that the emergence of long range magnetic order enhances the electron phonon coupling strength by ~50% and that the transition from layered antiferromagnetic to ferromagnetic order tunes the spectral intensity of the periodic broad modes, suggesting a strong coupling among the lattice, charge and spin in two dimensional CrI3. Our study opens opportunities for tailoring light matter interactions in two dimensional magnetic semiconductors.
author_names: Wencan Jin

Hyun Ho Kim

Zhipeng Ye

Gaihua Ye

Laura Rojas

Xiangpeng Luo

Bowen Yang

Fangzhou Yin

Jason Shih An Horng

Shangjie Tian

Yang Fu

Gongjun Xu

Hui Deng

Hechang Lei

Adam W Tsen

Kai Sun

Rui He

Liuyan Zhao
title: Observation of the polaronic character of excitons in a two dimensional semiconducting magnet CrI3
venue: Nature communications
year: 2020

abstract: We demonstrate a significant pump helicity dependence in the amplitude of coherent Raman active phonon oscillations in the van der Waals magnet CrI3, revealing a strong non equilibrium coupling between spin and structural order.
author_names: Prashant Padmanabhan

Kevin W C Kwock

L M Martinez

Roxanne Tutchton

Finn Lasse Buessen

Samuel Gilinsky

Min-Cheol Lee

J -X Zhu

Arun Paramekanti

Michael A McGuire

Dmitry A Yarotski

Srinivasa R Singamaneni

Rohit Prativadi Prasankumar
title: Helicity Dependent Coherent Spin Phonon Oscillations in the Ferromagnetic van der Waals Crystal CrI3
venue: 2020 Conference on Lasers and Electro Optics (CLEO)
year: 2020

abstract: Exploring new parameter regimes to realize and control novel phases of matter has been a main theme in modern condensed matter physics research. The recent discovery of 2D magnetism in nearly freestanding monolayer atomic crystals has already led to observations of a number of novel magnetic phenomena absent in bulk counterparts. Such intricate interplays between magnetism and crystalline structures provide ample opportunities for exploring quantum phase transitions in this new 2D parameter regime. Here, using magnetic field and temperature dependent circularly polarized Raman spectroscopy of phonons and magnons, we map out the phase diagram of CrI3 that has been known to be a layered AFM in its 2D films and a FM in its 3D bulk. We, however, reveal a novel mixed state of layered AFM and FM in 3D CrI3 bulk crystals where the layered AFM survives in the surface layers and the FM appears in deeper bulk layers. We then show that the surface layered AFM transits into the FM at a critical magnetic field of 2 T, similar to what was found in the few layer case. Interestingly, concurrent with this magnetic phase transition, we discover a first order structural phase transition that alters the crystallographic point group from C3i to C2h and thus, from a symmetry perspective, this monoclinic structural phase belongs to the 3D nematic order universality class. Our result not only unveils the complex single magnon behavior in 3D CrI3, but also settles down the puzzle of how CrI3 transits from a bulk FM to a thin layered AFM semiconductor, despite recent efforts in understanding the origin of layered AFM in CrI3 thin layer, and reveals the intimate relationship between the layered AFM to FM and the crystalline rhombohedral to monoclinic phase transitions. These findings further open up opportunities for future 2D magnet based magneto mechanical devices.
author_names: Siwen Li

Zhipeng Ye

Xiangpeng Luo

Gaihua Ye

Hyun Ho Kim

Bowen Yang

Shangjie Tian

Chenghe Li

Hechang Lei

Adam W Tsen

Kai Sun

Rui He

Liuyan Zhao
title: Magnetic Field Induced Quantum Phase Transitions in a van der Waals Magnet
year: 2020

abstract: Following the recent isolation of monolayer CrI3 (ref. 1) many more two dimensional van der Waals magnetic materials have been isolated2 12. Their incorporation in van der Waals heterostructures offers a new platform for spintronics5 9, proximity magnetism13 and quantum spin liquids14. A primary question in this field is how exfoliating crystals to the few layer limit influences their magnetism. Studies of CrI3 have shown a different magnetic ground state for ultrathin exfoliated films1,5,6 compared with the bulk, but the origin is not yet understood. Here, we use electron tunnelling through few layer crystals of the layered antiferromagnetic insulator CrCl3 to probe its magnetic order and find a tenfold enhancement of the interlayer exchange compared with bulk crystals. Moreover, temperature and polarization dependent Raman spectroscopy reveals that the crystallographic phase transition of bulk crystals does not occur in exfoliated films. This results in a different low temperature stacking order and, we hypothesize, increased interlayer exchange. Our study provides insight into the connection between stacking order and interlayer interactions in two dimensional magnets, which may be relevant for correlating stacking faults and mechanical deformations with the magnetic ground states of other more exotic layered magnets such as RuCl3 (ref. 14) Few layer magnetic materials sometimes show a different form of magnetism from their thicker equivalents. The authors contend that the mechanism is changes in the stacking order in the thin limit that modify the interlayer exchange interaction.
author_names: D R Klein

David MacNeill

Qian Song

Daniel T Larson

Shiang Fang

Mingyu Xu

Raquel de Almeida Ribeiro

Paul C Canfield

Efthimios Kaxiras

Riccardo Comin

Pablo Jarillo-Herrero
title: Enhancement of interlayer exchange in an ultrathin two dimensional magnet
venue: Nature Physics
year: 2019

abstract: We apply the density functional theory to study various phases (including non magnetic (NM) anti ferromagnetic (AFM) and ferromagnetic (FM) in monolayer magnetic chromium triiodide (CrI3) a recently fabricated 2D magnetic material. It is found that: (1) the introduction of magnetism in monolayer CrI3 gives rise to metal to semiconductor transition; (2) the electronic band topologies as well as the nature of direct and indirect band gaps in either AFM or FM phases exhibit delicate dependence on the magnetic ordering and spin orbit coupling; and (3) the phonon modes involving Cr atoms are particularly sensitive to the magnetic ordering, highlighting distinct spin lattice and spin phonon coupling in this magnet. First principles simulations of the Raman spectra demonstrate that both frequencies and intensities of the Raman peaks strongly depend on the magnetic ordering. The polarization dependent A1g modes at 77 cm 1 and 130 cm 1 along with the Eg mode at about 50 cm 1 in the FM phase may offer a useful fingerprint to characterize this material. Our results not only provide a detailed guiding map for experimental characterization of CrI3, but also reveal how the evolution of magnetism can be tracked by its lattice dynamics and Raman response.
author_names: Lucas Goncalves Webster

Liangbo Liang

Jia-an Yan
title: Distinct spin lattice and spin phonon interactions in monolayer magnetic CrI3.
venue: Physical chemistry chemical physics PCCP
year: 2018

abstract: Twist engineering, or the alignment of two dimensional (2D) crystalline layers with desired orientations, has led to tremendous success in modulating the charge degree of freedom in hetero and homo structures, in particular, in achieving novel correlated and topological electronic phases in moir\'e electronic crystals. However, although pioneering theoretical efforts have predicted nontrivial magnetism and magnons out of twisting 2D magnets, experimental realization of twist engineering spin degree of freedom remains elusive. Here, we leverage the archetypal 2D Ising magnet chromium triiodide (CrI3) to fabricate twisted double bilayer homostructures with tunable twist angles and demonstrate the successful twist engineering of 2D magnetism in them. Using linear and circular polarization resolved Raman spectroscopy, we identify magneto Raman signatures of a new magnetic ground state that is sharply distinct from those in natural bilayer (2L) and four layer (4L) CrI3. With careful magnetic field and twist angle dependence, we reveal that, for a very small twist angle 0.5 degree) this emergent magnetism can be well approximated by a weighted linear superposition of those of 2L and 4L CI3 whereas, for a relatively large twist angle 5 degree) it mostly resembles that of isolated 2L CrI3. Remarkably, at an intermediate twist angle 1.1 degree) its magnetism cannot be simply inferred from the 2L and 4L cases, because it lacks sharp spin flip transitions that are present in 2L and 4L CrI3 and features a dramatic Raman circular dichroism that is absent in natural 2L and 4L ones. Our results demonstrate the possibility of designing and controlling the spin degree of freedom in 2D magnets using twist engineering.
author_names: Hongchao Xie

Xiangpeng Luo

Gaihua Ye

Zhipeng Ye

Haiwen Ge

S H Sung

Emily Rennich

Shaohua Yan

Yang Fu

Shangjie Tian

Hechang Lei

Robert Hovden

Kai Sun

Rui He

Liuyan Zhao
title: Twist engineering of the two dimensional magnetism in double bilayer chromium triiodide homostructures
year: 2021

abstract: In this article, we calculate the magnon spectrum of Kitaev Heisenberg magnets. This model has been recently proposed as a spin Hamiltonian to model \text{CrI}_3$ and other two dimensional magnets. It is a minimal spin Hamiltonian that includes a contribution stemming from a Heisenberg, isotropic exchange, and a contribution arising from a Kitaev interaction, anisotropic and frustrated exchange. Our calculations reveal the topological nature of the magnons and a gap that opens at the $K$ and $K^\prime$ points. These topological properties give rise to effects such as thermal Hall effect. In addition to the bulk properties, we calculate the magnon spectrum of nanoribbons illustrating the corresponding edge states.
author_names: Esteban Aguilera

R Jaeschke-Ubiergo

Nicolas Vidal-Silva

Alvaro S Nunez
title: Topological magnonics in the two dimensional van der Waals magnet CrI3
year: 2020