Two dimensional magnetic material

The discovery of two-dimensional van der Waals magnet has attracted wide attention in basic physics and potential applications. Two dimensional magnetic materials, not only have the optical and electrical properties of traditional two-dimensional materials, but also have a long-range magnetic order to the thickness of the atomic layer, which is an ideal platform for understanding two-dimensional magnetism. Due to the coupling between spin and other degrees of freedom, two-dimensional magnetic materials show many interesting phenomena, which show potential applications in magnetoelectric memory, spin filter, spin FET and so on. In our research group, mechanical peeling, electron beam exposure, chemical etching and other methods were used to prepare a number of two-dimensional magnetic material samples. Based on the customized Oxford low-temperature strong magnetic field system and the built spectral system, the magnetic sequence change of cri3 was systematically studied, and the related research work of other two-dimensional magnetic materials was proposed based on the current system. Representative works include:

(1) Magnetic order changes of CrI3

“Magnetic order induced polarization anomaly of Raman scattering in CrI3 layers”, arXiv, 2019, arXiv: 1910.04542. 

  

Charge density wave of low dimensional materials

 

Charge density wave (CDW) is one of the frontier of condensed matter physics, but its formation mechanism has not been fully understood. On the one hand, the periodic lattice distortion caused by CDW phase transition is reflected in the study of photon phonon mode. On the other hand, the CDW transition temperature can be determined by detecting the temperature dependence of CDW vibration mode, which also provides important information for the study of phonon coupling in the system. In our research group, many CDW materials were prepared by mechanical stripping, electron beam exposure and chemical etching. The complex properties of these materials with temperature, pressure, light field and material thickness were studied by Raman spectroscopy. The representative work includes:

(1) CDWs study of TiSe2 thin films

“Raman spectroscopy of optical phonon and charge density wave modes in 1T-TiSe2 exfoliated flakes”, Solid State Communications, 2017, 266, 21-25.

(2) CDWs study of 2H-TaSe2 slices

“Raman spectroscopy of optical phonon and incommensurate charge density wave modes in 2H-TaSe2 exfoliated flakes”, arXiv, 2017, arXiv: 1712.01514.

(3)CDWs study of GdTe3 few layers

“Raman spectra and dimensional effect on the charge density wave transition in GdTe3”, Applied PhysicsLetters, 2019, 115, 15, 151905.

  

Quantum spin liquid

 

Quantum spin liquid (QSL) is a new matter state in the field of condensed matter physics. In this system, even if the material is cooled to absolute zero, it is difficult to form a long-range order, but to form a spin liquid state due to the strong spin frustration and quantum fluctuation. The quantum spin liquid has some strange properties, for example, although the spin is disordered at low temperature, there is a long-range entanglement between them, and it has the characteristics of spin fraction excitation. This concept was first proposed by condensed matter physicist Anderson in theory in 1973 and was used to explain the mechanism of high temperature superconductivity. In 2006, Kitaev proposed a completely solvable Kitaev model in two-dimensional cellular structure, which greatly promoted the development of this field. At present, our research group mainly uses self-made materials, Raman spectroscopy and second harmonic wave(SHG) technology, combined with the means of changing temperature and high pressure, to study the structure and magnetic properties of Kitaev materials. Representative works include:

(1) Determination of the properties of H3LiIr2O6 quantum spin liquid

“Magnetic Raman continuum in single crystalline H3LiIr2O6”, arXiv, 2019, arXiv: 1906.03601.

(2) Study on the magnetic properties and chemical bond of α-RuCl3

“Raman spectroscopy evidence for dimerization and Mott collapse in a-RuCl3 under pressures”, Physical Review Materials, 2019, 3, 2, 023601.

 

Strain control of low dimensional materials

 

In recent years, low dimensional materials have been widely concerned and studied for their unique physical and chemical properties. They have been widely used in the experiment to make devices close to the atomic size. Theoretical guidance makes the traditional quantum devices continue to miniaturize. Due to the ubiquity of heterogeneous interface or local deformation, the local strain of low dimensional materials (such as surface strain) is universal. There are many unclear details about the local strain of low dimensional materials, and the effect of these strains on the properties of low dimensional materials is still a research hotspot. Huang Mingyuan, the director of our research group, has carried out a large number of strain experiments on low dimensional materials and nano materials with the equipment at that time during his doctoral study and postdoctoral work. He has accumulated rich experience in the preparation of materials and the measurement of experimental means, and has also carried out relevant exploration after returning to China. Representative works include:

(1) Graphene material

“Mechanisms governing phonon scattering by topological defects in graphene nanoribbons”, Nanotechnology, 2016, 27, 5.

“Electronic-mechanical coupling in graphene from in situ nanoindentation experiments and multiscale atomistic simulations”, Nano Letters, 2011, 11, 3, 1241-1246.

“Probing strain-induced electronic structure change in graphene by Raman spectroscopy”, Nano Letters, 2010, 10,10, 4074-4079.

“Phonon softening and crystallographic orientation of strained graphene studied by Raman spectroscopy”, Proceedings of the National Academy of Sciences of the United States of America, 2009, 106, 18, 7304-7308.

(2) Carbon nanotubes

“Direct measurement of strain-induced changes in the band structure of carbon nanotubes”, Physical Review Letters, 2008, 100, 13.

 

 

Growth and characterization of low latitude materials

The discovery of new materials often contains new physical phenomena, and provides a basis for the preparation of new devices (such as photodiodes, broadband optical modulators, exciton semiconductor lasers, etc.). Moreover, the quality of materials is also the key of physical research, especially for nano materials and low-dimensional materials. The tiny change of impurity content and material defects will bring great deviation to the research.In cooperation with other research groups with material growth laboratories, our research group took chemical vapor deposition (CVD) as the main technology, combined with metal organic compound vapor phase epitaxy (MOVPE) technology, combined with a variety of chemical raw materials and reagents, grew several kinds of low latitude materials for experiments on metal substrate, semiconductor substrate and organic substrate, and used atomic force microscope (AFM) Raman spectroscopy and X-ray diffraction were used to characterize the materials, which provided convenience for the research of low latitude materials. Representative works include:

(1) Generation of single crystal GdTe3

“Raman spectra and dimensional effect on the charge density wave transition in GdTe3”, Applied PhysicsLetters, 2019, 115, 15, 151905.

(2) Generation of single crystal H3LiIr2O6

“Magnetic Raman continuum in single crystalline H3LiIr2O6”, arXiv, 2019, arXiv: 1906.03601.

(3) Generation of high quality α - RuCl3 single crystal from industrial RuCl3 crystal

“Raman spectroscopy evidence for dimerization and Mott collapse in a-RuCl3 under pressures”, Physical Review Materials, 2019, 3, 2, 023601.

(4) Generation of GaN microrods on silicon substrate

“Strong exciton–photon coupling and polariton lasing in GaN microrod”, Journal of Materials Science, 2019, 54, 11, 8472-8481.

“Effect of incident laser power and incorporating polariton effects in GaN microrods”, Journal of Luminescence, 2019, 209, 328-332.

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