Bachelor of Science, Central China Normal University (2017)
Doctor of Philosophy, University of Washington (2023)
Ph.D., University of Washington, Physics (2023)
- Nematic fluctuations in an orbital selective superconductor Fe1+yTe1-xSex COMMUNICATIONS PHYSICS 2023; 6 (1)
Dynamical criticality of spin-shear coupling in van der Waals antiferromagnets
2022; 13 (1): 6598
The interplay between a multitude of electronic, spin, and lattice degrees of freedom underlies the complex phase diagrams of quantum materials. Layer stacking in van der Waals (vdW) heterostructures is responsible for exotic electronic and magnetic properties, which inspires stacking control of two-dimensional magnetism. Beyond the interplay between stacking order and interlayer magnetism, we discover a spin-shear coupling mechanism in which a subtle shear of the atomic layers can have a profound effect on the intralayer magnetic order in a family of vdW antiferromagnets. Using time-resolved X-ray diffraction and optical linear dichroism measurements, interlayer shear is identified as the primary structural degree of freedom that couples with magnetic order. The recovery times of both shear and magnetic order upon optical excitation diverge at the magnetic ordering temperature with the same critical exponent. The time-dependent Ginzburg-Landau theory shows that this concurrent critical slowing down arises from a linear coupling of the interlayer shear to the magnetic order, which is dictated by the broken mirror symmetry intrinsic to the monoclinic stacking. Our results highlight the importance of interlayer shear in ultrafast control of magnetic order via spin-mechanical coupling.
View details for DOI 10.1038/s41467-022-34376-5
View details for Web of Science ID 000878823900035
View details for PubMedID 36329063
View details for PubMedCentralID PMC9633802
Gate-Tunable Proximity Effects in Graphene on Layered Magnetic Insulators
2022; 22 (21): 8495-8501
The extreme versatility of van der Waals materials originates from their ability to exhibit new electronic properties when assembled in close proximity to dissimilar crystals. For example, although graphene is inherently nonmagnetic, recent work has reported a magnetic proximity effect in graphene interfaced with magnetic substrates, potentially enabling a pathway toward achieving a high-temperature quantum anomalous Hall effect. Here, we investigate heterostructures of graphene and chromium trihalide magnetic insulators (CrI3, CrBr3, and CrCl3). Surprisingly, we are unable to detect a magnetic exchange field in the graphene but instead discover proximity effects featuring unprecedented gate tunability. The graphene becomes highly hole-doped due to charge transfer from the neighboring magnetic insulator and further exhibits a variety of atypical gate-dependent transport features. The charge transfer can additionally be altered upon switching the magnetic states of the nearest CrI3 layers. Our results provide a roadmap for exploiting proximity effects arising in graphene coupled to magnetic insulators.
View details for DOI 10.1021/acs.nanolett.2c02931
View details for Web of Science ID 000877142100001
View details for PubMedID 36279401
- Correlation-driven electronic reconstruction in FeTe1-xSex COMMUNICATIONS PHYSICS 2022; 5 (1)
Magnetism and Its Structural Coupling Effects in 2D Ising Ferromagnetic Insulator VI3
2021; 21 (21): 9180-9186
van der Waals (vdW) magnets have emerged as a tunable platform for exploring a variety of layer-dependent magnetic phenomena. Here we probe the thickness-dependent magnetism of vanadium triiodide (VI3), a material known as a layered ferromagnetic Mott insulator in its bulk form, using magnetic circular dichroism microscopy. Robust ferromagnetism is observed in all thin layers, down to the monolayer limit with large coercive fields. In contrast to known vdW magnets, the Curie temperature shows an anomalous increase as the layer number decreases, reaching a maximum of 60 K in monolayers. Second harmonic generation measurements reveal broken inversion symmetry in exfoliated flakes, down to trilayers. This observation demonstrates that the exfoliated flakes take a layer stacking arrangement that differed from the inversion-symmetric parent bulk counterpart. Our results suggest a coupling effect between magnetic and structural degrees of freedom in VI3 and its potential for engineering layer and twist angle-dependent magnetic phenomena.
View details for DOI 10.1021/acs.nanolett.1c03027
View details for Web of Science ID 000718298700031
View details for PubMedID 34724786
Observation of Giant Optical Linear Dichroism in a Zigzag Antiferromagnet FePS3
2021; 21 (16): 6938-6945
Direct optical probing of the antiferromagnetic order parameter in atomically thin samples is challenging, for example, via magneto-optical spectroscopy, due to the lack of net magnetization. Here, we report zigzag-antiferromagnetism (AFM) induced optical linear dichroism (LD) in layered transition-metal thiophosphate FePS3 down to the monolayer limit. The observed LD is giant despite having the optical wave vector parallel to the Néel vector. The LD is at least one order of magnitude larger than those reported in other antiferromagnetic systems, where the optical wave vector is orthogonal to the Néel vector. The large LD enables the probe of 60° orientated zigzag-AFM domains. The optical anisotropy in FePS3 originates from an electronic anisotropy associated with the zigzag direction of the AFM order and is independent of the spin-pointing direction. Our findings point to a new optical approach for the investigation and control of zigzag or stripe magnetic order in strongly correlated systems.
View details for DOI 10.1021/acs.nanolett.1c02188
View details for Web of Science ID 000691792400028
View details for PubMedID 34428905
- Quantum oscillations in the field-induced ferromagnetic state of MnBi2-xSbxTe4 PHYSICAL REVIEW B 2021; 103 (20)
Intertwined Topological and Magnetic Orders in Atomically Thin Chern Insulator MnBi2Te4
2021; 21 (6): 2544-2550
MnBi2Te4, a van der Waals magnet, is an emergent platform for exploring Chern insulator physics. Its layered antiferromagnetic order was predicted to enable even-odd layer number dependent topological states. Furthermore, it becomes a Chern insulator when all spins are aligned by an applied magnetic field. However, the evolution of the bulk electronic structure as the magnetic state is continuously tuned and its dependence on layer number remains unexplored. Here, employing multimodal probes, we establish one-to-one correspondence between bulk electronic structure, magnetic state, topological order, and layer thickness in atomically thin MnBi2Te4 devices. As the magnetic state is tuned through the canted magnetic phase, we observe a band crossing, i.e., the closing and reopening of the bulk band gap, corresponding to the concurrent topological phase transition in both even- and odd-layer-number devices. Our findings shed new light on the interplay between band topology and magnetic order in this newly discovered topological magnet.
View details for DOI 10.1021/acs.nanolett.0c05117
View details for Web of Science ID 000634766600027
View details for PubMedID 33710884
Highly anisotropic excitons and multiple phonon bound states in a van der Waals antiferromagnetic insulator
2021; 16 (6): 655-+
Two-dimensional (2D) semiconductors enable the investigation of light-matter interactions in low dimensions1,2. Yet, the study of elementary photoexcitations in 2D semiconductors with intrinsic magnetic order remains a challenge due to the lack of suitable materials3,4. Here, we report the observation of excitons coupled to zigzag antiferromagnetic order in the layered antiferromagnetic insulator NiPS3. The exciton exhibits a narrow photoluminescence linewidth of roughly 350 μeV with near-unity linear polarization. When we reduce the sample thickness from five to two layers, the photoluminescence is suppressed and eventually vanishes for the monolayer. This suppression is consistent with the calculated bandgap of NiPS3, which is highly indirect for both the bilayer and the monolayer5. Furthermore, we observe strong linear dichroism (LD) over a broad spectral range. The optical anisotropy axes of LD and of photoluminescence are locked to the zigzag direction. Furthermore, their temperature dependence is reminiscent of the in-plane magnetic susceptibility anisotropy. Hence, our results indicate that LD and photoluminescence could probe the symmetry breaking magnetic order parameter of 2D magnetic materials. In addition, we observe over ten exciton-A1g-phonon bound states on the high-energy side of the exciton resonance, which we interpret as signs of a strong modulation of the ligand-to-metal charge-transfer energy by electron-lattice interactions. Our work establishes NiPS3 as a 2D platform for exploring magneto-exciton physics with strong correlations.
View details for DOI 10.1038/s41565-021-00873-9
View details for Web of Science ID 000627694000001
View details for PubMedID 33707746
- Suppression of superconductivity by anisotropic strain near a nematic quantum critical point NATURE PHYSICS 2020; 16 (12)
Two-Dimensional van der Waals Nanoplatelets with Robust Ferromagnetism
2020; 20 (3): 2100-2106
We have synthesized unique colloidal nanoplatelets of the two-dimensional (2D) van der Waals ferromagnet CrI3 and have characterized these nanoplatelets structurally, magnetically, and by magnetic circular dichroism spectroscopy. The CrI3 nanoplatelets have lateral dimensions of ∼25 nm and thicknesses of only ∼4 nm, corresponding to just a few CrI3 monolayers. Magnetic and magneto-optical measurements demonstrate robust 2D ferromagnetic ordering with Curie temperatures similar to bulk CrI3, despite their small size. These data also show magnetization steps akin to those observed in micron-sized few-layer 2D sheets associated with concerted spin-reversal of individual CrI3 layers within few-layer van der Waals stacks. Similar data have also been obtained for CrBr3 and anion-alloyed Cr(I1-xBrx)3 nanoplatelets. These results represent the first example of lateral nanostructures of 2D van der Waals ferromagnets of any composition. The demonstration of robust ferromagnetism at nanometer lateral dimensions opens new doors for miniaturization in spintronics devices based on van der Waals ferromagnets.
View details for DOI 10.1021/acs.nanolett.0c00102
View details for Web of Science ID 000526408800080
View details for PubMedID 32031382
Apparatus design for measuring of the strain dependence of the Seebeck coefficient of single crystals
REVIEW OF SCIENTIFIC INSTRUMENTS
2020; 91 (2): 023902
We present the design and construction of an apparatus that measures the Seebeck coefficient of single crystals under in situ tunable strain at cryogenic temperatures. A home-built three piezostack apparatus applies uni-axial stress to a single crystalline sample and modulates anisotropic strain up to 0.7%. An alternating heater system and cernox sensor thermometry measure the Seebeck coefficient along the uniaxial stress direction. To demonstrate the efficacy of this apparatus, we applied uniaxial stress to detwin single crystals of BaFe2As2 in the orthorhombic phase. The obtained Seebeck coefficient anisotropy is in good agreement with previous measurements using a mechanical clamp.
View details for DOI 10.1063/1.5127530
View details for Web of Science ID 000519231300002
View details for PubMedID 32113413
Switching 2D magnetic states via pressure tuning of layer stacking.
The physical properties of two-dimensional van der Waals crystals can be sensitive to interlayer coupling. For two-dimensional magnets1-3, theory suggests that interlayer exchange coupling is strongly dependent on layer separation while the stacking arrangement can even change the sign of the interlayer magnetic exchange, thus drastically modifying the ground state4-10. Here, we demonstrate pressure tuning of magnetic order in the two-dimensional magnet CrI3. We probe the magnetic states using tunnelling8,11-13 and scanning magnetic circular dichroism microscopy measurements2. We find that interlayer magnetic coupling can be more than doubled by hydrostatic pressure. In bilayer CrI3, pressure induces a transition from layered antiferromagnetic to ferromagnetic phase. In trilayer CrI3, pressure can create coexisting domains of three phases, one ferromagnetic and two antiferromagnetic. The observed changes in magnetic order can be explained by changes in the stacking arrangement. Such coupling between stacking order and magnetism provides ample opportunities for designer magnetic phases and functionalities.
View details for DOI 10.1038/s41563-019-0505-2
View details for PubMedID 31659293