Strong Correlation Effects Research Articles

A House Price Prediction Model Based on K-means Clustering and Random Forest in Guangzhou

This paper addresses the key issues in house price forecasting from multiple perspectives by establishing a house price forecasting model for Guangzhou city, providing valuable information and decision support for home buyers, developers, and the government. First, this paper employs the Person coefficient, stepwise regression model and t-test to address the problem of quantifying data and exploring house price factors. By analyzing the correlation between the relevant variables and house prices, the key characteristics that have significant and strong correlation effects on house prices are obtained. Second, the K-means clustering model was used to classify houses into three categories: economic houses, comfortable houses and high-end houses. This classification result provides a more detailed data base for the subsequent construction of the house price prediction model. Finally, the random forest house price prediction model was established in this paper, and the model was validated by error analysis and stability analysis. The average absolute value error and goodness-of-fit obtained were 0.08 and 0.92, respectively, indicating that the model has high accuracy and reliability. The research in this paper has important implications for all parties, including home buyers, developers, and the government. For home buyers, the model can help them better understand the market situation; for developers, the model can guide their reasonable pricing and development strategies; for the government, the model can provide a scientific basis for real estate market regulation and policy control to promote market stability and sustainable development.

Selective Electron-Phonon Coupling in Dimerized 1T-TaS2 Revealed by Resonance Raman Spectroscopy.

The layered transition-metal dichalcogenide material 1T-TaS2 possesses successive phase transitions upon cooling, resulting in strong electron-electron correlation effects and the formation of charge density waves (CDWs). Recently, a dimerized double-layer stacking configuration was shown to form a Peierls-like instability in the electronic structure. To date, no direct evidence for this double-layer stacking configuration using optical techniques has been reported, in particular through Raman spectroscopy. Here, we employ a multiple excitation and polarized Raman spectroscopy to resolve the behavior of phonons and electron-phonon interactions in the commensurate CDW lattice phase of dimerized 1T-TaS2. We observe a distinct behavior from what is predicted for a single layer and probe a richer number of phonon modes that are compatible with the formation of double-layer units (layer dimerization). The multiple-excitation results show a selective coupling of each Raman-active phonon with specific electronic transitions hidden in the optical spectra of 1T-TaS2, suggesting that selectivity in the electron-phonon coupling must also play a role in the CDW order of 1T-TaS2.

Observation of a long-lived triplet excited state and strong electron correlation effects in the copper oxide anion (CuO-) using cryogenic photoelectron imaging.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation G. Stephen Kocheril, Han-Wen Gao, Lai-Sheng Wang; Observation of a long-lived triplet excited state and strong electron correlation effects in the copper oxide anion (CuO−) using cryogenic photoelectron imaging. J. Chem. Phys. 21 June 2023; 158 (23): 236101. https://doi.org/10.1063/5.0151516 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioThe Journal of Chemical Physics Search Advanced Search |Citation Search

Assessment of village resilience in flood storage areas based on complex networks: From the perspective of safety and low-carbon development

This study has built a modified gravity model to quantify the connection strength between villages, and complex networks were used to analyze and deconstruct the resilience characteristics of network structure and simulated resilience change characteristics under different scenarios including climate change, and identified the network core of the villages. The improvement of the resilience levels of rural systems under changing environments is an important sustainable development. The objective of this study is to provide a basis for the construction of rural emergency disaster prevention in flood storage areas and provide a reference for sustainable rural low-carbon development of village system. The results show that (1) from the perspective of spatial patterns of rural networks, there are obvious spatial differences in Mengwa rural network, showing a spindle-shaped spatial structure with dense middle and sparse on both sides. (2) From the perspective of structural resilience characteristics, the network has significant hierarchy and agglomeration, high local transmission and no obvious characteristics of homogeneity or heterogeneity. Amongst them, the core node has a prominent position, strong control ability and significant correlation effect. (3) The results of scenario simulations on rural network resilience show deliberate disturbance can significantly reduce network resilience compared with random disturbance. A large number of high-energy consumption and low-efficiency phenomena occur earlier in the network, leading to the collapse of the network.

Intertwining of Magnetism and Charge Ordering in Kagome FeGe.

Recent experiments report a charge density wave (CDW) in the antiferromagnet FeGe, but the nature of the charge ordering and the associated structural distortion remains elusive. We discuss the structural and electronic properties of FeGe. Our proposed ground state phase accurately captures atomic topographies acquired by scanning tunneling microscopy. We show that the 2 × 2 × 1 CDW likely results from the Fermi surface nesting of hexagonal-prism-shaped kagome states. FeGe is found to exhibit distortions in the positions of the Ge atoms instead of the Fe atoms in the kagome layers. Using in-depth first-principles calculations and analytical modeling, we demonstrate that this unconventional distortion is driven by the intertwining of magnetic exchange coupling and CDW interactions in this kagome material. The movement of Ge atoms from their pristine positions also enhances the magnetic moment of the Fe kagome layers. Our study indicates that magnetic kagome lattices provide a material candidate for exploring the effects of strong electronic correlations on the ground state and their implications for transport, magnetic, and optical responses in materials.

Thermodynamics and robust n-type charge carrier density in Co-doped FeTe2: strain strategy

Herein, we investigated the combined effect of Co-doping and strain (biaxial [110] and hydrostatic [111]) on the thermodynamics and electronic structure of the FeTe2 motif using ab-initio calculations by considering the strong correlation effects. The pristine one has a non-magnetic semiconducting nature with an indirect band gap (E g ) of 0.384 eV. Interestingly, our results revealed that the Co-doping at the Fe site induced an n-type conductivity (i.e. few states are crossing the Fermi level from the valence to conduction band) in the system having a substantial charge carrier density magnitude of 0.14 × 1021 cm−3. The metallicity mainly comprises the Co-3d orbitals along with a significant contribution from Fe-3d states. Thermodynamic, mechanical, and dynamical stability of the Co-doped FeTe2 structure is confirmed by computing the formation energetic, elastic constants, and phonon band structure, respectively. Generally, an increasing and decreasing trend in E g value is evident against the applied compressive and tensile strains having ranged from −5% to +5% for the case of the undoped system, respectively. On the other hand, the Co-doped structure maintained its n-type conduction against considered both types of strains. Moreover, it is demonstrated that compressive strains strengthen the charge carrier density amplitude, while tensile strains show a negative impact. Hence, the present work displays that robust n-type conductivity and stable structure of Co-doped FeTe2 system, makes it a desirable candidate for device applications.

Magnetic Interactions in a [Co(II)3Er(III)(OR)4] Model Cubane through Forefront Multiconfigurational Methods

Strong electron correlation effects are one of the major challenges in modern quantum chemistry. Polynuclear transition metal clusters are peculiar examples of systems featuring such forms of electron correlation. Multireference strategies, often based on but not limited to the concept of complete active space, are adopted to accurately account for strong electron correlation and to resolve their complex electronic structures. However, transition metal clusters already containing four magnetic centers with multiple unpaired electrons make conventional active space based strategies prohibitively expensive, due to their unfavorable scaling with the size of the active space. In this work, forefront techniques, such as density matrix renormalization group (DMRG), full configuration interaction quantum Monte Carlo (FCIQMC), and multiconfiguration pair-density functional theory (MCPDFT), are employed to overcome the computational limitation of conventional multireference approaches and to accurately investigate the magnetic interactions taking place in a [Co(II)3Er(III)(OR)4] (chemical formula [Co(II)3Er(III)(hmp)4(μ2-OAc)2(OH)3(H2O)], hmp = 2-(hydroxymethyl)-pyridine) model cubane water oxidation catalyst. Complete active spaces with up to 56 electrons in 56 orbitals have been constructed for the seven energetically lowest different spin states. Relative energies, local spin, and spin-spin correlation values are reported and provide crucial insights on the spin interactions for this model system, pivotal in the rationalization of the catalytic activity of this system in the water-splitting reaction. A ferromagnetic ground state is found with a very small, ∼50 cm-1, highest-to-lowest spin gap. Moreover, for the energetically lowest states, S = 3-6, the three Co(II) sites exhibit parallel aligned spins, and for the lower states, S = 0-2, two Co(II) sites retain strong parallel spin alignment.

Symmetries as the Guiding Principle for Flattening Bands of Dirac Fermions

Since the discovery of magic-angle twisted bilayer graphene, flat bands in Dirac materials have become a prominent platform for realizing strong correlation effects in electronic systems. Here we show that the symmetry group protecting the Dirac cone in such materials determines whether a Dirac band may be flattened by the tuning of a small number of parameters. We devise a criterion that, given a symmetry group, allows for the calculation of the number of parameters required to make the Dirac velocity vanish. This criterion is employed to study band flattening in twisted bilayer graphene and in surface states of 3D topological insulators. Following this discussion, we identify the symmetries under which the vanishing of the Dirac velocity implies the emergence of perfectly flat bands. Our analysis allows us to construct additional model Hamiltonians that display perfectly flat bands at certain points in the space of parameters: the first is a toy model of two coupled 3D topological insulator surfaces, and the second is a quasicrystalline generalization of the chiral model of twisted bilayer graphene.6 MoreReceived 11 June 2022Revised 6 March 2023Accepted 27 March 2023DOI:https://doi.org/10.1103/PhysRevX.13.021012Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectronic structurePhysical SystemsStrongly correlated systemsTopological insulatorsTopological materialsTwisted bilayer grapheneCondensed Matter, Materials & Applied Physics

Ecological response of land use change in a large opencast coal mine area of China

Land is the carrier of ecological environment, and the change of land use is bound to cause changes in many natural phenomena and ecological processes. In turn, the change of ecological environment will largely restrict the degree and direction of land use change in a certain region. With the development of current land use, the ecological response of regional land use has become a research hot spot. The study is mainly based on the improved remote sensing ecological index calculated by MATLAB software. The land use transfer matrix method is used to identify the transferred area and key land types, and spatial multiple regression analysis is used to establish the ecological response equation of key land types. The study provides a reference for land resource development and ecological environment protection in large opencast coal mining areas by quantitatively evaluating the land use change and ecological response process in the study area. The research results show that the remote sensing ecological index is mainly obtained through remote sensing technology, which has the advantages of easy parameter acquisition, large time series span, and wide evaluation range. The improved remote sensing ecological index can better quantitatively reflect the quality of the ecological environment in the study area. The calculation method is intuitive and clear, and has strong theoretical significance and reference function. The conceptual model of ecological response to land use change constructed on this basis can better reveal the dynamic process, action mechanism and changing trend of ecological response. The ecological environment quality of the study area is generally poor, and the ecological environment quality of the poor grade accounts for a large proportion. The change of land use from cultivated land to industrial and mining land is the Granger reason that leads to the decline of ecological environment quality in the study area, and the process of transformation has a strong negative correlation effect on ecological environment quality. Different land use types have different transfer processes and different losses to the quality of the ecological environment.

Variation of Strong Correlation Effects in A-site Ordered Perovskites CaCu3Ti4−xRuxO12: Photoemission and Inverse Photoemission Studies

We have systematically studied the strong correlation effects in A-site ordered perovskites CaCu3Ti4-xRuxO12 (x = 0, 1, 3.5, and 4) by using photoemission and inverse photoemission spectroscopies. In x = 0, 1, 3.5, the peak positions of the strongly correlated Cu 3d states around -3.8 eV and Ti 3d states around 3.6 eV little change. On the other hand, in x = 4, the Cu 3d states split into two peaks around -2.5 and -4 eV. These indicate that Ti plays an important role to retain the strong correlation effects. In addition, the multiplet structures of Cu 3d final states from -8 to -14 eV become weak as Ru increases, indicating the reduction of the localized characters of Cu 3d states. At the Fermi level, we observe the absence of spectral weight in x = 0, 1 and the development of Ru 4d in-gap states in x = 3.5, 4, which give rise to the metal-insulator transition between x = 1 and x = 3.5.

Selenizing Possibilities of Cu2HgSnS4—i.e., Cu2HgSn(SexS1−x)4 Compound Semiconductor: Potential Candidate for Solar Photovoltaics and Photodetectors

Using first-principles calculation with considering the strong correlation effect and spin–orbit coupling, Ambesh Dixit and co-workers (article number 2200524) studied the optoelectronics of selenium alloying in the Cu2HgSn(SexS1−x)4 compound. These compounds are found to span a range of bandgaps from visible (1.33 eV) to infrared (0.81 eV). The direct nature with a good absorption coefficient make them suitable for optical transitions, enabling photovoltaics (single or multijunction solar cells) and infrared photodetectors. Examining the mechanical properties, these are found stable with ductile character, which also opens the possibility for flexible absorber-based devices.

Origin of superconductivity in hole doped SrBiO3 bismuth oxide perovskite from parameter-free first-principles simulations

The recent discovery of nickel oxide superconductors have highlighted the importance of first-principles simulations for understanding the formation of the bound electrons at the core of superconductivity. Nevertheless, superconductivity in oxides is often ascribed to strong electronic correlation effects that density functional theory (DFT) cannot properly take into account, thereby disqualifying this technique. Being isostructural to nickel oxides, Sr1-xKxBiO3 superconductors form an ideal testbed for unveiling the lowest theory level needed to model complex superconductors and the underlying pairing mechanism yielding superconductivity. Here I show that parameter-free DFT simulations capture all the experimental features and related quantities of Sr1-xKxBiO3 superconductors, encompassing the prediction of an insulating to metal phase transition upon increasing the K doping content and of an electron-phonon coupling constant of 1.22 in sharp agreement with the experimental value of 1.3 ± 0.2. The proximity of a disproportionated phase is further demonstrated to be a prerequisite for superconductivity in bismuthates.

Customizing Radiative Decay Dynamics of Two-Dimensional Excitons via Position- and Polarization-Dependent Vacuum-Field Interference.

Embodying bosonic and interactive characteristics in two-dimensional space, excitons in transition metal dichalcogenides (TMDCs) have garnered considerable attention. The utilization of the strong-correlation effects, long-range transport, and valley-dependent properties requires customizing exciton decay dynamics. Vacuum-field manipulation allows radiative decay engineering without disturbing intrinsic material properties. However, conventional flat mirrors cannot customize the radiative decay landscape in TMDC's plane or support vacuum-field interference with desired spectrum and polarization properties. Here, we present a meta-mirror platform resolving the issues with more optical degrees of freedom. For neutral excitons of the monolayer MoSe2, the optical layout formed by meta-mirrors manipulated the radiative decay rate in space by 2 orders of magnitude and revealed the statistical correlation between emission intensity and spectral line width. Moreover, the anisotropic meta-mirror demonstrated polarization-dependent radiative decay control. Our platform would be promising to tailor two-dimensional distributions of lifetime, density, diffusion, and polarization of TMDC excitons in advanced opto-excitonic applications.

Manipulation and observation of atomic-scale superlattices in perovskite manganate

Superlattices in crystals, particularly in perovskite oxides with strong correlation effects, can create new states of matter and produce peculiar physicochemical phenomena. However, the newfangled perovskite superlattices depend on physical deposition with unit-cell precision. It has been challenging to explore a new suitable chemical method to tailor perovskite superlattices. Herein, we present a new bottom-up strategy to precisely prepare atomic-scale oxide superlattices of (LaMnO3)1-(La1-x-yCaxKyMnO3)2 in a monodispersed perovskite La0.66Ca0.29K0.05MnO3 (LCKMO). The special atomic-scale perovskite superlattices are demonstrated using SAED, HAADF-STEM, XRD, and atomic-resolution elemental mapping. Our experiments reveal that the perovskite superlattices can be fabricated under extreme hydrothermal conditions utilizing ultra-high concentrations of KOH. An approximate molten salt system in the hydrothermal process can induce the disproportionation reaction of MnO2 solids, which is vital to the growth of ordered perovskite superlattices. This work not only clarifies the hydrothermal growth process of perovskite oxides in extreme conditions, but also proposes a novel engineering route toward perovskite superlattices.

Steady-state Peierls transition in nanotube quantum simulator

Quantum dots placed along a vibrating nanotube provide a quantum simulation platform that can directly address the electron-phonon interaction. This offers promising prospects for the search of new quantum materials and the study of strong correlation effects. As this platform is naturally operated by coupling the dots to an electronic reservoir, state preparation is straightforwardly achieved by driving into the steady state. Here we show that for intermediate electron-phonon coupling strength, the system with spin-polarized quantum dots undergoes a Peierls transition into an insulating regime which exhibits charge-density wave order in the steady state as a consequence of the competition between electronic Coulomb repulsive interactions and phonon-induced attractive interactions. The transport phenomena can be directly observed as fingerprints of electronic correlations. We also present powerful methods to numerically capture the physics of such an open electron-phonon system at large numbers of phonons. Our work paves the way to study and detect correlated electron-phonon physics in the nanotube quantum simulator with current experimentally accessible techniques.

Effects of the surface termination and the oxygen vacancy position on LaNiO3 ultra-thin films: First-principles study

While ultra-thin layers of the ${\mathrm{LaNiO}}_{3}$ film exhibit a remarkable metal-insulator transition as the film thickness becomes smaller than a few unit cell (u.c.), the formation of possible oxygen vacancies and their effects on the correlated electronic structure have been rarely studied using first principles. Here, we investigate the effects of the surface termination and the oxygen vacancy position on the electronic properties and vacancy energetics of ${\mathrm{LaNiO}}_{3}$ ultra-thin films under the compressive strain using density functional theory plus U $(\mathrm{DFT}+\mathrm{U})$. We find that oxygen vacancies can be easily formed in the Ni layers with the ${\mathrm{NiO}}_{2}$ terminated surface (0.5 u.c. and 1.5 u.c. thickness) compared to the structures with the LaO terminated surface and the in-plane vacancy is energetically favored than the out-of-plane vacancy. When two vacancy sites are allowed, the Ni square plane geometry is energetically more stable in most cases as two oxygen vacancies tend to stay near a Ni ion. Strong anisotropy between the in-plane and out-of-plane vacancy formation as well as the layer and orbital dependent electronic structure occur due to strain, surface termination, charge reconstruction, and quantum confinement effects. The in-plane vacancy of the ${\mathrm{NiO}}_{2}$ terminated structure is favored since the released charge due to the oxygen vacancy can be easily accommodated in the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbital, which is less occupied than the ${d}_{{z}^{2}}$ orbital. Remarkably, the oxygen vacancy structure containing the Ni square-plane geometry becomes an insulating state in $\mathrm{DFT}+\mathrm{U}$ with a sizable band gap of 1.2 eV because the large crystal field splitting between ${d}_{{z}^{2}}$ and ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbitals in the square-plane favors an insulating state and the Mott insulating state is induced in other Ni sites due to strong electronic correlations. In the thin-film structure without oxygen vacancies, the strong correlation effect in $\mathrm{DFT}+\mathrm{U}$ drives a pseudogap ground state at the Fermi energy, similarly as the experimental photo-emission spectra; however, the variation of the $\mathrm{DFT}+\mathrm{U}$ electronic structure depending on the surface termination becomes weaker compared to those obtained in DFT.

Mottness in two-dimensional van der Waals Nb3X8 monolayers (X=Cl,Br,andI)

We investigate strong electron-electron correlation effects on two-dimensional van der Waals materials ${\mathrm{Nb}}_{3}{X}_{8} (X=\mathrm{Cl},\mathrm{Br},\phantom{\rule{0.28em}{0ex}}\text{and}\phantom{\rule{0.28em}{0ex}}\mathrm{I})$. We find that the monolayers ${\mathrm{Nb}}_{3}{X}_{8}$ are ideal systems close to the strong correlation limit. They can be described by a half-filled single band Hubbard model in which the ratio between the Hubbard, $U$, and the bandwidth, $W, U/W\ensuremath{\approx}5--10$. Both Mott and magnetic transitions of the material are calculated by the slave boson mean-field theory. Doping the Mott state, a ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}+i{d}_{xy}$ superconducting pairing instability is found. We also construct a tunable bilayer Hubbard system for two sliding ${\mathrm{Nb}}_{3}{X}_{8}$ layers. The bilayer system displays a crossover between the band insulator and Mott insulator.

Kondo resonance effects in emergent flat band materials

Macroscopic degrees of freedom that are involved in the transport of carriers through mesoscopic electronic devices are susceptible to the effects of strong many-body correlations. The presence of magnetic impurities in dilute magnetic alloys typically allow for insights into Kondo effect from the scattering of free carriers by localized electron states of the magnetic impurities but this effect is not well understood when there are no d-band electron states. Herein, the signatures of Kondo resonance effect are elucidated in quantum dots derived from a carbon-nanoline embedded monolayer hexagonal boron nitride whose electron states host flat band ferromagnetism as distinct broken symmetry states. Quantum transport state of mesoscopic devices modelled as quantum dots tunnel coupled to metallic leads is computed by direct diagonalization of the Hamiltonian. The possibility of realizing quantum dots with highly tunable electron states in energy interconversion devices is discussed to show the importance of screening effects on single-electron energy levels. The quantum master equation is solved within different formalisms to determine the stationary-state particle and energy currents. Stability diagrams are calculated to show the dependence of the conductance on experimental control variables of the quantum dot device. The computed responses of the stationary-state transport signatures are used to characterize Kondo resonance effects from flat band states of embedded carbon nanoline-based quantum dots. It is found that the local network structure of the hexagonal ring carbon cluster-based quantum dot has a broken particle-hole symmetry in the transport state. This signals the formation of the quasiparticle states expected in second order scattering when the macroscopic “charge” pseudospin symmetry of the tunnelling electron state is broken dynamically due to charging. The results are discussed to show the implications of a vanishing particle-hole symmetry in the carrier transport state of quantum dots for energy conversion applications.

Tunable anomalous valley Hall effect and magnetic phase transition in MHfN2Cl2 (M = V, Cr) bimetallic nitrogen halide monolayers

Transition metal nitrogen halides (TMNHs) are environmentally friendly and widely studied van der Waals two-dimension (2D) materials. However, there are still few 2D TMNHs with magnetic properties that have been synthesized, which greatly limits the further applications of them in spintronics and valleytronics. Here, we substitute Hf atoms by magnetic elements V and Cr in β-type TMNHs Hf2N2Cl2, which evolved into ferromagnetic half-metals and ferrovalley semiconductors MHfN2Cl2 (M = V, Cr). Meanwhile, the valley splitting (VS) properties and magnetic properties can be effectively regulated by modulating the strong correlation effect of transition metals and applying biaxial strain. VS in VHfN2Cl2 increases linearly with the increasing strain and the U value; however, VS is robust to the strain and decreases linearly with the increasing U value in CrHfN2Cl2, and the maximum VS reaches to 175 and 62 meV for the two monolayers. CrHfN2Cl2 remains robustly ferromagnetic under different strain and U values, while there is magnetic phase transition in VHfN2Cl2 from ferromagnetic to antiferromagnetic, accompanied by a half-metal-to-semiconductor transition. The Curie temperatures of VHfN2Cl2 and CrHfN2Cl2 can be increased by a maximum of 2.5 and 2.36 times under modulation. This opens different ideas for the study of bimetallic TMNHs in spintronics and valleytronics.

Topological phase transitions in Tl<sub>2</sub>Ta<sub>2</sub>O<sub>7 </sub> under strain regulation

Topological electronic materials exhibit many novel physical properties, such as low dissipation transport and high carrier mobility. These extraordinary properties originate from their non-trivial topological electronic structures in momentum space. In recent years, topological phase transitions based on topological electronic materials have gradually become one of the hot topics in condensed matter physics. Using first-principles calculations, we explore the topological phase transitions driven by in-plane strain in ternary pyrochlore oxide Tl<sub>2</sub>Ta<sub>2</sub>O<sub>7</sub>. Firstly, we analyze the atomic-orbital-resolved band structure and find that the O (p<sub><i>x</i></sub>+p<sub><i>y</i></sub>) and p<sub><i>z</i></sub> orbitals of the system near the Fermi level have band inversion, indicating the emergence of topological phase transitions in the system. Then the tight-binding models are constructed to calculate the <i>Z</i><sub>2</sub> topological invariants, which can determine the topologically non-trivial feature of the system. Finally, topological properties such as surface states and a three-dimensional Dirac cone are studied. It is found that Tl<sub>2</sub>Ta<sub>2</sub>O<sub>7</sub> without strain is a semimetal with a quadratic band touching point at Fermi level, while the in-plane strain can drive the topological phase transition via breaking crystalline symmetries. When the system is under the –1% in-plane compression strain and without considering the spin orbit coupling (SOC), the application of strain results in two triply degenerate nodal points formed in the –<i>Z</i> to <i>Γ</i> direction and <i>Γ</i> to <i>Z</i> direction, respectively. When the SOC is included, there are two fourfold degenerate Dirac points on the –<i>Z</i> to <i>Γ</i> path and <i>Γ</i> to <i>Z</i> path<i>,</i> respectively. Thus, the –1% in-plane compression strain makes the system transit from the quadratic contact point semimetal to a Dirac semimetal. When 1% in-plane expansion strain is applied and the SOC is neglected, there exists one band intersection along <i>Y→</i><i>Γ</i>. When the SOC is taken into consideration, the gap is opened. Therefore, the 1% in-plane expansion strain drives Tl<sub>2</sub>Ta<sub>2</sub>O<sub>7</sub> into a strong topological insulator. In addition, the system is also expected to have strong correlation effect and superconductivity due to the possible flat band. This work can guide the study of topological phase transitions in three-dimensional materials and provide a good material platform for the design of low-dissipation electronic devices.