Abstract
Transition metal dichalcogenides (TMDs) WTe_{2} and MoTe_{2} with orthorhombic Td phase, being potential candidates as typeII Weyl semimetals, are attracted much attention recently. Here we synthesized a series of miscible Mo_{1−x}W_{x}Te_{2} single crystals by bromine vapor transport method. Compositiondependent Xray diffraction and Raman spectroscopy, as well as composition and temperaturedependent resistivity prove that the tunable crystal structure (from hexagonal (2H), monoclinic (β) to orthorhombic (Td) phase) can be realized by increasing W content in Mo_{1−x}W_{x}Te_{2}. Simultaneously the electrical property gradually evolves from semiconductor to semimetal behavior. Temperaturedependent Raman spectroscopy proves that temperature also can induce the structural phase transition from β to Td phase in Mo_{1−x}W_{x}Te_{2} crystals. Based on aforementioned characterizations, we map out the temperature and composition dependent phase diagram of Mo_{1−x}W_{x}Te_{2} system. In addition, a series of electrical parameters, such as carrier type, carrier concentration and mobility, have also been presented. This work offers a scheme to accurately control structural phase in Mo_{1−x}W_{x}Te_{2} system, which can be used to explore typeII Weyl semimetal, as well as temperature/composition controlled topological phase transition therein.
Introduction
Recently, layered transition metal dichalcogenides (TMDs) materials have attracted extensive attention because of their superior properties, for example, large thermoelectric effect in TiSe_{2} at room temperature^{1}, superconductivity^{2}, charge density waves^{3}, extremely large magnetoresistance in WTe_{2}^{4}, topological phase^{5,6} and nextgeneration (opto) electronics devices^{7,8}. Among these transition metal dichalcogenides, hereafter we focus on Mo_{1−x}W_{x} (Te, Se, S)_{2} compounds.
Mo_{1−x}W_{x}(S, Se, Te)_{2} compounds demonstrate a rich crystal structures and diversified physical properties^{9,10,11,12}. In the viewpoint of crystal structure, Mo_{1−x}W_{x} (Te, Se, S)_{2} can crystallize into three phases under different experimental conditions, including 2H (hexagonal, space group P63/mmc), Td (orthorhombic, space group Pmn2_{1}) and βphase (monoclinic, space group P2_{1}/m), as shown in Fig. 1(a)^{13}. The common structure of MoTe_{2} is 2Hphase, while the WTe_{2} is normally taken Tdphase. The βphase MoTe_{2}, a metastable phase, can also be obtained by quenching method at high temperature of about 1173 K^{14,15}. It has the inversion symmetry which does not in Td phase. In addition, these phases may be changed under thermal agitation, for example, MoTe_{2} has a firstorder structural phase transition (around 250 K) from the β to the Td polytype^{15,16}. In the viewpoint of physical properties, generally speaking, the 2H phase is a semiconductor, but Td and β phase are semimetallic. For example, 2Hphase Mo_{1−x}W_{x}S_{2} and Mo_{1−x}W_{x}Se_{2} are semiconductors whose electronic band gap can be continuously tuned by alloy^{9,10,11,12}. While, MoTe_{2} compounds with β and Td phase show the metallic conductivity. It should be emphasized that both MoTe_{2} and WTe_{2} with Td phase belong to a typeII topological Weyl semimetal according to recent theoretical predictions^{17,18}. The condensed matter physics counterparts of Weyl fermions have been realized firstly in typeI Weyl semimetals in the TaAs family^{19,20,21,22}. Different from typeI Weyl semimetal, Dirac cone in typeII Weyl semimetal is tilted^{17,18}. Currently, several angleresolved photoemission spectroscopy and transport works have claimed to observe the Fermi arc and tilted Dirac cones in typeII Weyl semimetals of WTe_{2} and MoTe_{2}^{23,24,25,26,27,28}. In addition, Mo_{1−x}W_{x}Te_{2} can demonstrate the topological phase transition under thermal agitation or alloy. For example, the length of Fermi arc in Td phase WTe_{2} is tunable by temperatures or by Moalloy as theoretically predicted^{29,30}.
Here we summarized the previous effort to elucidate the phase transition in Mo_{1−x}W_{x}Te_{2}. For βMoTe_{2}, there is a phase transition from the β to the Td polytype at about 250 K in βMoTe_{2}^{15,16}. It is worthwhile to mention that the Tdphase is an important candidate to materialize the newly predicted typeII Weyl semimetal. TypeII Weyl semimetals have a series of novel physical properties, such as anisotropic negative magentoresistance, topological anomalous Hall effect^{17,18}. The transition from β to Tdphase is also characterized by the temperaturedependent XRD^{31,32}, as well as temperaturedependent Raman spectroscopy^{33,34}. However, the existence of orthorhombic Td phase MoTe_{2} is still under hot debate because it is quite challenging to directly distinguish the subtle differences between the Td and β phase. As for the Mo_{1−x}W_{x}Te_{2} system, there are some experimental studies on ceramic samples^{35,36} and theoretical predictions on monolayers^{37,38}, but no any phasetransitions works for single crystal samples at present, to the best of our knowledge.
Based on abovementioned discussions, it is quite crucial to map out the phase diagram of Mo_{1−x}W_{x}Te_{2} at different temperature and their corresponding electrical properties in order to explore the typeII topological Weyl semimetals and corresponding novel physical properties in this system. Here, we synthesized a series of Mo_{1−x}W_{x}Te_{2} single crystals by the chemical vapour transport method. Xray diffraction and chemical composition analysis confirm that the obtained samples have single crystalline quality, in which the Mo and W elements are miscible. The compositiondependent and temperaturedependent phase evolutions in Mo_{1−x}W_{x}Te_{2} are determined by Raman spectroscopic characterization. These characterizations substantiate that by increasing the W composition, the crystal structure of Mo_{1−x}W_{x}Te_{2} gradually changes from 2H, β to Td phase^{13}. Simultaneously, the electrical properties gradually evolve from semiconductor to semimetal behavior revealed by temperaturedependent resistivity and Hall curves. Based on these data, we also map out the composition and temperaturedependent phase diagram of Mo_{1−x}W_{x}Te_{2} system.
Methods
Crystal Growth
A series of Mo_{1−x}W_{x}Te_{2} single crystals were prepared by the chemical vapor transport (CVT) method that is discussed in detail elsewhere^{39}. Figure 1(b) shows a schematic of the doublezone CVT growth furnace with wellcontrolled temperature. The singlecrystal growth procedure includes two steps. Firstly, all Mo_{1−x}W_{x}Te_{2} polycrystalline samples were synthesized by heating a stoichiometric mixture of high purity elemental powders W (Alfa Aesar 99.99%), Mo (Alfa Aesar 99.99%) and Te (Alfa Aesar 99.999%) by solid state reaction at 1073 K in evacuated quartz tubes. Secondly, Mo_{1−x}W_{x}Te_{2} crystals were grown by CVT method using Br_{2} (about 5 mg/mL) as transport agent in the sealed evacuated quartz tube at a double zone furnace. By means of optimized the growth parameters, large size (centimetrelevel) and highquality crystals with regular shape can be obtained. The βMoTe_{2} crystals can be grown at high temperature profile of 1173~1273 K. The growth quartz tube was quenched in ice water to yield the hightemperature β phase. And 2HMoTe_{2} and TdWTe_{2} crystals were obtained with a temperature profile of 1023~1123 K using usual cooling treatment (100 K/h) without quenching.
Material Characterization
The elemental compositions of the samples were determined by energy dispersive Xray spectroscopy (EDS) analysis conducted on an FEI Quanta 200 FEG environmental scanning electron microscope (SEM). Xray diffraction (XRD) measurements were performed on the crystals using an Xray diffractometer (Ultima III Rigaku, CuK_{α} radiation as an Xray source). The scanning rate of 3° per minute and 2θ scanned from 10° to 70° were used to collect XRD data. Raman spectra were taken by a backscattering geometry on a LabRam HR800 Microscope system (Horiba Jobin Yvon), using the 633 nm a HeNe laser as an optical source. Standard fourprobe technique was used for resistivity and Halleffect measurements on a Quantum Design PPMS9.
The density functional theory (DFT) Calculation
The Raman frequencies of MoTe_{2} and WTe_{2} for different structures were calculated by DFT in the generalized gradient approximation implemented in the Vienna Abinitio Simulation Package (VASP) code^{40,41} and the Phonopy software^{42}. The projected augmented wave method^{43,44} and the van der Waals corrected optB86bvdw functional^{45,46} are used. The planewave cutoff energy is 500 eV throughout the calculations. The k point mesh is 12 × 12 × 4 for the 2H phase and 8 × 14 × 4 for the β and Tdphase. The atom positions and lattice constants are optimized until the maximal residual force is less than 0.002 eV/Å. The optimized lattice constants are very well consistent with the reported values which are shown in Table S1 at Supplementary Information.
Results and Discussion
Figure 1(c) depicts the SEM images of the asgrown Mo_{0.5}W_{0.5}Te_{2} crystals and the corresponding EDS mapping of Mo, W and Te elements, respectively. As can be seen, the three elements are uniformly distributed in the sample, strongly suggesting the growth is homogeneous. The composition analysis substantiates that the composition ratio between Mo and W in this sample is 1.00:1.02, which is in agreement to the designed chemical compositions. All the EDS spectra of the asgrown Mo_{1−x}W_{x}Te_{2} crystals are depicted in Fig. S1. The elemental compositions of all the crystal samples and cross section used in EDS analysis are shown in Table II and III in Supplementary Information. The XRD patterns of single crystal samples are presented in Fig. 1(d). All peaks indexed as the (0 0 2k) reflections, indicating that the exposed surfaces of the crystals belong to cplane. The fullwidth at half maximum of Mo_{1−x}W_{x}Te_{2} (002 pole) series samples varies from 0.07° to 0.09°, which infers the asgrown single crystals have high crystalline quality. In order to show the effect of isovalent substitution on the crystal structure clearly, we enlarge of the series (002) peaks in Fig. 1(e) for all Mo_{1−x}W_{x}Te_{2} samples. It is evident that there are three continuous change regimes (x = 0~0.07, 0.10~0.50, and 0.70~1, respectively), which implies there may be three different phases. This may be due to the different lattice parameter c of 2HMoTe_{2}, βMoTe_{2} and TdWTe_{2} (13.97, 13.86, and 14.07 Å, respectively) that causes the angleshift of the (002)peaks^{13}. In addition, we also can see that the diffraction peaks gradually shift to lower angle degree with increasing x within each concentration range. This is because that the lattice parameter c changes large due to the ionic radius of W^{4+} (0.66 Å) being larger than that of Mo^{4+} ions (0.65 Å)^{39,47}. But, by careful inspection, we find that from x = 0.08 to 0.10 and from x = 0.50 to 0.70, the diffraction (002) peaks gradually shift to higher angle degree with increasing x (W composition). The estimated caxis lattice parameter d_{c} as a function of x for Mo_{1−x}W_{x}Te_{2} system and βMoTe_{2} is given as Fig. S2 at Supplementary Information. So it may be reasonable to conclude that the phase transitions occur from x = 0.08 to 0.1 and from x = 0.50 to 0.70. Crystal structures of Mo_{1−x}W_{x}Te_{2} compounds change from 2H, β to Td phase with increasing x.
In order to substantiate the compositiondependent structure phase transitions, Raman spectra measurements were further used to characterize these single crystals at room temperature. Figure 2 shows the normalized unpolarized Raman spectra from the ab plane of the asgrown Mo_{1−x}W_{x}Te_{2} single crystalline samples and the Raman spectrum of pure βMoTe_{2} obtained from high temperature quenching (upmost in Fig. 2). Obviously, there are three different types of Raman spectra mapped to different x range (0~0.09, 0.10~0.50, and 0.70~1, respectively) and the Raman spectrum of βMoTe_{2} (upmost) is in good agreement with that of x from 0.1 to 0.50. These general trends are in agreement to XRD results.
To understand the Raman modes of different crystalline phases in the Mo_{1−x}W_{x}Te_{2} system, we also calculated the Raman frequencies by the DFT and the results are well consistent with the experimental one (see Fig. S3 at Supplementary Information). According to the group theory analysis, the irreducible representations of the phonons in bulk 2HMoTe_{2} ( point group) at the center (Γ point) of the Brillouin zone (BZ) are , where E_{2g} (24.993 and 230.043 cm^{−1}), E_{1g} (116.540 cm^{−1}), A_{1g} (171.893 cm^{−1}) are Ramanactive. In bulk βMoTe_{2} or WTe_{2} (), the calculated phonon modes at the Γ point include , where there are 18 Raman active phonon modes (12A_{g} + 6B_{g}), as shown in Fig. S3. Bulk TdMoTe_{2} and TdWTe_{2} both belong to the point group, the group theory analysis indicates that the BZcenter vibration modes decompose into 36 onedimensional irreducible representations: , where all modes are Raman active (see Fig. S3). All the above calculation results are in agreement with the previous theoretical works^{48,49,50}.
To analyse the Raman results of Mo_{1−x}W_{x}Te_{2} compounds, the Raman results of some pure phases are mentioned here firstly. As depicted in Fig. 2, in Raman spectra measurements of 2HMoTe_{2} (the bottom black line), we detect two sharp peaks at 172.8 and 232.9 cm^{−1} which are attributed to the A_{1g} and E_{2g} modes, respectively. For βMoTe_{2} crystals (see upmost line of Fig. 2), we observe six Raman peaks at around 78.0, 88.0, 94.0, 127.4, 162.2 and 256.8 cm^{−1}, associated with the A_{g} and B_{g} modes, respectively. And in the Raman spectrum of TdWTe_{2} (the second line from the top in Fig. 2), there are eight peaks centred at 80.2, 90.0, 111.3, 116.2, 131.7, 133.5, 162.8 and 210.3 cm^{−1}, respectively, which are ascribed to the A_{1} and A_{2} modes. These experimental Raman frequencies are very well reproduced by our DFT calculations (see Fig. S3 in Supplementary Information).
Using the abovementioned Raman data in the pure phases, we can track the compositiondependent structure evolution in the whole Mo_{1−x}W_{x}Te_{2} systems. The evolutions of the prominent Raman peaks for different x in three frequencyranges are plotted in Fig. 3(a–c). And the corresponding shifts of these peaks as functions of x are summarized in Fig. 3(d), respectively. We compare the Raman active modes of the three phases, two prominent peaks, A_{1g} (near 171.893 cm^{−1}) and E_{2g} (near 230.043 cm^{−1}), in the 2H phase spectra are assigned as fingerprint peaks. Because there are no Raman active modes near the above two positions in β and Td phases. As shown in Fig. 3(a), from x = 0 to 0.09, two prominent peaks were observed at about 173 and 233 cm^{−1}, respectively. These two peaks are related to the A_{1g} and E_{2g} modes of 2HMoX_{2}, confirming the corresponding samples being 2H phase. Figure 3(d) indicates that there is no noticeable frequency change of the two peaks with the x composition increased from 0 to 0.09. But the intensity and fullwidthat halfmaximum of A_{1g} and E_{2g} mode in 2H phase are irregularly dependent on Wconcentration, whose mechanism will be explored in the near future. It also should be mentioned that according to a previous report^{51}, the Raman spectrum was strongly dependent on electron/hole doping in single layered MoS_{2}. In that case, Fermi level adjustment should affect electron/hole concentration, which will in turns affect the electronphonon scattering and Raman peaks. Different from this scenario, isovalence Wdoping to Mo in our samples does not induce significantly the electron/hole concentration, therefore the peaks of A_{1g} and E_{2g} have not obviously changed as shown in Fig. 3(d).
According to the previous works^{33,34}, the evolution of the Raman mode at near 130 cm^{−1} is a direct verification of the structural phase transition of MoTe_{2} from high temperature β to low temperature Td phase. In addition, there are different Raman signals for β and Tdphase at the range of 150~300 cm^{−1}. Here we used peaks from 120 to 300 cm^{−1} to determine the βTd phase transition. The Raman peaks around 130 cm^{−1}, and those from 150 to 300 cm^{−1} are enlarged in Fig. 3(b) and (c) for βMoTe_{2} and the Mo_{1−x}W_{x}Te_{2} (x = 0.1~1.0), respectively. We can see that from x = 0.1 to 0.5 there is only one peak found near 127 cm^{−1} in the Raman spectra between 120~150 cm^{−1}, as well as βMoTe_{2} (see Fig. 3(bI)). The position of this peak exhibits slight redshift compared with that of βMoTe_{2} (see Fig. 3(d)). There are also two peaks found at around 162 and 257 cm^{−1} in the Raman spectra of Mo_{1−x}W_{x}Te_{2} crystals (x = 0.1~0.5) (see Fig. 3(bII)), which agree to the Raman signal (A_{g} modes) of βMoTe_{2}. From Fig. 3(d), it can be seen that the positions of the peaks (162 and 257 cm^{−1}) exhibit slight blueshift compared with that of βMoTe_{2}. The above results infer that these samples within x = 0.1~0.5 may belong to βphase. On the other hand, when x changed into the range of 0.7–1.0, we find a multiple peak at around 130 cm^{−1} in the Raman spectra between 120~150 cm^{−1} (shown in Fig. 3(cI)). The whole peak is fitted by the Lorentz function. As shown in Fig. 3(cI), the experimental peaks can be fitted with two Lorentz line shapes with central peaks at approximately 130 and 133 cm^{−1}, respectively. It suggests that the compound structure change from β to Td phase and the Mo_{1−x}W_{x}Te_{2} samples with x ranged from 0.7 to 1.0 have Td structure. Compared with pure TdWTe_{2}, the positions of the two peaks (near 130 and 133 cm^{−1}) in all other samples exhibit redshift and the difference is increased gradually with Mo composition increased (see Fig. 3(d)). In addition, from x = 0.7 to 1, we detect another two peaks at around 162 and 210 cm^{−1} in the Raman spectra measurements (shown in Fig. 3(c)II), confirming all the Mo_{1−x}W_{x}Te_{2} samples (x = 0.7~1) belong to Td phase too. The positions of the two peaks in all other samples exhibit redshift compared to pure TdWTe_{2} (see Fig. 3(d)).
It is worth mentioning the Raman spectra of Mo_{0.7}W_{0.3}Te_{2}, Mo_{0.5}W_{0.5}Te_{2} and M_{0.3}W_{0.7}Te_{2} are enlarged in Fig. S4. In Mo_{0.5}W_{0.5}Te_{2}, except the characteristic peaks of β phase, there is a very weak peak around 210 cm^{−1}, which is likely to be related to the Raman signal of the A_{1} modes of Td phase^{33}. And broad Raman peak at around 130 cm^{−1} of Mo_{0.5}W_{0.5}Te_{2} also could be approximately as overlap of multiple peaks. These results indicate that Mo_{0.5}W_{0.5}Te_{2} have mixture of β and Tdphase. In addition, a lowintensity peak around 264 cm^{−1} is observed in the Mo_{0.3}W_{0.7}Te_{2} Raman spectrum, which is contributed to the Raman signal of the A_{g} modes in βMoTe_{2}. It suggests that around x = 0.7, the phase can be approximately changed into β phase. Based on abovementioned analysis, we conclude that the samples with x range of 0~0.09, 0.10~0.50, and 0.70~1, belong to 2H, β and Td phase, respectively. And at the range of x = 0.5~0.7, the phase of Mo_{1−x}W_{x}Te_{2} can be ascribed to be a mixing phase of β and Td. The critical compositions of phase transition in the Mo_{1−x}W_{x}Te_{2} system are approximately located at around x = 0.1 and 0.5, respectively.
Except the compositiondependent structure phase transition, we further characterized the temperaturedependent structure phase transition in Mo_{1−x}W_{x}Te_{2} compounds. As shown in Fig. 4(a) and (b), with decreasing the temperature of 2HMoTe_{2} and TdWTe_{2} samples from 300 to 100 K, no new Raman peaks appear although all peaks exhibit different blueshift. This result implies that no temperature phase transition occurs in 2HMoTe_{2} and TdWTe_{2} systems at lowtemperature range under atmospheric pressure. In Fig. 4(c), we present temperaturedependent Raman spectra for βMoTe_{2} at the range between 100~300 K. One can see the intensity of all peaks is strengthened although the magnitude of the blueshift is different. Surprisingly, at around 240 K, the Raman peaks of 129 cm^{−1} become two new peaks at about 127 and 132 cm^{−1}, respectively, reaching the maximum intensity below 200 K, as highlighted in pink wireframe. In accordance with previous analysis^{33,34} and our calculation results, the two new Raman peaks occur only at the low temperature Td phase in the Mo_{1−x}W_{x}Te_{2} system. It suggests that splitting of this Raman peak may infer the structural phase transition in βMoTe_{2}. In order to verify the lowtemperature phase transition, we also characterized the temperature dependence Raman spectra on Mo_{0.9}W_{0.1}Te_{2} of β phase. The evolution of the peak 129 cm^{−1} is shown in Fig. 4(d). Upon cooling, the peak develops into two new Raman peaks at about 280 K, confirming that the two sample change from high temperature β to low temperature Td phase.
Based on the above analysis, we plot a structural phase diagram of Mo_{1−x}W_{x}Te_{2} as functions of composition x and the temperature in Fig. 5. It is evident that 2 H phase appears in a composition range from x = 0 to 0.09 at room temperature and pure 2HMoTe_{2} transforms into the hightemperature phase βMoTe_{2} at about 1173 K^{14,15}. β phase exists in a composition range of x = 0.1~0.5 at room temperature and would change from β to low temperature Td phase at 240~300 K. Td phase is a candidate of typeII Weyl semimetal, so the corresponding phase transition can be designated as the temperatureinduced topological phase transition. In the Mo_{1−x}W_{x}Te_{2} alloys, Td phase (a candidate of typeII Weyl semimetal) lies in a composition x range of 0.7~1, but they have no temperaturedependent phase transitions. In addition, at the range of x = 0.5~0.7, the phase of Mo_{1−x}W_{x}Te_{2} can be described as a mixing phase of β and Td.
The electrical properties of the Mo_{1−x}W_{x}Te_{2} compounds were also characterized. As shown in Fig. 6(a), from x = 0 to 0.09, the Mo_{1−x}W_{x}Te_{2} samples all show the semiconductor behavior. While the other Mo_{1−x}W_{x}Te_{2} samples with a composition range of x = 0.1~1 and βMoTe_{2} samples show the semimetallic behavior as presented in Fig. 6(b). Interestingly, for βMoTe_{2} and Mo_{0.9}W_{0.1}Te_{2}, obvious electrical resistivity anomalies are observed at 250 and 230 K respectively, which are associated with the structural phase transition from the β to Td phase. However, there are no resistivity anomaly appeared in the temperaturedependentresistivity curves of Mo_{1−x}W_{x}Te_{2} samples (x = 0.15~0.50). In addition, the resistivity of TdWTe_{2} below 71 K (see upper inset of Fig. 6(c)) can be well fitted by
where ρ_{0} is the resistivity at 0 K and A is constant. It suggests that electrons in TdWTe_{2} at low temperature can be well described by Landau Fermi liquid theory. The temperature dependent resistance of TdWTe_{2} indeed shows a transition (T^{*}) from linear behaviour originating from the electronphonon coupling at high temperatures to the Landau Fermi liquid behaviour with dominant electronelectron scattering at low temperatures^{52}. With the same method, we fitted the temperaturedependent resistivity of the other metallic phase samples. As shown in Fig. 6(c), it is found that upon raising the Mo concentration, T^{*} of these samples gradually decreases, compared with TdWTe_{2}. And the T^{*} of βMoTe_{2} is 75 K. The calculation procedure of carrier concentrations and carrier mobilities is shown in Supplementary Information. Figure 6(d) summarized compositiondependent of the abplane resistivities (I), carrier concentration (II) and mobility (III) of Mo_{1−x}W_{x}Te_{2} single crystals measured at the room temperature. One can see, with increasing x, the abplane resistivity gradually decreases, the carrier concentration first increases and then rapidly decreases, while the mobility first decreases and then increases. Quantitatively, the abplane resistivities of 2HMoTe_{2}, βMoTe_{2}, and TdWTe_{2} are 0.5, 1.0 × 10^{−3} and 3.4 × 10^{−4} Ω·cm, respectively. The carrier concentrations are 4.0 × 10^{17}, 1.4 × 10^{21} and 3.0 × 10^{20} cm^{−3}, respectively. And the mobilities are 32.2, 4.1, and 61.9 cm^{2}V^{−1}s^{−1}, respectively.
Conclusions
In conclusion, we successfully synthesized a series of Mo_{1−x}W_{x}Te_{2} single crystals. By means of XRD, Raman spectroscopy, and DFT calculations, we find that by increasing the W composition (x), the structure gradually changes from 2H, β to typeII Weyl semimetal Td phase. By changing temperature, the high temperature βphase of Mo_{1−x}W_{x}Te_{2} is evolved to low temperature Tdphase. Accordingly, temperaturedependent and compositiondependent phase diagram of Mo_{1−x}W_{x}Te_{2} is proposed. Simultaneously, the electrical property gradually evolves from semiconductor in 2H phase to semimetal β phase then to semimetal Td phase. This work provides a useful map to explore the typeII topological Weyl semimetal phase and temperature/compositiondependent topological phase transition, as well as the corresponding novel physical properties in Mo_{1−x}W_{x}Te_{2} compounds.
Additional Information
How to cite this article: Lv, Y.Y. et al. Composition and temperaturedependent phase transition in miscible Mo_{1x}W_{x}Te_{2} single crystals. Sci. Rep. 7, 44587; doi: 10.1038/srep44587 (2017).
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Acknowledgements
We’d like to acknowledge the financial support from the National Basic Research Program of China (973 Program) (2015CB921203 and 2013CB632702), the National Natural Science Foundation of China (51032003, 51472112, 11374149, 91622122, 11474150 and 10974083), and the Program for New Century Excellent Talents in University (NCET090451). Y.Y.L. acknowledges the financial support from the Graduate Innovation Fund of Nanjing University (2015CL11). We also acknowledge the support for the computational resources by the High Performance Computing Center of Nanjing University.
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S.H.Y. and Y.Y.L. performed the crystal growth in assist of D.J.L. and B.P. Y.Y.L., C.L., K.W. and L.G.M. did the EDS analyses, XRD measurements and Raman spectra of the crystals. Y.Y.L., X.L. and B.B.Z. conducted the transport measurements. S.H.Y., J.Z. and Y.Y.L analyzed the data and refined the measurements. Y.B.C., Y.F.C. and Y.L.C. contributed to the result analysis. J.Z. did the density functional theory calculations. Y.Y.L., S.H.Y. and J.Z. cowrote the manuscript. M.H.L., Y.B.C., W.C.L. and S.T.D. revised the manuscript. All authors discussed the results and commented on the manuscript.
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Correspondence to ShuHua Yao or Jian Zhou or Y. B. Chen.
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Lv, Y., Cao, L., Li, X. et al. Composition and temperaturedependent phase transition in miscible Mo_{1−x}W_{x}Te_{2} single crystals. Sci Rep 7, 44587 (2017) doi:10.1038/srep44587
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