MoTe2 is an exfoliable transition metal dichalcogenide (TMD) which crystallizes in three symmetries; the semiconducting trigonal-prismatic 2H−phase, the semimetallic 1T ′ monoclinic phase, and the semimetallic orthorhombic T d structure 1-4 . The 2H−phase displays a band gap of ∼ 1 eV 5 making it appealing for flexible and transparent optoelectronics. The T d−phase is predicted to possess unique topological properties 6-9 which might lead to topologically protected non-dissipative transport channels 9 . Recently, it was argued that it is possible to locally induce phasetransformations in TMDs 3,10,11,14 , through chemical doping 12 , local heating 13 , or electric-field 14,15 to achieve ohmic contacts or to induce useful functionalities such as electronic phase-change memory elements 11 . The combination of semiconducting and topological elements based upon the same compound, might produce a new generation of high performance, low dissipation optoelectronic elements. Here, we show that it is possible to engineer the phases of MoTe2 through W substitution by unveiling the phase-diagram of the Mo1−xWxTe2 solid solution which displays a semiconducting to semimetallic transition as a function of x. We find that only ∼ 8 % of W stabilizes the T d−phase at room temperature. Photoemission spectroscopy, indicates that this phase possesses a Fermi surface akin to that of WTe2 16 .The properties of semiconducting and of semimetallic MoTe 2 are of fundamental interest in their own right, but are also for their potential technological relevance. In the mono-or few-layer limit it is a direct-gap semiconductor, while the bulk has an indirect bandgap 5,17,18 of ∼ 1 eV. The size of the gap is similar to that of Si, making 2H−MoTe 2 particularly appealing for both purely electronic devices 19,20 and optoelectronic applications 21 . Moreover, the existence of different phases opens up the possibility for many novel devices and architectures. For example, controlled conversion of the 1T ′ −MoTe 2 phase to the 2H−phase, as recently reported 22 , could

In this study, a facile and inexpensive and self-assembled strategy to massively fabricate Ni/Co layered double hydroxides (LDHs) is developed under mild reaction conditions (55 °C). The resulting composite material displays a special three-dimensional hierarchical microsphere structure with well-defined flower-like configuration. The fabrication mechanism can be ascribed to stepwise and regular reaction process of nanoparticles and nanosheets gradually growing to nanopetals and then assembling into flower-like microspheres, based on the systematically investigation of various reaction factors including the Ni:Co feeding ratio, the reaction time and the initial pH-value. Because of its large surface, ultrathin feature and synergetic results of this Ni/Co LDHs nanosheets (20 nm), these Ni/Co-LDHs microspheres deliver an excellent capacitance value about 2228 F·g(-1) (1 A·g(-1)). An all-solid-state flexible asymmetric supercapacitor is designed and assembled by exploiting this Ni/Co-LDHs as the positive materials, which exhibits energy density of 165.51 Wh·kg(1-) at 1.53 KW·kg(1-). It may have vast potential significance in personal wearable equipment. Moreover, this monolithic design provides a promising approach for large scale fabrication of other LDHs materials.

We have performed polarized Raman scattering measurements on WTe2, for which an extremely large positive magnetoresistance has been reported recently. We observe 5 A1 phonon modes and 2 A2 phonon modes out of 33 Raman active modes, with frequencies in good accordance with firstprinciples calculations. The angular dependence of the intensity of the peaks observed is consistent with the Raman tensors of the C2v point group symmetry attributed to WTe2. Although the phonon spectra suggest neither strong electron-phonon nor spin-phonon coupling, the intensity of the A1 phonon mode at 160.6 cm −1 shows an unconventional decrease with temperature decreasing, for which the origin remains unclear.PACS numbers: 74.70. Xa, 75.47.De, 74.25.Kc Giant magnetoresistance is at the core of several important applications, notably for the storage of information. The recent discovery of extremely large positive magnetoresistance (XMR) in layered WTe 2 [1] triggered sudden interest for this material. In particular, the nonsaturating XMR in WTe 2 has been attributed to perfectly balanced electron-hole populations [1,2], similar as in pure bismuth and graphite [3,4]. Interestingly, this effect is strongly affected by external pressure [5], and pressure-induced superconductivity has even been reported [6,7], which questions the importance of the interactions between the electronic structure and the lattice in WTe 2 , and offers additional possibilities for development of devices. Unfortunately, literature still lacks of report on the dynamical properties of the lattice in this system.In this letter, we use Raman scattering spectroscopy to characterize the phonons of WTe 2 single-crystals. We observe 7 out of 33 Raman active modes, with frequencies in good accordance with our first-principles calculations. The angular dependence of the Raman intensity of these modes is consistent with their symmetry assignments in terms of the C 2v point group symmetry of WTe 2 . In contrast to our expectation, none of the phonons observed shows evidence for an electron-phonon coupling. However, the intensity of a A 1 phonon peak at 160.6 cm −1 exhibits an unusual decrease upon cooling, whose origin remains unclear.The WTe 2 single crystals used in our Raman scattering measurements were grown by solid-state reactions. The resistivity of the samples was measured with a Quantum Design physical properties measurement system (PPMS). The crystals were cleaved in air to obtain flat surfaces and then transferred into a low-temperature cryostat ST500 (Janis) for the Raman measurements between 5 and 300 * These two authors contributed equally to this work.† p.richard@iphy.ac.cn ‡ dingh@iphy.ac.cn K with a working vacuum better than 8 × 10 −7 mbar. Raman scattering measurements were performed using a 514.5 nm excitation laser in a back-scattering microRaman configuration, with a triple-grating spectrometer (Horiba Jobin Yvon T64000) equipped with a nitrogencooled CCD camera. In this manuscript, we define x and y as the directions along the a axis (W-W chains) a...

By combining angle-resolved photoemission spectroscopy and quantum oscillation measurements, we performed a comprehensive investigation on the electronic structure of LaSb, which exhibits near-quadratic extremely large magnetoresistance (XMR) without any sign of saturation at magnetic fields as high as 40 T. We clearly resolve one spherical and one intersecting-ellipsoidal hole Fermi surfaces (FSs) at the Brillouin zone (BZ) center Γ and one ellipsoidal electron FS at the BZ boundary X. The hole and electron carriers calculated from the enclosed FS volumes are perfectly compensated, and the carrier compensation is unaffected by temperature. We further reveal that LaSb is topologically trivial but shares many similarities with the Weyl semimetal TaAs family in the bulk electronic structure. Based on these results, we have examined the mechanisms that have been proposed so far to explain the near-quadratic XMR in semimetals.

By using angle-resolved photoemission spectroscopy combined with first-principles calculations, we reveal that the topmost unit cell of ZrSnTe crystal hosts two-dimensional (2D) electronic bands of topological insulator (TI) state, though such a TI state is defined with a curved Fermi level instead of a global band gap. Furthermore, we find that by modifying the dangling bonds on the surface through hydrogenation, this 2D band structure can be manipulated so that the expected global energy gap is most likely to be realized. This facilitates the practical applications of 2D TI in heterostructural devices and those with surface decoration and coverage. Since ZrSnTe belongs to a large family of compounds having the similar crystal and band structures, our findings shed light on identifying more 2D TI candidates and superconductor-TI heterojunctions supporting topological superconductors.Comment: 5 pages, 4 figure

In Nrf2-activated tumors, G6pd inhibition depletes TCA intermediates and suppresses tumor growth.

No abstract

Ultrafast optical pump-probe spectroscopy is used to track carrier dynamics in the large magnetoresistance material WTe2. Our experiments reveal a fast relaxation process occurring on a sub-picosecond time scale that is caused by electron-phonon thermalization, allowing us to extract the electron-phonon coupling constant. An additional slower relaxation process, occurring on a time scale of ∼5-15 picoseconds, is attributed to phonon-assisted electron-hole recombination. As the temperature decreases from 300 K, the timescale governing this process increases due to the reduction of the phonon population. However, below ∼50 K, an unusual decrease of the recombination time sets in, most likely due to a change in the electronic structure that has been linked to the large magnetoresistance observed in this material. has aroused tremendous interest, due not only to its potential application in devices such as magnetic sensors and hard drives, but also to the enigmatic nature of this effect. The observed MR in Cd 3 As 2 has been attributed to the recovery of backscattering that is strongly suppressed in zero magnetic field [2]. In WTe 2 , the large non-saturating MR is believed to arise from perfect electron-hole (e-h) compensation [1], similar to bismuth (Bi) and graphite [4][5][6]. This is supported by angle-resolved photoemission spectroscopy (ARPES) [7] and quantum oscillation [8] experiments, which have found hole and electron pockets with the same size in WTe 2 at low temperatures. Further support for the e-h compensation scenario came from the application of pressure, which increases the difference between the sizes of the hole and electron pockets, dramatically suppressing the MR [9][10][11]. However, a recent high resolution ARPES study revealed a more complicated Fermi surface (FS) with nine pockets [12]. In addition, circular dichroism was observed in the photoemission spectra, signaling strong spin-orbit coupling, which may also play an important role in WTe 2 . Finally, a detailed study of the Shubnikov-de-Haas (SdH) effect, in combination with density functional theory (DFT) calculations, indicated that perfect e-h compensation breaks down under an external magnetic field in WTe 2 [13], challenging the e-h compensation scenario.More insight into the physics of WTe 2 can be obtained using ultrafast optical spectroscopy, which tracks the relaxation of photoexcited carriers in the time domain as they return to equilibrium. Carrier relaxation depends sensitively on the band structure and scattering mechanisms in a solid [14][15][16][17], and therefore an understanding of the ultrafast carrier dynamics in WTe 2 may shed new light on the mechanism of the anomalous MR. This also directly resolves the timescales that ultimately limit potential applications of WTe 2 in electronic devices, e.g., high speed solid-state drives. However, ultrafast optical studies have not yet been performed on this material.Here, we present a detailed ultrafast transient reflectivity (∆R(t)/R) study on WTe 2 while varying the temperatu...