Weyl semimetals with time reversal symmetry breaking are expected to show various fascinating physical behaviors, such as intrinsic giant anomalous Hall effect, chiral anomaly effect in the bulks, and Fermi arcs on the surfaces. Here we report a scanning tunneling microscopy study on the magnetic Weyl semimetal candidate Co3Sn2S2. According to the morphology and local density of states of the surface, we provide assignments to different surface terminations. The measured local density of states reveals a semimetal gap of ~300 mV, which is further verified as the gap in spin-minority bands using spinresolved tunneling spectra. Additionally, signature for the nontrivial surface states around 50 mV is proposed. This is further confirmed by the observations of standing waves around a step-edge of the sample. Our observations and their comparison with band structure calculations provide direct yet timely evidence for the bulk and surface band structures of the magnetic Weyl semimetal Co3Sn2S2. † These authors contributed equally ‡ Present address:
We performed polarized Raman spectroscopy on mechanically exfoliated few-layer MoTe2 samples and observed both 1T′ and Td phases at room temperature. Few-layer 1T′ and Td MoTe2 exhibited a significant difference especially in interlayer vibration modes, from which the interlayer coupling strengths were extracted using the linear chain model: strong in-plane anisotropy was observed in both phases. Furthermore, temperature-dependent Raman measurements revealed a peculiar phase transition behavior in few-layer 1T′ MoTe2. In contrast to bulk 1T′ MoTe2 crystals where the phase transition to the Td phase occurs at ~250 K, the temperature-driven phase transition to the Td phase is increasingly suppressed as the thickness is reduced, and the transition and the critical temperature varied dramatically from sample to sample even for the same thickness. Raman spectra of intermediate phases that correspond to neither 1T′
Transition metal dichalcogenides exhibit phase transitions through atomic migration when triggered by various stimuli, such as strain, doping, and annealing. However, since atomically thin 2D materials are easily damaged and evaporated from these strategies, studies on the crystal structure and composition of transformed 2D phases are limited. Here, the phase and composition change behavior of laser‐irradiated molybdenum ditelluride (MoTe2) in various stacked geometry are investigated, and the stable laser‐induced phase patterning in hexagonal boron nitride (hBN)‐encapsulated MoTe2 is demonstrated. When air‐exposed or single‐side passivated 2H‐MoTe2 are irradiated by a laser, MoTe2 is transformed into Te or Mo3Te4 due to the highly accumulated heat and atomic evaporation. Conversely, hBN‐encapsulated 2H‐MoTe2 transformed into a 1T′ phase without evaporation or structural degradation, enabling stable phase transitions in desired regions. The laser‐induced phase transition shows layer number dependence; thinner MoTe2 has a higher phase transition temperature. From the stable phase patterning method, the low contact resistivity of 1.13 kΩ µm in 2H‐MoTe2 field‐effect transistors with 1T′ contacts from the seamless heterophase junction geometry is achieved. This study paves an effective way to fabricate monolithic 2D electronic devices with laterally stitched phases and provides insights into phase and compositional changes in 2D materials.
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