Thickness dependent transition from the 1T′ to Weyl semimetal phase in ultrathin MoTe₂: electrical transport, noise and Raman studies

Abstract

The resistivity of the semiconducting ultra-thin 1T′-MoTe2 shows a clear signature of temperature induced transition to Weyl semimetallic Td phase. Resistivity upturn at low temperature (∼20 K) confirms electron–electron interaction physics at the Weyl nodes.

Low‐Frequency Electronic Noise in Quasi‐2D van der Waals Antiferromagnetic Semiconductor FePS3—Signatures of Phase Transitions

“…electrical bias and temperature, can shed light on electron transport, carrier recombination mechanisms and, what is most important in this case, magnetic and metal-insulator phase transitions. [40][41][42][43][44][45][46] We have previously used successfully the low-frequency noise measurements as the "noise spectroscopy" for monitoring phase transitions in the 2D charge-density-wave materials; [47][48][49] examining the specifics of magnon transport in magnetic electrical insulators; [50] and clarifying the nature of electron transport in quasi-1D vdW materials. [51,52] Our measurements of noise in thin films of FePS 3 reveal a number of interesting features, which contribute to a better understanding of the properties of this AF vdW semiconductor.…”

Structural Phase Transition and Interlayer Coupling in Few-Layer 1T′ and Td MoTe2

“…They attributed the stabilization of the T d phase to charge doping in semimetallic MoTe 2 induced by the quantum confinement effect. On the other hand, both the 1T′ and T d phases are observed in few-layer MoTe 2 samples grown by chemical vapor deposition (CVD). ,, In some previous studies, the appearance of the 1T′ phase in few-layer MoTe 2 was ascribed to the hole doping arising from the air exposure. , In our case, however, we placed the samples into a vacuum chamber immediately after exfoliation and kept them under vacuum for all measurements, minimizing air exposure. In order to see if air exposure turns our few-layer T d samples into the 1T′ phase, we intentionally exposed a 4L MoTe 2 sample to air for up to 1 week but found that the sample did not change to the 1T′ phase (see Supporting Information Figure S3).…”

“…The screw axis in the z direction and the glide plane of its bulk counterpart no longer exist in few-layer T d MoTe 2 , and so the symmetry analysis of few-layer 1T′ and T d MoTe 2 should in principle be different from that of bulk crystals. Furthermore, investigations on the temperature dependence of few-layer MoTe 2 have not yet revealed clear indications of the 1T′ to T d phase transition. ,, …”

“…Furthermore, investigations on the temperature dependence of few-layer MoTe 2 have not yet revealed clear indications of the 1T′ to T d phase transition. 32,34,35 Raman spectroscopy is a powerful tool to investigate the crystal symmetry, interlayer coupling, and layer stacking in two-dimensional materials. 36,37 In bulk crystals, the structural phase transition from the 1T′ to the T d phase leads to clear Raman signatures including the emergence of an interlayer shear mode, 16,17 but the interlayer vibration modes of few-layer 1T′ and T d MoTe 2 have not yet been studied in detail.…”

Symmetry induced phonon renormalization in few layers of 2H-MoTe$_2$ transistors: Raman and first-principles studies

“…As Raman spectroscopy does not require any sample preparation, it has been extensively used as a non-invasive, contact-less, fast and accurate tool to determine strain [42], doping effects [13], layer number [43,44], crystal orientation [45], structural transitions between different polytypes [9,[11][12][13][14][46][47][48] in fewlayer MoTe 2 devices in ambient as well as different sample environments. Furthermore, Raman scattering has been employed in various 2D materials to measure electron-phonon coupling (EPC) that governs electronic transport properties [30,31].…”