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2-Dimensional (2D) CrPS4 single crystals have been grown by the chemical vapor transport method. The crystallographic, magnetic, electronic, and thermal transport properties of the single crystals were investigated by the room-temperature X-ray diffraction, electrical resistivity ρ(T), specific heat CP(T), and the electronic spin response (ESR) measurements. CrPS4 crystals crystallize into a monoclinic structure. The electrical resistivity ρ(T) shows a semiconducting behavior with an energy gap Ea = 0.166 eV. The antiferromagnetic transition temperature is about TN = 36 K. The spin flipping induced by the applied magnetic field is observed along the c axis. The magnetic phase diagram of CrPS4 single crystal has been discussed. The extracted magnetic entropy at TN is about 10.8 J/mol K, which is consistent with the theoretical value R ln(2S + 1) for S = 3/2 of the Cr3+ ion. Based on the mean-field theory, the magnetic exchange constants J1 and Jc corresponding to the interactions of the intralayer and between layers are about 0.143 meV and -0.955 meV are obtained based on the fitting of the susceptibility above TN, which agree with the results obtained from the ESR measurements. With the help of the strain for tuning the magnetic properties, monolayer CrPS4 may be a promising candidate to explore 2D magnetic semiconductors. [ABSTRACT FROM AUTHOR]

Cr0.68Se single crystals with two-dimensional (2D) character have been grown, and the detailed magnetization M(T), electrical transport properties (including longitudinal resistivity qxx and Hall resistivity ρxy), and thermal transport properties [including heat capacity Cp(T) and thermoelectric power S(T)] have been measured. There are some interesting phenomena: (i) Cr0.68Se presents a non-collinear antiferromagnetic (AFM) semiconducting behavior at the Néeel temperature of TN=42K and with the activated energy of Eg = 3.9 meV; (ii) it exhibits the anomalous Hall effect (AHE) below TN and large negative magnetoresistance about 83.7% (2 K, 8.5 T). The AHE coefficient RS is 0.385 cm-3/C at T=2K, and the AHE conductivity rH is about 1 Ω-1 cm-1 at T=40 K; (iii) the scaling behavior between the anomalous Hall resistivity ρxyA and the longitudinal resistivity ρxx is linear, and further analysis implies that the origin of the AHE in Cr0.68Se is dominated by the skew-scattering mechanism. Our results may be helpful for exploring the potential application of these kinds of 2D AFM semiconductors. [ABSTRACT FROM AUTHOR]

Due to the time reversal symmetry, the metallic surface of the topological insulator (TI) survives and results in the resistivity plateau at low temperature, which is the transport signature of the metallic surface state. Such a universal character has been observed in many materials, such as Bi2Te2Se, SmB6, and so on. Recently, a similar behavior has also been found in the possible topological semimetal LaSb/Bi and the metallic compounds Nb/TaAs2. Herein, we have mainly explored the resistivity plateau and the magnetoresistance (MR) of TaTe4 single crystal with the charge density wave (CDW) transition temperature TCDW=475 K. There are some interesting observations: (i) The large MR (MR is about 1200% in a magnetic field 16 T at T=2K) is observed at low temperature; (ii) A field-induced universal TI resistivity with a plateau at roughly T10K and high quantum mobility of carriers in the plateau region are present; (iii) Quantum oscillations with the angle dependence of a two-dimensional Fermi surface are shown. Owing to the CDW character that existed in TaTe4, it represents an ideal system to investigate the relationship between the CDW and the topological physics. [ABSTRACT FROM AUTHOR]

We measured the magnetoresistivity properties of Td-MoTe2 single crystal under the magnetic field up to 33 T. By analyzing the Shubnikov-de Haas oscillations of the longitudinal resistance Δρxx, a linear dependence of the Landau index n on 1/B is obtained. The intercept of the Landau index plot is 0.47, which is between 3/8 and 1/2. This clearly reveals a nontrivial π Berry's phase, which is a distinguished feature of the surface state in Td-MoTe2 single crystal. Accompanied by the superconductivity observed at TC=0.1K, Td-MoTe2 may be a promising candidate of the topological superconductor and opens a door to study the relationship between the superconductivity and topological physics. [ABSTRACT FROM AUTHOR]

Two-dimensional transition-metal dichalcogenide (TMDs) MoTe2 has attracted much attention due to its predicted Weyl semimetal state and a quantum spin Hall insulator in bulk and monolayer form, respectively. We find that the superconductivity in MoTe2 single crystal can be greatly enhanced by the partial substitution of the Te ions by the S ones. The maximum superconducting temperature TC of MoTe1.8S0.2 single crystal is about 1.3 K. Compared with the parent MoTe2 single crystal (TC=0.1 K), nearly 13-fold in TC is improved in the MoTe1.8S0.2 one. The superconductivity has been investigated through the resistivity and magnetization measurements. MoTe2-xSx single crystals belong to weak coupling superconductors and the improvement of the superconductivity may be related to the enhanced electron-phonon coupling induced by the S-ion substitution. A dome-shaped superconducting phase diagram is obtained in the S-doped MoTe2 single crystals. MoTe2-xSx materials may provide a new platform for our understanding of superconductivity phenomena and topological physics in TMDs. [ABSTRACT FROM AUTHOR]

We report the superconductivity of CaSn3 single crystals with a AuCu3-type structure, namely cubic space group Pm3̅m. The superconducting transition temperature TC = 4.2 K is determined by the magnetic susceptibility, electrical resistivity, and heat capacity measurements. The magnetization versus magnetic field (M–H) curve at low temperatures shows a typical-II superconducting behavior. The estimated lower and upper critical fields are about 125 Oe and 1.79 T, respectively. The penetration depth λ(0) and coherence length ξ(0) are calculated to be approximately 1147 nm and 136 nm by the Ginzburg–Landau equations. The estimated Sommerfeld coefficient of the normal state γN is about 2.9 mJ mol−1 K−2. ΔC/γNTC = 1.13 and λep = 0.65 suggest that the CaSn3 single crystal is a weakly coupled superconductor. Electronic band structure calculations show a complex multi-sheet Fermi surface formed by three bands and a low density of states (DOSs) at the Fermi level, which is consistent with the experimental results. Based on the analysis of electron–phonon coupling of AX3 compounds (A = Ca, La, and Y; X = Sn and Pb), we theoretically proposed a way to increase TC in the system. [ABSTRACT FROM AUTHOR]

The extreme magnetoresistance (XMR) in orthorhombic W/MoTe2 arises from the combination of the perfect electron-hole (e-h) compensation effect and the unique orbital texture topology, which have comprised an intriguing research field in materials physics. Herein, we apply a special analytical approach as a function of mobility (μ-spectrum) without any hypothesis. Based on the interpretations of longitudinal and transverse electric transport of Td-MoTe2, the types and the numbers of carriers can be obtained. There are three observations: the large residual resistivity ratio can be observed in the MoTe2 single crystal sample, which indicates that the studied crystal is of high quality; we observed three electron-pockets and three hole-ones from the μ-spectrum and that the ratio of h/e is much less than 1, which shows that MoTe2 is more e-like; different from the separated peaks obtained from the hole-like μ-spectrum, those of the electron-like one are continuous, which may indicate the topological feature of electron-pockets in Td-MoTe2. The present results may provide an important clue to understanding the mechanism of the XMR effect in Td-MoTe2. [ABSTRACT FROM AUTHOR]

The extreme magnetoresistance (XMR) in orthorhombic W/MoTe2 arises from the combination of the perfect electron-hole (e-h) compensation effect and the unique orbital texture topology, which have comprised an intriguing research field in materials physics. Herein, we apply a special analytical approach as a function of mobility (μ-spectrum) without any hypothesis. Based on the interpretations of longitudinal and transverse electric transport of Td-MoTe2, the types and the numbers of carriers can be obtained. There are three observations: the large residual resistivity ratio can be observed in the MoTe2 single crystal sample, which indicates that the studied crystal is of high quality; we observed three electron-pockets and three hole-ones from the μ-spectrum and that the ratio of h/e is much less than 1, which shows that MoTe2 is more e-like; different from the separated peaks obtained from the hole-like μ-spectrum, those of the electron-like one are continuous, which may indicate the topological feature of electron-pockets in Td-MoTe2. The present results may provide an important clue to understanding the mechanism of the XMR effect in Td-MoTe2. [ABSTRACT FROM AUTHOR]

We did the resistivity and scanning tunneling microscope/spectroscopy (STM/STS) experiments at different temperatures and magnetic fields to investigate the origin of the turn-on (t-o) phenomenon of Td - MoTe2. There are two interesting observations. Firstly, magnetoresistance (MR) follows the Kohler's rule scaling: MR ~ (H/ρ0)m with m ≈ 1.92 and the t-o temperature T* under different magnetic fields can also be scaled by T* ~ (H - Hc)υ with υ = 1/2. Secondly, a combination of compensated electron-hole pockets and a possible electronic structure phase transition induced by the temperature have been validated in Td - MoTe2 by the STM/STS experiments. Compared with the STS of Td - MoTe2 single crystal under H = 0, the STS hardly changes even when the applied field is up to 7 T. The origins of the t-o phenomenon in Td - MoTe2 are discussed. Meanwhile, we analyzed the universality and applicability of the t-o phenomenon in the extreme MR materials with almost balanced hole and electron densities as well as with other systems where the density of hole or electron is in a dominant position. [ABSTRACT FROM AUTHOR]

Due to the time reversal symmetry, the metallic surface of the topological insulator (TI) survives and results in the resistivity plateau at low temperature, which is the transport signature of the metallic surface state. Such a universal character has been observed in many materials, such as Bi2Te2Se, SmB6, and so on. Recently, a similar behavior has also been found in the possible topological semimetal LaSb/Bi and the metallic compounds Nb/TaAs2. Herein, we have mainly explored the resistivity plateau and the magnetoresistance (MR) of TaTe4 single crystal with the charge density wave (CDW) transition temperature TCDW=475 K. There are some interesting observations: (i) The large MR (MR is about 1200% in a magnetic field 16 T at T=2K) is observed at low temperature; (ii) A field-induced universal TI resistivity with a plateau at roughly T10K and high quantum mobility of carriers in the plateau region are present; (iii) Quantum oscillations with the angle dependence of a two-dimensional Fermi surface are shown. Owing to the CDW character that existed in TaTe4, it represents an ideal system to investigate the relationship between the CDW and the topological physics. [ABSTRACT FROM AUTHOR]

Two-dimensional transition-metal dichalcogenide (TMDs) MoTe2 has attracted much attention due to its predicted Weyl semimetal state and a quantum spin Hall insulator in bulk and monolayer form, respectively. We find that the superconductivity in MoTe2 single crystal can be greatly enhanced by the partial substitution of the Te ions by the S ones. The maximum superconducting temperature TC of MoTe1.8S0.2 single crystal is about 1.3 K. Compared with the parent MoTe2 single crystal (TC=0.1 K), nearly 13-fold in TC is improved in the MoTe1.8S0.2 one. The superconductivity has been investigated through the resistivity and magnetization measurements. MoTe2-xSx single crystals belong to weak coupling superconductors and the improvement of the superconductivity may be related to the enhanced electron-phonon coupling induced by the S-ion substitution. A dome-shaped superconducting phase diagram is obtained in the S-doped MoTe2 single crystals. MoTe2-xSx materials may provide a new platform for our understanding of superconductivity phenomena and topological physics in TMDs. [ABSTRACT FROM AUTHOR]

We performed the angle dependent magnetoresistance (MR), Hall effect measurements, the temperature dependent magneto-thermoelectric power (TEP) S(T) measurements, and the first-principles calculations to study the electronic properties of orthorhombic phase Mo Te2 (Td - Mo Te2), which was proposed to be electronically two dimensional (2D). There are some interesting findings about Td - Mo Te2. (1) A scaling approach ɛθ = (sin²θ + γ-2 cos²θ)1/2 is applied, where θ is the magnetic field angle with respect to the c axis of the crystal and γ is the mass anisotropy. Unexpectedly, the electronically three-dimensional (3D) character with γ as low as 1.9 is observed in Td - Mo Te2. (2) The possible Lifshitz transition and the following electronic structure change can be verified around T ~ 150 K and T ~ 60 K, which is supported by the evidence of the slope changing of the temperature dependence of TEP, the carrier density extracted from Hall resistivity, and the onset temperature of γ obtained from the MR measurements. The extremely large MR effect in Td - Mo Te2 could originate from the combination of the electron-hole compensation and a particular orbital texture on the electron pocket, which is supported by the calculations of electronic structure. Our results may provide a general scaling relation for the anisotropic MR and help to recognize the origins of the MR effect in other systems, such as the Weyl semimetals and the Dirac ones. [ABSTRACT FROM AUTHOR]