Two-dimensional van der Waals materials have demonstrated fascinating optical and electrical characteristics. However, reports on magnetic properties and spintronic applications of van der Waals materials are scarce by comparison. Here, we report anomalous Hall effect measurements on single crystalline metallic Fe3GeTe2 nanoflakes with different thicknesses. These nanoflakes exhibit a single hard magnetic phase with a near square-shaped magnetic loop, large coercivity (up to 550 mT at 2 K), a Curie temperature near 200 K and strong perpendicular magnetic anisotropy. Using criticality analysis, the coupling length between van der Waals atomic layers in Fe3GeTe2 is estimated to be ~5 van der Waals layers. Furthermore, the hard magnetic behaviour of Fe3GeTe2 can be well described by a proposed model. The magnetic properties of Fe3GeTe2 highlight its potential for integration into van der Waals magnetic heterostructures, paving the way for spintronic research and applications based on these devices.

Atomically thin binary two-dimensional (2D) semiconductors exhibit diverse physical properties depending on their composition, structure, and thickness. By adding another element in these materials, which will lead to formation of ternary 2D materials, the property and structure would greatly change and significantly expanded applications could be explored. In this work, we report structural and optical properties of atomically thin chromium thiophosphate (CrPS), a ternary antiferromagnetic semiconductor. Its structural details were revealed by X-ray and electron diffraction. Transmission electron microscopy showed that preferentially cleaved edges are parallel to diagonal Cr atom rows, which readily identified their crystallographic orientations. Strong in-plane optical anisotropy induced birefringence that also enabled efficient determination of crystallographic orientation using polarized microscopy. The lattice vibrations were probed by Raman spectroscopy and exhibited significant dependence on thickness of crystals exfoliated down to a single layer. Optical absorption determined by reflectance contrast was dominated by d-d-type transitions localized at Cr ions, which was also responsible for the major photoluminescence peak at 1.31 eV. The spectral features in the absorption and emission spectra exhibited noticeable thickness dependence and hinted at a high photochemical activity for single-layer CrPS. The current structural and optical investigation will provide a firm basis for future study and application of this kind of atomically thin magnetic semiconductors.

Superconductivity in graphene has been highly sought after for its promise in various device applications and for general scientific interest. Ironically, the simple electronic structure of graphene, which is responsible for novel quantum phenomena, hinders the emergence of superconductivity. Theory predicts that doping the surface of the graphene effectively alters the electronic structure, thus promoting propensity towards Cooper pair instability (Profeta et al (2012) Nat. Phys. 8 131-4; Nandkishore et al (2012) Nat. Phys. 8 158-63) [1, 2]. Here we report the emergence of superconductivity at 7.4 K in Li-intercalated few-layer-graphene (FLG). The absence of superconductivity in 3D Li-doped graphite underlines that superconductivity in Li-FLG arises from the novel electronic properties of the 2D graphene layer. These results are expected to guide future research on graphene-based superconductivity, both in theory and experiments. In addition, easy control of the Li-doping process holds promise for various device applications.

Evidence of multiband behavior in the superconducting alloy Zr 0.96V0.04B2 ZrB 2 is a nonsuperconducting Pauli paramagnetic crystallizing in the AlB 2 structure. V substitution for Zr in Zr 1−x V x B 2 (0.01 x 0.1) at the few percentage level induces superconductivity with critical temperature reaching a maximum of 8.7 K for Zr 0.96 V 0.04 B 2 near the solid solubility limit. Specific-heat and lower critical field temperature dependence results suggest the possibility of unconventional superconductivity possibly arising from multiband effects.

We report the growth of potassium-doped BaFe 2 As 2 thin films, where the major charge carriers are holes, on Al 2 O 3 (0001) and LaAlO 3 (001) substrates by using an ex-situ pulsed laser deposition technique. The measured T c 's are 40 and 39 K for the films grown on Al 2 O 3 and LaAlO 3 , respectively and diamagnetism indicates that the films have good bulk superconducting properties below 36 and 30 K, respectively. The X-ray diffraction patterns for both films indicated a preferred c-axis orientation, regardless of the substrate structures of LaAlO 3 and Al 2 O 3 . The upper critical field at zero temperature was estimated to be about 155 T.

We investigate the relation of the critical current density (Jc) and the remarkably increased superconducting transition temperature (Tc) for the FeSe single crystals under pressures up to 2.43 GPa, where the Tc is increased by ~8 K/GPa. The critical current density corresponding to the free flux flow is monotonically enhanced by pressure which is due to the increase in Tc, whereas the depinning critical current density at which the vortex starts to move is more influenced by the pressure-induced magnetic state compared to the increase of Tc. Unlike other high-Tc superconductors, FeSe is not magnetic, but superconducting at ambient pressure. Above a critical pressure where magnetic state is induced and coexists with superconductivity, the depinning Jc abruptly increases even though the increase of the zero-resistivity Tc is negligible, directly indicating that the flux pinning property compared to the Tc enhancement is a more crucial factor for an achievement of a large Jc. In addition, the sharp increase in Jc in the coexisting superconducting phase of FeSe demonstrates that vortices can be effectively trapped by the competing antiferromagnetic order, even though its antagonistic nature against superconductivity is well documented. These results provide new guidance toward technological applications of high-temperature superconductors.

The remarkably high superconducting transition temperature and upper critical field of iron(Fe)-based layered superconductors, despite ferromagnetic material base, open the prospect for superconducting electronics. However, success in superconducting electronics has been limited because of difficulties in fabricating high-quality thin films.We report the growth of high-quality c-axis-oriented cobalt(Co)-doped SrFe 2 As 2 thin films with bulk superconductivity by using an in-situ pulsed laser deposition technique with a 248-nm-wavelength KrF excimer laser and an arsenic(As)-rich phase target. The temperature and field dependences of the magnetization showing strong diamagnetism and transport critical current density with superior J c -H performance are reported.These results provide necessary information for practical applications of Fe-based superconductors. \pacs{} The classes of Iron (Fe)-based superconductors [1][2][3][4][5][6][7][8] have remarkably high superconducting transition temperatures (T c ) in spite of the ferromagnetic material base; the highest T c is 55 K in LnFeAsO (FeAs-1111, Ln = lanthanide) [2] and 37.5 K in AEFe 2 As 2 (FeAs-122, AE = alkaline-earth element) [7]. The zero-temperature upper critical field (H c2 (0)) was found to be up to 65 T in the FeAs-1111 [9]. The discovery of these new classes of superconductors has regenerated interest in superconductivity because of an opportunity to tune these materials in many ways [10,11]. This potentially allows one to reveal the mechanism of high-temperature superconductors.Ever since discovering these compounds, much progress has been made in measuring the fundamental physical properties in order to understand the superconducting mechanism. However, controversy still exists because the measurements were carried out on bulk polycrystals, except for some works on single crystals [8,[12][13][14][15][16]. Highquality thin films are needed to investigate the physical properties and to develop superconducting electronic devices, such as Josephson junctions. However, controlling the stoichiometry of the FeAs-1111 phase is difficult because the crystal structure contains two different anions [17]. Also, in the FeAs-1111 phase, electrons are doped by partially replacing oxygen ions with fluorine (F), which is easily evaporated in a vacuum chamber at a high temperature because of its very high vapor pressure. These reasons make it difficult to fabricate high-quality thin film [17][18][19].Very recently, Hosono et al. reported success in growing cobalt (Co)-doped SrFe 2 As 2 thin film [18,19]. Even though this compound has a relatively lower T c , Codoping is more suitable for thin film growth than other types of doping (F or potassium (K)) because of the low vapor pressure of Co. Also, SrFe 2 As 2 contains only one anion species. Hosono et al. fabricated the thin films by using pulsed laser deposition (PLD) with a second-harmonic 532-nm-wavelength Nd:YAG laser and a stoichiometric target disk.In general, an ultraviolet (UV) wavelength is known ...

The recent observation of extremely large magnetoresistance (MR) in the transition-metal dichalcogenide MoTe2 has attracted considerable interest due to its potential technological applications as well as its relationship with novel electronic states predicted for a candidate type-II Weyl semimetal. In order to understand the origin of the MR, the electronic structure of MoTe2−x (x = 0.08) is systematically tuned by application of pressure and probed via its Hall and longitudinal conductivities. With increasing pressure, a monoclinic-to-orthorhombic (1 T′ to Td) structural phase transition temperature (T*) gradually decreases from 210 K at 1 bar to 58 K at 1.1 GPa, and there is no anomaly associated with the phase transition at 1.4 GPa, indicating that a T = 0 K quantum phase transition occurs at a critical pressure (Pc) between 1.1 and 1.4 GPa. The large MR observed at 1 bar is suppressed with increasing pressure and is almost saturated at 100% for P > Pc. The dependence on magnetic field of the Hall and longitudinal conductivities of MoTe2−x shows that a pair of electron and hole bands are important in the low-pressure Td phase, while another pair of electron and hole bands are additionally required in the high-pressure 1 T′ phase. The MR peaks at a characteristic hole-to-electron concentration ratio (nc) and is sharply suppressed when the ratio deviates from nc within the Td phase. These results establish the comprehensive temperature-pressure phase diagram of MoTe2−x and underscore that its MR originates from balanced electron-hole carrier concentrations.