We predict by first principles calculations that the recently prepared borophene is a pristine twodimensional (2D) monolayer superconductor, in which the superconductivity can be significantly enhanced by strain and charge carrier doping. The intrinsic metallic ground state with high density of states at Fermi energy and strong Fermi surface nesting lead to sizeable electron-phonon coupling, making the freestanding borophene superconduct with Tc close to 19.0 K. The tensile strain can increase Tc to 27.4 K, while the hole doping can notably increase Tc to 34.8 K. The results indicate that the borophene grown on substrates with large lattice parameters or under photoexcitation can show enhanced superconductivity with Tc far more above liquid hydrogen temperature of 20.3 K, which will largely broaden the applications of such novel material.

Two-dimensional (2D) transition-metal dichalcogenide (TMDs) MoTe 2 has attracted much attention due to its predicted Weyl semimetal (WSM) state and a quantum spin Hall insulator in bulk and monolayer form, respectively. We find that the superconductivity in MoTe 2 single crystal can be much enhanced by the partial substitution of the Te ions by the S ones. The maximum of the superconducting temperature T C of MoTe 1.8 S 0.2 single crystal is about 1.3 K. Compared with the parent MoTe 2 single crystal (T C =0.1 K), nearly 13-fold in T C is improved in MoTe 1.8 S 0.2 one.The superconductivity has been investigated by the resistivity and magnetization measurements.MoTe 2-x S x 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-shape superconducting phase diagram is obtained in the S-doped MoTe 2 single crystals. MoTe 2-x S x materials may provide a new platform for our understanding of superconductivity phenomena and topological physics in TMDs. II Experimental details 3MoTe 2 and MoTe 2-x S x (0≤x≤1) single crystals were grown by the chemical vapor transport method using polycrystalline MoTe 2 and MoTe 2-x S x as raw materials and I 2 as a transport agent.Firstly, we made the polycrystalline MoTe 2 and MoTe 2-x S x (0≤x≤1). Mo (Alfa Aesar, 99.9 %) and Te or S(Alfa Aesar, 99.9 %) powders with a stoichiometric ratio were ground, pressed into pellets, and put in an evacuated quartz tube. All were done in an Ar-filled glove box. The sealed quartz tube was heated to 800 o C for 20 hours and kept for 7 days, then quenched to ice water. The polycrystalline MoTe 2 or MoTe 2-x S x and the agent I 2 were mixed and sealed into another evacuated quartz tubes. The sealed quartz tubes were put in a two-zone tube furnace. The crystal growth recipe is followed the reported paper.[12] The hot side is about 1000 o C and the cold side is 900 o C, and dwelled for 7 days. In order to improve the quality of single crystals, we quenched the quartz tubes into ice-water as soon as possible before the growth sequence ending. Plate-like shape single crystals with shinning surfaces were obtained. The size of the crystal was about 4*4*0.5 mm 3 . The single crystals were air-stable and can be easily exfoliated. Powder X-ray diffraction (XRD) patterns were taken with Cu K α1 radiation (λ=0.15406 nm) using a PANalytical X'pert diffractometer at room temperature. The element analysis of the single crystals was performed using a commercial energy dispersive spectroscopy (EDS) microprobe. The element compositions of the single crystals used in the text are the ones obtained from EDS measurements.The magnetic properties were carried out by the magnetic property measurement system with a 3 He cryostat (MPMS-XL7). The electrical transport measurements were performed in a 4 He cryostat from 300 K to 2 K, and in a 3 He cryostat down to 0.35 K by a four-probe method to eliminate the contact resistan...