We report the quantum transport properties of Cd₃As₂ single crystals in a magnetic field. A large linear quantum magnetoresistance is observed near room temperature. With decreasing temperature, the Shubnikov-de Haas oscillations appear in both the longitudinal resistance R(xx) and the transverse Hall resistance R(xy). From the strong oscillatory component ΔR(xx), a linear dependence of the Landau index n on 1/B is obtained, and it gives an n-axis intercept between 1/2 and 5/8. This clearly reveals a nontrivial π Berry's phase, which is a distinguished feature of Dirac fermions. Our quantum transport results provide bulk evidence for the existence of a three-dimensional Dirac semimetal phase in Cd₃As₂.

The quantum oscillations of the magnetoresistance under ambient and high pressure have been studied for WTe2 single crystals, in which extremely large magnetoresistance was discovered recently. By analyzing the Shubnikov-de Haas oscillations, four Fermi surfaces are identified, and two of them are found to persist to high pressure. The sizes of these two pockets are comparable, but show increasing difference with pressure. At 0.3 K and in 14.5 T, the magnetoresistance decreases drastically from 1.25 × 10 5 % under ambient pressure to 7.47 × 10 3 % under 23.6 kbar, which is likely caused by the relative change of Fermi surfaces. These results support the scenario that the perfect balance between the electron and hole populations is the origin of the extremely large magnetoresistance in WTe2.

The in-plane thermal conductivity of iron-based superconductor RbFe2As2 single crystal (Tc ≈ 2.1 K) was measured down to 100 mK. In zero field, the observation of a significant residual linear term κ0/T = 0.65 mW K −2 cm −1 provides clear evidence for nodal superdonducting gap. The field dependence of κ0/T is similar to that of its sister compound CsFe2As2 with comparable residual resistivity ρ0, and lies between the dirty and clean KFe2As2. These results suggest that the (K,Rb,Cs)Fe2As2 serial superconductors have a common nodal gap structure.

The thermal conductivity of the doped topological crystalline insulator, Sn0.6In0.4Te superconducting single crystal with Tc = 4.1 K, was measured down to 50 mK. It is found that the residual linear term κ0/T is negligible in zero magnetic field. The κ0/T shows a slow field dependence at low magnetic field. These results suggest that the superconducting gap is nodeless, unless there exist point nodes with directions perpendicular to the heat current. Due to its high-symmetry fcc crystal structure of Sn0.6In0.4Te, however, such point nodes can be excluded. Therefore we demonstrate that this topological superconductor candidate has a full superconducting gap in the bulk. It is likely the unconventional odd-parity A1u state which supports a surface Andreev bound state.

We measured the low-temperature thermal conductivity of a new layered superconductor with quasi-one-dimensional characteristics, the ternary telluride Ta4Pd3Te16 with transition temperature Tc ≈ 4.3 K. The significant residual linear term of thermal conductivity in zero magnetic field and its rapid field dependence provide evidences for nodes in the superconducting gap. By measuring resistivity under pressures, we reveal a superconducting dome in the temperature-pressure phase diagram. The existence of gap nodes and superconducting dome suggests unconventional superconductivity in Ta4Pd3Te16, which may relate to a charge-density wave instability in this low-dimensional compound.