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We report the quantum transport properties of Cd3As3 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 Rxx and the transverse Hall resistance Rxy. From the strong oscillatory component ARxx, a linear dependence of the Landau index n on 1/5 is obtained, and it gives an n-axis intercept between 1/2 and 5/8. This clearly reveals a nontrivial n 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. [ABSTRACT FROM AUTHOR]

Low-temperature thermal conductivity measurements were performed on single crystals of TlNi2Se2, a nickel chalcogenide heavy-electron superconductor with Tc ≃ 3.7 K. In zero field, the residual electronic contribution at T → 0 K (k0/T ) was well separated from the total thermal conductivity, which is less than 0.45% of its normal-state value. Such a tiny residual k0/T is unlikely contributed by the nodal quasiparticles. The nodeless gap structure is supported by the very weak field dependence of k0(H)/T in low magnetic fields. In the whole field range, k0(H)/T exhibits an S-shaped curve, as in the case of nickel pnictides BaNi2As2 and SrNi2P2. This common feature of nickel-based superconductors can be explained by multiple nodeless superconducting gaps. [ABSTRACT FROM AUTHOR]

The thermal conductivity of iron-based superconductor CsFe2As2 single crystal (Tc=1.81 K) was measured down to 50 mK. A significant residual linear term κ0/T=1.27 mW K-2 cm-1 is observed in zero magnetic field, which is about 1/10 of the normal-state value in upper critical field Hc2. In low magnetic field, κ0/T increases rapidly with field. The normalized κ0/T(H) curve for our CsFe2As2 (with residual resistivity ρ0=1.80 μΩ cm) lies between the dirty KFe2As2 (with ρ0=3.32 μΩ cm) and the clean KFe2As2 (with ρ0=0.21 μΩ cm), which is consistent with its impurity level. These results strongly suggest a nodal superconducting gap in CsFe2As2, similar to its sister compound KFe2As2. [ABSTRACT FROM AUTHOR]

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

We report resistivity ρ and thermal conductivity K measurements on Ca³Ir4Sn13 single crystals, in which superconductivity with Tc ≈ 7 K was claimed to coexist with ferromagnetic spin fluctuations. Among three crystals, only one crystal shows a small hump in resistivity near 20 K, which was previously attributed to the ferromagnetic spin fluctuations. The other two crystals show the ρ ~ T² Fermi-liquid behavior at low temperature. For both single crystals with and without the resistivity anomaly, the residual linear term K0/ T is negligible in zero magnetic field. In low fields, K0(H)/T shows a slow field dependence. These results demonstrate that the superconducting gap of Ca3lr4Sn13 is nodeless and thus rule out a nodal gap caused by ferromagnetic spin fluctuations. [ABSTRACT FROM AUTHOR]

Low-temperature thermal conductivity measurements were performed on single crystal of PbTaSe2 a noncentrosymmetric superconductor with topological bulk nodal lines in the electronic band structure. It is found that the residual linear term Κ0/T is negligible in zero magnetic field. Furthermore, the field dependence of Κ0/T exhibits an S-shaped curve. These results suggest that PbTaSe2 has multiple nodeless superconducting gaps. Therefore, the spin-triplet state with gap nodes does not play an important role in this noncentrosymmetric superconductor with strong spin-orbital coupling. The fully gapped superconducting state also meets the requirement of a topological superconductor, if PbTaSe2 is indeed the case. [ABSTRACT FROM AUTHOR]

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 × 105% under ambient pressure to 7.47 × 103% 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. [ABSTRACT FROM AUTHOR]

We report low-temperature heat transport measurements on superconducting iron sulfide FeS with Tc∷5 K, which has the same crystal structure and similar electronic band structure to the superconducting iron selenide FeSe. In zero magnetic field, a significant residual linear term κ0/T is observed. At low field, κ0/T increases rapidly with increasing field. These results suggest a nodal superconducting gap in FeS. We compare it with the sister compound FeSe and other iron-based superconductors with nodal gaps. [ABSTRACT FROM AUTHOR]

High-quality K(Fe1-xCox)2As2 single crystals have been grown by using the KAs flux method. Instead of increasing the superconducting transition temperature Tc through electron doping, we find that Co impurities rapidly suppress Tc down to zero at only x ≈ 0.04. Such an effective suppression of Tc by impurities is quite different from that observed in Ba0.5K0.5Fe2As2 with multiple nodeless superconducting gaps. Thermal conductivity measurements in zero field show that the residual linear term K0/T only changes slightly with 3.4% Co doping, despite the sharp increase in the scattering rate. The implications of these anomalous impurity effects are discussed. [ABSTRACT FROM AUTHOR]

We measured the resistivity and the specific heat of CsFe2As2 single crystals, which were grown by using a self-flux method. The CsFe2As2 crystal shows a sharp superconducting transition at 1.8 K with a transition width of 0.1 K. The sharp superconducting transition and pronounced jump in specific heat indicate high quality of the crystals. A large ΔCp/Tc accompanying a very low Tc, nonexponential dependence of the lowest temperature ΔCp/ T and an H1/2 dependence of Δγ(H) are observed in the superconducting-state specific heat; Combined with the fitting results by the α model for the superconducting-state specific heat, a pairing symmetry with nodal gaps was suggested in CsFe2As2. [ABSTRACT FROM AUTHOR]

We present the ultralow-temperature specific heat and thermal conductivity measurements on single crystals of YbMgGaO4, which was recently argued to be a promising candidate for a quantum spin liquid (QSL). In a zero magnetic field, a large magnetic contribution of specific heat is observed, and exhibits a power-law temperature dependence (Cm ~ T0.74). On the contrary, we do not observe any significant contribution of thermal conductivity from magnetic excitations. In magnetic fields H ≥ 6 T, the exponential T dependence of Cm and the enhanced thermal conductivity indicate a magnon gap of the fully polarized state. The absence of magnetic thermal conductivity at the zero field in this QSL candidate puts a strong constraint on the theories of its ground state. [ABSTRACT FROM AUTHOR]

In the heavy-fermion superconductor Ce1-xYbxCoIn5, Yb doping was reported to cause a possible change from nodal d-wave superconductivity to a fully gapped d-wave molecular superfluid of composite pairs near x?≈0.07 (nominal value xnom=0.2). Here we present systematic thermal conductivity measurements on Ce1-xYbxCoIn5 (x=0.013, 0.084, and 0.163) single crystals. The observed finite residual linear term k0/T is insensitive to Yb doping, verifying the universal heat conduction of the nodal d-wave superconducting gap in Ce1-xYbxCoIn5. Similar universal heat conduction is also observed in the CeCo(In1-yCdy)5 system. These results reveal a robust nodal d-wave gap in CeCoIn5 upon Yb or Cd doping. [ABSTRACT FROM AUTHOR]