The effect of sample size and surface roughness on the phonon thermal conductivity κp of Nd2CuO4 single crystals was studied down to 50 mK. At 0.5 K, κp is proportional to √ A, where A is the cross-sectional area of the sample. This demonstrates that κp is dominated by boundary scattering below 0.5 K or so. However, the expected T 3 dependence of κp is not observed down to 50 mK. Upon roughing the surfaces, the T 3 dependence is restored, showing that departures from T 3 are due to specular reflection of phonons off the mirror-like sample surfaces. We propose an empirical power law fit, to κp ∼ T α (where α < 3) in cuprate single crystals. Using this method, we show that recent thermal conductivity studies of Zn doping in YBa2Cu3Oy re-affirm the universal heat conductivity of d-wave quasiparticles at T → 0. To understand the pairing mechanism in a superconductor, it is essential to know the symmetry of the order parameter. In this context, measurements of lowtemperature thermal conductivity κ, which probes the low-energy quasiparticle excitations, has emerged as a powerful probe of the order parameter in superconductors. For conventional s-wave superconductors with a fully gapped excitation spectrum, the linear-temperature electronic contribution to thermal conductivity is zero at T → 0, i.e. the residual linear term κ 0 /T = 0. This can be seen in the single-gap s-wave superconductor Nb,

The in-plane resistivity rho and thermal conductivity kappa of single crystal Na0.7CoO2 were measured down to 40 mK. Verification of the Wiedemann-Franz law, kappa/T=L(0)/rho as T-->0, and observation of a T2 dependence of rho at low temperature establish the existence of a well-defined Fermi-liquid state. The measured value of coefficient A reveals enormous electron-electron scattering, characterized by the largest Kadowaki-Woods ratio A/gamma(2) encountered in any material. The rapid suppression of A with magnetic field suggests a possible proximity to a magnetic quantum critical point. We also speculate on the possible role of magnetic frustration and proximity to a Mott insulator.

The magnetic and transport properties are systematically studied on the single crystal N a0.55CoO2 with charge ordering and divergency in resistivity below 50 K. A long-range ferromagnetic ordering is observed in susceptibility below 20 K with the magnetic field parallel to Co-O plane, while a negligible behavior is observed with the field perpendicular to the Co-O plane. It definitely gives a direct evidence for the existence of in-plane ferromagnetism below 20 K. The observed magnetoresistance (MR) of 30 % at the field of 6 T at low temperatures indicates an unexpectedly strong spin-charge coupling in triangle lattice systems.

We report infrared reflectivity study of charge ordering in a Na0.5CoO2 single crystal. In comparison with x=0.7 and 0.85 compounds, we found that the effective carrier density increases systematically with decreasing Na contents. The charge ordering transition only affects the optical spectra below 1000 cm(-1). A hump near 800 cm(-1) develops below 100 K, which is accompanied by the appearance of new lattice modes as well as the strong antiresonance feature of phonon spectra. These observations signify a polaronic characteristic of charge carriers. Below T(co), an optical gap develops at the magnitude of 2Delta approximately 3.5k(B)T(co) (T<

The heat carriers responsible for the unexpectedly large thermal Hall conductivity of the cuprate Mott insulator La2CuO4 were recently shown to be phonons. However, the mechanism by which phonons in cuprates acquire chirality in a magnetic field is still unknown. Here, we report a similar thermal Hall conductivity in two cuprate Mott insulators with significantly different crystal structures and magnetic orders – Nd2CuO4 and Sr2CuO2Cl2 – and show that two potential mechanisms can be excluded – the scattering of phonons by rare-earth impurities and by structural domains. Our comparative study further reveals that orthorhombicity, apical oxygens, the tilting of oxygen octahedra and the canting of spins out of the CuO2 planes are not essential to the mechanism of chirality. Our findings point to a chiral mechanism coming from a coupling of acoustic phonons to the intrinsic excitations of the CuO2 planes.

The thermal conductivity of the antiferromagnet Nd2CuO4 was measured down to 50 mK. Using the spin-flop transition to switch on and off the acoustic Nd magnons, we can reliably separate the magnon and phonon contributions to heat transport. We find that magnons travel ballistically below 0.5 K, with a thermal conductivity growing as T3, from which we extract their velocity. We show that the rate of scattering of acoustic magnons by phonons grows as T3, and the scattering of phonons by magnons peaks at twice the average Nd magnon frequency.

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The normal state resistivtity, upper critical field H c2 and Hall coefficientAbove 70 K, ρ(T ) fits well curve predicted by Bloch-Grüneisen theory consistently with electron-phonon scattering. H c2 (0) was estimated to be about 15.0 Tesla within the weak-coupling BCS theory, and the superconducting coherence length ξ(0) is approximately 47Å. R H of M gCN i 3 is negative for the whole temperature range which definitely indicates that the carrier in M gCN i 3 is electron-type. R H is temperature independent between T c and ∼ 140 K. Above ∼ 140 K, the magnitude of R H decreases as temperature rises. At T = 100 K, the carrier density is 1.0 × 10 22 /cm 3 , which is comparable with that in perovskite (Ba, K)BiO 3 , and less than that of the metallic binary M gB 2 .