Heat Capacity Evidence for the Suppression of Skyrmions at Large Zeeman Energy

Measurements on a multilayer two-dimensional electron system (2DES) near Landau level filling $\nu$=1 reveal the disappearance of the nuclear spin contribution to the heat capacity as the ratio $\tilde{g}$ between the Zeeman and Coulomb energies exceeds a critical value $\tilde{g}_c \approx$0.04. This disappearance suggests the vanishing of the Skyrmion-mediated coupling between the lattice and the nuclear spins as the spin excitations of the 2DES make a transition from Skyrmions to single spin-flips above $\tilde{g}_c$. Our experimental $\tilde{g}_c$ is smaller than the calculated $\tilde{g}_c$=0.054 for an ideal 2DES; we discuss possible origins of this discrepancy.Comment: Experimental paper, 6 figure

Critical Behavior of Nuclear-Spin Diffusion in GaAs/AlGaAs Heterostructures near Landau Level Filling \nu=1

Thermal measurements on a GaAs/AlGaAs heterostructure reveal that the state of the confined two-dimensional electrons dramatically affects the nuclear-spin diffusion near Landau level filling factor \nu=1. The experiments provide quantitative evidence that the sharp peak in the temperature dependence of heat capacity near \nu=1 is due to an enhanced nuclear-spin diffusion from the GaAs quantum wells into the AlGaAs barriers. We discuss the physical origin of this enhancement in terms the possible Skyrme solid-liquid phase transition.Comment: 1 LateX file, 3 figures, submitte

A silicon-on-insulator quantum wire

Thin, narrow silicon-on-insulator n-channel MOSFETs have been fabricated. The drain current characteristics, when measured as a function of gate voltage at low temperature, exhibit a series of oscillations, which is characteristic of current transport in one-dimensional systems (quantum wires). Theoretical calculation of the current oscillations in the device show reasonable agreement with the experimental characteristics

Specific heat measurements on U-2(Ru1-xRhx)(3)Si-5 ternary silicides

Specific heat (C) measurements have been performed on several compositions of the U-2(Ru1-xRhx)(3)Si-5 system showing an interesting magnetic phase diagram: (i) no magnetic ordering appears above 2 K for 0 less than or equal to xantiferromagnetic transition), a very strong enhancement of CIT is observed below 12 K, reaching a value as high as 255 mJ/U-mol K-2 at 2 K. This behaviour suggests either the occurrence of magnetic ordering below 2 K or that this silicide can be considered as the heaviest electron system. (C) 1998 Elsevier Science S.A

Transport and Magnetic-properties of U(2)m(3)si(5) Silicides (m=co,Rh,Ru)

We report and discuss experimental data on the electrical resistivity p, thermoelectric power S, thermal conductivity kappa, specific heat C and magnetic susceptibility chi of polycrystalline U(2)M(3)Si(5) silicides (M = Co, Rh, Ru). The magnetic and transport properties of these compounds depend strongly on the nature of the transition metal M. In U2Co3Si5, p(T) shows features that could be identified to Kondo systems while S(T) shows a two-peak structure. U2Rh3Si5 shows an antiferromagnetic ordering at T-N similar to 25 K, which is accompanied by steep changes in both p(T) and S(T). U2Ru3Si5 behaves like a nonmagnetic compound and displays distinct anomalies in the low-temperature domains of p(T, H) and S(T, H). The lattice thermal conductivity varies as T-2 at low temperatures, suggesting a dominant scattering of the phonons by the conduction electrons

Thermopower of Composite Fermions

Measured diffusion thermopower of a low-disorder two-dimensional hole system in the extreme quantum limit is used to probe the thermal properties of the recently proposed particle-flux composite fermions (CF's). The data are consistent with the CF's exhibiting the integral quantum Hall effect away from filling factor nu=1/2. The magnitudes of the thermopower maxima between the fractional quantum Hall states yield an estimate for the CF Landau-level broadening Gamma(CF) which agrees well with Gamma(CF) deduced from the analysis of the excitation energy gaps for the fractional liquid states