The influence of thermal conduction on the field dependence in spin-lattice relaxation experiments

It is demonstrated that heat transfer in magnetic samples and the surrounding liquid helium leads to a field dependence of the observed relaxation time in low-frequency relaxation measurements which deviates strongly from that of the intrinsic spin-lattice relaxation

Spin-lattice relaxation in potassium chromium alum

A comparison is made between the results of low-frequency relaxation measurements on potassium chromium alum placed in liquid helium and in vacuum, respectively. It is found that only a part of the lattice oscillations is involved in the spin-lattice relaxation process. The spin-lattice relaxation time was found after correcting the time constants of the vacuum measurements by experimental shortening factors. The differences between the spin-lattice relaxation time and the time constants from the liquid-helium measurements can be explained for the greater part by the finite thermal conductivity of the liquid helium

Spatially Resolved Stellar Kinematics of Field Early-Type Galaxies at z=1: Evolution of the Rotation Rate

We use the spatial information of our previously published VLT/FORS2 absorption line spectroscopy to measure mean stellar velocity and velocity dispersion profiles of 25 field early-type galaxies at a median redshift z=0.97 (full range 0.6<z<1.2). This provides the first detailed study of early-type galaxy rotation at these redshifts. From surface brightness profiles from HST imaging we calculate two-integral oblate axisymmetric Jeans equation models for the observed kinematics. Fits to the data yield for each galaxy the degree of rotational support and the mass-to-light ratio M/L_Jeans. S0 and Sa galaxies are generally rotationally supported, whereas elliptical galaxies rotate less rapidly or not at all. Down to M(B)=-19.5 (corrected for luminosity evolution), we find no evidence for evolution in the fraction of rotating early-type (E+S0) galaxies between z=1 (63+/-11%) and the present (61+/-5%). We interpret this as evidence for little or no change in the field S0 fraction with redshift. We compare M/L_Jeans with M/L_vir inferred from the virial theorem and globally averaged quantities and assuming homologous evolution. There is good agreement for non-rotating (mostly E) galaxies. However, for rotationally supported galaxies (mostly S0) M/L_Jeans is on average ~40% higher than M/L_vir. We discuss possible explanations and the implications for the evolution of M/L between z=1 and the present and its dependence on mass.Comment: To appear in ApJ 683 (9 pages, 7 figures). Minor changes included to match published versio

Superconductivity-Induced Transfer of In-Plane Spectral Weight in Bi2Sr2CaCu2O8: Resolving a Controversy

We present a detailed analysis of the superconductivity-induced redistribution of optical spectral weight in Bi2Sr2CaCu2O8 near optimal doping. It confirms the previous conclusion by Molegraaf et al. (Science 66, 2239 (2002)), that the integrated low-frequency spectral weight shows an extra increase below Tc. Since the region, where the change of the integrated spectral weight is not compensated, extends well above 2.5 eV, this transfer is caused by the transfer of spectral weight from interband to intraband region and only partially by the narrowing of the intraband peak. We show that the opposite assertion by Boris et al. (Science 304, 708 (2004)) regarding this compound, is unlikely the consequence of any obvious discrepancies between the actual experimental data.Comment: ReVTeX, 9 pages, 8 encapsulated postscript figures, several typo's correcte

Two high-frequency mutual inductance bridges with high resolution

Two mutual inductance bridges are described for operation up to about 100 kHz. Special attention is paid to the sensitivity and resolution of the bridges. Both bridges can be used to measure variations of about 10 pH in the mutual inductance. The first bridge consists of passive elements only whereas the second bridge is equipped with active circuits

On the influence of heat transport on low- frequency paramagnetic spin-Lattice relaxation experiments

In low-frequency relaxation experiments on paramagnetic crystals, placed in liquid helium, often dispersion- and absorption curves are found, strongly deviating from those following from the thermodynamic theory of Casimir and Du Pré. For the relaxation time τabs, related to the maximum in the absorption curve, a temperature dependence τabs αT-α with 1 < α < 6 has been found frequently, accompanied sometimes with a jump at the helium-transition temperature Tλ. We computed, starting from a model including the heat conduction of lattice and helium bath and a heat resistance from crystal to bath, dispersion- and absorption curves and found that, assuming the direct process for the spin—lattice relaxation, τabs(T) (related to the maximum of the calculated absorption curve) can be described roughly as mentioned above with a jump at Tγ

Common Fermi-liquid origin of T-squared resistivity and superconductivity in n-type SrTiO3

A detailed analysis is given of the T^2 term in the resistivity observed in electron-doped SrTiO3. Novel bandstructure data are presented, which provide values for the bare mass, density of states, and plasma frequency of the quasiparticles as a function of doping. It is shown that these values are renormalized by approximately a factor 2 due to electron-phonon interaction. It is argued that the quasiparticles are in the anti-adiabatic limit with respect to electron-phonon interaction. The condition of anti-adiabatic coupling renders the interaction mediated through phonons effectively non-retarded. We apply Fermi-liquid theory developed in the 70's for the T^2 term in the resistivity of common metals, and combine this with expressions for Tc and with the Brinkman-Platzman-Rice (BPR) sum-rule to obtain Landau parameters of n-type SrTiO3. These parameters are comparable to those of liquid 3He, indicating interesting parallels between these Fermi-liquids despite the differences between the composite fermions from which they are formed.Comment: 12 pages, 9 figure

Phase transitions in RbCoCl3 · 2H2O

Differential susceptibility measurements were performed on a single crystal of RbCoCl3 · 2H2O. An anti-ferromagnetic ordering was found at 2.975 K