arXiv subjects

R. Hänninen

Publications and source records attributed to R. Hänninen.

22 records · Page 2Linked to original sources

arXiv2003

Model of Inhomogeneous Impurity Distribution in Fermi Superfluids

The standard treatment of impurities in metals assumes a homogeneous distribution of impurities. In this paper we study distributions that are inhomogeneous. We discuss in detail the "isotropic inhomogeneous scattering model" which takes into account the spatially varying scattering on the scale of the superfluid coherence length. On a large scale the model reduces to a homogeneous medium with renormalized parameter values. We apply the model to superfluid 3He, where porous aerogel acts as the impurity. We calculate the transition temperature Tc, the order parameter, and the superfluid density. Both A- and B-like phases are considered. Two different types of behavior are identified for the temperature dependence of the order parameter. We compare the calculations with experiments on 3He in aerogel. We find that most of the differences between experiments and the homogeneous theory can be explained by the inhomogeneous model. All our calculations are based on the quasiclassical theory of Fermi liquids. The parameters of this theory for superfluid 3He in aerogel are discussed.

cond-mat↗

arXiv2003

Calculation of NMR Properties of Solitons in Superfluid 3He-A

Superfluid 3He-A has domain-wall-like structures, which are called solitons. We calculate numerically the structure of a splay soliton. We study the effect of solitons on the nuclear-magnetic-resonance spectrum by calculating the frequency shifts and the amplitudes of the soliton peaks for both longitudinal and transverse oscillations of magnetization. The effect of dissipation caused by normal-superfluid conversion and spin diffusion is calculated. The calculations are in good agreement with experiments, except a problem in the transverse resonance frequency of the splay soliton or in magnetic-field dependence of reduced resonance frequencies.

cond-mat↗

arXiv2003

Structure of surface vortex sheet between two rotating 3He superfluids

We study a two-phase sample of superfluid 3He where vorticity exists in one phase (3He-A) but cannot penetrate across the interfacial boundary to a second coherent phase (3He-B). We calculate the bending of the vorticity into a surface vortex sheet on the interface and solve the internal structure of this new type of vortex sheet. The compression of the vorticity from three to two dimensions enforces a structure which is made up of half-quantum units, independently of the structure of the source vorticity in the bulk. These results are consistent with our NMR measurements.

cond-mat↗

arXiv2000

One-Dimensional Textures and Critical Velocity in Superfluid 3He-A

We study theoretically the stability of flow in superfluid 3He-A. The calculations are done using a one-dimensional model where the order parameter depends only on the coordinate in the direction of the superfluid velocity v_s. We concentrate on the case that the external magnetic field H is perpendicular to v_s, where only few results are available analytically. We calculate the critical velocity v_c at which the superflow becomes unstable against the formation of continuous vortices. The detailed dependence of v_c on the temperature and on the form of the underlying orbital texture l(r) is investigated. Both uniform and helical textures and two types of domain-wall structures are studied. The results are partially in agreement with experiments made in a rotating cylinder.

cond-mat↗