Keiya Shirahama

Surface study of liquid3He using surface state electrons

We have measured the mobility of surface state electrons (SSE) on liquid3He, μ3, aiming to study the elementary surface excitations of the Fermi liquid. A gradual increase of μ3 below 300 mK is attributed to the scattering of electrons by ripplons. Ripplons do exist in3He down to 100 mK. We observe an abrupt decrease of μ3, due to the transition to the Wigner solid (WS). The dependences of the WS conductivity and mobility on temperature and magnetic field differ from the SSE behavior on liquid4He.

Sliding Wigner solid on liquid 4He

We report a systematic experimental study of the anomalous nonlinear magnetotransport in the Wigner solid (WS) trapped on a liquid4He surface. The ac Corbino conductivity σxx exhibits an abrupt jump at a certain driving voltage. The threshold input voltage Vth for the σxx jump varies as Vth ∝ B−0.8 ω−1 n1.5sE⊥, where B, ω, ns, and E⊥ are magnetic field, frequency, electron density and pressing electric field, respectively. We interpret the σxx jump as the transition between the WS accompanied with the periodic 4He surface deformation and the WS which decouples from the surface, due to the large driving force. A simple model is presented: The rigid-potential sliding model qualitatively explains the above mentioned behaviors of Vth. We have found that the dependences of σxx on B and E⊥ are different from those of the liquid phase. The anomalous behaviors of σxx play a crucial role on the sliding model.

Transport properties of the Wigner solid on liquid3He

We have studied the transport properties of the Wigner solid (WS) on a liquid3He surface down to 10 mK. The conductivity σzz obeys the Drude law σzzαB−2 whereB is magnetic field perpendicular the the electron sheet. It is quite in contrast to the case of the Wigner solid on liquid4He, in which σzz is proportional toB−1. The mobility μ is proportional toT2, whereT is temperature. ThisT2 dependence is attributed to theT−2 behavior of viscosity of Fermi liquid3He. Strongly nonlinear behaviors have been observed.

Sliding of the Wigner solid on liquid helium

Abstract We have studied strongly nonlinear transport phenomena in the Wigner solid (WS) on liquid 4 He. The Corbino conductivity σ XX exhibited an abrupt jump, which separates two states of the WS; in one state the WS is registered in the surface deformation, whereas in the other state the WS is decoupled from the deformation. The boundary between these two states is empirically described in terms of the input voltage V in , the magnetic field B perpendicular to the surface, measuring frequency ω, electron density n s , and pressing electric field E ⊥ as V in Ω n −1.5 s B 0.8 E −1 ⊥ ≈constant. This empirical relation is derived from a model to describe the collective sliding of the electrons out of the periodic deformation of the He surface. Anomalous behaviors of the conductivity of the WS are crucial to interpret the phenomenon.

Wigner solid on the free surface of superfluid 3He-A

Abstract We have measured the resistance of the Wigner solid (WS) on the free surface of superfluid 3 He-A. The A phase is formed by applying a magnetic field parallel to the surface. We have observed an abrupt decrease of resistance R at a temperature which decreases with increasing field. We attribute the decrease of R to the A–B superfluid transition. The WS resistance in the A-phase is found to be dominated by the scattering of 3 He quasiparticles excited in the gapless orientation, which is perpendicular to the surface.

Sliding of the wigner solid from the coupled plasmon-ripplon surface deformation

The Wigner solid (WS) on a liquid4He surface is accompanied with the periodic surface deformation, i.e. the ripplons whose wavevectors equal the reciprocal WS lattice vectors. This unique situation plays a crucial role in the dynamics of the WS. We have performed an extensive measurement of the ac Corbino conductivity σxx. The WS conductivity shows extremely nonlinear behavior, and it jumps abruptly at a certain input voltage. The threshold input voltage Vth varies as VthαB−0.8f−1ns1.5E⊥, where B, f, ns, and E⊥ are magnetic field, frequency, electron density and pressing electric field, respectively. We have interpreted the σxx jump as the collective sliding of the electrons out of the surface deformation.

Sliding dynamics of the electron crystal on liquid helium: A pulsed study

We report the study of the sliding dynamics of the Wigner crystal on a liquid4He surface, by means of pulsed electric field. A trapezoidal voltage pulse whoseramp rate at the pulse edges exceeds a certain threshold makes the crystal slide from the periodic surface dimples.

Experimental study of the surface properties of superfluid and normal 3He by plasma resonance of Wigner solid

A new experimental method has been developed for using plasma resonance of Wigner solid (WS) for the study of liquid 3He surface properties in superfluid and normal states. The behaviour of optical coupled plasmon-ripplon (CPR) resonances have been investigated in magnetic field 15 mT at temperatures down to 0.35 mK. The position of transverse optical plasma mode, which becomes visible when weak magnetic field is applied gives the information about WS coupling with helium surface. The line width of CPR resonance is used for getting the collision time in the scattering of surface electrons from the surface roughness. The influence of the superfluid transition on the collision time is observed.

Edge magnetoplasmons on a liquid helium surface and quantum transport in a high magnetic field

We have measured the linewidth of edge magnetoplasmons (EMP) propagated at the edge of surface state electrons on a liquid4He surface from 90 to 1400 mK and for magnetic fields up to 6.4 T. We have confirmed that σzz obtained from the linewidth at 1100 mK agrees with σzz obtained from the capacitive measurement of Dykman et al. Below 700 mK, where the scattering by ripplons predominates the transport, we have observed that σzz is inversely proportional to the square root of temperature and independent of magnetic field. The temperature dependence agrees with theories, while the absence of the magnetic field dependence does not.

Kosterlitz-Thouless superfluid transition in 4He films adsorbed on porous glasses

Abstract We have systematically studied the size- or frequency- dependent superfluid transition in 4He films adsorbed on porous glasses with pore diameters s from 50 to 10000A, using two sets of torsional oscillators containing different pore size glasses with a common 4He inlet. It is clarified that the transition temperature Tc is determined by the vortex pair unbinding on length scales comparable to the characteristic lengths, the half of the pore circumference π d 2 or the vortex diffusion length rd.