Hiroki Ikegami

Chiral Symmetry Breaking in Superfluid 3He-A

Quantum Handedness When a rotating object is placed in circulating fluid, an imbalance of pressures on either side of it causes a deflecting force called the Magnus force. The quantum analog of this effect has been predicted to appear in the low-temperature A phase of 3He, where the Cooper pairs forming the superfluid have a specific handedness. An impurity traveling through such a superfluid would experience a deflecting force in the direction determined by the chirality of the pairs. Ikegami et al. (p. 59) trapped impurities beneath the free surface of 3He, set them in motion, and demonstrated the existence of this deflecting force by measuring the differential transverse current. The sign of the deflection varied over different cooling runs, indicating that the system was choosing one or the other chirality upon entering the superfluid phase—a signature of spontaneous symmetry breaking. The asymmetric deflection of impurities beneath the surface of helium-3 reveals the handedness of the superfluid A phase. Spontaneous symmetry breaking is an important concept in many branches of physics. In helium-3 (3He), the breaking of symmetry leads to the orbital chirality in the superfluid phase known as 3He-A. Chirality is a fundamental property of 3He-A, but its direct detection has been challenging. We report direct detection of chirality by transport measurements of electrons trapped below a free surface of 3He-A. In particular, we observed the so-called intrinsic Magnus force experienced by a moving electron; the direction of the force directly reflected the chirality. We further showed that, at the superfluid transition, the system selected either right- or left-handed chirality. The observation of such selection directly demonstrates chiral symmetry breaking.

Reentrant Melting of a Classical Quasi-One-Dimensional Wigner Crystal on the Surface of Liquid Helium

We present transport measurements of electrons on the surface of liquid helium confined to a microscopic channel, the effective width of which can be controlled electrostatically. Above 1 K the electron system is liquid-like and the conductance varies smoothly with the channel width. At lower temperatures the system forms a classical quasi-one-dimensional Wigner crystal (WC). Close to the WC melting temperature, the current oscillates as the channel width is varied, due to reentrant melting as recently reported [H. Ikegami, H. Akimoto, D. G. Rees, and K. Kono: Phys. Rev. Lett. 109 (2012) 236802]. In the WC regime we observe Bragg–Cherenkov ripplon scattering, a signature of strong spatial electron order, for both the widely open channel and the single electron chain.

Study of dynamical properties of superfluid 3He film flow by inter-digitated capacitors

Abstract We have developed a new technique to study film flow of superfluid 3 He . By this technique utilizing inter-digitated capacitors, flow rate and thickness of the film can be controlled. We measured superfluid critical temperatures of film, Tcf , for thicknesses from 0.2 to 7.5 μm . The observed suppression of Tcf is consistent with the theoretical results of Fetter et al. and Kjaldman et al.

Mobility of Ions Trapped Below a Free Surface of Superfluid 3He

The \(p\)-wave superfluid phases of 3He-B and 3He-A are topologically nontrivial. Topological properties manifest themselves as the formation of bound states at a surface. Unusual properties of the \(p\)-wave superfluids also appear around impurities, such as an ion immersed in liquid 3He. In this article, we present the mobility of positive and negative ions trapped below a free surface of 3He-B and 3He-A measured down to 250 μK, which is much lower than the temperatures attained in previous experiments in the bulk. Mobility measurements are conducted for two purposes: one is to figure out details of the scattering of a quasiparticle by an impurity in \(p\)-wave superfluids, and the other is to detect the surface Andreev bound states (SABSs) at a free surface of 3He-B formed as a result of the nontrivial topology of 3He-B. We find, in both superfluid phases, that the mobility shows a considerable increase with decreasing temperature. In both superfluid phases, the mobility of a negative ion at high tempe...

Vapor Pressure and Heat Capacity Measurement of 3He Adsorbed on 18Å-Pores

We have measured the vapor pressure (0.84 K<T<9 K) and the heat capacity (80 mK<T<4 K) of 3He adsorbed on pores 18 Å in diameter. The results of the vapor pressure measurement indicate that 3He film grows up to the second layer. In the first layer, the heat capacity of 3He shows the same temperature and coverage dependence as 4He, indicating a solid phase. Above a little higher coverage than second layer promotion, heat capacity isotherms for 3He at several hundred mK increase with coverage while those for 4He decrease. This large heat capacity of 3He is the nuclear spin heat capacity of the second layer fluid 3He.

Observation of Intrinsic Magnus Force and Direct Detection of Chirality in Superfluid 3He-A

We report details of the observation of the intrinsic Magnus (IM) force acting on negative and positive ions trapped just below a free surface of the A phase of superfluid 3He (3He-A). From the transport measurements of the ions along the surface, we found that the IM force acts on both the negative and positive ions. We also demonstrate that the transport measurements could distinguish whether the surface is composed of a chiral monodomain or multiple chiral domains. For multiple chiral domains, the current of the ions was found to be irreproducible and unstable, which was reasonably explained by the formation of the chiral domain structure and the dynamics of the chiral domain walls. For chiral monodomains, the appearance ratio of chirality emerging upon cooling through the superfluid transition temperature was found to depend on the direction of the external magnetic field, which implies the existence of an unknown coupling between the chirality and the magnetic field.

Phonon velocity of 4He Bose fluid formed in one-dimensional 18 Å pores

Abstract We discuss the one-dimensional (1D) phonon velocities of 4 He adsorbed on straight 18 A pores deduced from our recent two experiments, the vapor pressure and the heat capacity measurements. The heat capacity of the second layer fluid is proportional to temperature below 0.2 K , which is attributed to 1D phonon excitations along the tube. The phonon heat capacity gives us the phonon velocity, vC. While, the phonon velocity, vP, also can be deduced from the vapor pressure. The magnitude and coverage dependence of vP and vC agree well. This fact strongly supports that the temperature-linear heat capacity is the 1D phonon heat capacity.

Quasiparticle Scattering Model for Interpreting the Wigner Solid Resistivity on the Surface of Superfluid 3He

A quasiparticle scattering model developed by Monarkha and Kono is explored further to include magnetic field effects on superfluid 3 He. It successfully explains the absence of magnetic field effects in superfluid 3 He-A and normal 3 He. Both an explicit magnetic-field-dependent term in the Bogoliubov quasiparticle energy and the distortion of energy gap are the origin of anisotropic properties of superfluid 3 He-B in magnetic field. In order to quantitatively compare the model with experimental observation, the energy gap distortion has been numerically evaluated by taking into account Landaus Fermi liquid effect up to F 0 a . The Leggett rotation is considered in an ad hoc fashion in 3 He-B. The experimental data can be satisfactorily interpreted by assuming that the rotation considered to be realized only in the vicinity of the free surface extends to the bulk. The numerical value of the Landau parameter is important in obtaining quantitative agreement. This might provide a new experimental possibili...

A millikelvin temperature scale in high magnetic fields based on 3He melting pressure

Abstract We propose a new millikelvin temperature scale (3.5 mK ⩽T⩽250 mK ) , which can be used in high magnetic fields (B⩽14.5 T ) , based on the melting pressure of 3 He . The new scale is defined by a set of three equations which gives a melting pressure decrease due to application of B at a fixed T. The estimated accuracies of this scale are ±0.1% and ±0.4% above and below 10 mK , respectively, besides uncertainties in the existing zero-field 3 He melting curve T-scale we stand for. It is useful to calibrate other more convenient thermometers in situ of high fields.

Layer-by-Layer Growth of 4He Adsorbed on One-dimensional 18Å-Pores

We have measured vapor pressures (P) of 4He adsorbed on one-dimensional pores of 18 Å diameter with a sensitivity of 2×10−3 mbar as a function of coverage down to 1.2 K. The isothermal compressibility (κT) calculated from P isotherm has two minima, which are associated with the completion of the first and the second layer. The adsorption energy was obtained quantitatively from an Arrhenius type temperature dependence of P. As the coverage is increased, the adsorption energy at T=0 per atom (Δ0/kB) decreases from 180 K to 35 K, followed by a clear step associated with a second layer promotion. After second layer completion, Δ0/kB is constant. The magnitude is the same value as the latent heat of the bulk 4He liquid (7 K). These results give us a clear picture that 4He film grows in a layer-by-layer fashion up to the second layer on one-dimensional pore walls.