arXiv subjects

S. Komatsu

Publications and source records attributed to S. Komatsu.

7 recordsLinked to original sources

arXiv2026

Commensurate-Incommensurate Transition in Submonolayer $^3$He on Graphite

We report high-precision heat-capacity measurements of submonolayer $^3$He adsorbed on highly crystalline graphite, revealing new aspects of the commensurate$-$incommensurate transition. Below 1\~K, two possible striped domain-wall phases emerge: $\alpha_1$ with variable wall spacing and $\alpha_2$ with fixed spacing. The $T$-linear heat capacity in $\alpha_1$ arises from one-dimensional phonons along the walls. $\alpha_2$ melts into $\alpha_1$ at a critical density via a second-order transition, consistent with a quantum nematic (quantum liquid-crystal) state in $\alpha_1$, and reconciling thermodynamic and prior nuclear-magnetic data.

cond-mat.other↗

arXiv2025

Experimental Results from Early Non-Planar NI-HTS Magnet Prototypes for the Columbia Stellarator eXperiment (CSX)

The Columbia Stellarator eXperiment (CSX) is an upgrade of the Columbia Non-neutral Torus (CNT) that aims to demonstrate a university-scale, quasi-axisymmetric stellarator using high-temperature superconducting (HTS) technology at an on-axis magnetic field target of 0.5 T. Due to the strain sensitivity of ReBCO (Rare-earth Barium Copper Oxides), adapting it to non-planar stellarator geometries requires new winding, structural, and cooling strategies. We report on the results of a staged prototype program (P1, P2, P3) employing 3D-printed, sectional aluminum coil frames with winding channels, gimballed constant-tension winding mechanics, and solder potting for radial current redistribution and passive quench mitigation. The first prototype, P1 (planar elliptical, double-pancake) tested additive manufacture, sectional joining and baseline winding, achieving predicted fields at 77 K. P2 (non-planar, higher strain) was wound to 42 turns, energized at 30-40 K to produce expected magnetic fields, and studied thermal gradients and resistance at up to 4.5 kAt. Design evolution in P3 introduces concave geometry with dual double-pancakes, 200 turns, and approaches the 70 kAt target at 20 K. In parallel, sub-microhm lap joints have been developed. Together, these results de-risk manufacturing, cooling interfaces, quench management, and diagnostics, paving the way for full-size non-planar HTS stellarator coils for CSX.

physics.ins-det↗

arXiv2021

Gate tuning of fractional quantum Hall states in InAs two-dimensional electron gas

We report the observation of fractional quantum Hall (FQH) effects in a two-dimensional electron gas (2DEG) confined to an InAs/AlGaSb quantum well, using a dual-gated Hall-bar device allowing for the independent control of the vertical electric field and electron density. At a magnetic field of 24 T, we observe FQH states at several filling factors, namely $ν= 5/3$, $2/3$, and $1/3$, in addition to the $ν= 4/3$ previously reported for an InAs 2DEG. The $ν= 4/3$ and $5/3$ states, which are absent at zero back-gate voltage, emerge as the quantum well is made more symmetric by applying a positive back-gate voltage. The dependence of zero-field electron mobility on the quantum-well asymmetry reveals a significant contribution of interface-roughness scattering, with much stronger scattering at the lower InAs/AlGaSb interface. However, the dependence of the visibility of the FQH effects on the quantum-well asymmetry is not entirely consistent with that of mobility, suggesting that a different source of disorder is also at work.

cond-mat.mes-hall↗

arXiv2013

Hybrid Monte Carlo on Lefschetz Thimbles -- A study of the residual sign problem

We consider a hybrid Monte Carlo algorithm which is applicable to lattice theories defined on Lefschetz thimbles. In the algorithm, any point (field configuration) on a thimble is parametrized uniquely by the flow-direction and the flow-time defined at a certain asymptotic region close to the critical point, and it is generated by solving the gradient flow equation downward. The associated complete set of tangent vectors is also generated in the same manner. Molecular dynamics is then formulated as a constrained dynamical system, where the equations of motion with Lagrange multipliers are solved by the second-order constraint-preserving symmetric integrator. The algorithm is tested in the lambda phi^4 model at finite density, by choosing the thimbles associated with the classical vacua for subcritical and supercritical values of chemical potential. For the lattice size L=4, we find that the residual sign factors average to not less than 0.99 and are safely included by reweighting and that the results of the number density are consistent with those obtained by the complex Langevin simulations.

hep-lat↗

arXiv2011

Study of the K0(L) --> pi0 pi0 nu nu-bar decay

The rare decay K0(L) --> pi0 pi0 nu nu-bar was studied with the E391a detector at the KEK 12-GeV proton synchrotron. Based on 9.4 x 10^9 K0L decays, an upper limit of 8.1 x 10^{-7} was obtained for the branching fraction at 90% confidence level. We also set a limit on the K0(L) --> pi0 pi0 X (X --> invisible particles) process; the limit on the branching fraction varied from 7.0 x 10^{-7} to 4.0 x 10^{-5} for the mass of X ranging from 50 MeV/c^2 to 200 MeV/c^2.

hep-ex↗

arXiv2010

Search for the decay $K_L^0 \rightarrow 3γ$

We performed a search for the decay $K_L^0 \rightarrow 3γ$ with the E391a detector at KEK. In the data accumulated in 2005, no event was observed in the signal region. Based on the assumption of $K_L^0 \rightarrow 3γ$ proceeding via parity-violation, we obtained the single event sensitivity to be $(3.23\pm0.14)\times10^{-8}$, and set an upper limit on the branching ratio to be $7.4\times10^{-8}$ at the 90% confidence level. This is a factor of 3.2 improvement compared to the previous results. The results of $K_L^0 \rightarrow 3γ$ proceeding via parity-conservation were also presented in this paper.

hep-ex↗

arXiv2001

SSC of MAXI experiment

Monitor of All-sky X-ray Image (MAXI) on the International Space Station (ISS) has two kinds of X-ray detectors: the Gas Slit Camera (GSC) and the Solid-state Slit Camera (SSC). SSC is an X-ray CCD array, consisting of 16 chips, which has the best energy resolution as an X-ray all-sky monitor in the energy band of 0.5 to 10 keV. Each chip consists of 1024x1024 pixels with a pixel size of 24$μ$m, thus the total area is ~200 cm^2. We have developed an engineering model of SSC, i.e., CCD chips, electronics, the software and so on, and have constructed the calibration system. We here report the current status of the development and the calibration of SSC.

astro-ph↗