arXiv subjects

Naofumi Matsuyama

Publications and source records attributed to Naofumi Matsuyama.

4 recordsLinked to original sources

arXiv2025

Fate of Pomeranchuk effect in ultrahigh magnetic fields

The Pomeranchuk effect is a counterintuitive phenomenon where liquid helium-3 (3He) solidifies under specific pressures, not when cooled, but when heated. This behaviour originates from the magnetic entropy of nuclear spins, suggesting a magnetic field should influence it. However, its detailed response to magnetic fields remains elusive due to the small nuclear magneton of 3He and lack of analogous fermion systems. Here, we show that an electron system also exhibit the Pomeranchuk effect, where the Fermi liquid state solidifies in a high magnetic field, unlike conventional electron systems where a field melts an electron solid into a metal. Remarkably, the electron system displays a reentrant liquid state in ultrahigh fields. These responses are explained by changes in magnetic entropy and magnetisation, extending the underlying physics to 3He. Our findings clarify magnetic-field impact on the Pomeranchuk effect and open avenues for magnetic control of chemical interactions.

cond-mat.str-el↗

arXiv2023

Simultaneous measurement of specific heat and thermal conductivity in pulsed magnetic fields

We report an experimental setup for simultaneously measuring specific heat and thermal conductivity in feedback-controlled pulsed magnetic fields of 50 msec duration at cryogenic temperatures. A stabilized magnetic field pulse obtained by the feedback control, which dramatically improves the thermal stability of the setup and sample, is used in combination with the flash method to obtain absolute values of thermal properties up to 37.2 T in the 2 K to 16 K temperature range. We describe the experimental setup and demonstrate the performance of the present method with measurements on single crystal samples of the geometrically frustrated quantum spin-dimer system SrCu$_2$(BO$_3$)$_2$. Our proof-of-principle results show excellent agreement with data taken using a standard steady-state method, confirming the validity and convenience of the present approach.

cond-mat.str-el↗

arXiv2023

Rhombic skyrmion lattice coupled with orthorhombic structural distortion in EuAl$_{4}$

The centrosymmetric tetragonal itinerant magnet EuAl$_{4}$ exhibits an intricate magnetic phase diagram including rhombic and square skyrmion-lattice (SkL) phases in the external magnetic field. Here, we report a multi-axis dilatometric investigation of EuAl$_{4}$ by means of a newly designed fiber-Bragg-grating technique complemented by a resonant x-ray scattering experiment, revealing anisotropic magnetostriction and magnetovolume effect associated with successive phase transitions. The rhombic and square SkL phases are found to possess $\sim$0.10% and $\sim$0.03% orthorhombic structural distortion within the $ab$ plane, respectively. We propose that the coupling between the spin system and the lattice deformation should be essential for the structural instability in EuAl$_{4}$, yielding a rich variety of topological spin textures with spontaneous rotational-symmetry breaking as well as a potential controllability of the SkL phases by uniaxial stress or pressure.

cond-mat.str-el↗

arXiv2022

Magnetically hidden state on the ground floor of the magnetic Devil's staircase

We investigated the low-temperature and high-field thermodynamic and ultrasonic properties of SrCu2(BO3)2, which exhibits various plateaux in its magnetization curve above 27~T, called a magnetic Devil's staircase. The results of the present study confirm that magnetic crystallization, the first step of the staircase, occurs above 27~T as a 1st-order transition accompanied by a sharp singularity in heat capacity $C_p$ and a kink in the elastic constant. In addition, we observe a thermodynamic anomaly at lower fields around 26~T, which has not been previously detected by any magnetic probes. At low temperatures, this magnetically hidden state has a large entropy and does not exhibit Schottky-type gapped behavior, which suggests the existence of low-energy collective excitations. Based on our observations and theoretical predictions, we propose that magnetic quadrupoles form a spin-nematic state around 26~T as a hidden state on the ground floor of the magnetic Devil's staircase.

cond-mat.str-el↗