arXiv subjects

Mari Einaga

Publications and source records attributed to Mari Einaga.

7 recordsLinked to original sources

arXiv2026

High-pressure magnetic transition in iron observed via diamond quantum sensing

Diamond quantum sensors offer high precision and spatial resolution as magnetic probes, making them promising for a wide range of applications. While diamond anvil cells (DACs) can generate extremely high pressures, techniques for magnetometry under such conditions remain limited. By fabricating an ensemble of NV centers directly on the anvil diamond surface, we enable precise magnetic measurements under high pressure. In this work, we employ this NV ensemble to image the stray magnetic field of iron up to 30 GPa, enabling the observation of the magnetic transition ($α$-$\varepsilon$ transition) in iron.

physics.app-ph↗

arXiv2025

GPa Pressure Imaging Using Nanodiamond Quantum Sensors

We demonstrate wide-field optical microscopy of the pressure distribution at approximately 20 GPa in a diamond anvil cell (DAC), using nitrogen-vacancy (NV) centers in nanodiamonds (NDs) as quantum sensors. Pressure and non-hydrostaticity maps are obtained by fitting optically detected magnetic resonance (ODMR) spectra with models incorporating hydrostatic and uniaxial stress conditions. Two methods for introducing NDs with a pressure-transmitting medium are compared, revealing that the embedding approach affects the degree of non-hydrostaticity. This ND-based technique offers a powerful imaging platform for probing pressure-induced phenomena and is extendable to other physical quantities such as magnetic fields.

cond-mat.mtrl-sci↗

arXiv2020

Electrical transport measurements for superconducting sulfur hydrides using boron-doped diamond electrodes on beveled diamond anvil

A diamond anvil cell (DAC) which can generate extremely high pressure of multi-megabar is promising tool to develop a further physics such a high-transition temperature superconductivity. However, electrical transport measurements, which is one of the most important properties of such functional materials, using the DAC is quite difficult because the sample space is very small and a deformation of electrodes under extreme condition. In this study, we fabricated a boron-doped diamond micro-electrode and an undoped diamond insulation on a beveled culet surface of the diamond anvil. By using the developed DAC, we demonstrated the electrical transport measurements for sulfur hydride H$_2$S which known as a pressure-induced high-transition temperature superconducting H$_3$S at high pressure. The measurements were successfully conducted under high pressure up to 192 GPa, and then a multi-step superconducting transition composed from pure sulfur and some kinds of surfer hydrides, which is possible HS$_2$, was observed with zero resistance.

cond-mat.supr-con↗

arXiv2019

Superconductivity of Pure H3S Synthesis from Elemental Sulfur and Hydrogen

Superconductive H3S synthesized from H2S is very poorly crystallized, and has excess sulfur as impurity (3H2S -> 2H3S + S). The phase transition process undergoes in sulfur excess condition, which might cause hydrogen deficiency. The influence of hydrogen deficiency is not clear. Therefore investigation on the superconductivity in H3S with no hydrogen deficiency is demanded. Two groups performed synthesis of H3S from elemental sulfur and hydrogen (direct synthesis) and their results have shown that no hydrogen deficiency is caused when the direct synthesis is performed under hydrogen excessive condition. However, no measurements of superconductivity has been carried out because of the major technical difficulties in hydrogen experiments in diamond anvil cells (DACs). Here, we report the first electrical resistance measurements in superconductive H3S synthesized from elemental sulfur and hydrogen (3H2 + 2S -> 2H3S). Our powder X-ray diffraction (PXRD) using a synchrotron X-ray revealed that synthesized H3S has much improved crystalline quality and no sulfur as reported in previous works. We observed a superconducting transition with a sharp drop of the resistance at Tonset = 200 K and we obtained the highest Toffset of 186 K in S-H system.

cond-mat.supr-con↗

arXiv2019

Superconducting Phase-Diagram of H3S under High Magnetic Fields

We report the temperature dependence of the upper critical fields $μ_0H_{c2}(T)$ of the high temperature superconductor H$_3$S under applied pressures of 155 and 160 GPa through the electrical resistance transition observed under DC and pulsed magnetic fields up to 65 T, a record high combination of fields and pressures. We find that $H_{c2}(T)$ generally follows the Werthamer, Helfand and Hohenberg (WHH) formalism at low fields, albeit with noticeable deviations upon approaching our experimental limit of $μ_0H = 65$ T. In fact, $H_{c2}(T)$ displays a remarkably linear dependence on temperature over an extended temperature range also found in multigap or in strongly-coupled superconductors. The best fit of $H_{c2}(T)$ to the WHH formula yields a negligible value for the Maki parameter $α$ and for spin-orbit scattering constant $λ_{\text{SO}}$. However, its behavior is relatively well-described by a model based on strong coupling superconductivity with a coupling constant $λ\sim 2$. Therefore, we conclude that H$_3$S behaves as a strong-coupled orbital-limited superconductor over the entire range of temperatures and fields used for our measurements.

cond-mat.str-el↗

arXiv2015

Crystal Structure of 200 K-Superconducting Phase of Sulfur Hydride System

This article reports the experimentally clarified crystal structure of a recently discovered sulfur hydride in high temperature superconducting phase which has the highest critical temperature Tc over 200 K which has been ever reported. For understanding the mechanism of the high superconductivity, the information of its crystal structure is very essential. Herein we have carried out the simultaneous measurements electrical resistance and synchrotron x-ray diffraction under high pressure, and clearly revealed that the hydrogen sulfide, H2S, decomposes to H3S and its crystal structure has body-centered cubic symmetry in the superconducting phase.

cond-mat.supr-con↗

arXiv2010

Pressure-induced phase transition of Bi2Te3 into the bcc structure

The pressure-induced phase transition of bismuth telluride, Bi2Te3, has been studied by synchrotron x-ray diffraction measurements at room temperature using a diamond-anvil cell (DAC) with loading pressures up to 29.8 GPa. We found a high-pressure body-centered cubic (bcc) phase in Bi2Te3 at 25.2 GPa, which is denoted as phase IV, and this phase apperars above 14.5 GPa. Upon releasing the pressure from 29.8 GPa, the diffraction pattern changes with pressure hysteresis. The original rhombohedral phase is recovered at 2.43 GPa. The bcc structure can explain the phase IV peaks. We assumed that the structural model of phase IV is analogous to a substitutional binary alloy; the Bi and Te atoms are distributed in the bcc-lattice sites with space group Im-3m. The results of Rietveld analysis based on this model agree well with both the experimental data and calculated results. Therefore, the structure of phase IV in Bi2Te3 can be explained by a solid solution with a bcc lattice in the Bi-Te (60 atomic% tellurium) binary system.

cond-mat.mtrl-sci↗