arXiv subjects

Y. Matsuda

Publications and source records attributed to Y. Matsuda.

At least 19 recordsLinked to original sources

arXiv2026

Isoscalar Giant Resonances in the even-A Pd Isotopes

Studies of the isoscalar giant monopole resonance (ISGMR) across the chart of nuclides provide insight into the incompressibility of nuclear matter near saturation density, K(infinity). Such studies had revealed a discrepancy between theoretical approaches: quasiparticle random phase approximation (QRPA) derived from Skyrme interactions reproduce the strength distributions of the ISGMR in the doubly-closed-shell nuclei 90Zr and 208Pb, but their descriptions of strength distributions in open-shell medium-heavy nuclei suggest higher centroid energies should be experimentally observed. The latter nuclei required a smaller K(infinity) and were thus deemed softer. The present work serves to add to this softness discourse by extracting ISGMR strength distributions for 104,106,108,110Pd via 386-MeV inelastic alpha-scattering. The extracted giant resonance strength distributions are consistent with expectations in this isotopic range. Additional Quasiparticle Vibration Coupling (QPVC) effects are included with the QRPA approach and compared to aforementioned ISGMR strength distributions.

nucl-ex↗

arXiv2026

High-field fate of the Kitaev quantum spin liquid in $\alpha$-RuCl$_3$

Kitaev quantum spin liquids (KQSLs) host fractionalized excitations described by itinerant Majorana quasiparticles and gapped $Z_2$ fluxes (visons), providing a platform for emergent topological matter. Whether such a state survives under strong magnetic fields, however, remains an open question. The layered honeycomb magnet $\alpha$-RuCl$_3$ is a leading candidate material: an in-plane field of $\sim$ 7 T suppresses antiferromagnetic order and induces a quantum-disordered phase exhibiting signatures consistent with Majorana excitations, including an anomalous thermal Hall effect and field-angle-dependent specific heat. At higher fields, the magnetization approaches saturation, suggesting a transition to a spin-polarized state, yet the microscopic evolution between these limits remains unresolved. Here we report high-field specific heat measurements up to 24 T that reveal a distinct crossover at $\mu_0H^*\approx$15 T, beyond which the perturbative Kitaev description breaks down. Above $H^*$, the characteristic six-fold angular modulation of the specific heat collapses and the excitation gap deviates from the predicted $H^3$ scaling. Meanwhile, the gap decreases with increasing field and the in-plane magnetization anisotropy persists up to $\sim$ 24 T, both in sharp contrast to a trivial spin-polarized state, indicating that KQSL signatures are preserved even at $\sim$ 90 % of magnetization saturation. These results reveal that the KQSL in $\alpha$-RuCl$_3$ extends well beyond the perturbative window, persisting as a nonperturbative regime in which the Majorana and vison energy scales merge, before eventually giving way to spin polarization. This thermodynamic roadmap provides a basis for understanding how fractionalized phases evolve under strong magnetic fields.

cond-mat.str-el↗

arXiv2026

Reply to Comment on: Microscopic signatures of an imaginary charge density wave in a kagome metal

We address a recent Comment [I. Nikolov {\it et al.}, arXiv:2608.13579 (2026)] proposing crystalline mosaicity as an alternative explanation for the asymmetric nuclear magnetic resonance (NMR) spectra reported in our study [S. Suetsugu {\it et al.}, Nat. Phys. {\bf 22}, 1251--1256 (2026)]. We show that this scenario requires substantial temperature- and site-dependent distributions of crystallographic orientations and additional site-dependent distributions of the electric field gradient (EFG) asymmetry parameter, none of which follow from ordinary crystalline mosaicity. We therefore conclude that crystalline mosaicity cannot account for the observed site-selective spectral asymmetry and does not provide an alternative explanation for the central spectroscopic observation underlying our interpretation.

cond-mat.str-el↗

arXiv2026

Microscopic evidence for imaginary charge density wave in a kagome metal

Dissipationless charge transport without any energy loss is one of the most fascinating phenomena in condensed matter physics. This extraordinary state manifests in two well-established systems: superconductors and quantum Hall systems. A proposed third category is associated with chiral loop current order, characterized by the spontaneous formation of microscopic electric current loops. The microscopic origin of these currents stems from imaginary hopping terms, conceptualized as an imaginary charge density wave (iCDW). Despite extensive investigations, its existence remains highly controversial. Here we report site-selective spectroscopic evidence for a pure iCDW in the kagome nonmagnetic metal CsV$_3$Sb$_5$. Nuclear quadrupole resonance spectra at out-of-plane $^{121}$Sb site sensitive to in-plane currents reveal anomalous broadening below $T^*\approx$120 K, coinciding with the nematic transition well above the real charge density wave (CDW). Under magnetic fields, the spectra exhibit asymmetric lineshapes, demonstrating that this broadening purely originates from magnetic effects rather than from electric quadrupolar effects associated with CDW fluctuations. The observed lineshapes are quantitatively consistent with ~1 mT local fields induced by chiral loop currents, indicating spontaneous time-reversal symmetry breaking. This microscopic identification of the long-sought pure iCDW establishes a novel form of quantum order, potentially revolutionizing our understanding of exotic electronic states in quantum materials.

cond-mat.str-el↗

arXiv2026

Pseudo Point Nodal Superconducting Gap in Spin-Triplet UTe$_2$

The unconventional superconductor UTe$_2$ represents a rare example of spin-triplet pairing with potentially topologically protected quantum states. However, conflicting reports on its gap structure, particularly regarding point nodes, have hindered understanding of the order parameter symmetry and topological properties. Here we report high-resolution thermal conductivity measurements on high-quality UTe$_2$ single crystals down to ~50 mK that resolve the gap anisotropy through bulk directional transport. The $b$-axis thermal conductivity $\kappa_b/T$ exhibits negligible residual conductivity as $T \to 0$, and its temperature dependence is consistent with a small superconducting energy gap along the $b$-axis. Under magnetic fields, the residual $\kappa_b/T$ shows only weak field-induced enhancement. Remarkably, a threshold field emerges at low fields for $H \parallel a$, characterized by a kink that signals a change in quasiparticle transport normal to the field. Below the threshold, $\kappa_b/T$ remains isotropic for all field orientations, whereas strong anisotropy between transport along and normal to the field develops above it. These signatures strongly suggest that UTe$_2$ exhibits a fully gapped state with a pseudo point-nodal structure, where gap minima approach but never reach zero. We estimate the minimal gap $\Delta_{min}/\Delta_0 \sim 0.1$ along the $b$-axis, where $\Delta_0$ is the characteristic superconducting gap. This unusual gap structure provides crucial insights into the pairing mechanism and topology of this spin-triplet superconductor and excludes non-unitary mixing of pairing symmetries.

cond-mat.supr-con↗

arXiv2026

First Extraction of the Matter Radius of $^{132}$Sn via Proton Elastic Scattering at 200 MeV/Nucleon

The angular distribution of the differential cross sections for proton elastic scattering from $^{132}$Sn at 196-210 MeV/nucleon was successfully measured over a momentum transfer range of 0.80 to 2.1 fm$^{-1}$. Using a relativistic impulse approximation, the root-mean-square matter radius of $^{132}$Sn was extracted to be $4.758^{+0.023}_{-0.024}$ fm, which was compared with the state-of-the-art ab initio calculations. Combined with the charge radius measured at ISOLDE, there are no theoretical calculations consistent with both matter and charge radii within the experimental errors.

nucl-ex↗

arXiv2025

Isoscalar Giant Resonances in Highly-Deformed $^{172}$Yb

To study the isoscalar giant resonances in a deformed case, background-free $\alpha$-particle inelastic scattering measurements using a 386 MeV $\alpha$ beam were performed on the highly-deformed $^{172}$Yb nucleus using the Grand Raiden spectrometer at the Research Center for Nuclear Physics (RCNP) at very forward angles, including $0^\circ$. The strength distributions for the isoscalar giant resonances up to $L \leq 3$ were obtained using multipole decomposition analysis. The isoscalar giant monopole resonance (ISGMR) strength exhibits a splitting into two components, interpreted as the coupling of the ISGMR with the $K=0$ component of the isoscalar giant quadrupole resonance (ISGQR). A \textit{bimodal} structure is observed in the strength distribution of the isoscalar giant dipole resonance. The ISGQR strength shows an enhancement near 25 MeV, attributed to the excitation of an overtone mode, while the broadening of the main-tone peak is associated with nuclear deformation. The experimental results are well reproduced by theoretical strength distributions calculated using the quasiparticle finite amplitude method for $L \leq 3$.

nucl-ex↗

arXiv2025

Precise measurement of the $\gamma$-decay probability of the Hoyle state with a new triple coincidence-detection method

We measured the $\gamma$-decay probability of the Hoyle state with a new method of triple coincidence detection of a scattered $\alpha$ particle, a recoil $\rm ^{12}C$ nucleus, and a $\gamma$ ray in inelastic alpha scattering on $\rm ^{12}C$. This method successfully enabled a low-background measurement and a precise determination of the $\gamma$-decay probability of the Hoyle state as $\Gamma_\mathrm{\gamma}/\Gamma=[4.00 \pm 0.22 \mathrm{(sta.)} \pm 0.18 \mathrm{(sys.)}]\times10^{-4}$, which is consistent with the previous literature value. Therefore, we concluded that the literature value can be reliably used in the study of nucleosynthesis in the universe.

nucl-ex↗

arXiv2025

Measured Properties of an Antihydrogen Beam

We report a factor of $100$ increase in the antihydrogen beam intensity downstream of ASACUSA's Cusp trap: $320$ atoms detected per $15$-minute run. The beam contains many Rydberg atoms, which we selectively ionize to determine their velocity and binding energy. The time of flight signal is modeled using a $1\mathrm{D}$ Maxwellian velocity distribution with a temperature of $1500\,\mathrm{K}$, which is close to the measured antiproton plasma temperature. A numerical simulation reproduces the observed distribution of binding energies and suggests that about $16\%$ of the atoms may be in the ground state.

physics.ins-det↗

arXiv2025

Potentiometric detection of spin polarization expected at the surface of FeTe0.6Se0.4 in the effective p-wave superconducting state

Nowadays, the quest for non-Abelian anyons is attracting tremendous attention. In particular, a Majorana quasiparticle has attracted great interest since the non-Abelian anyon is a key particle for topological quantum computation. Much effort has been paid for the quest of the Majorana state in solids, and some candidate material platforms are reported. Among various materials that can host the Majorana state, chiral p-wave superconductor is one of the suitable materials and the iron-based layered superconductor FeTeSe is one of the promising material platforms because its surface can host effective p-wave superconducting state that is analogous to chiral p-wave superconducting state thanks to its topological surface state. Given that a chiral p-wave superconductor possesses spin polarization, detecting the spin polarization can be evidence for the chiral p-wave trait, which results in the existence of Majorana excitation. Here, we show successful detection of the spin polarization at the surface of FeTe0.6Se0.4 in its superconducting state, where the spin polarization is detected via a potentiometric method. Amplitudes of the spin signal exhibit characteristic dependence for temperature and bias current, suggesting detection of spin polarization of the Bogoliubov quasiparticles. Our achievement opens a new avenue to explore topological superconductivity for fault-tolerant quantum computation.

cond-mat.mtrl-sci↗

arXiv2024

ADF22-WEB: A giant barred spiral starburst galaxy in the z = 3.1 SSA22 protocluster core

In the present-day universe, the most massive galaxies are ellipticals located in the cores of galaxy clusters, harboring the heaviest super-massive black holes (SMBHs). However the mechanisms that drive the early growth phase and subsequent transformation of these morphology and kinematics of galaxies remain elusive. Here we report (sub)kiloparsec scale observations of stars, gas, and dust in ADF22.A1, a bright dusty starburst galaxy at z=3.1, hosting a heavily obscured active galactic nucleus and residing in a proto-cluster core. ADF22.A1 is a giant spiral galaxy with the kinematics of a rotating disk with rotation velocity Vrot=530+/-10km/s and diameter larger than 30 kpc. The high specific stellar angular momentum of this system, j*=3400+/-600 kpc km/s, requires a mechanism to effectively spin-up ADF22.A1, indicating the importance of accretion from the cosmic web to supply both gas and angular momentum to galaxies in their early gas-rich starburst phase. In its inner region, gas flows along dust lanes in a bar connected with the bright dusty core and the estimated mass ratio of a bulge to SMBH matches the local relation, suggesting that bars are a key mechanism to shape the early co-evolution of these components. Comparison with cosmological simulations shows that ADF22.A1 will likely evolve into a massive elliptical at the present day, experiencing a significant reduction in angular momentum associated with subsequent galaxy mergers.

astro-ph.GA↗

arXiv2024

Magnetothermal transport in ultraclean single crystals of Kitaev magnet $\alpha$-RuCl$_3$

The layered honeycomb magnet $\alpha$-RuCl$_3$ has emerged as a promising candidate for realizing a Kitaev quantum spin liquid. Previous studies have reported oscillation-like anomalies in the longitudinal thermal conductivity and half-integer quantized thermal Hall conductivity above the antiferromagnetic critical field $H_c$, generating significant interest. However, the origins of these phenomena remain contentious due to strong sample dependence. Here we re-examine the magnetothermal transport properties using recently available ultra-pure $\alpha$-RuCl$_3$ single crystals to further elucidate potential signatures of the spin liquid state. Our findings reveal that while anomalies in thermal conductivity above $H_c$ persist even in ultraclean crystals, their magnitude is significantly attenuated, contrary to the quantum oscillations hypothesis. This suggests that the anomalies are likely attributable to localized stacking faults inadvertently introduced during magnetothermal transport measurements. The thermal Hall conductivity exhibits a half-quantized plateau, albeit with a narrower width than previously reported. This width reduction can be understood through two distinct mechanisms: sample-dependent magnetic critical fields that influence the lower boundary of the plateau region, and the decoupling between chiral Majorana edge currents and phononic thermal transport that determines the upper boundary. These results indicate that structural imperfections exert a substantial influence on both the oscillation-like anomalies and quantization effects observed in magnetothermal transport measurements of $\alpha$-RuCl$_3$.

cond-mat.str-el↗

arXiv2024

Gapless spin excitations in a quantum spin liquid state of S=1/2 perfect kagome antiferromagnet

Quantum spin liquids (QSLs) represent an exotic quantum many-body state characterized by the suppression of long-range magnetic order due to strong quantum fluctuations. The kagome spin-1/2 antiferromagnet (AFM) is a prime candidate for realizing QSLs, but its ground state remains an unresolved conundrum. Here we investigate the recently discovered perfect kagome AFM YCu$_3$(OH)$_{6.5}$Br$_{2.5}$ to elucidate two central enigmas surrounding the kagome AFM. Ultra-sensitive torque magnetometry experiments reveal that the intrinsic magnetic susceptibility arising from the kagome layer remains nearly temperature-independent down to exceedingly low temperatures. This observation seemingly implies the emergence of gapless fermionic spin excitations akin to Pauli paramagnetism in metals. However, most strikingly, these results stand in stark contrast to the conspicuous absence of a temperature-linear contribution to the specific heat. These findings appear irreconcilable with the widely-discussed theoretical frameworks assuming fermionic quasiparticles (QPs), instead suggesting a transition of bosonic QPs into a superfluid state with a gapless Goldstone mode. Furthermore, magnetocaloric measurements evince an entropy anomaly, constituting thermodynamic evidence that magnetic fields instigate the opening of a spin gap, driving a quantum phase transition into a 1/9 magnetization plateau state. These results shed light on the nature of the low-energy excitations in zero and strong magnetic fields, providing crucial insights into the long-standing unresolved issues of the ground state of the kagome AFM.

cond-mat.str-el↗

arXiv2024

Effect of ground-state deformation on the Isoscalar Giant Monopole Resonance and the first observation of overtones of the Isoscalar Giant Quadrupole Resonance in rare-earth Nd isotopes

The strength distributions of the Isoscalar Giant Monopole Resonance (ISGMR) and Isoscalar Giant Quadrupole Resonance (ISGQR) in 142,146-150Nd have been determined via inelastic alpha-particle scattering with the Grand Raiden (GR) Spectrometer at the Research Center for Nuclear Physics (RCNP), Japan. In the deformed nuclei 146-150Nd, the ISGMR strength distributions exhibit a splitting into two components, while the nearly spherical nucleus 142Nd displays a single peak in the ISGMR strength distribution. A noteworthy achievement in this study is the first-time detection of overtones in the Isoscalar Giant Quadrupole Resonance (ISGQR) strength distributions within Nd isotopes at an excitation energy around 25 MeV obtained through Multipole Decomposition Analysis (MDA).

nucl-ex↗

arXiv2024

Microwave Hall measurements using a circularly polarized dielectric cavity

We have developed a circularly polarized dielectric rutile (TiO$_2$) cavity with a high quality-factor that can generate circularly polarized microwaves from two orthogonal linearly polarized microwaves with a phase difference of $\pm \pi/2$ using a hybrid coupler. Using this cavity, we have established a new methodology to measure the microwave Hall conductivity of a small single crystal of metal in the skin-depth region. Based on the cavity perturbation technique, we have shown that all components of the surface impedance tensor can be extracted under the application of a magnetic field by comparing the right- and left-handed circularly polarized modes. To verify the validity of the developed method, we performed test measurements on tiny Bi single crystals at low temperatures. As a result, we have successfully obtained the surface impedance tensor components and confirmed that the characteristic field dependence of the ac Hall angle in the microwave region is consistent with the expectation from the dc transport measurements. These results demonstrate a significant improvement in sensitivity compared to previous methods. Thus, our developed technique allows more accurate microwave Hall measurements, opening the way for new approaches to explore novel topological quantum phenomena, such as time-reversal symmetry breaking in superconductors.

cond-mat.str-el↗

arXiv2024

Orders of Magnitude Improved Cyclotron-Mode Cooling for Non-Destructive Spin Quantum Transition Spectroscopy with Single Trapped Antiprotons

We demonstrate efficient sub-thermal cooling of the modified cyclotron mode of a single trapped antiproton and reach particle temperatures $T_+=E_+/k_\text{B}$ below $200\,$mK in preparation times shorter than $500\,$s. This corresponds to the fastest resistive single-particle cyclotron cooling to sub-thermal temperatures ever demonstrated. By cooling trapped particles to such low energies, we demonstrate the detection of antiproton spin transitions with an error-rate $<0.000025$, more than three orders of magnitude better than in previous best experiments. This method will have enormous impact on multi-Penning-trap experiments that measure magnetic moments with single nuclear spins for tests of matter/antimatter symmetry, high-precision mass-spectrometry, and measurements of electron $g$-factors bound to highly-charged ions that test quantum electrodynamics.

physics.atom-ph↗

arXiv2024

Measurement of the mesonic decay branch of the $\bar{K}\!N\!N$ quasi-bound state

We conducted measurements of $K^- + {^3{\rm He}} \to \pi \!Y \!N + N'$ reactions using a $1~{\rm GeV}/c$ $K^-$-beam, with the objective of understanding the broad decay width of $\bar{K} \!N \!N$ (approximately twice as broad as that of $\Lambda(1405)$ considered to be the $\bar{K} \!N$ quasi-bound state). We successfully reproduced distributions of the $\pi \! Y \! N$ invariant mass and momentum transfer for $\pi \! Y \! N$ using model fitting functions for $\bar{K} \!N \!N$ formation and quasi-free $\bar{K}$ absorption (${\rm QF}_{\bar{K}-{\rm abs}}$) processes. The model can describe the experimental data quite well, and four $\bar{K} \! N \! N \to \pi \! Y \! N $ cross-sections were obtained. The results indicate that mesonic decay is the dominant decay branch of $\bar{K} \! N \! N$. The results also suggest that $\Gamma_{\pi \Lambda N} \sim \Gamma_{\pi \Sigma N}$, which indicates that the $I_{\bar{K} \! N}=1$ absorption channel, in addition to the $I_{\bar{K} \! N}=0$ absorption channel, substantially contribute to the $\bar{K} \! N \! N$ decay, making the $\bar{K} \! N \! N$ state approximately twice as unstable as $\Lambda$(1405).

nucl-ex↗

arXiv2024

Imaging quantum interference in a monolayer Kitaev quantum spin liquid candidate

Single atomic defects are prominent windows to look into host quantum states because collective responses from the host states emerge as localized states around the defects. Friedel oscillations and Kondo clouds in Fermi liquids are quintessential examples. However, the situation is quite different for quantum spin liquid (QSL), an exotic state of matter with fractionalized quasiparticles and topological order arising from a profound impact of quantum entanglement. Elucidating the underlying local electronic property has been challenging due to the charge neutrality of fractionalized quasiparticles and the insulating nature of QSLs. Here, using spectroscopic-imaging scanning tunneling microscopy, we report atomically resolved images of monolayer $\alpha-RuCl_3$, the most promising Kitaev QSL candidate, on metallic substrates. We find quantum interference in the insulator manifesting as incommensurate and decaying spatial oscillations of the local density of states around defects with a characteristic bias dependence. The oscillation differs from any known spatial structures in its nature and does not exist in other Mott insulators, implying it is an exotic oscillation involved with excitations unique to $\alpha-RuCl_3$. Numerical simulations suggest that the observed oscillation can be reproduced by assuming that itinerant Majorana fermions of Kitaev QSL are scattered across the Majorana Fermi surface. The oscillation provides a new approach to exploring Kitaev QSLs through the local response against defects like Friedel oscillations in metals.

cond-mat.str-el↗