arXiv subjects

Hirotaka Manaka

Publications and source records attributed to Hirotaka Manaka.

7 recordsLinked to original sources

arXiv2026

Holonomy Analysis of Optical-polarization Temperature Trajectories in Stress-induced Ferroelectric SrTiO$_3$

We develop a data-induced geometric framework for temperature trajectories in optical-polarization data and apply it to temperature-dependent birefringence imaging of stress-induced ferroelectric SrTiO3. By treating the measured response as an observable projection of local material states, the optical-polarization response at each pixel is cast as a trajectory along the temperature axis. Singular value decomposition separates trajectory-induced geometric objects associated with optical-polarization-direction structure and temperature-evolution modes. Holonomies are then defined by transporting these objects around closed loops in real space. The resulting maps reveal spatially localized connection mismatches correlated with an enhanced ferroelectric transition temperature and stress-related optical anisotropy. Local order parameters and angular-gradient analyses confirm that these loop-level signals are distinct from orientational disorder and simple spatial variation. The signed holonomy of the temperature-evolution modes further resolves positive and negative connection structures under a fixed frame convention. These results demonstrate that the data-induced connection geometry of temperature trajectories provides an experimentally accessible diagnostic of electromechanical inhomogeneity in SrTiO3 under stress, without explicitly reconstructing hidden strain or electric-polarization fields.

cond-mat.mtrl-sci↗

arXiv2026

Holonomy-based Diagnostic of Strain Compatibility in Birefringence Imaging of Stress-induced Ferroelectric SrTiO$_3$

We introduce a holonomy-based geometric diagnostic for birefringence-derived director fields and apply it to stress-induced ferroelectric SrTiO$_3$. Treating the director as a line field in $\mathbb{R}P^2$, we define a holonomy angle $ω$ from residual rotations accumulated along closed loops in real space and compare it with a conventional local-gradient metric. Whereas the gradient quantifies local orientational variation, $ω$ probes the global compatibility of rotations along closed paths. The resulting $ω$ map cannot be reproduced by simple coarse-graining of local gradients, indicating sensitivity to loop-level orientational incompatibility. Analysis of alignment of holonomy rotation axes reveals a cooling-induced reorganization of the electromechanical response, consistent with strain- or stress-related inhomogeneity above the ferroelectric transition and additional ordering below it. These results demonstrate holonomy as a loop-based geometric diagnostic of strain compatibility in orientational fields derived from birefringence.

cond-mat.mtrl-sci↗

arXiv2022

Inelastic Neutron Scattering in Weakly Coupled Triangular Spin Tubes CsCrF$_4$

We performed inelastic neutron scattering (INS) experiments to measure spin dynamics on a polycrystalline sample of a spin tube candidate CsCrF$_{4}$. The compound exhibits a successive phase transition from a paramagnetic phase through an intermediate temperature (IT) phase of a 120$^{\circ}$ structure to a low temperature (LT) phase of another 120$^{\circ}$ structure. Elaborate comparison between observed and calculated neutron spectra in LT phase reveals that the spin Hamiltonian is identified as antiferromagnetic spin tubes including perturbative terms of intertube interaction, Dzyaloshinskii-Moriya interaction, and single ion anisotropy. A phase diagram for the ground state is classically calculated. A set of parameters in the spin Hamiltonian obtained from the INS spectra measured in LT phase is quite close to a boundary to the phase of the 120$^{\circ}$ structure of IT phase. The INS spectra measured in IT phase is, surprisingly, the same as those in LT phase in the level of powder averaged spectra, even though the magnetic structures in IT and LT phases are different. Identical dynamical structures compatible with two different static structures are observed. No difference in the observed spectra indicates no change of the spin Hamiltonian with the temperature, suggesting that the origin of the successive phase transition being order-by-disorder mechanism.

cond-mat.other↗

arXiv2020

Magnetic order in the chemically-substituted frustrated antiferromagnet CsCrF$_{4}$

The effect of chemical substitution on the ground state of the geometrically frustrated antiferromagnet CsCrF$_4$ has been investigated through a neutron powder diffraction experiment. Magnetic Fe-substituted CsCr$_{0.94}$Fe$_{0.06}$F$_{4}$ and nonmagnetic Al-substituted CsCr$_{0.98}$Al$_{0.02}$F$_{4}$ samples are measured, and magnetic Bragg peaks are clearly observed in both samples. Magnetic structure analysis revealed a 120$^{\circ}$ structure having a magnetic propagation vector $\mathbf{k}_{\rm mag}=(0,0,1/2)$ in CsCr$_{0.94}$Fe$_{0.06}$F$_{4}$. For CsCr$_{0.98}$Al$_{0.02}$F$_{4}$, a quasi-120$^{\circ}$ structure having $\mathbf{k}_{\rm mag}=(1/2,0,1/2)$ is formed. It is notable that the identified magnetic structure in CsCr$_{0.94}$Fe$_{0.06}$F$_{4}$ belongs to a different phase of ground states from those in CsCr$_{0.98}$Al$_{0.02}$F$_{4}$ and the parent CsCrF$_{4}$. These results suggest that the Fe-substitution strongly influences the ground state of CsCrF$_{4}$.

cond-mat.str-el↗

arXiv2013

Ground state of bond-disordered quasi-one-dimensional spin system (CH3)2CHNH3Cu(ClxBr1-x)3 with x = 0, 0.25 and 0.3

The ground state of the quasi-one-dimensional system with bond-disorder (CH3)2CHNH3Cu(ClxBr1-x)3 with x = 0, 0.25 and 0.3 has been investigated by muSR. The Fourier spectrum of electron spin fluctuation in x =0.25 and 0.3 obtained by LF-muSR technique shows that there exists a soft-mode toward a possible phase transition to an exotic phase such as Bose-glass. In gapped system with x = 0, the Fourier spectrum is totally different from the other two, indicating the existence of the quantum critical point at a finite x between 0 and 0.25.

cond-mat.stat-mech↗

arXiv2008

μSR-detection of the soft-mode toward the exotic magnetic ground state in bond-disordered quantum spin system IPA-Cu(Cl$_{0.35}$Br$_{0.65}$)$_3$

The spin-gap system with a bond-disorder (CH3)2CHNH3-Cu(ClxBr1-x)3 is reported by experiments on macroscopic quantities of the uniform susceptibility and the specific heat to show a magnetic order at low temperatures when the value of x is within the limited region between 0.44 and 0.87, and otherwise a gapped behavior. We have investigated microscopically the ground state of the sample with x=0.35 by muon spin relaxation (mSR) to observe that the frequency spectrum of the spin fluctuation tends to concentrate around zero energy as lowering temperatures. This behavior was interpreted as the soft-mode toward the possible magnetic phase transition at absolute zero.

cond-mat.str-el↗

arXiv2006

Impurity-induced magnetic order in the mixture of two spin gap systems (CH3)2CHNH3CuCl3 and (CH3)2CHNH3CuBr3

The ground state of the solid solution of the two spin gap systems (CH3)2CHNH3CuCl3 and (CH3)2CHNH3CuBr3 has been investigated by 1H-NMR. The existence of a magnetic ordering in the sample with the Cl-content x=0.85 was clearly demonstrated by a drastic splitting in a resonance line at low temperatures below TN=13.5K. The observed NMR spectra in the ordered state was qualitatively consistent with the simple antiferromagnetic state.

cond-mat.other↗