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The potential of deep learning in clinical speech processing is immense, yet the hurdles of limited and imbalanced clinical data samples loom large. This article addresses these challenges by showcasing the utilization of automatic speech recognition and self-supervised learning representations, pre-trained on extensive datasets of normal speech. This innovative approach aims to estimate voice quality of patients with impaired vocal systems. Experiments involve checks on PVQD dataset, covering various causes of vocal system damage in English, and a Japanese dataset focusing on patients with Parkinson's disease before and after undergoing subthalamic nucleus deep brain stimulation (STN-DBS) surgery. The results on PVQD reveal a notable correlation (>0.8 on PCC) and an extraordinary accuracy (<0.5 on MSE) in predicting Grade, Breathy, and Asthenic indicators. Meanwhile, progress has been achieved in predicting the voice quality of patients in the context of STN-DBS., Comment: Accepted by Interspeech 2024

We numerically investigate photo-responses of the charge ordered state upon stimuli of pulsed laser light, especially paying attention to the differences in the pulse width, whose shortness has been a key to experimentally realize large photo-induced effects. As a model for charge ordering, we consider an interacting spinless fermion model on a one-dimensional chain coupled to classical phonons and numerically simulate its real-time dynamics. First, we demonstrate the case where spatially uniform dynamics take place, and show the delayed response of phonons after the photo-irradiation causing destabilization of charge order. When a local impurity potential is introduced in the initial state, an inhomogeneous charge order melting occurs and the delay in the time scale also happens in the real space melting process. Finally, by investigating wider parameter ranges using different pulse widths, we find that the use of ultrashort pulses considerably expands the frequency window for charge order melting; it is indispensable in realizing the photo-induced phase transition with off-resonant conditions., Comment: 5 pages, 3 figures

Photoinduced topological phase transitions in the Dirac-electron systems have attracted intensive research interest since its theoretical prediction in graphene, where the application of circularly polarized light opens a gap at the Dirac points and renders the system a topologically nontrivial Chern insulator phase through breaking the time-reversal symmetry. However, most of the previously studied phenomena in two-dimensional Dirac systems are basically based on the same physicical mechanism, i.e., the gap opening in the Dirac electron bands with circularly polarized light, and it is lacking in variety of the physics. In this paper, we theoretically predict a novel type of photoinduced topological phase transition accompanied by collision and collapse of gapped Dirac points in the organic salt $\alpha$-(BEDT-TTF)$_2$I$_3$. By constructing the Floquet theory for this compound, we demonstrate that the irradiation of elliptically polarized light causes collision of the Dirac points through the photoinduced band deformation and their collapse, which eventually results in the topological phase transition from a topological semimetal with gapped Dirac cones to a normal insulator when the elliptical axis is oriented at a specfic angle with respect to the crystallographic axes. We argue that this novel photoinduced phase transition can be experimentally detected by the measurement of Hall conductivity. The present work enriches the fundamental physics of photoinduced topological phase transitions and thus contribute to development of this rapidly growing research field.

Photoinduced phase transitions and charge dynamics in the interacting Dirac-electron system with a charge-ordered ground state are theoretically studied by taking an organic salt $\alpha$-(BEDT-TTF)$_2$I$_3$. By analysing the extended Hubbard model for this compound using a combined method of numerical simulations based on the time-dependent Schr\"odinger equation and the Floquet theory, we observe successive dynamical phase transitions from the charge-ordered insulator to a gapless Dirac semimetal and, eventually, to a Chern insulator phase under irradiation with circularly polarized light. These phase transitions occur as a consequence of two major effects of circularly polarized light, i.e., closing of the charge gap through melting the charge order and opening of the topological gap by breaking the time reversal symmetry at the Dirac points. We demonstrate that these photoinduced phenomena are governed by charge dynamics of driven correlated Dirac electrons., Comment: 6 pages, 4 figures

Prolonged experimental attempts to find magnetic monopoles (i.e., elementary particles with an isolated magnetic charge in three dimensions) have not yet been successful despite intensive efforts made since Dirac's proposal in 1931. Particle physicists have predicted the possible collision and pair annihilation of two magnetic charges with opposite signs. However, if such annihilation exists, its experimental observation would be difficult because its energy scale is predicted to be tremendously high ($\sim$10$^{16}$ GeV). In the present work, we theoretically predict using the Floquet theory that a pair of slightly gapped Dirac-cone bands in a weakly-charge-ordered organic conductor $\alpha$-(BEDT-TTF)$_2$I$_3$, which behave as magnetic charges with opposite signs in the momentum space, exhibit pair annihilation under irradiation with linearly polarized light. This photoinduced pair annihilation is accompanied by a non-topological phase transition to the Floquet normal insulator phase in contrast to the well-known circularly-polarized-light-induced topological phase transition to the Floquet Chern insulator phase. We discuss that $\alpha$-(BEDT-TTF)$_2$I$_3$ has a peculiar band structure capable of realizing a suitable experimental condition (i.e., off-resonant condition) and a charge ordered state providing a required staggered site potential and thereby provides a rare example of materials that can be used to observe the predicted pair annihilation phenomenon. The feasibility of experimental observation is also discussed.

We theoretically investigate possible photoinduced topological phase transitions in the organic salt $\alpha$-(BEDT-TTF)$_2$I$_3$, which possesses a pair of inclined massless Dirac-cone bands between the conduction and valence bands under uniaxial pressure. The Floquet analyses of a driven tight-binding model for this material reveal rich photoinduced variations of band structures, Chern numbers, and Hall conductivities under irradiation with elliptically polarized light. The obtained phase diagrams contain a variety of nonequilibrium steady phases, e.g., the Floquet Chern insulator, Floquet semimetal, and Floquet normal insulator phases. This work widens a scope of target materials for research on photoinduced topological phase transitions and contributes to development of research on the optical manipulations of electronic states in matters., Comment: 14 pages, 9 figures, to be published in Journal of the Physical Society of Japan

We demonstrate that a machine learning technique with a simple feedforward neural network can sensitively detect two successive phase transitions associated with the Berezinskii-Kosterlitz-Thouless (BKT) phase in q-state clock models simultaneously by analyzing the weight matrix components connecting the hidden and output layers. We find that the method requires only a data set of the raw spatial spin configurations for the learning procedure. This data set is generated by Monte-Carlo thermalizations at selected temperatures. Neither prior knowledge of, for example, the transition temperatures, number of phases, and order parameters nor processed data sets of, for example, the vortex configurations, histograms of spin orientations, and correlation functions produced from the original spin-configuration data are needed, in contrast with most of previously proposed machine learning methods based on supervised learning. Our neural network evaluates the transition temperatures as T_2/J=0.921 and T_1/J=0.410 for the paramagnetic-to-BKT transition and BKT-to-ferromagnetic transition in the eight-state clock model on a square lattice. Both critical temperatures agree well with those evaluated in the previous numerical studies., Comment: 11pages, 9 figures

We theoretically study the real-time dynamics of the photoinduced topological phase transition to a nonequilibrium Floquet Chern insulator in an organic conductor $\alpha$-(BEDT-TTF)$_2$I$_3$, which was recently predicted using the Floquet theory. By using a tight-binding model of $\alpha$-(BEDT-TTF)$_2$I$_3$ that hosts a pair of tilted Dirac-cone bands at the Fermi level, we solve the time-dependent Schr\"odinger equation and obtained time evolutions of physical quantities for continuous-wave and pulse excitations with circularly polarized light. We demonstrate that, for the continuous-wave excitations, time profiles of the Chern number and the Hall conductivity show indications of the Floquet topological insulator. We argue that the Hall conductivity exhibits a slow oscillation with its frequency corresponding to a photoinduced direct gap determined by the Floquet band structure. With pulse excitations, transient excitation spectra are obtained, from which we infer the formation of Floquet bands and the gap opening at the Dirac point during the pulse irradiation. This dynamical gap formation is also manifested by the slow oscillation component of the Hall conductivity; that is, its frequency increases with time toward the pulse peak at which it nearly coincides with the photoinduced direct gap. The relevance of the results to experiments is also discussed., Comment: 8 pages, 5 figures, to appear in Phys. Rev. B

We investigate the condition for the photoinduced enhancement of an excitonic order in a two-orbital Hubbard model, which has been theoretically proposed in our previous work [Phys. Rev. B 97, 115105 (2018)], and analyze it from the viewpoint of the Rabi oscillation. Within the mean-field approximation, we simulate real-time dynamics of an excitonic insulator with a direct gap, where the pair condensation in the initial state is of BEC nature and the photoexcitation is introduced by electric dipole transitions. We first discuss that in the atomic limit our model is reduced to a two-level system that undergoes the Rabi oscillation, so that for single cycle pulses physical quantities after the photoirradiation are essentially determined by the ratio of the Rabi frequency to the pump-light frequency. Then, it is shown that this picture holds even in the case of nonzero transfer integrals where each one-particle state exhibits the Rabi oscillation leading to the enhancement of the excitonic order. We demonstrate that effects of electron-phonon interactions do not alter the results qualitatively. We also examine many-body dynamics by the exact diagonalization method on small clusters, which strongly suggests that our mechanism for the enhancement of the exctionic order survives even when quantum fluctuations are taken into account., Comment: 21 pages, 37 figures, to be published in Phys. Rev. B

We theoretically study the inverse Faraday effect, i.e., the optical induction of spin polarization with circularly polarized light, by particularly focusing on effects of band dispersions and Fermi surfaces in crystal systems with the spin-orbit interaction (SOI). By numerically solving the time-dependent Schr\"odinger equation of a tight-binding model with the Rashba-type SOI, we reproduce the light-induced spin polarization proportional to $E_0^2/\omega^3$ where $E_0$ and $\omega$ are the electric-field amplitude and the angular frequency of light, respectively. This optical spin induction is attributed to dynamical magnetoelectric coupling between the light electric field and the electron spins mediated by the SOI. We elucidate that the magnitude and sign of the induced spin polarization sensitively depend on the electron filling. To understand these results, we construct an analytical theory based on the Floquet theorem. The theory successfully explains the dependencies on $E_0$ and $\omega$ and ascribes the electron-filling dependence to a momentum-dependent effective magnetic field governed by the Fermi-surface geometry. Several candidate materials and experimental conditions relevant to our theory and model parameters are also discussed. Our findings will enable us to engineer the magneto-optical responses of matters via tuning the material parameters., Comment: 21 pages, 7 figures, to appear in New J. Phys

We theoretically investigate photoresponses of a correlated electron system upon stimuli of a pulsed laser light. Real-time dynamics of an interacting spinless fermion model on a one-dimensional chain, as a model of charge order (CO), are numerically simulated using the time-dependent Hartree-Fock method. In particular, we discuss the differences between two situations as the initial state:the homogeneous order and the presence of a domain wall, i.e., a kink structure embedded in the CO bulk. Coherent dynamics are seen in the former case: When the frequency of the pump light $\omega_{p}$ is varied, along with single particle excitations across the CO gap ($\Delta_\textrm{CO}$), the resonantly-excited collective phase mode near $\omega_{p} \simeq \Delta_\textrm{CO}/2$ efficiently destabilizes CO. In clear contrast, in the latter case, when $\omega_{p}$ is tuned at such in-gap frequencies and the intensity of light is sufficiently large,inhomogeneity spreads out from the kink to the bulk region through kink creations. Moreover, even stronger intensity induces the inhomogeneous melting of CO where the CO gap is destroyed., Comment: 8 pages, 9 figures, published version

Photoinduced dynamics in an excitonic insulator is studied theoretically by using a two-orbital Hubbard model on the square lattice where the excitonic phase in the ground state is characterized by the BCS-BEC crossover as a function of the interorbital Coulomb interaction. We consider the case where the order has a wave vector $Q=(0,0)$ and photoexcitation is introduced by a dipole transition. Within the mean-field approximation, we show that the excitonic order can be enhanced by the photoexcitation when the system is initially in the BEC regime of the excitonic phase, whereas it is reduced if the system is initially in the BCS regime. The origin of this difference is discussed from behaviors of momentum distribution functions and momentum-dependent excitonic pair condensation. In particular, we show that the phases of the excitonic pair condensation have an important role in determining whether the excitonic order is enhanced or not., Comment: 20 pages, 14 figures, to appear in Phys. Rev. B

The effects of electron correlation in the quasi-two-dimensional organic conductor \alpha-(BEDT-TTF)2I3 are investigated theoretically by using an extended Hubbard model with on-site and nearest-neighbor Coulomb interactions. A variational Monte Carlo method is applied to study its ground-state properties. We show that there appears a nonmagnetic horizontal-stripe charge order in which nearest-neighbor correlation functions indicate a tendency toward a spin-singlet formation on the bonds with large transfer integrals along the charge-rich stripe. Under uniaxial pressure, a first-order transition from the nonmagnetic charge order to a zero-gap state occurs. Our results on a spin correlation length in the charge-ordered state suggest that a spin gap is almost unaffected by the uniaxial pressure in spite of the suppression of the charge disproportionation. The relevance of these contrasting behaviors in spin and charge degrees of freedom to recent experimental observations is discussed., Comment: 15 pages, 9 figures, accepted for publication in J. Phys. Soc. Jpn

Many-electron dynamics induced by a symmetric monocycle electric-field pulse of large amplitude is theoretically investigated in one- and two-dimensional half-filled extended Hubbard models on regular lattices (i.e., without dimerization) using the exact diagonalization method for small systems and the Hartree-Fock approximation for large systems. The formation of a negative-temperature state and the change from repulsive interactions to effective attractive interactions are shown to be realized for a wide region of the field amplitude and the excitation energy. For a nonnegligible intersite repulsive interaction, the numerical results are consistent with the fact that the phase separation between charge-rich and charge-poor regions is caused by the corresponding effective attraction., Comment: 20 pages, 10 figures, accepted for publication in J. Phys. Soc. Jpn

Dynamical localization, i.e., reduction of the intersite electronic transfer integral t by an alternating electric field, E(omega) , is a promising strategy for controlling strongly correlated systems with a competing energy balance between t and the Coulomb repulsion energy. Here we describe a charge localization induced by the 9.3 MV/cm instantaneous electric field of a 1.5 cycle (7 fs) infrared pulse in an organic conductor alpha-(bis[ethylenedithio]-tetrathiafulvelene)_2I_3. A large reflectivity change of > 25% and a coherent charge oscillation along the time axis reflect the opening of the charge ordering gap in the metallic phase. This optical freezing of charges, which is the reverse of the photoinduced melting of electronic orders, is attributed to the 10% reduction of t driven by the strong, high-frequency (omega>t/h_bar) electric field., Comment: 20 pages, 6 figure

A negative differential resistance (NDR) in a one-dimensional band insulator attached to electrodes is investigated. We systematically examine the effects of an electrode bandwidth and a potential distribution inside the insulator on current-voltage characteristics. We show that, in uncorrelated systems, the NDR is generally caused by a linear potential gradient as well as by a finite electrode bandwidth. In particular, the former reduces the effective bandwidth of the insulator for elastic tunneling by tilting its energy band, so that it brings about the NDR even in the limit of large electrode bandwidth.