arXiv subjects

Hirotake Itoh

Publications and source records attributed to Hirotake Itoh.

8 recordsLinked to original sources

arXiv2026

Ultrafast decoupling of quasiparticles and spin fluctuations in superconducting cuprates

Understanding how quasiparticles are generated following a rapid quench of superconductivity in high-Tc cuprates is a key unresolved problem in nonequilibrium superconductivity. Here we resolve these processes in optimally doped YBCO [YBa2Cu3Oy(y=6.94, Tc=92 K)] using broadband (0.16 -4.1 eV, ca. 100 fs) and nearly single-cycle (6 fs) transient reflectivity spectroscopy. We show that within a few femtosecond, enhanced electron-electron Umklapp scattering dominates, signaling a transient modulation of long-range Coulomb interactions on the eV scale. This regime is followed by a rapid suppression of the scattering rate of the mid-infrared absorption associated with carriers dressed by spin fluctuations. We attribute this observation to an ultrafast decoupling of quasiparticles from the spin-fluctuation background, occurring on a 90 fs timescale set by the inverse optical gap. These findings reveal the correlated many-body dynamics underlying quasiparticle generation in cuprates and provide further clues for unconventional pairing mechanism.

cond-mat.str-el↗

arXiv2025

Magneto-optical spectra of an organic antiferromagnet as a candidate for an altermagnet

We have measured the magneto-optical Kerr effect (MOKE) in an orthorhombic organic antiferromagnet $κ$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Cl, which is a candidate for an altermagnet. From the Maxwell equations, we derived matrix-type general formulae describing the optical propagation and reflection for arbitrary crystals. These formulae enabled us to correctly measure and obtain the off-diagonal optical responses of $κ$-Cl. The MOKE of $κ$-Cl appeared at around the Néel temperature and exhibited a nonlinear field dependence in the antiferromagnetic phase. These nonlinear field dependence eliminates a simple origin due to the net canted magnetization. The obtained off-diagonal optical conductivity spectra for almost entire $π$-electron band clearly shows three features. One is the large peaks at the spectral ends due to the magnetic origin with the large energy scale compared to the very small spin-orbit interaction in $κ$-Cl. The others are the middle region spectra proportional to the diagonal conductivities, possibly related to the symmetric piezomagnetic effect and the standard antisymmetric origins. These results suggest the altermagnetic response of $κ$-Cl. We also discuss the analogy between the magnetization in ferromagnets and the net magnetization and Néel vector with respect to the magneto-optical configurations.

cond-mat.str-el↗

arXiv2018

Strong light-field effects driven by nearly single-cycle 7-fs light field in correlated organic conductors

We have demonstrated transient charge localization effects with a driving high-frequency field of 7-fs, 1.5-cycle near infrared light in correlated organic conductors. In a layered organic conductor alpha-(BEDT-TTF)2I3 (BEDT-TTF: bis[ethylenedithio]-tetrathiafulvalene), a transient short-range charge order (CO) state is induced in a metallic phase. In contrast to such drastic change in the electronic state from the metal to the transient CO in alpha-(BEDT-TTF)2I3, dynamics of a field-induced reduction of a transfer integral are captured as a red shift of the plasma-like reflectivity edge in a quasi-one-dimensional organic conductor (TMTTF)2AsF6 (TMTTF: tetramethyltetrathiafulvalene). These studies on the field-induced charge localization have been motivated by the theory of dynamical localization on the basis of tight-binding models with no electron correlation under a strong continuous field. However, the results of pump-probe transient reflectivity measurements using nearly single-cycle 7-fs, 11 MV/cm pulses and the theoretical studies which are presented in this review indicate that the pulsed field contributes to the similar phenomenon with the help of a characteristic lattice structure and Coulomb repulsion.

cond-mat.str-el↗

arXiv2015

Optical freezing of charge motion in an organic conductor

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.

cond-mat.str-el↗

arXiv2005

Room-temperature excitonic absorption in quantum wires

We measured absorption spectra of T-shaped quantum wires at room temperature using waveguide-transmission spectroscopy. Strong and narrow room-temperature one-dimensional-exciton absorption peak was observed, which shows peak modal absorption coefficient of 160 cm$^{-1}$ per 20 wires with $Γ$-factor of $4.3\times10^{-3}$, width of 7.2 meV, and strong polarization anisotropy.

cond-mat.mes-hall↗

arXiv2005

Strong photo-absorption by a single quantum wire in waveguide-transmission spectroscopy

We measured the absorption spectrum of a single T-shaped, 14x6 nm lateral-sized quantum wire embedded in an optical waveguide using waveguide-transmission spectroscopy at 5 K. In spite of its small volume, the one-dimensional-exciton ground state shows a large absorption coefficient of 80 /cm, or a 98 % absorption probability for a single pass of the 500-um-long waveguide.

cond-mat.other↗

arXiv2003

Polarization-dependent photoluminescence-excitation spectra of one-dimensional exciton and continuum states in T-shaped quantum wires

We measured polarization-dependent photoluminescence-excitation spectra of highly uniform T-shaped quantum wires at 5 K. We attribute one peak to the 1D-exciton ground state and the continuous absorption band to 1D continuum states. These had similar polarization-dependences. We also observed some other peaks above the 1D-exciton ground state and attribute them to exciton states consisting of excited hole subbands. These results show good agreement with a model calculation of a single electron-hole pair in T-shaped geometry with exact diagonalizations of the Coulomb interaction.

cond-mat.mtrl-sci↗

arXiv2003

Imaging of emission patterns in a T-shaped quantum wire laser

Spatially and spectrally resolved microscopic images of spontaneous and stimulated emissions are imaged at the mirror facets of a GaAs T-shaped quantum wire laser with high uniformity. Laser emission from the one-dimensional ground state reveals a circular image located at the core of a T-shaped optical waveguide but significantly smaller in area than the low power spontaneous emission from the same waveguide. These images unambiguously allow assignment of all spontaneous and laser emissions to the wire ground state and respective intersecting wells in the structure.

cond-mat.mtrl-sci↗