arXiv subjects

Y. Kurita

Publications and source records attributed to Y. Kurita.

7 recordsLinked to original sources

arXiv2012

Threshold of Terahertz Population Inversion and Negative Dynamic Conductivity in Graphene Under Pulse Photoexcitation

We theoretically study the population inversion and negative dynamic conductivity in intrinsic graphene in the terahertz (THz) frequency range upon pulse photoexcitation with near-/mid-infrared wavelength. The threshold pulse energy required for the population inversion and negative dynamic conductivity can be orders-of-magnitude lower when the pulse photon energy is lower, due to the inverse proportionality of the photoexcited carrier concentration to the pulse photon energy and to the weaker carrier heating. We also investigate the dependence of the dynamic conductivity on the momentum relaxation time. The negative dynamic conductivity takes place either in high- or low-quality graphene, where the Drude absorption by carriers in the THz frequency is weak.

cond-mat.mes-hall↗

arXiv2005

Electronically competing phases and their magnetic field dependence in electron-doped nonsuperconducting and superconducting Pr0.88LaCe0.12CuO4

We present comprehensive neutron scattering studies of nonsuperconducting and superconducting electron-doped Pr0.88LaCe0.12CuO4(PLCCO). At zero field, the transition from antiferromagnetic (AF) as-grown PLCCO to superconductivity without static antiferromagnetism can be achieved by annealing the sample in pure Ar at different temperatures, which also induces an epitaxial (Pr,La,Ce)2O3 phase as an impurity. When the superconductivity first appears in PLCCO, a quasi-two-dimensional (2D) spin-density-wave (SDW) order is also induced, and both coexist with the residual three-dimensional (3D) AF state. A magnetic field applied along the [-1,1,0] direction parallel to the CuO2 plane induces a ``spin-flop'' transition, where the noncollinear AF spin structure of PLCCO is transformed into a collinear one. The spin-flop transition is continuous in semiconducting PLCCO, but gradually becomes sharp with increasing doping and the appearance of superconductivity. A c-axis aligned magnetic field that suppresses the superconductivity also enhances the quasi-2D SDW order at (0.5,0.5,0) for underdoped PLCCO. However, there is no effect on the 3D AF order in either superconducting or nonsuperconducting samples. Since the same field along the [-1,1,0] direction in the CuO2 plane has no (or little) effect on the superconductivity, (0.5,0.5,0) and (Pr,La,Ce)2O3 impurity positions, we conclude that the c-axis field-induced effect is intrinsic to PLCCO and arises from the suppression of superconductivity.

cond-mat.supr-con↗

arXiv2005

Electronic inhomogeneity and competing phases in electron-doped superconducting Pr0.88LaCe0.12CuO4

We use neutron scattering to demonstrate that electron-doped superconducting Pr0.88LaCe0.12CuO4 in the underdoped regime is electronically phase separated in the ground state, showing the coexistence of a superconducting phase with a three-dimensional antiferromagnetically ordered phase and a quasi-two-dimensional spin density wave modulation. The Neel temperature of both antiferromagnetic phases decreases linearly with increasing superconducting transition temperature (Tc) and vanishes when optimal superconductivity is achieved. These results indicate that the electron-doped copper oxides are close to a quantum critical point, where the delicate energetic balance between different competing states leads to microscopic heterogeneity.

cond-mat.supr-con↗

arXiv2004

Evolution of the Hall Coefficient and the Peculiar Electronic Structure of the Cuprate Superconductors

Although the Hall coefficient R_H is an informative transport property of metals and semiconductors, its meaning in the cuprate superconductors has been ambiguous because of its unusual characteristics. Here we show that a systematic study of R_H in La_{2-x}Sr_{x}CuO_{4} single crystals over a wide doping range establishes a qualitative understanding of its peculiar evolution, which turns out to reflect a two-component nature of the electronic structure caused by an unusual development of the Fermi surface recently uncovered by photoemission experiments.

cond-mat.supr-con↗

arXiv2004

Electronic Phase Diagram of High-T_c Cuprate Superconductors from a Mapping of the In-Plane Resistivity Curvature

We propose that Resistivity Curvature Mapping (RCM) based on the in-plane resistivity data is a useful way to objectively draw an electronic phase diagrams of high-T_c cuprates, where various crossovers are important. In particular, the pseudogap crossover line can be conveniently determined by RCM. We show experimental phase diagrams obtained by RCM for Bi_{2}Sr_{2-z}La_{z}CuO_{6+δ}, La_{2-x}Sr_{x}CuO_{4}, and YBa_{2}Cu_{3}O_{y}, and demonstrate the universal nature of the pseudogap crossover. Intriguingly, the electronic crossover near optimum doping depicted by RCM appears to occur rather abruptly, suggesting that the quantum critical regime, if exists, must be very narrow.

cond-mat.supr-con↗

arXiv2004

"Spin-Flop" Transition and Anisotropic Magnetoresistance in Pr_{1.3-x}La_{0.7}Ce_{x}CuO_{4}: Unexpectedly Strong Spin-Charge Coupling in Electron-Doped Cuprates

We use transport and neutron-scattering measurements to show that a magnetic-field-induced transition from noncollinear to collinear spin arrangement in adjacent CuO_{2} planes of lightly electron-doped Pr_{1.3-x}La_{0.7}Ce_{x}CuO_{4} (x=0.01) crystals affects significantly both the in-plane and out-of-plane resistivity. In the high-field collinear state, the magnetoresistance (MR) does not saturate, but exhibits an intriguing four-fold-symmetric angular dependence, oscillating from being positive at B//[100] to being negative at B//[110]. The observed MR of more than 30% at low temperatures induced by a modest modification of the spin structure indicates an unexpectedly strong spin-charge coupling in electron-doped cuprates.

cond-mat.supr-con↗

arXiv2003

Thermal Conductivity of Pr_{1.3-x}La_{0.7}Ce_xCuO_4 Single Crystals and Signatures of Stripes in an Electron-Doped Cuprate

It was recently demonstrated that the anisotropic phonon heat transport behavior is a good probe of the stripe formation in La_{2-x}Sr_xCuO_4 (LSCO) [X. F. Sun {\it et al.}, Phys. Rev. B {\bf 67}, 104503 (2003)]. Using this probe, we examined an electron-doped cuprate Pr_{1.3-x}La_{0.7}Ce_xCuO_4 (PLCCO) and found that essentially the same features as those in LSCO are observed. Moreover, the in-plane resistivity ρ_{ab} of lightly-doped PLCCO shows metallic behavior (dρ_{ab}/dT > 0) in the Néel ordered state with a mobility comparable to that in LSCO. It is discussed that these peculiar properties in common with LSCO signify the existence of stripes in electron-doped cuprates.

cond-mat.supr-con↗