著者

Tomimoto Shinichi Nozawa Shinsuke Terai Yoshikazu Kuroda Shinji Takita Kôki Masumoto Yasuaki

出版者

The American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.81, no.12, pp.125313, 2010-03

被引用文献数

11

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We have studied the spin dynamics of confined electrons in an ultrathin CdTe/ZnTe quantum well andself-assembled quantum dots by time-resolved Kerr-rotation technique. The dependence of the spin-precessionfrequency on the magnetic field direction shows the anisotropy of the g-factor tensor, which is the opposite ofthe usual quantum wells with moderate widths. The geometrical anisotropy of the confinement also affects theinitial orientation of the electron spins created optically, as revealed clearly with the use of oblique-incidencepump pulses.

著者

Nomura S. Tamura H. Yamaguchi M. Akazaki T. Hirayama Y.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.87, no.8, pp.085318, 2013-02

被引用文献数

5 1

---

We report on measurement of the electron-hole effective g-factors (geff*) depending on electron filling factors ν from magnetophotoluminescence spectroscopy at low magnetic fields B<1 T in low electron density regime in a GaAs/Al0.33Ga0.67As-gated quantum well. Enhancement of geff* at odd ν is observed. The oscillatory behavior of geff* is compared with results of a theory that takes into account the lowest-order exchange interaction of the screened Coulomb interaction. Good agreement of the observed geff* with theoretical results is obtained except ν at around 3. The enhancement of geff* at even ν with decrease in electron density has not been observed.

著者

Cuong Nguyen Thanh Otani Minoru Okada Susumu

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.87, no.4, pp.045424, 2013

被引用文献数

14 3

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Based on first-principles total-energy calculations, we studied the energetics and electronic structure of zigzag graphene nanoribbons with nanometer-scale corners. We found that the formation energy of a short zigzag edge with a 120∘ corner is substantially smaller than that of a straight zigzag edge with an infinite length. We also found that zigzag graphene ribbons with 120∘ corners are semiconductors for which the band-gap decreases with increasing length between adjacent corners. The edge state is absent for zigzag graphene ribbons with short corner-corner distances, while the edge state emerges for zigzag ribbons that have a corner-corner distance greater than 1.5 nm. The remarkable stability of the 120∘ corner of the short zigzag edges is in good agreement with the experimental observation of such corners of graphene edges.

著者

Zhao Jialong Nair Selvakumar V. Masumoto Yasuaki

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.63, no.3, pp.033307, 2001-01

被引用文献数

7 11

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The size dependence of excitonic states and vibrational modes in CuCl cubic quantum dots embedded in NaCl crystals was studied by means of site-selective persistent spectral hole burning spectroscopy. It is shown that the interaction of the longitudinal optical (LO) phonon with the exciton results in the formation of coupled exciton-phonon modes when the energy of the LO phonon approaches the energy spacings between the ground and excited states of the exciton. The energy anticrossings of the LO phonon modes with two higher optically allowed excited states of the exciton in CuCl QD’s were clearly observed at confinement energies of about 10 and 6 meV, respectively. In addition, the linewidth of the LO phonon sideband in CuCl QD’s in NaCl crystals was found to increase abruptly from 0.3 meV to about 1.2 meV at a confinement energy of about 23 meV, which appears to result from the exciton-phonon mixing of the LO phonon mode with the first excited state of the exciton. The experimental results are qualitatively understood by the LO phonon renormalization theory.

著者

Ignatiev Ivan V. Kozin Igor E. Davydov Valentin G. Nair Selvakumar V. Lee Jeong-Sik Ren Hong-Wen Sugou Shigeo Masumoto Yasuaki

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.63, no.7, pp.075316, 2001-02

被引用文献数

38 48

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Phonon resonances observed in the photoluminescence (PL) spectra of InP and In0.35Ga0.65As self-assembled quantum dots (QD’s) in an external electric field are studied in detail. The resonances are shown to arise from fast phonon-assisted relaxation of hot carriers, and to become observable when the PL is quenched by nonradiative losses from excited states. A simple model is developed that considers tunneling of the carriers from the QD’s into the barrier layer as the main process responsible for PL quenching in the presence of an electric field. From this model, the depth of the potential well for holes is estimated to be 10–20 meV for the InP QD’s. The PL kinetics measurement is performed with a time resolution of 6 ps. Clear evidence of surprisingly fast carrier relaxation with emission of high-energy acoustic phonons is found. Further acceleration of the carrier relaxation is observed under strong optical pumping. We consider this effect to be caused by Auger-like carrier-carrier scattering processes. Acceleration of the relaxation observed at elevated temperatures is ascribed to stimulated phonon emission.

著者

Matsumoto Takahiro Suzuki Jun-ichi Ohnuma Masato Kanemitsu Yoshihiko Masumoto Yasuaki

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.63, no.19, pp.195322, 2001-05

被引用文献数

62

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The optical absorption spectrum in nanocrystalline silicon (n-Si) was determined from both light transmittance and reflectance measurements. We observed that n-Si has a phonon structure in the optical absorption spectrum. This structure originates from momentum-conserving TO phonon absorption and emission, and provides direct evidence that n-Si is an indirect-band-gap semiconductor with quantum size effects. By using small-angle x-ray scattering to measure the nanocrystal size distribution, we found that the band-gap widening varies as (1/L)1.6 with decreasing nanocrystal diameter L.

著者

Tokunaga Eiji Ivanov A. L. Nair Selvakumar V. Masumoto Yasuaki

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.63, no.23, pp.233203, 2001-06

被引用文献数

11 6

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We report observation of the inverse polariton series and a detailed experimental study of the exciton components in polaritons (Hopfield coefficients). Spontaneous emission of excitonic molecules into outgoing polaritons associated with the i(=1,2,3,4,5)th exciton states in bulk CuCl is detected and analyzed by the bipolariton model. Because the intensities of the emission lines, which form the inverse polariton series, are determined by the exciton components in the final-state polaritons, we are able to measure the Hopfield coefficients for the highly composite outgoing polaritons. Quantum interference in the optical decay of excitonic molecules, due to the multiple exciton components in the polariton and biexciton states, is also demonstrated.

著者

Tokunaga Eiji Kurihara Kazuyoshi Baba Motoyoshi Masumoto Yasuaki Matsuoka Masahiro

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.64, no.4, pp.045209, 2001-07

被引用文献数

10 9

---

Radiative decay of biexcitons wave-vector (K) selectively generated in a low-K region (0<~

著者

Gerlovin I. Ya. Dolgikh Yu. K. Eliseev S. A. Ovsyankin V. V. Efimov Yu. P. Petrov V. V. Ignatiev I. V. Kozin I. E. Masumoto Y.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.65, no.3, pp.035317, 2002-01

被引用文献数

21 17

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Picosecond kinetics of polarized resonant photoluminescence (PL) of HH excitons in the GaAs/AlGaAs superlattices is studied in an external magnetic field. The measurements were made in real time using a streak camera. For the magnetic field aligned along the heterostructure growth direction, the resonant PL exhibits oscillations in the degree of linear polarization. The oscillations are ascribed to quantum beats between sublevels of the optically active excitonic doublet split by the magnetic field. For the magnetic field aligned along the plane of the layers, the resonant PL is found to exhibit oscillations in circular polarization. These oscillations are related to beats between states of the optically active and optically inactive excitonic doublets. Experimental dependence of the oscillation frequency on the magnetic field strength and orientation has allowed us to determine the hole and electron g factors and the electron-hole exchange energy. Dynamics of the degree of circular polarization of the PL in magnetic field is used to measure the energy relaxation rate of the exciton spin states. In the magnetic field exceeding 1 T, the energy relaxation rate is shown to be magnetic-field independent and equal (1±0.2)×1010 s-1. This value is found to be much smaller than the spin phase relaxation rate determined from decay of the quantum beats in linear polarization. Unlike the energy relaxation rate, the latter grows linearly with the field strength and equals (5±0.5)×1010 s-1 at 5 T. It is concluded that the main mechanism responsible for loss of macroscopic spin coherence is the reversible dephasing within inhomogeneously broadened system.

著者

Kozin I. E. Davydov V. G. Ignatiev I. V. Kavokin A. V. Kavokin K. V. Malpuech G. Ren Hong-Wen Sugisaki M. Sugou S. Masumoto Y.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.65, no.24, pp.241312, 2002-06

被引用文献数

61 53

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Spins of resident electrons in charged quantum dots (QD’s) act as local magnets inducing the Zeeman splitting of excitons trapped into dots. This is evidenced by the observation of quantum beats in the linearly polarized time-resolved photoluminescence of a biased array of self-assembled InP QD’s. An external magnetic field is found to shorten the spin beats’ decay time keeping constant the frequency of the beats. A model using the pseudospin formalism allows one to attribute the observed quantum beats to the radiative decay of hot trions having two electrons that occupy different energy levels in a QD.

著者

Yugova I. A. Gerlovin Ya. Davydov V. G. Ignatiev I. V. Kozin I. E. Ren H. W. Sugisaki M. Sugou S. Masumoto Y.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.66, no.23, pp.235312, 2002-12

被引用文献数

37 36

---

The paper reports on quantum beats observed in the photoluminescence kinetics of a single layer of the InPself-assembled quantum dots in a magnetic field. It is found that the beats arise only after removal of excesscharges from the quantum dots by an external electrical bias. The quantum beats are shown to be related to theinterference of the excitonic fine-structure states split by the magnetic-field. The dependences of the beatcharacteristics on the magnetic-field strength and orientation are studied. Theoretical analysis based on a modelspin Hamiltonian has allowed us to describe adequately the shape of the oscillating component of the signal.We have determined the values of the electron g-factor components and estimated the spread and the meanvalue of the hole g factor, as well as of the electron-hole exchange splitting parameters.

著者

Morishita M. Nagatani H.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.65, no.10, pp.104524, 2002-03

被引用文献数

15

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Nuclear-spin heat capacities of submonolayer solid 3He adsorbed on a graphite surface are measured down to 100 μK, a factor of 20 lower temperature than in previous works. This system is one of the most ideal two-dimensional quantum spin systems (S=1/2). In a wide areal density region (6.1 nm-2<~ρ<~8.7 nm-2), anomalous temperature dependencies of the heat capacity, C∝Tα(-1.6≲α≲-0.7), are observed in a temperature range over two orders of magnitude (0.1 mK<~T<~20 mK) instead of the expected high-temperature behavior (α=-2) for localized spins. The α value shows a complicated density dependence which is accompanied by a density variation of a heat capacity isotherm at an extremely low temperature (=0.2 mK). This anomaly is similar to the previously observed high-temperature behavior (α≈-1) of the lowest density solid in the second layer. Although quantitative explanations are lacking for these anomalies, they are likely due to the high frustration caused by competing ferromagnetic and antiferromagnetic multiple-spin exchange interactions at least up to the six-spin exchange. We find that the excess heat-capacity (Cex) due to the amorphous 3He adsorbed on substrate heterogeneities is certainly not an origin of the anomalous behavior in C of the uniform submonolayer. Only at and below the density for the sqrt[3]×sqrt[3] commensurate phase (ρ=6.4 nm-2) heat capacity bumps at around 20 mK are observed. We suggest the possibility of spin-polaron effects caused by delocalized vacancies to explain this anomaly.

著者

Kojima Seiji Tsumura Naoki Wada Takeda Mitsuo Nishizawa Seizi

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.67, no.3, pp.035102, 2003-01

被引用文献数

52 39

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We report observations of the intensity and phase transmission spectra related to phonon-polariton propagation using coherent far-infrared radiation for a high-quality ferroelectric bismuth titanate crystal plate. In order to determine the polariton-dispersion relation, the phase delay was determined minutely as a function of the THz radiation frequency in the region between 3 and 100 cm-1. The anisotropy of polariton dispersion relation was also successfully determined on the c plate simply by switching the polarization direction of an incident beam from E∥a to E∥b. The observed polariton dispersion relations are consistently reproduced by the calculation using Kurosawa’s formula.

著者

Hirai H. Tanaka T. Kawamura T. Yamamoto Y. Yagi T.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.68, no.17, pp.172102, 2003-11

被引用文献数

53 45

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High-pressure experiments on methane hydrate were performed in the pressure range of 0.2–42 GPa using diamond-anvil cell. In situ x-ray-diffraction study revealed that methane hydrate of a high-pressure form, filled ice structure, survived up to 42 GPa. Pressure versus volume data were obtained in the pressure region. The filled ice structure represented large anisotropic compressibility and the volume change attained 40% at 42 GPa. The anisotropic compressibility was explained by the characteristic channel framework of the filled ice structure.

著者

Umeda T. Isoya J. Morishita N. Ohshima T. Kamiya T.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.69, pp.121201, 2004-03

被引用文献数

42

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The EI5 and EI6 centers are typical intrinsic defects in radiation-damaged and semi-insulating 4H-SiC. So far, their origins have been assigned to positively charged carbon vacancies (VC+) and silicon antisites (SiC+), respectively. However, our complete set of 29Si hyperfine (HF) data clearly reveals that both the centers should originate from VC+ but their locations are different, i.e., quasicubic sites for EI5 and hexagonal sites for EI6, as recently predicted by the first-principle calculation [M. Bockstedte et al., Phys. Rev. B 67, 193102 (2003)]. The two types of VC+ centers showed remarkable differences in their atomic structures as well as in the temperature dependence of HF interactions, which are closely related to the nature of the two sites.

著者

Morita Y. Hatsugai Y. Otsuka Y.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.70, no.24, pp.245101, 2004-12

被引用文献数

2 1

---

We study quasiparticle structure in the vicinity of the Heisenberg model. At first, we focus on the model in one dimension and show how solitonic quasiparticles (and their bound states) emerge. Further we discuss its anlaog in higher dimensions. Related to this subject, numerical data are presented and a discussion is given for the quasiparticles in the two-dimensional Hubbard model at half filling on a triangular-type lattice.

著者

Kaminski A. Fretwell H. M. Norman M. R. Randeria M. Rosenkranz S. Chatterjee U. Campuzano J. C. Mesot J. Sato T. Takahashi T. Terashima T. Takano M. Kadowaki K. Li Z. Z. Raffy H.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.71, pp.014517, 2005-01

被引用文献数

82 80

---

We examine the momentum and energy dependence of the scattering rate of the high-temperature cuprate superconductors using angle-resolved photoemission spectroscopy. The scattering rate is of the form a + bomega around the Fermi surface for under-and optimal doping. The inelastic coefficient b is found to be isotropic. The elastic term a, however, is found to be highly anisotropic for under-and optimally doped samples, with an anisotropy which correlates with that of the pseudogap. This is contrasted with heavily overdoped samples, which show an isotropic scattering rate and an absence of the pseudogap above Tc. We find this to be a generic property for both single-and double-layer compounds.

著者

Baelus B. J. Kadowaki K. Peeters F. M.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.71, pp.024514, 2005-01

被引用文献数

26

---

Solving the nonlinear Ginzburg-Landau equations self-consistently we investigated the influence of surface defects on the vortex penetration and expulsion in thin mesoscopic superconducting samples. The effect of the number, size, and position of surface defects on the vortex entry and exit fields and on the entrance and exit positions of the vortex are studied for very thin circular, square, and rectangular samples. For specific vortex configurations we found that due to the interplay between the vortex-vortex repulsion and the vortex-defect interaction, the vortex does not enter or leave the sample through the surface defect.

著者

Taniguchi H. Morita Y. Hatsugai Y.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.71, no.13, pp.134417, 2005-04

被引用文献数

6 5

---

Based on quantum Monte Carlo calculations, we shall discuss the regime where ferromagnetic correlation isdominant in the two-dimensional t-t8 Hubbard model at a finite temperature. In this model, ferromagnetismcompetes with antiferromagnetism and we reveal how crossover occurs between them at a finite temperature bythe bias-free method. We shall investigate the data in the context of the so-called “low-density ferromagnetism.”The weak-coupling result is also shown and the data are compared with the “Nagaokaferromagnetism.”

著者

Baelus B. J. Kanda A. Peeters F. M. Ootuka Y. Kadowaki K.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.71, pp.140502, 2005-04

被引用文献数

30 29

---

The temperature dependence of the vortex penetration and expulsion fields in mesoscopic superconducting disks are studied. We experimentally find that the penetration field decreases with increasing temperature for all values of the vorticity. On the other hand, the temperature dependence of the expulsion fields shows two regimes: For some vortex states the expulsion field increases with temperature, while for other states it is almost temperature independent. A numerical study based on the nonlinear Ginzburg-Landau theory confirms that the former regime corresponds to multivortex states and the latter to giant vortex states. The origin of this difference is discussed.