Pump-Probe Study of Carrier-Spin Injection in a Diluted Magnetic Double Quantum Well of CdMnTe/CdTe

A. Murayama,K. Nishibayashi,N. Kono,K. Saito,I. Souma,Y. Oka 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.1

We study the dynamics of carrier-spin injection in a diluted magnetic semiconductor double quantum well (DMS-DQW) of CdMnTe/CdTe by means of pump-probe absorption spectroscopy. The time dependences of the absorption saturation intensity show the injection dynamics of spinpolarized electrons and heavy holes (hhs) from the DMS-CdMnTe into the non-magnetic CdTe wells, where separate tunneling of the electron and the hh is directly elucidated with time constants of 150 ps and 1 ns, respectively. The degree of circular polarization P of the absorption saturation increases from 0 to 70 ps after pumping in the non-magnetic CdTe well, which is caused by the injection of polarized electron spins in the DMS well. We observe a systematic dependence of the rise time of P on the magnetic eld. The faster polarization of the electron spin in the DMS well results in a faster electron-spin injection. The electron's spin polarization is accelerated in the DMS well by LO-phonon scattering at 6 T, where the electron spin splitting is close to the one-LO-phonon energy, which enables us to demonstrate a fast electron-spin injection with a time constant of 10 ps. We study the dynamics of carrier-spin injection in a diluted magnetic semiconductor double quantum well (DMS-DQW) of CdMnTe/CdTe by means of pump-probe absorption spectroscopy. The time dependences of the absorption saturation intensity show the injection dynamics of spinpolarized electrons and heavy holes (hhs) from the DMS-CdMnTe into the non-magnetic CdTe wells, where separate tunneling of the electron and the hh is directly elucidated with time constants of 150 ps and 1 ns, respectively. The degree of circular polarization P of the absorption saturation increases from 0 to 70 ps after pumping in the non-magnetic CdTe well, which is caused by the injection of polarized electron spins in the DMS well. We observe a systematic dependence of the rise time of P on the magnetic eld. The faster polarization of the electron spin in the DMS well results in a faster electron-spin injection. The electron's spin polarization is accelerated in the DMS well by LO-phonon scattering at 6 T, where the electron spin splitting is close to the one-LO-phonon energy, which enables us to demonstrate a fast electron-spin injection with a time constant of 10 ps.

Spin-Injection Dynamics and Eects of Spin Relaxation in Self-Assembled Quantum Dots of CdSe

T. Furuta,K. Hyomi,I. Souma,Y. Oka,A. Murayama,D. Dagnelund,I. A. Buyanova,W. M. Chen 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.1

We study the spin injection dynamics and the eects of spin relaxation in self-assembled quantum dots (QDs) of CdSe coupled with a diluted magnetic semiconductor (DMS) layer of ZnMnSe, where spin-polarized excitons can be injected from the DMS into the QDs because of the potential dierence. The degree of circular polarization, P, of excitonic photoluminescence (PL) at 5 T in the coupled QDs shows a rapid increase with increasing delay time after a linearly polarized pulse excitation, indicating the spin-injection dynamics. The P value tends to decay gradually because of the exciton-spin relaxation in the QDs after the spin injection. The spin-polarized excitons in the QD ensemble migrate simultaneously from QDs with higher exciton energies to those with lower exciton energies. This inter-dot transfer of excitons also aects the P value in the lower energy region of the QD-emission band because the excitons lose their spin polarizations due to the spin relaxation in the dots during the migration. The detailed analysis for the exciton-spin transfer is presented in a coupled QD system after spin injection. We study the spin injection dynamics and the eects of spin relaxation in self-assembled quantum dots (QDs) of CdSe coupled with a diluted magnetic semiconductor (DMS) layer of ZnMnSe, where spin-polarized excitons can be injected from the DMS into the QDs because of the potential dierence. The degree of circular polarization, P, of excitonic photoluminescence (PL) at 5 T in the coupled QDs shows a rapid increase with increasing delay time after a linearly polarized pulse excitation, indicating the spin-injection dynamics. The P value tends to decay gradually because of the exciton-spin relaxation in the QDs after the spin injection. The spin-polarized excitons in the QD ensemble migrate simultaneously from QDs with higher exciton energies to those with lower exciton energies. This inter-dot transfer of excitons also aects the P value in the lower energy region of the QD-emission band because the excitons lose their spin polarizations due to the spin relaxation in the dots during the migration. The detailed analysis for the exciton-spin transfer is presented in a coupled QD system after spin injection.

Heterogeneity in Trajectories of Body Mass Index and Their Associations with Mortality in Old Age: A Literature Review

Hiroshi Murayama,Benjamin A. Shaw 대한비만학회 2017 The Korean journal of obesity Vol.26 No.3

This article reviewed studies to investigate the association between trajectories of body mass index (BMI) and mortality among older adults. Investigators conducted a systematic search of published peer-reviewed literature in the PubMed database, and three articles that satisfied the inclusion criteria for the review were identified. All of these studies used group-based trajectory models to identify distinct BMI trajectories. Two studies were derived from the U.S. and used data from the Health and Retirement Study, with up to nine repeated observations. Most of the BMI trajectories in older Americans were increasing and fell primarily within the overweight and obese ranges. The other study was from Japan and used nationwide data, with up to seven repeated observations. BMI trajectories identified in the older Japanese were mostly decreasing and fell primarily within the normal weight range. Although the distribution of BMI trajectories was different between the two nations, the findings from these three studies consistently demonstrated that people with stable overweight trajectories had the lowest all-cause mortality rates in both countries. Beyond this, however, these studies suggested that priorities for weight control in old age should likely differ between Western and non-Western countries. Research regarding BMI trajectories and mortality in old age is very limited at present. Evidence from countries other than the U.S. and Japan is warranted in order to validate current findings and guide the development of local clinical and public health strategies for body weight management aimed at improving the health and survival of older adults.

Temperature dependence of the radiative recombination time in ZnO nanorods under an external magnetic field of 6 T.

Lee, W,Kiba, T,Murayama, A,Sartel, C,Sallet, V,Kim, I,Taylor, R A,Jho, Y D,Kyhm, K Optical Society of America 2014 Optics express Vol.22 No.15

<P>The Temperature dependence of the exciton radiative decay time in ZnO nanorods has been investigated, which is associated with the density of states for the intra-relaxation of thermally excited excitons. The photoluminescence decay time was calibrated by using the photoluminescence intensity in order to obtain the radiative decay time. In the absence of an external magnetic field, we have confirmed that the radiative decay time increased with temperature in a similar manner to that seen in bulk material (similar to T-1.5). Under an external magnetic field of 6T parallel to the c-axis, we found that the power coefficient of the radiative decay time with temperature decreased (similar to T-1.3) when compared to that in the absence of a magnetic field. This result can be attributed to an enhancement of the effective mass perpendicular to the magnetic field and a redshift of the center-of-mass exciton as a consequence of perturbation effects in the weak-field regime. (C) 2014 Optical Society of America</P>

Electron-Spin Relaxation Induced by Mn Spins and Eects of LO-Phonon Scattering in CdMnTe Quantum Wells

K. Saito,I. Souma,Y. Oka,A. Murayama 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.1

We study electron-spin relaxation induced by Mn spins and eects of LO-phonon scattering in CdMnTe quantum wells, where Mn contents of 3.6 and 5.0 at% are examined. By using pump-probe absorption a under magnetic eld, the time constant of the electron-spin relaxation e is deduced as a function of the magnetic eld. Values of e under magnetic elds are ve times dierent between both the Mn contents, while those at 0 T re ect the Mn content. The latter fact for the spin-relaxation times at 0 T shows that the electron-spin relaxation is induced by Mn spins via the s-d exchange interaction. However, the former signicant dierence in e suggests that the number of eective Mn spins involved in the electron-energy relaxation is greatly dierent in the spin-relaxation between the spin-splitting electron levels under dierent magnetic elds. The eects of LO-phonon scattering on the electron-spin relaxation are observed when the spin-splitting is close to the one-LO-phonon energy, indicating an eective path of the electron-spin relaxation involving both the LO phonon and the Mn spins. We study electron-spin relaxation induced by Mn spins and eects of LO-phonon scattering in CdMnTe quantum wells, where Mn contents of 3.6 and 5.0 at% are examined. By using pump-probe absorption a under magnetic eld, the time constant of the electron-spin relaxation e is deduced as a function of the magnetic eld. Values of e under magnetic elds are ve times dierent between both the Mn contents, while those at 0 T re ect the Mn content. The latter fact for the spin-relaxation times at 0 T shows that the electron-spin relaxation is induced by Mn spins via the s-d exchange interaction. However, the former signicant dierence in e suggests that the number of eective Mn spins involved in the electron-energy relaxation is greatly dierent in the spin-relaxation between the spin-splitting electron levels under dierent magnetic elds. The eects of LO-phonon scattering on the electron-spin relaxation are observed when the spin-splitting is close to the one-LO-phonon energy, indicating an eective path of the electron-spin relaxation involving both the LO phonon and the Mn spins.

세계화 시대의 기업경영

이상문,Homes,Matin,Motofusa,Murayama,Digman,Lester A. 한국지역사회연구소 1996 地域社會 Vol.1996 No.3

Polarization anisotropy of exciton in self-assembled elliptical InP/InGaP quantum dots

Kim, I.,Kiba, T.,Murayama, A.,Song, J.D.,Kyhm, K. Elsevier 2015 CURRENT APPLIED PHYSICS Vol.15 No.6

Optical anisotropy of self-assembled elliptical InP quantum dots has been investigated in terms of the polarization dependence of excitons. Although large size inhomogeneity is present, two kinds of characteristic quantum dots, which are classified into large and small quantum dots, were found in terms of the polarization anisotropy. We have confirmed that the large quantum dots are more pronounced in the polarization anisotropy, where the degree of linear polarization for the large quantum dots is significantly larger (~60%) than that for the small ones (~36%). The effective shape of quantum dots is also estimated by using the size dependence of oscillator strength, which is in agreement with the AFM image. We also suggest that the anisotropy of exciton oscillator strength can be modified via the dipole-dipole interaction between nearest exciton dipoles.

Transfer Dynamics of Spin-Polarized Excitons in ZnCdMnSe/ZnCdSe Double Quantum Wells

J. H. Park,I. Souma,Y. Oka,A. Murayama,D. Dagnelund,I. A. Buyanova,W. M. Chen 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.1

We study the transfer dynamics of spin-polarized excitons in diluted magnetic semiconductor (DMS) double quantum wells (QWs) of ZnCdMnSe/ZnCdSe, where the spin-polarized excitons tunnel from the non-magnetic ZnCdSe to DMS-ZnCdMnSe wells and subsequently relax to the ground state in the DMS well with phonon emissions. The exciton-transfer time decreases when the exciton-energy dierence between both the wells is equal to the one-LO-phonon energy, indicating the LO-phonon-assisted acceleration of the spin transfer. Moreover, the exciton transfer alters into the separate transfer of the electron and the heavy hole when the electron potential dierence becomes larger than the LO-phonon energy. This observation demonstrates the importance of energy-relaxation dynamics in the spatial transport of spins in semiconductor quantum structures. We study the transfer dynamics of spin-polarized excitons in diluted magnetic semiconductor (DMS) double quantum wells (QWs) of ZnCdMnSe/ZnCdSe, where the spin-polarized excitons tunnel from the non-magnetic ZnCdSe to DMS-ZnCdMnSe wells and subsequently relax to the ground state in the DMS well with phonon emissions. The exciton-transfer time decreases when the exciton-energy dierence between both the wells is equal to the one-LO-phonon energy, indicating the LO-phonon-assisted acceleration of the spin transfer. Moreover, the exciton transfer alters into the separate transfer of the electron and the heavy hole when the electron potential dierence becomes larger than the LO-phonon energy. This observation demonstrates the importance of energy-relaxation dynamics in the spatial transport of spins in semiconductor quantum structures.