Browsing by Author "Sheu, Y. M."

Now showing 1 - 6 of 6

Accurate modeling and characterization of mobility in tensile and compressive stress for state-of-the-art manufacturing NMOSFETs
(2007)
Wang, J. -S.
;
Chen, William P. N.
;
Shih, C. -H.
;
Lien, C.
;
Su, Pin
Photocreating supercooled spiral-spin states in a multiferroic manganite
(2016-08-18)
Sheu, Y. M.
;
Ogawa, N.
;
Kaneko, Y.
;
Tokura, Y.
;
電子物理學系
We demonstrate that the dynamics of the ab-spiral-spin order in a magnetoelectric multiferroic Eu0.55Y0.45MnO3 can be unambiguously probed through optical second harmonic signals, generated via spin-induced ferroelectric polarization. In the case of weak excitation, the ferroelectric and the spiral-spin order remains interlocked, both relaxing through spin-lattice relaxation in the nonequilibrium state. When the additional optical pulse illuminating the sample is intense enough to induce a local phase transition thermally, the system creates ametastable state of the bc-spiral-spin order (with the electric polarization P parallel to c) via supercooling across the first-order phase transition between the ab and bc spiral. The supercooled state of the bc-spiral spin is formed in the thermodynamical ground state of the ab spiral (P parallel to a), displaying a prolonged lifetime with strong dependence on the magnetic field along the a axis. The observed phenomena provide a different paradigm for photoswitching between the two distinct multiferroic states, motivating further research into a direct observation of the photocreated supercooled bc-spiral spin in multiferroic manganites.
Picosecond Creation of Switchable Optomagnets from a Polar Antiferromagnet with Giant Photoinduced Kerr Rotations
(2019-08-30)
Sheu, Y. M.
;
Chang, Y. M.
;
Chang, C. P.
;
Li, Y. H.
;
Babu, K. R.
On-demand spin orientation with a long polarized lifetime and an easily detectable signal is the ultimate goal for spintronics. However, there still exists a trade-off between controllability and stability of spin polarization, awaiting a significant breakthrough. Here, we demonstrate switchable optomagnet effects in (Fe1-xZnx)(2)Mo3O8, from which we can obtain tunable magnetization (spanning from -40% to 40% of a saturated magnetization) that is created from zero magnetization in the antiferromagnetic state without magnetic fields. It is accomplishable by utilizing circularly polarized laser pulses to excite spin-flip transitions in polar antiferromagnets that have no spin canting, traditionally hard to control without very strong magnetic fields. The spin controllability in (Fe1-xZnx)(2)Mo3O8 originates from its polar structure that breaks the crystal inversion symmetry, allowing distinct on-site d-d transitions for selective spin flip. By chemical doping, we exploit the phase competition between antiferromagnetic and ferrimagnetic states to enhance and stabilize the optomagnet effects, which result in long-lived photoinduced Kerr rotations. The present study creating switchable giant optomagnet effects in polar antiferromagnets sketches a new blueprint for the function of antiferromagnetic spintronics.
Relaxation-free strained SiGe with super anneal for 32nm high performance PMOS and beyond
(2006)
Yu, Ming H.
;
Li, J. H.
;
Lin, H. H.
;
Chen, C. H.
;
Ku, K. C.
The interaction of epitaxially strained SiGe and super annealing or millisecond anneal in high performance PFET fabrication was, for the first time, systematically investigated. When super annealing was applied, the quality of SiGe/Si interface, affected by subsequent ion implantation and post-SiGe thermal treatment, played an important role in SiGe strain relaxation incurring channel stress loss and defect injection to Si substrate resulting in high junction leakage. Defect injection mechanism was proposed to explain the defect formation in Si substrate. The new processing scheme, which preserved SiGe as relaxation-free and avoided defect injection, was developed and for 32nm technology. The device performance gain with 10% Id,sat increment resulting from fully strained SiGe was achieved.
Selective probe of coherent polar phonon and quasiferromagnetic resonance modes in multiferroic GdFeO3
(2018-09-26)
Sheu, Y. M.
;
Ogawa, N.
;
Tokunaga, Y.
;
Chan, H. C.
;
Tokura, Y.
Using time-resolved second harmonic generation (TRSHG) and optical transmission, we demonstrate simultaneous optical access to both magnetic and ferroelectric order parameters in a magnetoelectric multiferroic GdFeO3 below the transition temperature 2.2 K. In magnetoelectric phase, the pump pulses impulsively generate polar phonon modes of B-2 and A(1) symmetry and a quasiferromagnetic resonance mode, creating coherent lattice and spin motions. While collective motions associated with the ferroelectric and antiferromagnetic ordering are simultaneously excited, only the polar motion is detected in TRSHG, resulting in a direct subpicosecond excitation of the improper ferroelectric order. Our result also experimentally indicates that the soft mode in improper ferroelectrics is IR inactive above the phase transition, unlike proper ferroelectrics. Furthermore, we investigate the crystal polar symmetry and potential coupling between the polar phonons and the quasiantiferromagnetic resonance mode, which can shed light on the studies of subpicosecond magnetoelectric coupling based on collective quasiparticle excitations.
Unraveling thickness-dependent spin relaxation in colossal magnetoresistance manganite films
(2018-07-02)
Sheu, Y. M.
;
Trugman, S. A.
;
Chen, A. P.
;
Jia, Q. X.
;
Taylor, A. J.
We used ultrafast optical spectroscopy to study photoinduced spin relaxation in 10-100 nm thick La0.7Ca0.3MnO3 films. The spin-lattice relaxation time displays a strong dependence on thickness below the Curie temperature. Our simulations show that the observed thickness-dependent relaxation results from much faster thermal decay through the substrate in thinner films that leads to artificially faster demagnetization. Furthermore, we provide an analytical approach to gain insight into the spin-lattice relaxation time for highly thermal dissipative films. Our study strongly suggests that careful consideration of the influence of transient thermal variations on photoinduced demagnetization is mandatory when incorporating absorbing thin magnetic films into heterostructures and devices. Published by AIP Publishing.