370 research outputs found
時空間反転対称な磁性体における非線形電流生成の理論的研究
京都大学新制・課程博士博士(理学)甲第22991号理博第4668号新制||理||1670(附属図書館)京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)教授 柳瀬 陽一, 教授 川上 則雄, 教授 石田 憲二学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDFA
Chiral photocurrent in parity-violating magnet and enhanced response in topological antiferromagnet
Rectified electric current induced by irradiating light, so-called
photocurrent, is an established phenomenon in optoelectronic physics. In this
paper, we present a comprehensive classification of the photocurrent response
arising from the parity violation in bulk systems. We clarify the contrasting
role of - and -symmetries and consequently find a
new type of photocurrent phenomena characteristic of parity-violating magnets,
intrinsic Fermi surface effect and gyration current. Especially, the gyration
current is induced by the circularly-polarized light and it is the counterpart
of the shift current caused by the linearly-polarized light. This photocurrent
adds a new functionality of materials studied in various fields of condensed
matter physics such as multiferroics and spintronics. A list of materials is
provided. Furthermore, we show that the gyration current is strongly enhanced
by topologically nontrivial band dispersion. On the basis of the microscopic
analysis of Dirac models, we demonstrate the divergent photocurrent response
and elucidate the importance of tilting of Dirac cones.Comment: 28 pages, 8 figures, 4 table
Nonlinear optical responses in noncentrosymmetric superconductors
The unique nonreciprocal responses of superconductors, which stem from the
Cooper pairs' quantum condensation, have been attracting attention. Recently,
theories of the second-order nonlinear response in noncentrosymmetric
superconductors were formulated based on the Bogoliubov-de Gennes theory. In
this paper, we study the mechanism and condition for second-order optical
responses of time-reversal symmetric superconductors. The numerical results
show the characteristic photocurrent and second harmonic generation in the
superconducting state. However, the superconductivity-induced nonlinear optical
responses disappear under some conditions on pair potential. We show that the
coexistence of intraband and interband pairing is necessary for the
second-order superconducting optical responses. In addition, the
superconducting Berry curvature factor, which is related to a component of
Berry curvature in the superconducting state, is essential for the nonlinear
responses. Thus, we derived the microscopic conditions where the
superconducting nonlinear response appears.Comment: 21 pages and 9 figure
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