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Geometric aspects of nonlinear and nonequilibrium phenomena
Takahiro Morimoto, Sota Kitamura, Naoto Nagaosa
We review recent developments in the research of nonlinear and nonequilibrium phenomena in solids focusing on their geometrical aspects. We start with introducing the basic concept…
Photocurrent induced by a bicircular light drive in centrosymmetric systems
Yuya Ikeda, Sota Kitamura, Takahiro Morimoto
A bicircular light (BCL) consists of left and right circularly polarized lights with different frequencies, and draws a rose-like pattern with a rotational symmetry determined by t…
Effects of relaxation on photovoltaic effect and possibility of photocurrent within transparent region
Yugo Onishi, Hikaru Watanabe, Takahiro Morimoto +1
We theoretically study photocurrents in metals that break both inversion and symmetries within the transparent region. We find that the system under the…
Observation of a flat and extended surface state in a topological semimetal
Ryo Mori, Kefeng Wang, Takahiro Morimoto +3
A topological flatband, also known as drumhead states, is an ideal platform to drive new exotic topological quantum phases. Using angle-resolved photoemission spectroscopy experime…
Floquet engineering of electric polarization with two-frequency drive
Yuya Ikeda, Sota Kitamura, Takahiro Morimoto
Electric polarization is a geometric phenomenon in solids and has a close relationship to the symmetry of the system. Here we propose a mechanism to dynamically induce and manipula…
Topological charge pumping in quasiperiodic systems characterized by Bott index
Mao Yoshii, Sota Kitamura, Takahiro Morimoto
We study topological charge pumping in one-dimensional quasiperiodic systems. Since these systems lack periodicity, we cannot use the conventional approach based on the topological…
Experimental signature of parity anomaly in semi-magnetic topological insulator
M. Mogi, Y. Okamura, M. Kawamura +9
A three-dimensional topological insulator features a two-dimensional surface state consisting of a single linearly-dispersive Dirac cone. Under broken time-reversal symmetry, the s…
Possible dimensionality transition behavior in localized plasmon resonances of confinement-controlled graphene devices
Takahiro Morimoto, Yoshiue Ikuta, Toshiya Okazaki
We investigated the dimensionality transition behavior of graphene localized plasmon resonances in confinement-controlled graphene devices. We first demonstrated a possibility of d…
Photocurrent of exciton polaritons
Takahiro Morimoto, Naoto Nagaosa
We study photocurrent of exciton polaritons in inversion broken systems. We use an effective Hamiltonian and Green's function approaches to deduce the formula for polariton photocu…
Current-induced second harmonic generation in inversion-symmetric Dirac and Weyl semimetals
Kazuaki Takasan, Takahiro Morimoto, Joseph Orenstein +1
Second harmonic generation (SHG) is a fundamental nonlinear optical phenomenon widely used both for experimental probes of materials and for application to optical devices. Even-or…
Optical rotation in thin chiral/twisted materials and the gyrotropic magnetic effect
Yan-Qi Wang, Takahiro Morimoto, Joel E. Moore
The rotation of the plane of polarization of light passing through a non-magnetic material is known as natural optical activity or optical gyrotropy. The behavior of this effect in…
Nonreciprocal Landau-Zener tunneling
Sota Kitamura, Naoto Nagaosa, Takahiro Morimoto
Application of strong dc electric field to an insulator leads to quantum tunneling of electrons from the valence band to the conduction band, which is a famous nonlinear response k…
Difference frequency generation in topological semimetals
Fernando de Juan, Yang Zhang, Takahiro Morimoto +3
When two lasers are applied to a non-centrosymmetric material, light can be generated at the difference of the incoming frequencies , a phenomenon known as difference frequency…
Observation of Topological Photocurrents in the Chiral Weyl Semimetal RhSi
Dylan Rees, Kaustuv Manna, Baozhu Lu +6
Weyl semimetals are crystals in which electron bands cross at isolated points in momentum space. Associated with each crossing point (or Weyl node) is an integer topological invari…
Chiral Optical Response of Multifold Fermions
Felix Flicker, Fernando de Juan, Barry Bradlyn +3
Multifold fermions are generalizations of two-fold degenerate Weyl fermions with three-, four-, six- or eight-fold degeneracies protected by crystal symmetries, of which only the l…
Current-voltage characteristic and shot noise of shift current photovoltaics
Takahiro Morimoto, Masao Nakamura, Masashi Kawasaki +1
We theoretically study the current-voltage relation, characteristic, of the photovoltaics due to the shift current, i.e., the photocurrent generated the exter…
Berry Phases in Symmetry Protected Topological Phases
Toshikaze Kariyado, Takahiro Morimoto, Yasuhiro Hatsugai
We show that the Berry phase (Berry phase quantized into ) provides a useful tool to characterize symmetry protected topological phases with correlation that can be dir…
Nonlinear spin current generation in noncentrosymmetric spin-orbit coupled systems
Keita Hamamoto, Motohiko Ezawa, Kun Woo Kim +2
Spin current plays a central role in spintronics. In particular, finding more efficient ways to generate spin current has been an important issue and studied actively. For example,…
Quantitative relationship between polarization differences and the zone-averaged shift photocurrent
Benjamin M. Fregoso, Takahiro Morimoto, Joel E. Moore
A relationship is derived between differences in electric polarization between bands and the "shift vector" that controls part of a material's bulk photocurrent, then demonstrated…
Large bulk photovoltaic effect and spontaneous polarization of single-layer monochalcogenides
Tonatiuh Rangel, Benjamin M. Fregoso, Bernardo S. Mendoza +3
We use a first-principles density functional theory approach to calculate the shift current and linear absorption of uniformly illuminated single-layer Ge and Sn monochalcogenides.…
Semiclassical theory of nonlinear magneto-optical responses with applications to topological Dirac/Weyl semimetals
Takahiro Morimoto, Shudan Zhong, Joseph Orenstein +1
We study nonlinear magneto-optical responses of metals by a semiclassical Boltzmann equation approach. We derive general formulas for linear and second order nonlinear optical effe…
Shift charge and spin photocurrents in Dirac surface states of topological insulator
Kun Woo Kim, Takahiro Morimoto, Naoto Nagaosa
The generation of photocurrent in condensed matter is of main interest for photovoltaic and optoelectronic applications. Shift current, a nonlinear photoresponse, has attracted rec…
Chiral anomaly and giant magnetochiral anisotropy in noncentrosymmetric Weyl semimetals
Takahiro Morimoto, Naoto Nagaosa
We theoretically propose that giant magnetochiral anisotropy is achieved in Weyl semimetals in noncentrosymmetric crystals as a consequence of the chiral anomaly. The magnetochiral…
Topological aspects of nonlinear excitonic processes in noncentrosymmetric crystals
Takahiro Morimoto, Naoto Nagaosa
We study excitonic processes second order in the electric fields in noncentrosymmetric crystals. We derive formulas for shift current and second harmonic generation produced by exc…