Chirality-dependent spin polarization in metals: linear and quadratic responses
The University of Tokyo（东京大学）；Institute for Molecular Science（分子科学研究所）；RIKEN Center for Emergent Matter Science（理化学研究所新兴物质科学中心）；National Institutes of Natural Sciences（国立自然科学研究院）；Institute of Science Tokyo（东京科学大学）；Osaka Metropolitan University（大阪公立大学）
Kosuke Yoshimi, Yusuke Kato, Yuta Suzuki, Shuntaro Sumita, Takuro Sato, Hiroshi M. Yamamoto, Yoshihiko Togawa, Hiroaki Kusunose, Jun-ichiro Kishine
We study spin polarization induced by locally injected electric currents in a metal whose spin--orbit coupling reflects its structural chirality. We reveal both spin polarization in the bulk in the linear response and antiparallel spin polarization near the interface in the quadratic response to external electric currents, and reproduce the experimentally observed correlation between the chirality of the metal and the direction of spin polarization. In particular, we elucidate that the sign of the spin polarization in the quadratic response is opposite to that expected from the bulk spin current. This sign discrepancy originates from spin polarization induced by dipole-like charge distribution appearing in the quadratic response.
Chirality-induced spin selectivity (CISS) refers to the fact that electrons get spin polarized after passing through organic chiral molecules in a nanoscale device. In CISS, chiral molecules are commonly believed to be a spin filter through which one favored spin transmits and the opposite spin gets reflected, i.e., transmitted and reflected electrons exhibit opposite spin polarization. In this work, we point out that such a spin filter scenario contradicts the principle that equilibrium spin current must vanish. Instead, we find that both transmitted and reflected electrons present the same t…
Surface physics dominated by bulk properties has been one of the central interests in modern condensed matter physics, from electric polarization to bulk-boundary correspondence of topological insulators and superconductors. Here, we extend theory of electric polarization to chirality polarizations, that is, surface charges corresponding to local antisymmetries characterized as a bulk property. Using the notion of chirality polarizations, we prove the recently proposed spectral bulk-boundary correspondence, a generalization of bulk-boundary correspondence in chiral symmetric systems into compl…
Real Space Imaging of Spin Scattering in Chirality-Induced Spin Selectivity
Ulsan National Institute of Science and Technology (UNIST)（蔚山科学技术院）；Weizmann Institute of Science（魏茨曼科学研究所）；Pennsylvania State University（宾夕法尼亚州立大学）；Max Planck Institute for the Structure and Dynamics of Matter（物质结构与动力学马普研究所）
We report chirality-induced current-in-plane magnetoresistance (CIP-MR) in chiral molecule/ferromagnetic metal bilayer at room temperature. The previously reported chiralityinduced current-perpendicular-to-plane magnetoresistance (CPP-MR) originates from the chiral induced spin-selectivity (CISS) effect that needs charge-current passing through the molecule. In contrast, the observed CIP-MR in the present study requires no bias charge current through the molecule. The temperature dependence of CIP-MR suggests thermally induced spin-polarization in the chiral molecules is the key for the observ…
Antiparallel spin polarizations as quadratic response in chiral systems
Graduate School of Science, Hokkaido University（北海道大学理学研究科）；Department of Applied Physics, The University of Tokyo（东京大学应用物理系）；Department of Physics, Meiji University（明治大学物理学系）
We propose to directly probe the chirality of Majorana edge states in 2D topological superconductors using polarization selective photon absorption. When shining circularly polarized light on a 2D topological superconductor in disk geometry, the photons can excite quasiparticles only when the polarization of the light matches the chirality of the Majorana edge states required by the angular momentum conservation. Hence one can obtain the chirality of the Majorana edge states by measuring the photon absorption rate. We show that the polarization selective photon absorption can also serve as a s…
Topological aspects of the geometry of DNA and similar chiral molecules have received a lot of attention, while the topology of their electronic structure is less explored. Previous experiments have revealed that DNA can efficiently filter spin-polarized electrons between metal contacts, a process called chiral-induced spin-selectivity (CISS). However, the underlying correlation between chiral structure and electronic spin remains elusive. In this work, we reveal an orbital texture in the band structure, a topological characteristic induced by the chirality. We find that this orbital texture e…
In a magnetic texture, the spin of a conduction electron is forced to be aligned to the localized moment. As a result, the topology of the magnetic texture affects the electron dynamics in nontrivial ways. A representative example is the topological Hall effect in noncoplanar spin textures with finite spin chirality. While propagating in the noncoplanar spin texture, electrons acquire Berry phase, and their motion is deflected as if they were in a magnetic field. Here, we report a distinct Berry phase effect in a coplanar helimagnet: the spin moment of the conduction electron is polarized unde…
The universality of $k$-dependent electron-photon and electron-phonon matrix elements is discussed for graphene nanoribbons and carbon nanotubes. An electron undergoes a change in wavevector in the direction of broken translational symmetry, depending on the light polarization direction. We suggest that this phenomenon originates from a microscopic feature of chirality.
Circular dichroism is widely used for characterizing organic and biological materials, but measurements at a single molecule level are challenging because differences in absorption for opposite helicities are small. Here we show that extrinsic chirality can induce giant circular dichroism in individual carbon nanotubes, with degree of polarization reaching 65%. The signal has a large dependence on the incidence angle, consistent with the interpretation that mirror symmetry breaking by the optical wave vector is responsible for the effect. We propose that field-induced charge distribution resul…
Interplay of spin-orbit coupling and magnetic chirality: Multidirectional spin polarization in a helical antiferromagnet
School of Vocational Studies and Applied Sciences, Gautam Buddha University（古特木佛陀大学职业与应用科学学院）；Department of Physics, Adamas University（亚当斯大学物理系）；Physics and Applied Mathematics Unit, Indian Statistical Institute（印度统计学院物理与应用数学单元）
We study theoretically the anomalous Hall effect due to the vector spin chirality carried by the local spins in the $s$-$d$ model. We will show that the vector spin chirality indeed induces local Hall effect in the presence of the electron spin polarization, while the global Hall effect vanishes if electron transport is homogeneous. This anomalous Hall effect can be interpreted in terms of the rotational component of the spin current associated with the vector chirality.
Here we propose a mechanism by which spin polarization can be generated dynamically in chiral molecular systems undergoing photo-induced electron transfer. The proposed mechanism explains how spin polarization emerges in systems where charge transport is dominated by incoherent hopping, mediated by spin orbit and electronic exchange couplings through an intermediate charge transfer state. We derive a simple expression for the spin polarization that predicts a non-monotonic temperature dependence consistent with recent experiments. We validate this theory using approximate quantum master equati…
What Is the Real-Time Atomistic Mechanism Behind Chirality-Induced Spin Selectivity in Donor-Chiral Bridge-Acceptor Molecules?
School of Physics and Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology（华中科技大学物理学院与武汉国家强磁场中心）；Institute for Quantum Science and Engineering, Huazhong University of Science and Technology（华中科技大学量子科学与工程研究院）
Chiral induced spin selectivity is a phenomenon that has been attributed to chirality, spin-orbit interactions, and non-equilibrium conditions, while the role of electron exchange and correlations have been investigated only marginally until very recently. However, as recent experiments show that chiral molecules acquire a finite spin-polarization merely by being in contact with a metallic surface, these results suggest that electron correlations play a more crucial role for the emergence of the phenomenon than previously thought. Here, it is demonstrated that molecular vibrations give rise to…
Surface plasmons in a centrosymmetric metal nanocrystal have been perceived as achiral, based on the quantum-mechanical theory of molecular optical activity. The one-electron theory is insufficient to describe optical activity in crystals, where spatial variation of polarization states along the light propagation direction is crucial in dimensions exceeding molecules. Such spatial-dispersion, which can drastically modify the optical near-field in plasmonic nanocrystals, has yet to be experimentally proved at the nanometer scale. Here, the experimental observation of natural circular dichroism …
We report a new type of spin-orbit coupling (SOC) called geometric SOC. Starting from the relativistic theory in curved space, we derive an effective nonrelativistic Hamiltonian in a generic curve embedded into flat three dimensions. The geometric SOC is $O(m^{-1})$, in which $m$ is the electron mass, and hence much larger than the conventional SOC of $O(m^{-2})$. The energy scale is estimated to be a hundred meV for a nanoscale helix. We calculate the current-induced spin polarization in a coupled-helix model as a representative of the chirality-induced spin selectivity. We find that it depen…
Spin-Orbit Coupling-Driven Chirality Switching of Spin Waves in Altermagnets
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所凝聚态物理国家实验室）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；School of Physics, Sun Yat-Sen University（中山大学物理学院）；Songshan Lake Materials Laboratory（松山湖材料实验室）
We study the chiral electric separation effect (CESE) in Weyl semimetals (WSM). Within the model based on the kinetic equation we show that there is a non-zero chirality current in external electric and magnetic fields. We distinguish longitudinal, in-plane transverse, Hall, and anomalous Hall components of the CESE. It is shown that the first two components are quadratic in electric field and linear in magnetic field, while the Hall component is quadratic in both the electric and magnetic fields. All three are due to the chiral anomaly. In WSMs the chirality current can be associated with the…
Spin Polarization from Circularly Polarized Light Induced Charge Transfer
University of California, Berkeley（加州大学伯克利分校）；Kavli Energy Nanoscience Institute at Berkeley（加州大学伯克利分校卡弗里纳米科学能源研究所）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）
Chirality induced spin selectivity, discovered about two decades ago in helical molecules, is a non-equilibrium effect that emerges from the interplay between geometrical helicity and spin-orbit interactions. Several model Hamiltonians building on this interplay have been proposed and while these can yield spin-polarized transport properties that agrees with experimental observations, they simultaneously depend on unrealistic values of the spin-orbit interaction parameters. It is likely, however, that a common deficit originates from the fact that all these models are uncorrelated, or, single-…
The elucidation of the mechanisms behind chiral-induced spin selectivity remains an outstanding scientific challenge. Here we consider the role of delocalised phonon modes in electron transport in chiral structures and demonstrate that spin selectivity can originate from spin-dependent energy and momentum conservation in electron-phonon scattering events. While this mechanism is robust to the specifical nature of the vibrational modes, the degree of spin polarization depends on environmental factors, such as external driving fields, temperatures and phonon relaxation rates. This dependence is …
Symmetry considerations in chirality-induced spin selectivity
Helmholtz-Institut Mainz（亥姆霍兹美因茨研究所）；GSI Helmholtzzentrum für Schwerionenforschung GmbH（GSI重离子研究中心有限公司）；QUANTUM, Institut für Physik, Johannes Gutenberg-Universität（约翰内斯·古腾堡大学量子物理研究所）；Department of Physics, University of California（加州大学物理系）；Institute of Physics, Johannes Gutenberg-University Mainz（约翰内斯·古腾堡大学美因茨分校物理研究所）
