Complexity of quantum phases of matter is often understood by the underlying gauge structures, as... more Complexity of quantum phases of matter is often understood by the underlying gauge structures, as was recognized by the Z2 and U(1) gauge theory description of spin liquid in frustrated magnets. Anomalous Hall effect of conducting electrons can intrisically arise from U(1) gauges expressing the spatial modulation of ferromagnetic moments or from SU(2) gauges representing the spin-orbit coupling effect. Similarly, in insulating ferro and antiferromagnets, the magnon excitations can contribute to anomalous transports by feeling the U(1) and SU(2) gauges arising from the features of ordered moments or interactions. In this work, we report the emergent higher rank SU(3) gauge structure in the magnon transport based on the thermal conductivity measurements of MnSc2S4 in an applied field up to 14 T. The thermal Hall coefficient takes a substantial value when the material enters a three-sublattice antiferromagnetic skyrmion phase, which is confirmed by the large-scale spin wave theory. The excited magnons are dressed with SU(3) gauge field, which is a mixture of three species of U(1) gauge fields originating from the slowly varying magnetic moments on these sublattices.
Journal of the Physical Society of Japan, Feb 15, 2018
We consider a series of Mott insulators in unit of two orbitals each hosting spin-1/2 electron, a... more We consider a series of Mott insulators in unit of two orbitals each hosting spin-1/2 electron, and by pairing two spin-1/2 into spin-1 triplet, derive the effective exchange interaction between the adjacent units via fourth order perturbation theory. It turns out that the biquadratic exchange interaction between spin-1, which is one of the origins of the nematic order, arises only in processes where the four different electrons exchange cyclically along the twisted loop, which we call "twisted ring exchange" processes. We show that the term becomes the same order with the Heisenberg exchange interactions when the on-orbital Coulomb interaction is not too large. Whereas, the inter-orbital Coulomb interactions give rise to additional processes that cancel the twisted ring exchange, and strongly suppresses the biquadratic term. The Mott insulator with two electrons on degenerate two orbitals is thus not an ideal platform to study such nematic orders.
We examine the performance of the density matrix embedding theory (DMET) recently proposed in [G.... more We examine the performance of the density matrix embedding theory (DMET) recently proposed in [G. Knizia and G. K.-L. Chan, Phys. Rev. Lett. 109, 186404 (2012)]. The core of this method is to find a proper one-body potential that generates a good trial wave function for projecting a large scale original Hamiltonian to a local subsystem with a small number of basis. The resultant ground state of the projected Hamiltonian can locally approximate the true ground state. However, the lack of the variational principle makes it difficult to judge the quality of the choice of the potential. Here we focus on the entanglement spectrum (ES) as a judging criterion; accurate evaluation of the ES guarantees that the corresponding reduced density matrix well reproduces all physical quantities on the local subsystem. We apply the DMET to the Hubbard model on the one-dimensional chain, zigzag chain, and triangular lattice and test several variants of potentials and cost functions. It turns out that a symmetric potential reproduces the ES of the phase that continues from a noninteracting limit. The Mott transition as well as symmetry-breaking transitions can be detected by the singularities in the ES. However, the details of the ES in the strongly interacting parameter region depends much on these choices, meaning that the present algorithm allowing for numerous variants of the DMET is insufficient to fully fix the quantum many-body problem.
Spin-orbit interaction has established itself as a key player in the emergent phenomena in modern... more Spin-orbit interaction has established itself as a key player in the emergent phenomena in modern condensed matter, including topological insulator, spin liquid and spin-dependent transports. However, its function is rather limited to adding topological nature to band kinetics, leaving behind the growing interest in the direct interplay with electron correlation. Here, we prove by our spinor line graph theory that a very strong spin-orbit interaction realized in 5d pyrochlore electronic systems generates multiply degenerate perfect flat bands. Unlike any of the previous flat bands, the electrons in this band localize in real space by destructively interfering with each other in a spin selective manner governed by the SU(2) gauge field. These electrons avoid the Coulomb interaction by self-organizing their localized wave functions, which may lead to a flat-band state with a stiff spin chirality. It also causes perfectly trimerized charge ordering, which may explain the recently disco...
Spin-orbit interaction established itself as a major role player for emergent phenomena in modern... more Spin-orbit interaction established itself as a major role player for emergent phenomena in modern condensed matter including a topological insulator, spin liquid and spin-dependent transports. However, its function is rather limited to adding topological nature to each phases of matter. We prove by our spinor line graph theory that a very strong spin-orbit interaction realized in 5d pyrochlore electronic systems generates multiply degenerate perfect flat bands. Unlike any of the previous flat bands, the electrons living there localize in real space by destructively interfering with each other in a spin selective manner ruled by the SU(2) gauge field. These electrons avoid the Coulomb interaction by self-organizing their localized wave functions. This gives rise to the trimerized charge ordering hand in hand with a stiff spin chirality, which may explain the recently found exotic low-temperature insulating phase of CsW2O6.
We perform magnetic susceptibility and magnetic torque measurements on the organic κ-(BEDT-TTF)2H... more We perform magnetic susceptibility and magnetic torque measurements on the organic κ-(BEDT-TTF)2Hg(SCN)2Br, which is recently suggested to host an exotic quantum dipole-liquid in its low-temperature insulating phase. Below the metal-insulator (MI) transition temperature, the magnetic susceptibility follows a Curie–Weiss law with a positive Curie–Weiss temperature, and a particular $$M\propto \sqrt{H}$$ M ∝ H curve is observed. The emergent ferromagnetically interacting spins amount to about 1/6 of the full spin moment of localized charges. Taking account of the possible inhomogeneous quasi-charge-order that forms a dipole-liquid, we construct a model of antiferromagnetically interacting spin chains in two adjacent charge-ordered domains, which are coupled via fluctuating charges on a Mott-dimer at the boundary. We find that the charge fluctuations can draw a weak ferromagnetic moment out of the spin singlet domains.
We explore several classes of quadrupolar ordering in a system of antiferromagnetically coupled q... more We explore several classes of quadrupolar ordering in a system of antiferromagnetically coupled quantum spin-1 dimers, which are stacked in the triangular lattice geometry forming a bilayer. Lowenergy properties of this model is described by an S = 1 hard-core bosonic degrees of freedom defined on each dimer-bond, where the singlet and triplet states of the dimerized spins are interpreted as the vacuum and the occupancy of boson, respectively. The number of bosons per dimer and the magnetic and density fluctuations of bosons are controlled by the inter-dimer Heisenberg interactions. In a solid phase where each dimer hosts one boson and the inter-dimer interaction is weak, a conventional spin nematic phase is realized by the pair-fluctuation of bosons. Larger inter-dimer interaction favors Bose Einstein condensates (BEC) carrying quadrupolar moments. Among them, we find one exotic phase where the quadrupoles develop a spatially modulated structure on the top of a uniform BEC, interpreted in the original dimerized spin-1 model as coexistent p-type nematic and 120 • -magnetic correlations. This may explain an intriguing nonmagnetic phase found in Ba3ZnRu2O9.
One of the major strategies to control magnetism in spintronics is to utilize the coupling betwee... more One of the major strategies to control magnetism in spintronics is to utilize the coupling between electron spin and its orbital motion. The Rashba and Dresselhaus spin–orbit couplings induce magnetic textures of band electrons called spin momentum locking, which produces a spin torque by the injection of electric current. However, joule heating had been a bottleneck for device applications. Here, we propose a theory to generate further rich spin textures in insulating antiferromagnets with broken spatial inversion symmetry (SIS), which is easily controlled by a small magnetic field. In antiferromagnets, the ordered moments host two species of magnons that serve as internal degrees of freedom in analogy with electron spins. The Dzyaloshinskii–Moriya interaction introduced by the SIS breaking couples the two-magnon-degrees of freedom with the magnon momentum. We present a systematic way to design such texture and to detect it via magnonic spin current for the realization of antiferro...
We show that the two dimensional spatial inversion-symmetry (SIS) broken square lattice antiferro... more We show that the two dimensional spatial inversion-symmetry (SIS) broken square lattice antiferromagnet with easy-plane spin anisotropy exhibits a thermal Hall effect and the edge modes characterized by the Z2 topological invariant. These topological properties require a nonzero Berry curvature, and its origin is ascribed to the Dzyaloshinskii-Moriya (DM) interactions or the noncoplanar magnetic ordering generating a U(1) gauge field that couples to the kinetic motion of magnons. Although this picture is established in ferromagnets on the kagome and pyrochlore lattices, it does not apply to our square lattice model since such gauge field cancels out in an edge shared geometry. Instead, our case has an analogy with the anomalous Hall effect of Rashba electronic system where the spin orbit coupling generates an SU(2) gauge field. The two species of magnons defined on antiferromagnetic sublattices can be regarded as the pseudo-spin degrees of freedom of magnons. The DM interactions that emerge due to the SIS breaking serve as a pseudo-spin orbit coupling of magnons and generate a Berry curvature, when the direction of the magnetic moments is properly controlled by the magnetic field. The thermal Hall conductivity of our antiferromagnet shows rapid growth in temperature T beyond the power-law, reflecting the almost gapless low energy branch of the antiferromagnet, which distinctively differs from the T 7/2 -dependence in the pyrochlore ferromagnets. The present system serves as a standard model for the noncentrosymmetric crystals Ba2MnGe2O7 and Ba2CoGe2O7.
Submitted for the MAR11 Meeting of The American Physical Society Quantum electric dipoles in spin... more Submitted for the MAR11 Meeting of The American Physical Society Quantum electric dipoles in spin liquid dimer Mott insulator CHISA HOTTA, Kyoto Sangyo University-We present an effective dipolar-spin model based on the strong coupling analysis, which may explain the possible origin of the "spin liquid Mott insulator" of the organic triangular lattice system, kappa-ET 2 Cu 2 (CN) 3 , whose gapless spin liquid state had been discussed in the context of geometrical frustration of exchange coupling, J, between spins on dimer orbitals. We find out that another degrees of freedom within the insulator, quantum electricdipoles on dimers, interacts with each other by the Coulomb interaction and brings about a significant suppression ofJ through the dipolar-spin coupling.
We present an effective dipolar-spin model based on the strong coupling analysis, which may expla... more We present an effective dipolar-spin model based on the strong coupling analysis, which may explain the possible origin of "spin liquid insulator". The issue is related to a dimer Mott insulator reminiscent of an organic triangular lattice system, κ-ET2Cu2(CN)3, whose gapless spin liquid state has been discussed in the context of geometrical frustration of exchange coupling, J, between spins on dimer orbitals. It turns out that another degrees of freedom within the insulator, quantum electric-dipoles on dimers, interact with each other and significantly suppress J through the dipolar-spin coupling, resulting in a possible "dipolar-spin liquid".
We study electrons hopping on a kagome lattice at third filling described by an extended Hubbard ... more We study electrons hopping on a kagome lattice at third filling described by an extended Hubbard Hamiltonian with on-site and nearest-neighbour repulsions in the strongly correlated limit. As a consequence of the commensurate filling and the large interactions, each triangle has precisely two electrons in the effective low energy description, and these electrons form chains of different lengths. The effective Hamiltonian includes the ring exchange around the hexagons as well as the nearestneighbor Heisenberg interaction. Using large scale exact diagonalization, we find that the effective model exhibits two different phases: If the charge fluctuations are small, the magnetic fluctuations confine the charges to short loops around hexagons, yielding a gapped charge ordered phase. When the charge fluctuations dominate, the system undergoes a quantum phase transition to a resonating plaquette phase with ordered spins and gapless spin excitations. We find that a peculiar conservation law is fulfilled: the electron in the chains can be divided into two sublattices, and this division is conserved by the ring exchange term.
The possibility of ferromagnetic ground states of divalent boride systems has been theoretically ... more The possibility of ferromagnetic ground states of divalent boride systems has been theoretically investigated by taking into account realistic three-dimensional structures with three pairs of valence and conduction bands which overlap at the X points. It is indicated that because of the particular relationships between on-site Coulomb and exchange interactions, metallic ferromagnetism is difficult to stabilize even within a mean-field calculation. On the other hand, the ferromagnetic metal is seen to be more easily stabilized in the model of a single pair of semimetallic bands, suggesting the preference of tetragonal symmetry for ferromagnetism. Also, a comment is made against excitonic ferromagnetism.
Some of the polytypes in two-dimensional organic conductors, such as κ and λ, are known for the e... more Some of the polytypes in two-dimensional organic conductors, such as κ and λ, are known for the existence of dimers, whose band structure is reproduced well by use of a dimer model. We propose that α-type also has a hidden dimer structure, where the dimer-based band structure shows quite good agreement with the original ones. The dimer picture enables us to relate α with other polytypes in a unified model we proposed earlier. The deeper understanding of the characteristic structure of bands is provided which might be a help in clarifying the ground state of this polytype in the future studies.
Complexity of quantum phases of matter is often understood by the underlying gauge structures, as... more Complexity of quantum phases of matter is often understood by the underlying gauge structures, as was recognized by the Z2 and U(1) gauge theory description of spin liquid in frustrated magnets. Anomalous Hall effect of conducting electrons can intrisically arise from U(1) gauges expressing the spatial modulation of ferromagnetic moments or from SU(2) gauges representing the spin-orbit coupling effect. Similarly, in insulating ferro and antiferromagnets, the magnon excitations can contribute to anomalous transports by feeling the U(1) and SU(2) gauges arising from the features of ordered moments or interactions. In this work, we report the emergent higher rank SU(3) gauge structure in the magnon transport based on the thermal conductivity measurements of MnSc2S4 in an applied field up to 14 T. The thermal Hall coefficient takes a substantial value when the material enters a three-sublattice antiferromagnetic skyrmion phase, which is confirmed by the large-scale spin wave theory. The excited magnons are dressed with SU(3) gauge field, which is a mixture of three species of U(1) gauge fields originating from the slowly varying magnetic moments on these sublattices.
Journal of the Physical Society of Japan, Feb 15, 2018
We consider a series of Mott insulators in unit of two orbitals each hosting spin-1/2 electron, a... more We consider a series of Mott insulators in unit of two orbitals each hosting spin-1/2 electron, and by pairing two spin-1/2 into spin-1 triplet, derive the effective exchange interaction between the adjacent units via fourth order perturbation theory. It turns out that the biquadratic exchange interaction between spin-1, which is one of the origins of the nematic order, arises only in processes where the four different electrons exchange cyclically along the twisted loop, which we call "twisted ring exchange" processes. We show that the term becomes the same order with the Heisenberg exchange interactions when the on-orbital Coulomb interaction is not too large. Whereas, the inter-orbital Coulomb interactions give rise to additional processes that cancel the twisted ring exchange, and strongly suppresses the biquadratic term. The Mott insulator with two electrons on degenerate two orbitals is thus not an ideal platform to study such nematic orders.
We examine the performance of the density matrix embedding theory (DMET) recently proposed in [G.... more We examine the performance of the density matrix embedding theory (DMET) recently proposed in [G. Knizia and G. K.-L. Chan, Phys. Rev. Lett. 109, 186404 (2012)]. The core of this method is to find a proper one-body potential that generates a good trial wave function for projecting a large scale original Hamiltonian to a local subsystem with a small number of basis. The resultant ground state of the projected Hamiltonian can locally approximate the true ground state. However, the lack of the variational principle makes it difficult to judge the quality of the choice of the potential. Here we focus on the entanglement spectrum (ES) as a judging criterion; accurate evaluation of the ES guarantees that the corresponding reduced density matrix well reproduces all physical quantities on the local subsystem. We apply the DMET to the Hubbard model on the one-dimensional chain, zigzag chain, and triangular lattice and test several variants of potentials and cost functions. It turns out that a symmetric potential reproduces the ES of the phase that continues from a noninteracting limit. The Mott transition as well as symmetry-breaking transitions can be detected by the singularities in the ES. However, the details of the ES in the strongly interacting parameter region depends much on these choices, meaning that the present algorithm allowing for numerous variants of the DMET is insufficient to fully fix the quantum many-body problem.
Spin-orbit interaction has established itself as a key player in the emergent phenomena in modern... more Spin-orbit interaction has established itself as a key player in the emergent phenomena in modern condensed matter, including topological insulator, spin liquid and spin-dependent transports. However, its function is rather limited to adding topological nature to band kinetics, leaving behind the growing interest in the direct interplay with electron correlation. Here, we prove by our spinor line graph theory that a very strong spin-orbit interaction realized in 5d pyrochlore electronic systems generates multiply degenerate perfect flat bands. Unlike any of the previous flat bands, the electrons in this band localize in real space by destructively interfering with each other in a spin selective manner governed by the SU(2) gauge field. These electrons avoid the Coulomb interaction by self-organizing their localized wave functions, which may lead to a flat-band state with a stiff spin chirality. It also causes perfectly trimerized charge ordering, which may explain the recently disco...
Spin-orbit interaction established itself as a major role player for emergent phenomena in modern... more Spin-orbit interaction established itself as a major role player for emergent phenomena in modern condensed matter including a topological insulator, spin liquid and spin-dependent transports. However, its function is rather limited to adding topological nature to each phases of matter. We prove by our spinor line graph theory that a very strong spin-orbit interaction realized in 5d pyrochlore electronic systems generates multiply degenerate perfect flat bands. Unlike any of the previous flat bands, the electrons living there localize in real space by destructively interfering with each other in a spin selective manner ruled by the SU(2) gauge field. These electrons avoid the Coulomb interaction by self-organizing their localized wave functions. This gives rise to the trimerized charge ordering hand in hand with a stiff spin chirality, which may explain the recently found exotic low-temperature insulating phase of CsW2O6.
We perform magnetic susceptibility and magnetic torque measurements on the organic κ-(BEDT-TTF)2H... more We perform magnetic susceptibility and magnetic torque measurements on the organic κ-(BEDT-TTF)2Hg(SCN)2Br, which is recently suggested to host an exotic quantum dipole-liquid in its low-temperature insulating phase. Below the metal-insulator (MI) transition temperature, the magnetic susceptibility follows a Curie–Weiss law with a positive Curie–Weiss temperature, and a particular $$M\propto \sqrt{H}$$ M ∝ H curve is observed. The emergent ferromagnetically interacting spins amount to about 1/6 of the full spin moment of localized charges. Taking account of the possible inhomogeneous quasi-charge-order that forms a dipole-liquid, we construct a model of antiferromagnetically interacting spin chains in two adjacent charge-ordered domains, which are coupled via fluctuating charges on a Mott-dimer at the boundary. We find that the charge fluctuations can draw a weak ferromagnetic moment out of the spin singlet domains.
We explore several classes of quadrupolar ordering in a system of antiferromagnetically coupled q... more We explore several classes of quadrupolar ordering in a system of antiferromagnetically coupled quantum spin-1 dimers, which are stacked in the triangular lattice geometry forming a bilayer. Lowenergy properties of this model is described by an S = 1 hard-core bosonic degrees of freedom defined on each dimer-bond, where the singlet and triplet states of the dimerized spins are interpreted as the vacuum and the occupancy of boson, respectively. The number of bosons per dimer and the magnetic and density fluctuations of bosons are controlled by the inter-dimer Heisenberg interactions. In a solid phase where each dimer hosts one boson and the inter-dimer interaction is weak, a conventional spin nematic phase is realized by the pair-fluctuation of bosons. Larger inter-dimer interaction favors Bose Einstein condensates (BEC) carrying quadrupolar moments. Among them, we find one exotic phase where the quadrupoles develop a spatially modulated structure on the top of a uniform BEC, interpreted in the original dimerized spin-1 model as coexistent p-type nematic and 120 • -magnetic correlations. This may explain an intriguing nonmagnetic phase found in Ba3ZnRu2O9.
One of the major strategies to control magnetism in spintronics is to utilize the coupling betwee... more One of the major strategies to control magnetism in spintronics is to utilize the coupling between electron spin and its orbital motion. The Rashba and Dresselhaus spin–orbit couplings induce magnetic textures of band electrons called spin momentum locking, which produces a spin torque by the injection of electric current. However, joule heating had been a bottleneck for device applications. Here, we propose a theory to generate further rich spin textures in insulating antiferromagnets with broken spatial inversion symmetry (SIS), which is easily controlled by a small magnetic field. In antiferromagnets, the ordered moments host two species of magnons that serve as internal degrees of freedom in analogy with electron spins. The Dzyaloshinskii–Moriya interaction introduced by the SIS breaking couples the two-magnon-degrees of freedom with the magnon momentum. We present a systematic way to design such texture and to detect it via magnonic spin current for the realization of antiferro...
We show that the two dimensional spatial inversion-symmetry (SIS) broken square lattice antiferro... more We show that the two dimensional spatial inversion-symmetry (SIS) broken square lattice antiferromagnet with easy-plane spin anisotropy exhibits a thermal Hall effect and the edge modes characterized by the Z2 topological invariant. These topological properties require a nonzero Berry curvature, and its origin is ascribed to the Dzyaloshinskii-Moriya (DM) interactions or the noncoplanar magnetic ordering generating a U(1) gauge field that couples to the kinetic motion of magnons. Although this picture is established in ferromagnets on the kagome and pyrochlore lattices, it does not apply to our square lattice model since such gauge field cancels out in an edge shared geometry. Instead, our case has an analogy with the anomalous Hall effect of Rashba electronic system where the spin orbit coupling generates an SU(2) gauge field. The two species of magnons defined on antiferromagnetic sublattices can be regarded as the pseudo-spin degrees of freedom of magnons. The DM interactions that emerge due to the SIS breaking serve as a pseudo-spin orbit coupling of magnons and generate a Berry curvature, when the direction of the magnetic moments is properly controlled by the magnetic field. The thermal Hall conductivity of our antiferromagnet shows rapid growth in temperature T beyond the power-law, reflecting the almost gapless low energy branch of the antiferromagnet, which distinctively differs from the T 7/2 -dependence in the pyrochlore ferromagnets. The present system serves as a standard model for the noncentrosymmetric crystals Ba2MnGe2O7 and Ba2CoGe2O7.
Submitted for the MAR11 Meeting of The American Physical Society Quantum electric dipoles in spin... more Submitted for the MAR11 Meeting of The American Physical Society Quantum electric dipoles in spin liquid dimer Mott insulator CHISA HOTTA, Kyoto Sangyo University-We present an effective dipolar-spin model based on the strong coupling analysis, which may explain the possible origin of the "spin liquid Mott insulator" of the organic triangular lattice system, kappa-ET 2 Cu 2 (CN) 3 , whose gapless spin liquid state had been discussed in the context of geometrical frustration of exchange coupling, J, between spins on dimer orbitals. We find out that another degrees of freedom within the insulator, quantum electricdipoles on dimers, interacts with each other by the Coulomb interaction and brings about a significant suppression ofJ through the dipolar-spin coupling.
We present an effective dipolar-spin model based on the strong coupling analysis, which may expla... more We present an effective dipolar-spin model based on the strong coupling analysis, which may explain the possible origin of "spin liquid insulator". The issue is related to a dimer Mott insulator reminiscent of an organic triangular lattice system, κ-ET2Cu2(CN)3, whose gapless spin liquid state has been discussed in the context of geometrical frustration of exchange coupling, J, between spins on dimer orbitals. It turns out that another degrees of freedom within the insulator, quantum electric-dipoles on dimers, interact with each other and significantly suppress J through the dipolar-spin coupling, resulting in a possible "dipolar-spin liquid".
We study electrons hopping on a kagome lattice at third filling described by an extended Hubbard ... more We study electrons hopping on a kagome lattice at third filling described by an extended Hubbard Hamiltonian with on-site and nearest-neighbour repulsions in the strongly correlated limit. As a consequence of the commensurate filling and the large interactions, each triangle has precisely two electrons in the effective low energy description, and these electrons form chains of different lengths. The effective Hamiltonian includes the ring exchange around the hexagons as well as the nearestneighbor Heisenberg interaction. Using large scale exact diagonalization, we find that the effective model exhibits two different phases: If the charge fluctuations are small, the magnetic fluctuations confine the charges to short loops around hexagons, yielding a gapped charge ordered phase. When the charge fluctuations dominate, the system undergoes a quantum phase transition to a resonating plaquette phase with ordered spins and gapless spin excitations. We find that a peculiar conservation law is fulfilled: the electron in the chains can be divided into two sublattices, and this division is conserved by the ring exchange term.
The possibility of ferromagnetic ground states of divalent boride systems has been theoretically ... more The possibility of ferromagnetic ground states of divalent boride systems has been theoretically investigated by taking into account realistic three-dimensional structures with three pairs of valence and conduction bands which overlap at the X points. It is indicated that because of the particular relationships between on-site Coulomb and exchange interactions, metallic ferromagnetism is difficult to stabilize even within a mean-field calculation. On the other hand, the ferromagnetic metal is seen to be more easily stabilized in the model of a single pair of semimetallic bands, suggesting the preference of tetragonal symmetry for ferromagnetism. Also, a comment is made against excitonic ferromagnetism.
Some of the polytypes in two-dimensional organic conductors, such as κ and λ, are known for the e... more Some of the polytypes in two-dimensional organic conductors, such as κ and λ, are known for the existence of dimers, whose band structure is reproduced well by use of a dimer model. We propose that α-type also has a hidden dimer structure, where the dimer-based band structure shows quite good agreement with the original ones. The dimer picture enables us to relate α with other polytypes in a unified model we proposed earlier. The deeper understanding of the characteristic structure of bands is provided which might be a help in clarifying the ground state of this polytype in the future studies.
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