京都大学 · 物理学・天文学
北垣康介教授の研究室は、強い電子相関とトポロジカルな電子状態が共存する新規量子物質の設計と物性解明を柱としています。特に、非中心対称系におけるパリティ非保存超伝導や、磁場誘発超伝導、Rashbaスピン軌道結合と相関効果の競合を解明する理論的研究が進んでいます。また、数値的・数理的手法として、因果律を保つ解析接続法(Nevanlinna法)の開発とJulia言語を用いた高速実装も行い、第一原理計算との連携により実験と理論を結ぶ橋渡しを果たしています。
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The discovery of the multiple $H\text{\ensuremath{-}}T$ phase diagram of ${\mathrm{CeRh}}_{2}{\mathrm{As}}_{2}$ offers a new route to designing topological superconductors. Although weak-coupling theories explain the experimental phase diagram qualitatively, a quantitative discrepancy between them has discouraged a conclusive interpretation. In this Letter, we thoroughly study the effect of the Coulomb interaction and the phase diagrams of locally noncentrosymmetric superconductors. We reveal an
Analytical continuation (AC) connects theoretical calculations and experimentally measurable quantities. The recently proposed Nevanlinna AC method is capable of accurately reproducing the sharp features of spectral functions at high frequencies while maintaining the causality of the response function. However, their use is currently limited to fermions. Here, we present an extension of this method to bosons using the hyperbolic tangent trick, allowing us to transform bosons into auxiliary fermi
Heterostructures containing strongly correlated electron systems provide a platform to clarify interplay of electron correlation and Rashba spin-orbit coupling in unconventional superconductors. Motivated by recent fabrication of artificially engineered heavy fermion superlattices and high-temperature cuprate superconductors, we conduct a thorough study on superconductivity in the Rashba-Hubbard model. In contrast to previous weak coupling approaches, we employ fluctuation-exchange approximation
We introduce a Julia implementation of the recently proposed Nevanlinna analytic continuation method. The method is based on Nevanlinna interpolants and inherently preserves the causality of a response function due to its construction. For theoretical calculations without statistical noise, this continuation method is a powerful tool to extract real-frequency information from numerical input data on the Matsubara axis. This method has been applied to first-principles calculations of correlated m
Magnetic field induced superconductivity is a counterintuitive phenomenon and has long been a challenge in the realm of condensed matter physics. The authors present here a novel mechanism to realize magnetic field induced superconductivity, in which the interplay between sublattice degrees of freedom and the Coulomb interaction plays a crucial role. This study significantly advances our understanding of the untapped phenomena in strongly correlated electron systems endowed with sublattice degre
We introduce a Julia implementation of the recently proposed Nevanlinna analytic continuation method. The method is based on Nevanlinna interpolants and inherently preserves the causality of a response function due to its construction. For theoretical calculations without statistical noise, this continuation method is a powerful tool to extract real-frequency information from numerical input data on the Matsubara axis. This method has been applied to first-principles calculations of correlated m
We introduce a Julia implementation of the recently proposed Nevanlinna analytic continuation method. The method is based on Nevanlinna interpolants and, by construction, preserves the causality of a response function. For theoretical calculations without statistical noise, this continuation method is a powerful tool to extract real-frequency information from numerical input data on the Matsubara axis. This method has been applied to first-principles calculations of correlated materials. This pa
Field-induced superconductivity has long presented a counterintuitive phenomenon and a pivotal challenge in condensed matter physics. In this Letter, we introduce a mechanism for achieving field-induced superconductivity wherein the sublattice degree of freedom and the Coulomb interaction are tightly entwined. Our multipole-resolved analysis elucidates that lifting the fluctuation degeneracy results in an unconventional Cooper pairing channel, thereby realizing field-induced superconductivity. T
Analytical continuation (AC) connects theoretical calculations and experimentally measurable quantities. The recently proposed Nevanlinna AC method is capable of accurately reproducing the sharp features of spectral functions at high frequencies while maintaining the causality of the response function. However, their use is currently limited to fermions. Here, we present an extension of this method to bosons using the hyperbolic tangent trick, allowing us to transform bosons into auxiliary fermi
We introduce a Julia implementation of the recently proposed Nevanlinna analytic continuation method. The method is based on Nevanlinna interpolants and, by construction, preserves the causality of a response function. For theoretical calculations without statistical noise, this continuation method is a powerful tool to extract real-frequency information from numerical input data on the Matsubara axis. This method has been applied to first-principles calculations of correlated materials. This pa
We introduce a Julia implementation of the recently proposed Nevanlinna analytic continuation method. The method is based on Nevanlinna interpolants and inherently preserves the causality of a response function due to its construction. For theoretical calculations without statistical noise, this continuation method is a powerful tool to extract real-frequency information from numerical input data on the Matsubara axis. This method has been applied to first-principles calculations of correlated m
We present a symmetry-adapted extension of sample-based quantum diagonalization (SQD) that rigorously embeds space-group symmetry into the many-body subspace sampled by quantum hardware. The method is benchmarked on the two-leg ladder Hubbard model using both molecular orbital and momentum bases. Energy convergence is shown to be improved in the momentum basis compared to the molecular orbital basis for both the spin-quintet ground state and the spin-singlet excited state. We clarify the relatio
Heterostructures containing strongly correlated electron systems provide a platform to clarify interplay of electron correlation and Rashba spin-orbit coupling in unconventional superconductors. Motivated by recent fabrication of artificially-engineered heavy fermion superlattices and high-temperature cuprate superconductors, we conduct a thorough study on superconductivity in Rashba-Hubbard model. In contrast to previous weak coupling approaches, we employ fluctuation-exchange approximation to
We introduce a Julia implementation of the recently proposed Nevanlinna analytic continuation method.The method is based on Nevanlinna interpolants and, by construction, preserves the causality of a response function.For theoretical calculations without statistical noise, this continuation method is a powerful tool to extract real-frequency information from numerical input data on the Matsubara axis.This method has been applied to first-principles calculations of correlated materials.This paper
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