New Trends in Condensed Matter Theory 2024 @ ISSP UTokyo
Date and Place
December 9th, 10th & 11th
Lecture Room (A632), Institute for Solid State Physics, University of Tokyo
Introduction
Condensed matter physics continues to advance in the study of quantum materials that exhibit remarkable quantum phenomena due to strong interactions between degrees of freedom and unique electronic structures.
In recent years, there has been significant progress in the study of non-equilibrium phenomena in these materials,
as well as notable developments at the interface with fields such as biophysics of active matter, artificial materials, and quantum information science.
Additionally, numerical techniques and mathematical approaches that underpin these studies are steadily being established.
This workshop is designed to focus on the latest developments in condensed matter theory,
encompassing a broad range of these fields.
In particular, the program will be organized with an emphasis on young researchers who have recently achieved remarkable success in their respective areas.
Three years ago, we held a similar ISSP workshop titled “New Trends in Quantum Condensed Matter Theory 2021”
(link1,
link2).
This time, we plan to incorporate even more recent research findings.
Invited Speakers
Kyosuke Adachi (RIKEN iTHEMS/BDR)
Ching-Kai Chiu (RIKEN iTHEMS)
Akito Daido (Kyoto University)
Ryusuke Hamazaki (RIKEN CPR/iTHEMS)
Shintaro Hoshino (Saitama University)
Satoshi Ikegaya (Nagoya University)
Tatsuya Kaneko (Osaka University)
Takuto Kawakami (Osaka University)
Koji Kudo (Kyushu University)
Taiki Matsushita (Kyoto University)
Kaoru Mizuta (University of Tokyo)
Yoshifumi Nakata (YITP, Kyoto University)
Tokiro Numasawa (ISSP, University of Tokyo)
Shunsuke Sato (CCS, University of Tsukuba)
Jun Takahashi (ISSP, University of Tokyo)
Nayuta Takemori (Osaka University)
Rina Tazai (YITP, Kyoto University)
Han Yan (ISSP, University of Tokyo)
Organizers
Takeo Kato (ISSP, University of Tokyo)
Kohei Kawabata (ISSP, University of Tokyo)
Takashi Oka (ISSP, University of Tokyo; Chair)
Masaki Oshikawa (ISSP, University of Tokyo)
Registration
This workshop will be held in a hybrid style (both onsite and online).
Please register from this form to obtain the Zoom information for access.
Application deadline for onsite participation and poster presentations: December 2nd, 2024 (Mon) We closed applications for onsite participation and poster presentations, but still accept online participation.
1. Tokiro Numasawa (ISSP, University of Tokyo) [9:30 - 10:10] Universal CFT dynamics under SSD and Mobius Hamiltonians Abstract (Click)
The Sine Square Deformation (SSD) and Möbius deformations
introduce spatially inhomogeneous modifications to Hamiltonians in
quantum many-body systems. Interestingly, at the quantum critical point,
these deformations share the same ground state as the homogeneous
Hamiltonian under periodic boundary conditions.In conformal field theory
(CFT), SSD and Möbius deformations are fully described by conformal
symmetry, which also governs the properties of excited states. This
universality may provide new insights into the structure of tensor
networks for time-dependent states and the emergence of spacetime in
holographic contexts.
In this talk, we present our work on the dynamics of quantum quenches
driven by SSD and Möbius Hamiltonians in CFT. Our analysis shows that
Weyl and conformal transformations map these quenches to local quench
problems, allowing us to determine the energy density under the SSD and
Möbius Hamiltonians and explore their holographic duals. Additionally,
we investigate Floquet dynamics induced by these Hamiltonians to reverse
time evolution, which is important for realizing out-of-time-ordered
correlators (OTOCs).
References
[1]J.Kudler-Flam, M.Nozaki, T.Numasawa M-T. Tan and S.Ryu
[2] X.Liu, A.McDonald,T.Numasawa, B.Lian and S.Ryu
[3] B.Lapierre, T.Neupert, T.Numasawa, S.Ryu
2. Ryusuke Hamazaki (RIKEN CPR/iTHEMS) [10:10 - 10:50] Measurement-induced spectral transitions Abstract (Click)
Spectral transitions of time-independent generators of dynamics have been an essential indicator for phase transitions, such as the Hamiltonian’s gap closing transition at the quantum critical point. Recently, measurement-induced phase transition has been discovered as a new type of non-equilibrium quantum phenomenon caused by the interplay between unitary dynamics and non-unitary measurement [1]. In particular, changing the strength of measurement causes sudden change of, e.g., entanglement and purification properties. However, since measurement causes noisy trajectories in time, the transition cannot be understood from conventional spectral transitions for time-independent generators. In this talk, we demonstrate that the measurement causes gap-closing spectral transitions for the Lyapunov spectrum, which is defined from the non-unitary time-evolution operator of quantum trajectories [2]. We use unitary circuit and mid-circuit measurement with tunable errors and find that the gapless/gapped phases correspond to volume/area law entanglement phases. We also show that this spectral transition indicates the sudden transition of the relaxation timescale for any observables, in addition to the purification timescale. Furthermore, we investigate another quantum circuit composed only of measurements, finding that the entanglement transition coincides with the topological phase transition of Lyapunov spectrum [3].
[1] B. Skinner, J. Ruhman, and A. Nahum, Phys. Rev. X 9, 031009 (2019).
[2] K. Mochizuki and R. Hamazaki, arXiv:2406.18234.
[3] H. Oshima, K. Mochizuki, R. Hamazaki, and Y. Fuji, in preparation.
3. Takuto Kawakami (Osaka University) [11:20 - 12:00] Exploring topological phases of matter through spin degrees of freedom Abstract (Click)
The study of topological phases of matter has advanced significantly over the past two decades, following the discovery of the quantum spin Hall effect. Within this trend, our focus has been on the role of spin degrees of freedom in broadening the diversity of quantum phases. In this talk, I will discuss two examples of topological phenomena driven by various spin degrees of freedom. The first example is spin ordering in the edge states of graphene nanoribbons [1]. While graphene nanoribbons exhibit flat edge states in the absence of interactions, incorporating electron correlations activates spin polarization. Furthermore, upon charge injection, polarized spins spontaneously form domain walls, where topological bound states associated with these domain walls trap the injected charge. The second example involves the quantum spin Hall effect in systems with particles possessing spin greater than 1/2 [2,3]. In such systems, a quantum "higher-spin" Hall effect emerges, characterized by multiple edge states and highly degenerate bound states arising from large topological indices. Through these examples, I aim to share insights into novel topological phenomena enabled by spin degrees of freedom.
[1] T. Kawakami, G. Tamaki, and M. Koshino Phys. Rev. B 108, 045401 (2023), [2] T. Kawakami, T. Okamura, S. Kobayashi, and M. Sato Phys. Rev. X 8 041026 (2018). [3] T. Kawakami, I. Kuzmenko, Y. Avishai, Y. Meir, and M. Sato in preparation.
4. Nayuta Takemori (Osaka University) [13:30 - 14:10] Superconductivity and Supercurrent Anomalies in Quasicrystals Abstract (Click)
Superconductivity has been observed in systems lacking periodicity, such as amorphous metals Sn0.9Cu0.1 and Pb0.75Bi0.25, which exhibit a strong electron-phonon interaction. However, weak-coupling superconductivity with spatially extended Cooper pairs in aperiodic systems remains a highly nontrivial issue. In 2018, bulk superconductivity was discovered in Al-Mg-Zn quasicrystals [1] where quasicrystal is a solid that shows sharp Bragg peaks dispite exhibiting rotational symmetry incompatible with periodicity [2,3]. The temperature dependence of the electronic specific heat was found to be consistent with BCS theory.
In this talk, we present the results of a theoretical analysis of the attractive Hubbard model [4-7] using Bogoliubov-de Gennes mean-field theory. We show that quasicrystals exhibit weak-coupling superconductivity that differs from BCS superconductivity [4]. The specific heat jump in quasicrystals is also found to be 10-20% smaller than the BCS theoretical value due to the lack of Fermi surface and coherence peaks [5].
We further studied the spatial distributions of the local supercurrent induced by a uniform vector potential [6,7]. The attractive Hubbard model was numerically studied within the Bogoliubov-de Gennes mean field theory. We will show that non-uniform supercurrent distributions can be realized under inhomogeneous superconducting states in quasicrystals. Furthermore, it is clarified that the paramagnetic components of the supercurrents can flow in a direction perpendicular to the applied vector potential and are finite even at zero temperature. Such phenomena can also be expected in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state [8,9], however, we note that our results make experimental access much easier because proper adjustment of the magnetic field is unnecessary.
References [1] K. Kamiya et al., Nat. Commun. 9, 154 (2018). [2] D. Shechtman et al., Phys. Rev. Lett. 53, 1951 (1984). [3] D. Levine et al., Phys. Rev. Lett. 53, 2477 (1984). [4] S. Sakai et al., Phys. Rev. B 95, 024509 (2017). [5] N. Takemori et al., Phys. Rev. B 102, 115108 (2020). [6] T. Fukushima et al., J. Phys.: Conf. Ser. 2461, 012014 (2023). [7] T. Fukushima et al., Phys. Rev. Res. 5, 043164 (2023). [8] P. Fulde and R. A. Ferrell, Phys. Rev. 135, A550 (1964). [9] A. I. Larkin and Y. N. Ovchinnikov, Sov. Phys. JETP 20, 762 (1965).
5. Akito Daido (Kyoto University) [14:10 - 14:50] Nonreciprocal charge transport caused by fluctuating finite-momentum Cooper pairs Abstract (Click)
Noncentrosymmetric materials show various nonreciprocal current responses including the magnetochiral anisotropy, nonlinear Hall effect, and superconducting diode effect [1,2]. They can serve as novel probes of noncentrosymmetric systems and are among the hallmarks of modern condensed matter physics. Further study of nonreciprocal phenomena would illuminate unprecedented phenomena in noncentrosymmetric materials. In particular, noncentrosymmetric superconductors offer a fertile ground to explore exotic physical phenomena arising from the interplay of nonreciprocity and macroscopic quantum coherence of Cooper pairs.
In this talk, we theoretically study the intrinsic nonreciprocity in the charge transport of noncentrosymmetric superconductors under magnetic fields. It is known that Cooper pairs spontaneously acquire a finite center-of-mass momentum in such systems even in equilibrium owing to the magnetoelectric coupling of electrons by the Rashba spin-orbit coupling. We discuss the fingerprint of finite-momentum Cooper pairs in nonreciprocal charge transport such as the directional resistance and nonlinear Hall effect [3]. The obtained results uncover the novel aspect of finite-momentum superconductors and show that nonreciprocal charge transport offers a versatile probe of the finite-momentum superconductivity.
[1] Y. Tokura and N. Nagaosa, Nat. Commun. 9, 3740 (2018).
[2] T. Ideue and Y. Iwasa, Annu. Rev. Condens. Matter Phys. 12, 201 (2021).
[3] A. Daido and Y. Yanase, Physical Review Research 6, L022009 (2024).
6. Kaoru Mizuta (University of Tokyo) [15:30 - 16:10] Efficient quantum algorithms for simulating time-dependent Hamiltonians Abstract (Click)
Simulating quantum many-body systems is one of the most significant applications of quantum computers for condensed matter physics and quantum chemistry. The ultimate goal in this field is to construct the fastest quantum algorithms calculating various properties such as quantum dynamics and energy eigenstates with guaranteed accuracy. In the past several decades, various quantum algorithms such as Trotterization and quantum singular value transform [1] have been developed for this purpose, which can exactly or nearly achieve the theoretically-best cost. However, their analysis is restricted to time-independent Hamiltonians.
In this talk, we discuss our recent results on quantum algorithms for time-dependent Hamiltonians [2,3,4]. Time-dependent Hamiltonians have become of great interest owing to their nonequilibrium phenomena (e.g. Floquet systems) and their applications to other quantum algorithms (e.g. adiabatic state preparation). Nevertheless, it has been an open problem whether there exist quantum algorithms for time-dependent Hamiltonians as fast as those for time-independent ones and whether they can achieve the theoretically-best cost, due to the difficulty of dealing with time-dependency. In our study, using Floquet theory invented for analyzing time-periodic systems, we have constructed such optimal quantum algorithms for simulating quantum dynamics [2,4] and energy eigenstates [3] for time-dependent Hamiltonians.
[1] J. M. Martyn, et al., PRX Quantum 2, 040203 (2021).
[2] K. Mizuta, K. Fujii, Quantum 7, 962 (2023)
[3] K. Mizuta, arXiv:2401.02700
[4] K. Mizuta, T. N. Ikeda, and K. Fujii, arXiv:2410.14243.
7. Yoshifumi Nakata (YITP, Kyoto University) [16:10 - 16:50] Towards Quantum Error Correction in Hamiltonian Systems Abstract (Click)
Quantum chaos, information scrambling, and quantum error correction (QEC) are topics of growing interest, bridging high-energy physics, quantum many-body physics, and quantum information. While these concepts are speculated to be deeply connected, rigorous studies remain limited. In this talk, we explore their interplay and investigate the potential for QEC based on complex quantum many-body dynamics. We focus on two questions: what types of "chaotic" dynamics achieve QEC, and how can such dynamics be decoded? For the first, we numerically show a subtle distinction between quantum chaos and QEC [1]. For the second, we show that the decoding problem can be simplified to decoding classical information encoded in two complementary bases, significantly easing the decoding process [2].
[1] Hayden-Preskill recovery in Hamiltonian systems, YN, and M. Tezuka, Phys. Rev. Research 6, L022021 (2024).
[2] Decoding general error correcting codes and the role of complementarity, YN, T. Matsuura, and M. Koashi, arXiv:2210.06661 (2022).
December 10th, 2024
8. Han Yan (ISSP, University of Tokyo) [9:30 - 10:10] Designing Emergent Light in QED from Quantum Spin Liquids Abstract (Click)
Quantum spin ice (QSI) is a lattice spin-model realization of full-fledged quantum electrodynamics, including photons, electric charges, and magnetic monopoles. As one of the most interesting quantum spin liquids, a significant amount of experimental and theoretical investigation has been done in this field. I will present an overview of the quantum spin ice physics and also discuss our recent ongoing work [1] on how, in the so-called dipole-octupole QSI [2], one can experimentally have clean control of the dynamics of its emergent QED, including the transition between different symmetry-enriched phases, tuning the dispersion of photons and fine-structure constants, etc. One of the most straightforward experiments can achieve this: turning on the external magnetic field in the right direction.
[1] Experimentally tunable QED in dipolar-octupolar quantum spin ice. HY, Alaric Sanders, Claudio Castelnovo, Andriy H Nevidomskyy, arXiv:2312.11641.
[2] Fractional matter coupled to the emergent gauge field in a quantum spin ice, V Porée, HY, F Desrochers et al., accepted by Nature Physics.
9. Koji Kudo (Kyushu University) [10:10 - 10:50] Quantum anomalous, spin, and valley Hall phases in pentalayer graphene moiré superlattice Abstract (Click)
Since the integer and fractional quantum anomalous Hall effects were observed [1], pentalayer rhombohedral graphene moiré superlattices have been intensively studied. Here, we extend quantum anomalous Hall physics at a moiré filling factor of ν=1 [2] to more complex scenarios at higher filling factors. Specifically, we numerically show that at ν=2, electron-electron interactions can lead to the emergence of quantum spin Hall and quantum valley Hall states, in addition to the quantum anomalous Hall state, even in the absence of spin-orbit coupling or valley-dependent potentials. Furthermore, at ν=3 and ν=4, we demonstrate that many-body effects produce the ground state that consists of both topological and nontopological states. This disrupts the straightforward relationship between ν and its particle-hole counterpart 4-ν typically seen in the quantum Hall effect in graphene. [3]
[1] Z. Lu, T. Han, Y. Yao, A. P. Reddy, J. Yang, J. Seo, K. Watanabe, T. Taniguchi, L. Fu, and L. Ju, Nature 626, 759 (2024).
[2] Z. Dong, A. S. Patri, and T. Senthil, Phys. Rev. Lett. 133, 206502 (2024); B. Zhou, H. Yang, and Y.-H. Zhang, Phys. Rev. Lett. 133, 206504 (2024); J. Dong, T. Wang, T. Wang, T. Soejima, M. P. Zaletel, A. Vishwanath, and D. E. Parker, Phys. Rev. Lett. 133, 206503 (2024); Z. Guo, X. Lu, B. Xie, and J. Liu, Phys. Rev. B 110, 075109(2024); Y. H. Kwan, J. Yu, J. Herzog-Arbeitman, D. K. Efetov, N. Regnault, and B. A. Bernevig, arXiv: 2312.11617.
[3] K. Kudo, R. Nakai, and K. Nomura, arXiv: 2406.14354.
10. Kyosuke Adachi (RIKEN iTHEMS/BDR) [11:20 - 12:00] Finding Rules for Condensation of Disordered Protein Sequences Abstract (Click)
Protein condensates, such as nucleoli and nuclear speckles, coexist in cells and play essential roles in cellular functions. Though the interactions among intrinsically disordered regions have been identified as a fundamental mechanism for condensation, the rules for amino acid sequences that drive the coexistence of distinct condensates remain largely unknown. In this talk, I will explain our theoretical work on calculating heteropolymer interactions between disordered protein sequences [1]. With this framework, we predict the properties of condensates, such as the critical temperature and the coexistence of distinct condensates.
[1] K. Adachi and K. Kawaguchi, Phys. Rev. X 14, 031011 (2024).
11. Ching-Kai Chiu (RIKEN iTHEMS) [13:30 - 14:10] Searching for Moiré flat bands beyond twisted bilayer graphene Abstract (Click)
At specific "magic" twist angles, Dirac cones in twisted bilayer graphene (TBG) evolve into Moiré flat bands, offering a fertile ground for the exploration of strongly correlated physics. However, TBG is not unique in exhibiting such absolute band flatness. The flatness phenomenon fundamentally hinges on the presence of topological nodes and their specific locations within the Brillouin zone (BZ).
In this talk, we explore new platforms for achieving band flatness, focusing on (A) monolayer graphene with periodic potentials and (B) twisted bilayer nodal systems, both of which preserve chiral symmetry. (A) We show that a periodic substrate potential introduces intervalley coupling that mimics the Dirac cone coupling in TBG. By tuning the lattice constant of the substrate, we can control this coupling, leading to the emergence of Moiré flat bands at specific "magic" lattice constants. (B) We classify various ordered topological nodes in base layers and systematically map their possible locations across different BZs. To ensure uniform interlayer coupling, we constrain these nodes to rotational centers, such as the Γ and M points. Using this classification, we identify the conditions necessary for the emergence of Moiré flat bands. These findings pave the way for realizing flat bands in a broader class of materials and deepen our understanding of the interplay between topology and symmetry.
(1) Q. Lu, C.-K. Chiu, C. Le, J. Cook, X. Zhang, X. He, M. Zarenia, M. Vaninger, P. F. Miceli, C. Liu, T.-C. Chiang, G. Vignale, G. Bian, Advanced Materials 34, 2200625 (2022)
(2) F. Cui, C. Le, Q. Zhang, X. Wu, J. Hu, C.-K. Chiu, Science China Physics, Mechanics & Astronomy 67 (9), 297012 (2024)
(3) C. Le, Q. Zhang, F. Cui, X. Wu, C.-K. Chiu, Physical Review Letters 132 (24), 246401 (2024)
12. Rina Tazai (YITP, Kyoto University) [14:10 - 14:50] Study of time-reversal and inversion symmetry breaking in AV3Sb5 Abstract (Click)
In kagome superconductor AV3Sb5 [1], 2×2 CDW, time-reversal-symmetry-breaking (TRSB), and inversion symmetry breakiang have been reported by STM and μSR study, Kerr rotation analysis, field-tuned chiral transport study [2]. More recently, magnetic torque measurement reveals the first order transition with TRSB at 130 [K] [3]. However, the microscopic origin of CDW, superconductivity and TRSB has been unsolved. In the present study [4,5], we focus on the important roles of CDW fluctuations developed near the quantum-critical point of CDW phase. By considering the higher-order many body effects among the d-orbital electrons, we reveal that the chiral loop current phase is mediated by the CDW fluctuations in AV3Sb5. In addition, we revealed that the chiral transport, so called eMChA, is explained by the inversion symmetry breaking due to the loop current and uni axial CDW states [6], related to the quasi-Quamtum metric tensor.
[1] Jiang, YX et al., 20, 1353 Nat. Mater (2021). [2] C. Guo et al., Nature 611, 461 (2022). [3] T. Asaba et al., Nat. Phys. 20, 40 (2024). [4] R. Tazai et al., Nat. Commun. 14, 7845 (2023). [5] R. Tazai, et al. PNAS 121, e2303476121 (2024). [6] R. Tazai, et al, arXiv:2408.04233.
Poster session with banquet [15:00 - ]
At the beginning of the poster session, we have a gong show for all the poster presenters.
December 11th, 2024
13. Satoshi Ikegaya (Nagoya University) [9:30 - 10:10] Exotic Andreev bound states beyond the “conventional” bulk-boundary correspondence Abstract (Click)
My basic question now is: Are there interesting “non-topological” Andreev bound states that may have been buried in the enthusiasm for “topological” superconductivity? As a first step towards answering this question, we have found two Andreev bound states that exhibit exotic properties not found in the conventional Majorana bound states (MBSs) of topological superconductors.
The first one is named “multilocational” Majorana bound states (MMBSs)[1]. Based on the bulk-boundary correspondence, a conventional MBS must be localized at one end/surface of one topological superconductor. In contrast, the MMBS is characterized by the wave function splitting into multiple parts located at different ends of different TSs. In this talk, we specifically discuss the MMBS in a three-terminal Josephson junction consisting of three one-dimensional topological superconductors. We also show drastic nonlocal transport phenomena that manifest the nonlocal nature of the MMBS.
The second one is named “oscillating-charged” Andreev bound states (OCABSs)[2]. The vast majority of surface Andreev bound states, including MBSs, are charge neutral. In contrast, the charge density of the OCABSs, which occur in a superconductor with a sublattice degree of freedom, oscillates in sign between the two sublattices. In this talk, we show that the OCABSs lead to a complete breakdown of the well-known proportionality between the local density of states and the tunneling conductance spectrum. We also discuss the possible occurrence of the OCABSs in UTe2.
[1] Yutaro Nagae, Andreas P. Schnyder, Yukio Tanaka, Yasuhiro Asano, and Satoshi Ikegaya, Phys. Rev. B 110, L041110 (2024).
[2] Satoshi Ando, Shingo Kobayashi, Andreas P. Schnyder, Yasuhiro Asano, Satoshi Ikegaya, arXiv: 2403.01502.
14. Tatsuya Kaneko (Osaka University) [10:10 - 10:50] Bilayer nickelate superconductor and its nonlinear phonon dynamics Abstract (Click)
The discovery of high-temperature superconductivity in La3Ni2O7 has set a new trend in condensed matter physics. The bilayer structure is the host of the essential electronic properties, and the emergence of superconductivity is strongly associated with the structural phase transition under pressure. We theoretically study the mechanism of superconductivity in the bilayer nickelate. After a brief review of superconductivity in strongly correlated bilayer systems, we present the numerical results obtained by the density-matrix renormalization group calculations in an effective model for the bilayer nickelate. We also investigate the phonon dynamics of the bilayer nickelate to provide helpful information for understanding the superconducting transition. We evaluate the phonon dynamics based on the framework of nonlinear phononics and discuss how light can be used to manipulate the crystal structure.
15. Taiki Matsushita (Kyoto University) [11:20 - 12:00] Anomalous thermal responses in spin-triplet superconductors Abstract (Click)
Spin-triplet superconductors are characterized by the spin 1 of Cooper pairs [1], offering platforms for novel superconducting spintronics phenomena [2]. At the same time, the spin-triplet superconducting order is a source of topological superconductivity [3], and its importance has grown significantly with the emergence of topological electronic materials. Spin-triplet superconducting orders have primarily been discussed in heavy fermion materials, but the shapes of the order parameters remain under debate. In this talk, we discuss responses to temperature gradients as potential probes of spin-triplet superconducting orders.
In the first half of this talk, we focus on chiral superconducting order, which is a key ingredient of time-reversal-symmetry-broken (TRSB) topological superconductors (TSCs), and discuss the anomalous thermal Hall effect (ATHE) as a unique property of these systems [3]. The ATHE has two distinct mechanisms: intrinsic (topological) and extrinsic (impurity-scattering) mechanisms [4,5]. The intrinsic mechanism of the ATHE relies on gapless Majorana boundary modes, ensuring the T-linear behavior of the zero-field thermal Hall conductivity at low temperatures. Remarkably, the intrinsic contribution to the thermal Hall conductivity is quantized in TRSB TSCs at low temperatures, providing a definitive probe of Majorana boundary modes [5]. To identify TRSB TSCs through thermal Hall measurements, the intrinsic ATHE should dominate over the extrinsic ATHE at low temperatures. However, whether the extrinsic contribution to the ATHE results in a T-linear contribution at low temperatures—and if so, how large it is—depends on the details of disorder. We analyzed the ATHE to identify the dominant mechanism and found that the extrinsic ATHE dominates the thermal Hall response even at low temperatures if impurity bands lie near the Fermi energy and contribute to thermal transport [6], while the intrinsic mechanism governs the low-temperature behavior of the thermal Hall response in clean systems.
In the second half of this talk, we consider spin current responses in helical superconductors and nonunitary (spin-polarized spin-triplet) superconductors. Helical superconducting states represent two time-reversal copies of chiral superconducting states and thus realize time-reversal-invariant TSCs [3]. Here, we show that the helical (spin-dependent chiral) nature of the order parameters influences scattering events of quasiparticles at impurity sites via vertex corrections to the thermal current [7]. This introduces spin-dependent asymmetries in the scattering direction, inducing the spin Nernst effect, which is a spin current generation perpendicular to temperature gradients. In nonunitary superconducting states, the spin polarization of the condensate induces a spin current along temperature gradients [8]. Remarkably, the thermoelectric spin current survives in the Meissner state while the Meissner effect sharply suppresses the thermoelectric charge current. We dub this the superconducting spin Seebeck effect. Our proposals of these spin current responses establish spin caloritronics as sensitive probes of the spin structure of spin-triplet superconducting order parameters.
References
[1] M. Sigrist and K. Ueda, Rev. Mod. Phys. 63, 239 (1991)
[2] M. Eshrig, Rep. Prog. Phys. 78 104501 (2015)
[2] M. Sato and Y. Ando, Rep. Prog. Phys. 80 076501 (2017)
[4] H. Sumiyoshi and S. Fujimoto, J. Phys. Soc. Jpn. 82, 023602 (2013)
[5] B. Arfi, H. Bahlouli, C. J. Pethick, and D. Pines, Phys. Rev. Lett. 60, 2206 (1988).
[6] T. Matsushita, N. Kimura, T. Mizushima, I. Vekhter, and S. Fujimoto, arXiv: 2405. 09840 (2024). (Accepted in Physical Review B)
[7] T. Matsushita, J. Ando, Y. Masaki, T. Mizushima, S. Fujimoto, and I. Vekhter, Phys. Rev. Lett. 128, 097001 (2022).
[8] T. Matsushita, T. Mizushima, Y. Masaki, S. Fujimoto, and I. Vekhter, arXiv: 2405. 09840 (2024). (Accepted in Science Advances)
16. Shintaro Hoshino (Saitama University) [13:30 - 14:10] Exploring relativistic corrections beyond spin-orbit coupling Abstract (Click)
In systems containing strongly localized f- or d-electrons,
correlation effects give rise to various quantum phenomena. To
understand such strongly correlated electron systems, it is essential
to classify the degrees of freedom of electrons within atomic
orbitals. This can be effectively done by considering multipole
operators based on the total angular momentum [1,2]. Typically, these
multipoles are introduced through multipole expansions of charge,
spin, and current distributions in real space. However, the electric
toroidal multipole does not emerge from these expansions. Revisiting
the microscopic physical quantities [3,4], it was found that
considering the electric polarization originating from spin degrees of
freedom and the electron chirality operator (\gamma^5) derived from
the Dirac field is crucial. These quantities can be utilized to
quantify asymmetry in solids [5]. In addition, examining higher-order
relativistic correction terms in the Hamiltonian reveals how
electronic chirality couples to external fields [4].
On a more general level, relativistic corrections also introduce
modifications to the Coulomb interaction. Recently, a representation
suitable for the atomic limit has been derived based on
electron-photon interactions [6]. In the presentation, I will
systematically discuss relativistic corrections in electronic systems.
[1] Y. Wang, H. Weng, L. Fu, X. Dai, Phys. Rev. Lett. 119, 187203 (2017).
[2] H. Kusunose, R. Oiwa, S. Hayami, J. Phys. Soc. Jpn. 89, 104704 (2020).
[3] S. Hoshino, M.-T. Suzuki, and H. Ikeda, Phys. Rev. Lett. 130, 256801 (2023).
[4] S. Hoshino, T. Miki, M.-T. Suzuki, and H. Ikeda, arXiv:2408.16983 (2024).
[5] T. Miki, H. Ikeda, M.-T. Suzuki, and S. Hoshino, arXiv:2410.23549 (2024).
[6] S. Hoshino, arXiv:2311.05294 (2023).
17. Shunsuke Sato (CCS, University of Tsukuba) [14:10 - 14:50] Time-dependent density functional theory for real-time electron dynamics in solids Abstract (Click)
First-principles electron dynamics calculations based on time-dependent density functional theory (TDDFT) provide a non-empirical framework for analyzing light-induced nonlinear and ultrafast phenomena in solids. In this talk, I will introduce a numerical pump-probe scheme, based on TDDFT, to compute the optical properties of solids in nonequilibrium phases [1]. Additionally, I will discuss the application of pump-probe simulations to attosecond transient absorption spectroscopy [2]. Finally, I will present a microscopic current density analysis for nonlinear optical phenomena, offering real-space insights into these complex processes [3].
[1] S.A. Sato et al., Phys. Rev. B 89, 064304 (2014)
[2] S.A. Sato, Comput. Mater. Sci. 194, 110274 (2021)
[3] S.A. Sato, J. Phys. Soc. Jpn. 92, 094401 (2023)
18. Jun Takahashi (ISSP, University of Tokyo) [15:30 - 16:10] Classifying Frustration-Freeness and Approximating Ground States via Semidefinite Programming Abstract (Click)
A Hamiltonian H=Σhi is said to be frustration-free when the ground state is a simultaneous ground state of all h_i terms. Frustration-free Hamiltonians are fundamental in understanding quantum phases of matter, with models like the toric code and AKLT as key examples. However, identifying frustration-freness in a general Hamiltonian H is challenging [1], especially when the decomposition of the Hamiltonian H=Σhi is unspecified. This difficulty arises because apparent frustration in the ground state might vanish with a suitable decomposition, as seen in the Majumdar-Ghosh model.
In this talk, I present a new polynomial-time algorithm that determines the optimal frustration-free decomposition under locality constraints [2]. The algorithm exploits the fact that if such decomposition exists, it must be interpretable as a low-degree sum-of-squares (SoS) which is the dual of a semidefinite programming hierarchy [3]. This duality further implies that we can also quantify the "minimal frustration" under the optimal decomposition, and that corresponds to the approximability of the ground state of quantum systems using semidefinite programming.As a demonstration, we rigorously classify the frustration-free regions of the J1-J2-J3 Heisenberg chain, proving that frustration-free points exist only in the ferromagnetic region and the Majumdar-Ghosh point. If time permits, I will also explain how the dual algorithm can be seen as a natural quantum analogue of the Goemans-Williamson algorithm, which is conjecturally optimal for the classical Ising model ground state problem.
[1] O. Sattath, S. C. Morampudi, C. R. Laumann, and R. Moessner, PNAS 113 6433 (2016).
[2] J. Takahashi, C. Rayudu, C. Zhou, R. King, K. Thompson, and O. Parekh, arXiv:2307.15688.
[3] M. Navascués, S. Pironio, and A. Acín, New J. Phys. 10 073013 (2008).
Closing [16:10 - 16:20]
Poster session (15:00 - , December 10th, 2024)
At the beginning of the poster session, we have a gong show for all the poster presenters.
1. Yuuki Sugiyama (ISSP, University of Tokyo), Anomaly-Inflow in Quantum Hall System with an expanding edge: Application to Hawking radiation
2. Hongchao Li (University of Tokyo), Dissipative Superfluidity in a Molecular Bose-Einstein Condensate
3. Shunsuke Furuya (Saitama Medical University), Spin pumping into quantum spin chains
4. Daichi Nakamura (ISSP, University of Tokyo), Non-Hermitian Origin of Wannier Localizability and Detachable Topological Boundary States
16. Ryoga Miwa (Osaka University), The Collective Excitation Modes in the Fulde-Ferrell-Larkin-Ovchinnikov States
17. Yuta Sekino (RIKEN), Thermomagnetic anomalies by magnonic criticality in ultracold atomic transport
18. Takahiro Misawa (ISSP, University of Tokyo), Topological altermagnet: Quantization of the Zak phase in a collinear antiferromagnet
19. Tatsuhiko Ikeda (RIKEN RQC), Robust effective ground state in a nonintegrable Floquet quantum circuit
20. Hikaru Goto (Tokyo University of Science), Chern insulating phase in a kagome system with strong light-matter interaction
21. Tsugumi Matsumoto (Kyoto University), Reciprocal and nonreciprocal paraconductivity in bilayer multiphase superconductors
22. Takeo Kato (ISSP, University of Tokyo), Theory of Phonon-Spin Conversion in Junction Systems
23. Teruki Matsuzaki (Chiba University), Luminescence of heavy d2 transition metal antifluorites
24. Tsukasa Goto (Osaka University), Tolerance of Majorana Teleportation in Mesoscopic Topological Superconductors
25. Eiki Yamaguchi (Chiba University), Magnetoelectric Effect and Magnetic Structure Analysis of RbO2
26. Kazuki Yamamoto (Institute of Science Tokyo), Non-Hermitian Kondo effect in a quantum dot coupled to environments
27. Xinye Guan (University of Tokyo), Disorder-free Quantum Breakdown Model: exact solution and dynamics
28. Takahiro Orito (ISSP, University of Tokyo), Strong-to-weak symmetry breaking states in stochastic dephasing stabilizer circuits
29. Tetsuya Iwasaki (University of Tokyo), Exact analysis of nonlinear Drude weights in the Hubbard chain
30. Alpin Novianus Tatan (ISSP, University of Tokyo), Electronic structure description of magnetic and nonmagnetic superconductors with modern ab initio density functional theory calculations
31. Haruki Shimizu (ISSP, University of Tokyo), Tensor network simulations for non-orientable surfaces
32. Koudai Sugimoto (Keio University), Single-particle excitation spectra of the one-dimensional Hubbard model in DC electric fields
33. Naomichi Hatano (IIS, University of Tokyo), Quantum transport on Bethe lattices with non-Hermitian sources and a drain
34. Manami Yamagishi (University of Tokyo), Proposal of Kondo quantum walks
35. Zhi-Yao Ning (ISSP, University of Tokyo), Quantum phase transition and composite excitations of antiferromagnetic quantum spin trimer chains in a magnetic field
36. Musashi Kato (Kyoto University), Exceptional points and correlation's effects in bosonic systems
