Nonreciprocal transport in U(1) gauge theory of high-Tc cuprates

The nature of the charge carriers in high-Tc cuprates is an essential issue to reveal their novel physical properties and the mechanism of their superconductivity. However, the experimental probes and the theoretical analysis have been mostly restricted to the linear responses. On the other hand, recent observations of Rashbatype spin-orbit coupling (SOC) on the surface of high-Tc cuprates imply the possible nonlinear and nonreciprocal transport phenomena under in-plane magnetic fields. In this paper, we study the nonreciprocal transport properties on the surface of cuprates by employing a U(1) gauge theory framework, where the electrons are considered to be fractionalized. Our investigation highlights the intricate variations in nonreciprocal transport with respect to temperatures and dopings. First, it reveals contrasting behavior of nonreciprocity in each normal phase. Second, it discerns the tendencies between underdoped and overdoped superconducting states and their paraconductivity. The complex behaviors of nonreciprocal transport originate from the spinful and spinless nature of the charge carriers and their kinetic energy scales. These findings pave a new avenue to explore the electronic states in high-Tc cuprates in terms of nonreciprocal transport phenomena.Comment: 13 pages, 8 figure

Unconventional Anomalous Hall Effect from Antiferromagnetic Domain Walls of Nd\u3csub\u3e2\u3c/sub\u3eIr\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e7\u3c/sub\u3e Thin Films

Ferroic domain walls (DWs) create different symmetries and ordered states compared with those in single-domain bulk materials. In particular, the DWs of an antiferromagnet with noncoplanar spin structure have a distinct symmetry that cannot be realized in those of their ferromagnet counterparts. In this paper, we show that an unconventional anomalous Hall effect (AHE) can arise from the DWs of a noncoplanar antiferromagnet, Nd2Ir2O7. Bulk Nd2Ir2O7 has a cubic symmetry; thus, its Hall signal should be zero without an applied magnetic field. The DWs generated in this material break the twofold rotational symmetry, which allows for finite anomalous Hall conductivity. A strong f−d exchange interaction between the Nd and Ir magnetic moments significantly influences antiferromagnetic (AFM) domain switching. Our epitaxial Nd2Ir2O7 thin film showed a large enhancement of the AHE signal when the AFM domains switched, indicating that the AHE is mainly due to DWs. Our paper highlights the symmetry-broken interface of AFM materials as a means of exploring topological effects and their relevant applications

Unconventional anomalous Hall effect from antiferromagnetic domain walls of N d2 i r2 O7 thin films

Ferroic domain walls (DWs) create different symmetries and ordered states compared with those in single-domain bulk materials. In particular, the DWs of an antiferromagnet with noncoplanar spin structure have a distinct symmetry that cannot be realized in those of their ferromagnet counterparts. In this paper, we show that an unconventional anomalous Hall effect (AHE) can arise from the DWs of a noncoplanar antiferromagnet, Nd2Ir2O7. Bulk Nd2Ir2O7 has a cubic symmetry; thus, its Hall signal should be zero without an applied magnetic field. The DWs generated in this material break the twofold rotational symmetry, which allows for finite anomalous Hall conductivity. A strong f-d exchange interaction between the Nd and Ir magnetic moments significantly influences antiferromagnetic (AFM) domain switching. Our epitaxial Nd2Ir2O7 thin film showed a large enhancement of the AHE signal when the AFM domains switched, indicating that the AHE is mainly due to DWs. Our paper highlights the symmetry-broken interface of AFM materials as a means of exploring topological effects and their relevant applications. © 2018 American Physical Societ

Magnetic field induced topological semimetals near the quantum critical point of pyrochlore iridates

Motivated by the recent experimental observation of anomalous magnetotransport properties near the Mott quantum critical point (QCP) of pyrochlore iridates, we study the generic topological band structure near QCP in the presence of magnetic field. We have found that the competition between different energy scales can generate various topological semimetal phases near QCP. Here the central role is played by the presence of a quadratic band crossing (QBC) with fourfold degeneracy in the paramagnetic band structure. Due to the large band degeneracy and strong spin-orbit coupling, the degenerate states at QBC can show an anisotropic Zeeman effect as well as the conventional isotropic Zeeman effect. Through the competition between three different magnetic energy scales including the exchange energy between Ir electrons and two Zeeman energies, various topological semimetals can be generated near QCP. Moreover, we have shown that these three magnetic energy scales can be controlled by modulating the magnetic multipole moment (MMM) of the cluster of spins in a unit cell, which can couple to the intrinsic MMM of the degenerate states at QBC. We propose the general topological band structure under magnetic field achievable near QCP, which would facilitate the experimental discovery of novel topological semimetal states in pyrochlore iridates. ©2018 American Physical Societ

Transverse Magnetization in Spin-Orbit Coupled Antiferromagnets

Some antiferromagnets under a magnetic field develop magnetization perpendicular to the field as well as more conventional ones parallel to the field. So far, the transverse magnetization (TM) has been attributed to either the spin canting effect or the presence of cluster magnetic multipolar ordering. However, a general theory of TM based on microscopic understanding is still missing. Here, we construct a general microscopic theory of TM in antiferromagnets with cluster magnetic multipolar ordering by considering classical spin Hamiltonians with spin anisotropy that arises from the spin-orbit coupling. First, from general symmetry analysis, we show that TM can appear only when all crystalline symmetries are broken other than the antiunitary mirror, antiunitary twofold rotation, and inversion symmetries. Moreover, by analyzing spin Hamiltonians, we show that TM always appears when the degenerate ground state manifold of the spin Hamiltonian is discrete, as long as it is not prohibited by symmetry. On the other hand, when the degenerate ground state manifold is continuous, TM generally does not appear except when the magnetic field direction and the spin configuration satisfy specific geometric conditions under single-ion anisotropy. Finally, we show that TM can induce the anomalous planar Hall effect, a unique transport phenomenon that can be used to probe multipolar antiferromagnetic structures. We believe that our theory provides a useful guideline for understanding the anomalous magnetic responses of the antiferromagnets with complex magnetic structures. © 2023 American Physical Society.11Nsciescopu

Magnetic-field induced multiple topological phases in pyrochlore iridates with Mott criticality

The interplay between electron correlation and spin–orbit coupling in solids has been proven to be an abundant gold mine for emergent topological phases. Here we report the results of systematic magnetotransport study on bandwidth-controlled pyrochlore iridates R2Ir2O7 near quantum metal-insulator transition (MIT). The application of a magnetic field along [001] crystallographic direction (H//[001]) significantly decreases resistivity while producing a unique Hall response, which indicates the emergence of the novel semi-metallic state in the course of the magnetic transformation from all-in all-out (AIAO, 4/0) to 2-in 2-out (2/2) spin configuration. For H//[111] that favours 3-in 1-out (3/1) configuration, by contrast, the resistivity exhibits saturation at a relatively high value typical of a semimetal. The observed properties can be identified to reflect the emergence of multiple Weyl semimetal states with varying numbers of Weyl points and line nodes in respective spin configurations. With tuning effective bandwidth, all these states appear to concentrate around the quantum MIT region, which may open a promising venue for topological phenomena and functions. (c) The Author(s) 20174

Higher harmonics in planar Hall effect induced by cluster magnetic multipoles

The lack of net magnetization in antiferromagnets makes them technologically promising, but it also makes detecting the spin orders challenging. Here, using electrical transport measurement, Song et al show how the planar Hall effect can detect different cluster magnetic multipoles in antiferromagnetic Nd2Ir2O7 film. Antiferromagnetic (AFM) materials are attracting tremendous attention due to their spintronic applications and associated novel topological phenomena. However, detecting and identifying the spin configurations in AFM materials are quite challenging due to the absence of net magnetization. Herein, we report the practicality of utilizing the planar Hall effect (PHE) to detect and distinguish "cluster magnetic multipoles" in AFM Nd2Ir2O7 (NIO-227) fully strained films. By imposing compressive strain on the spin structure of NIO-227, we artificially induced cluster magnetic multipoles, namely dipoles and A(2)- and T-1-octupoles. Importantly, under magnetic field rotation, each magnetic multipole exhibits distinctive harmonics of the PHE oscillation. Moreover, the planar Hall conductivity has a nonlinear magnetic field dependence, which can be attributed to the magnetic response of the cluster magnetic octupoles. Our work provides a strategy for identifying cluster magnetic multipoles in AFM systems and would promote octupole-based AFM spintronics.11Nsciescopu

Correlated Magnetic Weyl Semimetal State in Strained Pr 2

© 2021 The Authors. Advanced Materials published by Wiley-VCH GmbHCorrelated topological phases (CTPs) with interplay between topology and electronic correlations have attracted tremendous interest in condensed matter physics. Therein, correlated Weyl semimetals (WSMs) are rare in nature and, thus, have so far been less investigated experimentally. In particular, the experimental realization of the interacting WSM state with logarithmic Fermi velocity renormalization has not been achieved yet. Here, experimental evidence of a correlated magnetic WSM state with logarithmic renormalization in strained pyrochlore iridate Pr2Ir2O7 (PIO) which is a paramagnetic Luttinger semimetal in bulk, is reported. Benefitting from epitaxial strain, “bulk-absent” all-in–all-out antiferromagnetic ordering can be stabilized in PIO film, which breaks time-reversal symmetry and leads to a magnetic WSM state. With further analysis of the experimental data and renormalization group calculations, an interacting Weyl liquid state with logarithmically renormalized Fermi velocity, similar to that in graphene, is found, dressed by long-range Coulomb interactions. This work highlights the interplay of strain, magnetism, and topology with electronic correlations, and paves the way for strain-engineering of CTPs in pyrochlore iridates.11Nsciescopu

Correlated Magnetic Weyl Semimetal State in Strained Pr2Ir2O7

© 2021 The Authors. Advanced Materials published by Wiley-VCH GmbHCorrelated topological phases (CTPs) with interplay between topology and electronic correlations have attracted tremendous interest in condensed matter physics. Therein, correlated Weyl semimetals (WSMs) are rare in nature and, thus, have so far been less investigated experimentally. In particular, the experimental realization of the interacting WSM state with logarithmic Fermi velocity renormalization has not been achieved yet. Here, experimental evidence of a correlated magnetic WSM state with logarithmic renormalization in strained pyrochlore iridate Pr2Ir2O7 (PIO) which is a paramagnetic Luttinger semimetal in bulk, is reported. Benefitting from epitaxial strain, “bulk-absent” all-in–all-out antiferromagnetic ordering can be stabilized in PIO film, which breaks time-reversal symmetry and leads to a magnetic WSM state. With further analysis of the experimental data and renormalization group calculations, an interacting Weyl liquid state with logarithmically renormalized Fermi velocity, similar to that in graphene, is found, dressed by long-range Coulomb interactions. This work highlights the interplay of strain, magnetism, and topology with electronic correlations, and paves the way for strain-engineering of CTPs in pyrochlore iridates.11Nsciescopu