arXiv subjects

Ruo-Peng Yu

Publications and source records attributed to Ruo-Peng Yu.

5 recordsLinked to original sources

arXiv2025

Transverse superconducting diode without parity and time-reversal violation

The superconducting diode effect (SDE) is characterized by its nonreciprocal nature in critical supercurrents. However, realizing a longitudinal SDE typically requires simultaneous time-reversal ($\mathcal{T}$) and inversion ($\mathcal{P}$) symmetry breaking in the device, raising challenges in applications. In this Letter, we reveal that an off-axis direct-current bias applied to a planar anisotropic superconductor can convert intrinsic anisotropy into transverse nonreciprocity, generating ultra-tunable SDE without breaking either $\mathcal{P}$ or $\mathcal{T}$ symmetry. Using both Ginzburg-Landau theory and self-consistent mean-field calculations, we show that diode efficiency can be continuously tuned via bias current amplitude. Notably, when the injected bias current exceeds a critical threshold, the system is driven into a ``unidirectional superconductivity" regime, where transverse dissipationless currents are permitted in only one direction. Based on this mechanism, we propose the ``current-gated orthogonal superconducting transistor (CGOST)" and demonstrate its utility in tunable supercurrent range controllers and half-wave rectifiers. Our findings open new avenues for nonreciprocal superconducting electronics.

cond-mat.supr-con↗

arXiv2025

Topological Fermi-arc-like surface states in Kramers nodal line metals

The discovery of Kramers nodal line metals (KNLMs) and Kramers Weyl semimetals (KWSs) has significantly expanded the range of metallic topological materials to all noncentrosymmetric crystals. However, a key characteristic of this topology - the presence of topologically protected surface states in KNLMs - is not well understood. In this work, we use a model of a $C_{1v}$ KNLM with curved Kramers nodal lines (KNLs) to demonstrate that Fermi-arc-like surface states (FALSSs), which have a $\mathbb{Z}_2$ topological origin, appear on surfaces parallel to the mirror plane. These states connect two surface momenta, corresponding to the projections of two touching points on the Fermi surfaces. Notably, as achiral symmetries (mirrors and roto-inversions) are gradually broken, the KNLM transitions into a KWS, allowing the FALSSs to evolve continuously into the Fermi arc states of the KWS. We also explore the conditions under which FALSSs emerge in KNLMs with straight KNLs. Through bulk-boundary correspondence, we clarify the topological nature of KNLMs.

cond-mat.mtrl-sci↗

arXiv2024

Flat-band Fulde-Ferrell-Larkin-Ovchinnikov State from Quantum Geometric Discrepancy

We propose a new scheme for realizing Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) Cooper pairing states within flat bands, in contrast to the conventional paradigm such as the Zeeman effect. Central to our scheme is the concept of ``quantum geometric discrepancy'' (QGD) that measures differences in the quantum geometry of paired electrons and drives the flat-band FFLO instability. Remarkably, we find that this instability is directly related to a quantum geometric quantity known as ``anomalous quantum distance'', which formally captures QGD. To model both QGD and the anomalous quantum distance, we examine a flat-band electronic Hamiltonian with tunable spin-dependent quantum metrics. Utilizing the band-projection method, we analyze the QGD-induced FFLO instability from pairing susceptibility. Furthermore, we perform mean-field numerical simulations to obtain the phase diagram of the BCS-FFLO transition, which aligns well with our analytical results. Our work demonstrates that QGD offers a general and distinctive mechanism for stabilizing the flat-band FFLO phase.

cond-mat.supr-con↗

arXiv2023

Heesch Weyl Fermions in inadmissible chiral antiferromagnets

Symmetry is a crucial factor in determining the topological properties of materials. In nonmagnetic chiral crystals, the existence of the Kramers Weyl fermions reveals the topological nature of the Kramers degeneracy at time-reversal-invariant momenta (TRIMs). However, it is not clear whether Weyl nodes can also be pinned at points of symmetry in magnetic materials where the time-reversal is spontaneously broken. In this study, we introduce a new type of Weyl fermions, called Heesch Weyl fermions (HWFs), which are stabilized and pinned at points of symmetry by the Heesch groups in inadmissible chiral antiferromagnets. The emergence of HWFs is fundamentally different from that of Kramers Weyl fermions, as it does not rely on any anti-unitary symmetry $\mathcal{A}$ that satisfies $\mathcal{A}^2=-1$. Importantly, the emergence of HWFs is closely related to the antiferromagnetic order, as they are generally obscured by nodal lines in the parent nonmagnetic state. Using group theory analysis, we classify all the magnetic little co-groups of momenta where Heesch Weyl nodes are enforced and pinned by symmetry. With the guidance of this classification and first-principles calculations, we identify antiferromagnetic (AFM) materials such as YMnO$_3$ and Mn$_3$IrGe as candidate hosts for the AFM-order-induced HWFs.We also explore novel properties of Heesch Weyl antiferromagnets, such as nonlinear anomalous Hall effects and axial movement of Heesch Weyl nodes. Our findings shed new light on the role of symmetry in determining and stabilizing topological properties in magnetic materials, and open up new avenues for the design and exploration of topological materials.

cond-mat.mtrl-sci↗

arXiv2023

Experimental evidence for Berry curvature multipoles in antiferromagnets

Berry curvature multipoles appearing in topological quantum materials have recently attracted much attention. Their presence can manifest in novel phenomena, such as nonlinear anomalous Hall effects (NLAHE). The notion of Berry curvature multipoles extends our understanding of Berry curvature effects on the material properties. Hence, research on this subject is of fundamental importance and may also enable future applications in energy harvesting and high-frequency technology. It was shown that a Berry curvature dipole can give rise to a 2nd order NLAHE in materials of low crystalline symmetry. Here, we demonstrate a fundamentally new mechanism for Berry curvature multipoles in antiferromagnets that are supported by the underlying magnetic symmetries. Carrying out electric transport measurements on the kagome antiferromagnet FeSn, we observe a 3rd order NLAHE, which appears as a transverse voltage response at the 3rd harmonic frequency when a longitudinal a.c. current drive is applied. Interestingly, this NLAHE is strongest at and above room temperature. We combine these measurements with a scaling law analysis, a symmetry analysis, model calculations, first-principle calculations, and magnetic Monte-Carlo simulations to show that the observed NLAHE is induced by a Berry curvature quadrupole appearing in the spin-canted state of FeSn. At a practical level, our study establishes NLAHE as a sensitive probe of antiferromagnetic phase transitions in other materials, such as moir\'e superlattices, two-dimensional van der Waal magnets, and quantum spin liquid candidates, that remain poorly understood to date. More broadly, Berry curvature multipole effects are predicted to exist for 90 magnetic point groups. Hence, our work opens a new research area to study a variety of topological magnetic materials through nonlinear measurement protocols.

cond-mat.mes-hall↗