Akito Daido

Nonreciprocity in superconductors is attracting much interest owing to its fundamental importance as well as the potential applicability to engineering. In this paper, we generalize the previous theories of the intrinsic superconducting diode effect (SDE) and microscopically elucidate its relationship with the nonreciprocity of the transition lines under supercurrent. We derive a general formula for the intrinsic SDE by using the phenomenological Ginzburg-Landau theory and thereby show that the

Topological nonsymmorphic crystalline superconductivity (TNCS) is an intriguing phase of matter, offering a platform to study the interplay between topology, superconductivity, and nonsymmorphic crystalline symmetries. Interestingly, some of TNCSs are classified into Z_{4} topological phases, which have unique surface states referred to as a Möbius strip or an hourglass, and they have not been achieved in symmorphic superconductors. However, material realization of Z_{4} TNCS has never been know

We study two-dimensional noncentrosymmetric nodal superconductors under Zeeman field and clarify the field-angle dependence of topological properties. It has been shown that the nodal excitation acquires an excitation gap due to the Zeeman field perpendicular to antisymmetric spin-orbit coupling, and then gapful topological superconductivity is realized [A. Daido and Y. Yanase, Phys. Rev. B 94, 054519 (2016)]. We show that the system undergoes a gapful-gapless transition against tilting of the f

We propose a generic scenario for realizing gapful topological superconductors (TSCs) from gapless spin-singlet superconductors (SCs). Noncentrosymmetric nodal SCs in two dimensions are shown to be gapful under a Zeeman field, as a result of the cooperation of inversion-symmetry breaking and time-reversal-symmetry breaking. In particular, non-$s$-wave SCs acquire a large excitation gap. Such paramagnetically induced gapful SCs may be classified into TSCs in the symmetry class D specified by the

Higher-rank electric/magnetic multipole moments are attracting attention these days as candidate order parameters for exotic material phases. However, the quantum mechanical formulation of those multipole moments is still an ongoing issue. In this paper, we propose a thermodynamic definition of electric quadrupole moments as a measure of symmetry breaking, following previous studies of orbital magnetic dipole moments and magnetic quadrupole moments. The obtained formulas are illustrated with a m

Surface physics dominated by bulk properties has been one of the central interests in modern condensed matter physics, from electric polarization to bulk-boundary correspondence of topological insulators and superconductors. Here we extend theory of electric polarization to chirality polarizations, that is, surface charges corresponding to local antisymmetries characterized as a bulk property. Using the notion of chirality polarizations, we prove the recently proposed spectral bulk-boundary corr

Nonreciprocal charge transport is attracting much attention as a novel probe and functionality of noncentrosymmetric superconductors. In this work we show that both the longitudinal and the transverse nonlinear paraconductivity are hugely enhanced in helical superconductors under moderate and high magnetic fields, which can be observed by second-harmonic resistance measurements. The discussion is based on the generalized formulation of nonlinear paraconductivity in combination with the microscop

Bloch wave functions of electrons have properties called quantum geometry, which has recently attracted much attention as the origin of intriguing physical phenomena. In this paper, we introduce the notion of the quantum-geometric pair potentials (QGPP) based on the generalized band representation and thereby clarify how the quantum geometry of electrons is transferred to the Cooper pairs they form. QGPP quantifies the deviation of multiband superconductors from an assembly of single-band superc

Electric current is generally prohibited in equilibrium. This prevents a zero-resistance state realized solely under a finite electric current, namely, unidirectional superconductivity. Here, the authors propose a setup to realize unidirectional superconductivity as a nonequilibrium steady state, focusing on the in-plane transport of thin-film superconductors which lack in-plane inversion symmetry. Introducing dissipation with the out-of-plane electric field and current, the system realizes unid

Stimulated by the recent experiment [F. Ando et al., Nature (London) 584, 373 (2020).NATUAS0028-083610.1038/s41586-020-2590-4], we propose an intrinsic mechanism to cause the superconducting diode effect (SDE). SDE refers to the nonreciprocity of the critical current for the metal-superconductor transition. Among various mechanisms for the critical current, the depairing current is known to be intrinsic to each material and has recently been observed in several superconducting systems. We clarif

Nonreciprocity in superconductors is attracting much interest owing to its fundamental importance as well as its potential applicability to engineering. In this paper, we generalize the previous theories of the intrinsic superconducting diode effect (SDE) and microscopically elucidate its relationship with the nonreciprocity of the transition lines under supercurrent. We derive a general formula for the intrinsic SDE by using the phenomenological Ginzburg-Landau theory and thereby show that the

Nonreciprocal charge transport is attracting much attention as a novel probe and functionality of noncentrosymmetric superconductors. In this work, we show that both the longitudinal and transverse nonlinear paraconductivity are hugely enhanced in helical superconductors in moderate and high magnetic fields, which can be observed by second-harmonic resistance measurements. The discussion is based on the generalized formulation of nonlinear paraconductivity in combination with the microscopically

Topological nonsymmorphic crystalline superconductivity (TNCS) is an intriguing phase of matter, offering a platform to study the interplay between topology, superconductivity, and nonsymmorphic crystalline symmetries. Interestingly, some of TNCS are classified into $Z_4$ topological phases, which have unique surface states referred to as a M\obius strip or an hourglass, and have not been achieved in symmorphic superconductors. However, material realization of $Z_4$ TNCS has never been known, to

A general principle of condensed matter physics prohibits the electric current in equilibrium. This prevents a zero-resistance state realized solely under a finite electric current, namely unidirectional superconductivity. In this paper, we propose a setup to realize the unidirectional superconductivity as a nonequilibrium steady state. We focus on the in-plane transport of atomically thin bilayer superconductors lacking the in-plane inversion symmetry and introduce dissipation by applying the o