Aline Ramires

β-YbAlB4: A Critical Nodal Metal

We propose a model for the intrinsic quantum criticality of β-YbAlB(4), in which a vortex in momentum space gives rise to a new type of Fermi surface singularity. The unquenched angular momentum of the |J=7/2,m(J)=±5/2> Yb 4f states generates a momentum-space line defect in the hybridization between 4f and conduction electrons, leading to a quasi-two-dimensional Fermi surface with a k(⊥)(4) dispersion and a singular density of states proportional to E(-1/2). We discuss the implications of this line node in momentum space for our current understanding of quantum criticality and its interplay with topology.

Identifying detrimental effects for multiorbital superconductivity: Application to Sr2RuO4

We propose a general scheme to probe the compatibility of arbitrary pairing states with a given normal state Hamiltonian by the introduction of a concept called superconducting fitness. This quantity gives a direct measure of the suppression of the superconducting critical temperature in the presence of key symmetry-breaking fields. A merit of the superconducting fitness is that it can be used as a tool to identify nontrivial mechanisms to suppress superconductivity under various external influences, in particular, magnetic fields or distortions, even in complex multiorbital systems. In the light of this concept we analyze the multiband superconductor

Theory of the electron spin resonance in the heavy fermion metal β-YbAlB4.

{\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}

Supersymmetric approach to heavy fermion systems

and propose a new mechanism for the suppression of superconductivity in multiorbital systems, which we call interorbital effect, as a possible explanation for the unusual limiting feature observed in the upper critical field of this material.

A note on the upper critical field of Sr2RuO4 under strain

The heavy fermion metal β-YbAlB4 exhibits a bulk room temperature conduction electron spin resonance (ESR) signal which evolves into an Ising-anisotropic f-electron signal exhibiting hyperfine features at low temperatures. We develop a theory for this phenomenon based on the development of resonant scattering off a periodic array of Kondo centers. We show that the hyperfine structure arises from the scattering off the Yb atoms with nonzero nuclear spin, while the constancy of the ESR intensity is a consequence of the presence of crystal electric field excitations of the order of the hybridization strength.

Electrically Tunable Gauge Fields in Tiny-Angle Twisted Bilayer Graphene

We propose a generalization of the supersymmetric representation of spins with symplectic symmetry, generalizing the rotation group of the spin from SU(2) to SP(N). As a test application of this new representation, we consider two toy models involving a competition of the Kondo effect and antiferromagnetism: a two-impurity model and a frustrated three-impurity model. Exploring an ensemble of L-shaped representations with a fixed number of boxes in their respective Young tableaux, we allow the system to choose which representation is energetically more favorable in each region in parameter space. We discuss how the features of these preliminary applications can generalize to Kondo lattice models.

Tailoring Tc by symmetry principles: The concept of superconducting fitness

In the light of the recently discussed mechanism for suppression of superconductivity in multi-orbital systems called inter-orbital effect, here we extend our analysis of the upper critical field in Sr

Super-Symplectic spin and heavy fermion systems

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Supersymmetric SP(N) spin representation for heavy fermion systems

RuO

Theory for ESR in the heavy fermion system

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