Talks

We propose an effective Hamiltonian approach to understand a variety of partially magnetically ordered phases in a Kondo lattice. Such partial order, where only selected sites are Kondo-screened while the others develop local moments, have been observed in many heavy-fermion compounds. The proposed effective Hamiltonian retains two important features of the fundamental Kondo-lattice model: (i) formation of a Kondo singlet leading to vanishing of the local magnetic moment, and (ii) spatially correlated nature of the electronic kinetic energy. The Hamiltonian belongs to a class of coupled classical-quantum models that can be reliably studied using hybrid Monte Carlo simulations. I will try to motivate the model and demonstrate the approach for the case of a square lattice where we unveil a number of magnetic phases with partial order. I will further motivate a fully classical spin model to describe the partial magnetic order in Kondo lattices.

In this talk I will discuss transport experiments on twisted WSe2 layers that show evidence for magnetic states, and also superconductivity. I will discuss the relationship between the two phases in the phase diagram.

Gaining control over the electronic and magnetic phenomena in solids is a critical step to advance our understanding that can have technological implications. Thin film interfaces and layered materials offer a wide range of possibilities to engineer new phases of electron matter. In the first part of this talk, I will discuss about realizing topological electron transport in SrCuO2 (001)/SrIrO3 (001) epitaxial thin films [1]. When SrIrO3 is proximitized with an antiferromagnetic SrCuO2 layer, we observe an enhancement of effective phase coherence length (lφ) and the chiral anomaly induced topological response in longitudinal magnetoconductance (B‖E) (which is absent in bare SrIrO3 film). Both the above effects is discussed in view of possible quenching of undesired magnetic impurity scattering through antiferromagnetic proximity effect. In the last part of the talk, I will discuss about notable halide ligand tunability of non-collinear magnetism in Cu-based quasi 2D hybrid perovskites....

1T-TaS2 exhibits several resistivity phases due to the modulation of charge density wave (CDW). The fact that such phase transition can be driven electrically has attracted a lot of attention in the recent past toward active-metal based electronics. However, the bias-driven resistivity switching is not very large (less than five-fold), and an enhancement in the same will highly impact such phase transition devices. One aspect that is often overlooked is that such phase transition is also accompanied by a significant change in the local temperature due to the low thermal conductivity of 1T-TaS2. In this work, such electrically driven phase transition induced temperature change is exploited to promote carriers over a thermionic barrier in a 1T-TaS2/2H-TaSe2/2H-MoS2 T-Junction, achieving a 964-fold abrupt switching in the current through the MoS2 channel. The device is highly reconfigurable and exhibits an abrupt reduction in current as well when the biasing configuration changes. The res...

In recent years, tuning electrical polarization by magnetic field and vice versa in multiferroic and magnetoelectric materials received much attention. Impedance spectroscopy is frequently used to probe magnetic-field dependence of capacitance in these materials. However, impedance spectroscopy has been rarely used to study metallic or semiconducting oxides above 1 MHz and below 10 GHz. In this talk, I will show selected applications of the impedance spectroscopy to electrically detect spin resonance, domain magnetization processes and spin/charge conversion. Extension of this technique to 2D materials will also be outlined.

Cuscuton field theory is an extension of general relativity that does not introduce additional propagating degrees of freedom, or violate relativistic causality. We construct a general geometric description of the cuscuton field theory by introducing curvature corrections to both the volume (potential) and the surface (kinetic) terms in the original cuscuton action. Our assumptions involve a stack of spacelike branes, separated by 4-dimensional bulks. We conjecture that the cuscuton, initially a discrete field, becomes continuous in the limit, there are many such transitions. From this we derive an effective action for the cuscuton theory and show that at the quadratic level our theory propagates only the two tensorial degrees of freedom.

I will first introduce screened modified gravity theories and then discuss the chameleon mechanism. Light scalars can be produced from the sun and detected on earth. I will discuss the production of chameleons, including novel production channels, and discuss potential detection in helioscopes.

Layered nickelates have been of interest since the early days of high-Tc superconducting (SC) cuprates as possible additional representants of unconventional superconductors. But only in 2019, a stable SC phase has been identified in thin-films of Sr-doped NdNiO2 with a Tc∼ 20 K [1]. Further SC members from this class of low-valence nickelates have been spotted afterwards. And just when the debate about the similarity between SC cuprates and nickelates, both with akin 3d9−x formal transition-metal valence, was at its zenith, a SC bilayer nickelate of formal 3d8−x valence was detected at high pressure with Tc∼ 80 K in spring 2023 [2]. Interestingly, according to our theoretical investigations [3,4] all these SC nickelates have a multiorbital Ni-eg flat-band scenario in common.

In this talk, it will be shown that an advanced combination of density functional theory (DFT) and dynamical mean-field theory (DMFT) provides unique access to this novel playground of high-Tc nickelate superco...