Talks

Kagome materials have emerged as a promising platform to study novel quantum phases of matter that arise from the interplay between lattice geometry, band topology, and electronic correlations. They host a variety of electronic and structural instabilities, with charge density waves being a prominent example.

In this talk, I will describe how first principles calculations can be used to explore the rich physics associated with charge density waves. Using bilayer kagome metal ScV6Sn6 as an illustrative example, I will explore competing charge density waves, the role of anharmonic phonon-phonon interactions in the charge density wave transition, and the control of charge density waves by external parameters such as pressure and doping.

Traditionally, measurements have been synonymous with extracting information from physical systems. Yet, in quantum systems measurement can actively modify and steer quantum states, acting as a quantum chisel to sculpt new patterns of entanglement. I will describe how this power of measurements can be leveraged to efficiently create the long sought after non-Abelian topological phases. Surprisingly, the particular non-Abelian states created in this way are closely related to Galois' characterization of solvable polynomial equations.
Finally, I will describe our recent collaboration with Quantinuum that utilizes this approach. In particular, I will discuss the Borromean braiding of excitations, a signature unique to non Abelian topological order, and its measurement on the Quantinuum platform.

Two dimensional di-chalcogenide materials with Ising spin orbit coupling often show enhanced charge density wave transition temperature and signatures of unconventional superconductivity unlike their three dimensional bulk counterparts. Some of these experiments in monolayer NbSe2 include enhancement of superconducting transition temperature with increasing disorder concentration, observation of two fold symmetric gap in the presence of in plane magnetic field, and observation of Leggett modes in tunnelling experiments.
In this talk, we will first present our calculation of 3Q CDW ordering and role of disorder in normal state of monolayer NbSe2. We will then present our results for the superconducting state assuming a spin fluctuation mediated pairing scenario and explore the dominant gap functions within this theory. Finally, we will discuss the effects of an in-plane Zeeman field on the homogenous superconducting state.
Indian Institute Of Technology Ma

Pseudo entropy is an interesting quantity with a simple gravity dual, which generalizes entanglement entropy such that it depends on both an initial and a final state. In this talk we start with an introduction of this new quantity explaining its basic properties and its holographic calculations. Next, we will present recent numerical results of this quantity in a free scalar field theory and in a spin system, which imply that pseudo entropy can serve as a new quantum order parameter. Finally, we will discuss an application of pseudo entropy to holography in de Sitter spaces and to entanglement phase transitions.

Quantum properties, like superposition, entanglement, and fractionalization, enable fascinating functionalities for quantum technologies. However, it remains unclear whether these properties are exclusive to quantum concepts or can be generalized to the classical vector space. This talk addresses this question. We introduce a generic symmetry group construction built from a vector field in a plaquette of classical spins, demonstrating how classical spins superpose in the irreducible representations (irreps). The corresponding probability amplitudes serve as order parameters and local spins as fragmented excitations. Moreover, the formalism offers a many-body vector field representation for diverse ground states, encompassing spin liquids and fragmented phases described as degenerate ensembles of irreps. Finally, we apply the theory in a square Kagome lattice, showing how the spin liquid state is unstable to either vortex orderings or fragmented phases with any finite Dzyaloshinskii-Mor...

The phase diagram of the kagome metal family AV3Sb5 (A = K, Rb, Cs) features both super- conductivity and charge density wave (CDW) instabilities, which have generated tremendous attention. We've studied the temperature evolution and demise of the CDW state using low resolution X-ray diffraction x-ray scattering study of CsV3Sb5 over a broad range of temperatures from 300 K to ∼ 2 K, below the onset of its super-conductivity at Tc ∼ 2.9 K. Such measurements are optimized for diffuse X-ray scattering. Order parameter measurements of the 2 × 2 × 2 CDW structure show an unusual and extended linear temperature dependence onsetting at T ∗ ∼ 160 K, much higher than the susceptibility anomaly associated with CDW order at TCDW = 94 K. This implies strong CDW fluctuations exist to ∼ 1.7 × TCDW. The CDW order parameter is also observed to be constant from T = 16 K to 2 K, implying that the CDW and superconducting order co-exist below Tc, and, at ambient pressure, any possible competition between...

AdS/CFT correspondence has played crucial roles to understand difficult problems in quantum gravity in terms of quantum field theories.  When a conformal field theory (CFT) is defined on a manifold with boundaries, we can generalize the standard AdS/CFT by introducing so called end-of-the-world branes. This extended holographic duality, called AdS/BCFT, captures, for examples, the essential feature of quantum gravity such as the black hole information problem. In this lecture, I would like to explain how this holographic duality works and discuss recent developments.