arXiv subjects

Gautam K. Naik

Publications and source records attributed to Gautam K. Naik.

4 recordsLinked to original sources

arXiv2026

Defect Poisoning of Quantum Spin Ice

The hunt for a material realization of quantum spin ice has motivated more than two decades of experimental effort. The candidate materials inevitably contain crystal imperfections, such as magnetic vacancies, whose effects are often disregarded. Here, we show that experimentally relevant levels of dilution can qualitatively reshape the low-energy behavior, as nearby vacancies generate quantum fluctuations that are absent in the clean system. Already at dilution levels as low as two percent, well below those reported in cerium-based pyrochlores, these vacancy-induced processes connect percolating clusters of spins and dominate over the conventional quantum-spin-ice dynamics. We therefore argue that magnetic vacancies in current experiments can strongly contaminate, and potentially completely obscure, the sought-after signatures of quantum spin ice. We support these conclusions using large-scale, unbiased quantum Monte Carlo simulations and exact diagonalization.

cond-mat.str-el↗

arXiv2026

Hearing the light: stray-field noise from the emergent photon in quantum spin ice

Decisive experimental confirmation of the $U(1)$ quantum spin liquid phase in quantum spin ice remains an outstanding challenge. In this work, we propose stray-field magnetometry as a direct probe of the emergent photons -- the gapless excitation of the emergent electrodynamics in quantum spin ice. The emergent photons are transverse magnetization waves, which, in a finite sample, form discrete modes governed by one of two sets of natural boundary conditions: ``insulating'' or ``superconducting''. Considering cavity and thin film geometries, we find that the spectrum and spatial structure of the stray magnetic noise provide a sharp qualitative signature of the underlying electrodynamics. The predicted stray-field noise power lies comfortably within the detection range of present-day solid-state defect magnetometry.

cond-mat.str-el↗

arXiv2025

Theta electromagnetism in quantum spin ice: Microscopic analysis of improper symmetries

$U(1)$ gauge theories, including conventional Maxwell electromagnetism, allow $θ$-terms when parity and time-reversal symmetry are broken. In condensed matter systems, the physics of $θ$ as a magnetoelectric response has been explored extensively within the context of topological insulators and multiferroics. We show how $θ$-terms can arise in the internal dynamics of the emergent electromagnetism in a $U(1)$ quantum spin liquid. In its Coulomb phase, the minimal model of pyrochlore quantum spin ice is governed by a six-spin ring exchange Hamiltonian. We identify the next-order contribution to the microscopic Hamiltonian when parity, time-reversal, and all improper spatial symmetries are broken -- a seven-spin term which leads to a two-parameter lattice gauge theory with a $θ$-electromagnetic phase. We derive how the seven-spin term is generated perturbatively within each of the three symmetry classes of short-range pyrochlore spin ice. Within a complete microscopic symmetry analysis, we find that the most general nearest-neighbor Hamiltonians fail to generate the seven-spin term, and one must include next-nearest-neighbor interactions to obtain an emergent $θ$. Using gauge mean-field theory we compute additional contributions to the $θ$-term from the spinon sector. Finally, we determine the conditions required for an internal $θ$-term to generate a significant external magnetoelectic response.

cond-mat.str-el↗

arXiv2024

Synthetic magnetoelectric response of lattice bosonic insulators

In the absence of parity and time-reversal symmetries, insulators can exhibit magnetoelectric responses, in which applied magnetic fields induce charge polarization and, conversely, applied electric fields induce magnetization. While there is a long history of the study of magnetoelectric response in fermionic insulators, the same for bosonic insulators has been limited. We consider the magnetoelectric response in lattice insulators built out of charged bosonic degrees of freedom and derive a bulk formula for the corresponding linear response tensor. The resulting formulae feature several contributions including a Chern-Simons integral over the bands of the bosonic excitations. We construct several minimal microscopic models that illustrate the ingredients required to obtain a sizable bosonic magnetoelectric response. Our formalism can be applied to bosonic Mott insulators subject to synthetic gauge fields and/or tilted potentials as well as to the spinon sector in the Coulomb phase of a $U(1)$ quantum spin liquid.

cond-mat.str-el↗