## Condensed Matter / Biophysics Seminars – Andriy Nevidomskyy (Rice)

Quantum Melting of Spin `Solids’ in 2D

For several decades, the attention of both theoretical and experimental physicists has focused on finding examples of quantum spin liquids (QSL) Â— exotic phases of matter characterized by the spin fractionalization, whereby the energy and momentum are carried not by spin waves, but by the emergent elementary excitations. By contrast, defining a quantum spin `solid’ as a state that spontaneously breaks the lattice translation symmetry (be it via NÃ© order or by forming a valence bond crystal), I will pose the following question Â— how do quantum solids `melt’ and how does entanglement establish itself in a QSL? To answer this question, I will present our recent work on several 2D systems, from the familiar spin-1/2 on a frustrated square lattice, to the perhaps less familiar models of spin-1 and SU(3) objects. We study these models using the density matrix renormalization group (DMRG) and infinite projected entangled-pair states (iPEPS) techniques, supplemented by the analytical mean-field and linear flavor wave theory calculations. In the last part of the talk, I will discuss another mechanism of quantum `melting,’ induced by a strong magnetic field Â— the conventional picture is that this process can be understood as a BoseÂ—Einstein condensation of the auxiliary bosons. Here we show that a more exotic, non-BEC transition occurs when magnetic frustration drives the system across the Lifshitz point, and we find an exotic bosonic liquid that avoids the BEC altogether Â— so-called Bose metal Â— with algebraic correlations.