SungBin Lee

We consider possible exotic ground states of quantum spin ice as realized in rare earth pyrochlores. Prior work [Savary and Balents, Phys. Rev. Lett. 108, 037202 (2012).] introduced a gauge mean-field theory (gMFT) to treat spin or pseudospin Hamiltonians for such systems, reformulated as a problem of bosonic spinons coupled to a $U(1)$ gauge field. We extend gMFT to treat the most general nearest-neighbor exchange Hamiltonian, which contains a further exchange interaction. This term leads to in

Guided by experiment and band structure, we introduce and study a phenomenological Landau theory for the unusual charge and spin ordering associated with the Mott transition in the perovskite nickelates, with chemical formula RNiO3, where R=Pr, Nd,Sm, Eu, Ho, Y, and Lu. While the Landau theory has general applicability, we show that for the most conducting materials, R=Pr, Nd, both types of order can be understood in terms of a nearly nested spin-density wave. Furthermore, we argue that in this

Motivated by recent Fermi-surface and transport measurements on LaNiO${}_{3}$, we study the Mott metal-insulator transitions of perovskite nickelates, with the chemical formula $R$NiO${}_{3}$, where $R$is a rare-earth ion. We introduce and study a minimal two-band model, which takes into account only the e${}_{g}$ bands. In the weak to intermediate correlation limit, a Hartree-Fock analysis predicts charge and spin order consistent with experiments on $R=\text{Pr}$, Nd, driven by Fermi surface n

Motivated by experiments on Pr2Ir2O7, we consider metallic pyrochlore systems A2B2O7, where the A sites are occupied by rare-earth local moments and the B sites host 5d transition metal ions with itinerant strongly spin-orbit coupled electrons. Assuming non-Kramers doublets on the A site, we derive the RKKY interaction between them mediated by the B-site itinerant electrons and find extended non-Heisenberg interactions. Analyzing a simplified model of the RKKY interaction, we uncover a local mom

A series of $\mathrm{Pr}{(\mathrm{TM})}_{2}{\mathrm{X}}_{20}$ (with TM = Ti, V, Rh, Ir and X = Al, Zn) Kondo materials, containing non-Kramers ${\mathrm{Pr}}^{3+}\phantom{\rule{4pt}{0ex}}4{f}^{2}$ moments on a diamond lattice, have been shown to exhibit intertwined orders such as quadrupolar order and superconductivity. Motivated by these experiments, we propose and study a Landau theory of multipolar order to capture the phase diagram and its field dependence. In zero magnetic field, we show th

We study the finite-temperature phase diagram of the Heisenberg-Kitaev model on a three-dimensional hyperhoneycomb lattice. Using semiclassical analysis and classical Monte Carlo simulations, we investigate quantum and thermal order-by-disorder, as well as the magnetic-ordering temperature. We find the parameter regime where quantum and thermal fluctuations favor different magnetic orders, which leads to an additional finite-temperature phase transition within the ordered phase. This transition,

Helical nanofilaments (HNFs) have attracted much interest because of their unique optical properties, but there have been many hurdles to overcome in using them for the practical applications due to their structural complexity. Here we demonstrate that the molecular configuration and layer conformation of a modulated HNF (HNFs(mod)) can be studied using a physicochemical confinement system. The layer directions affected by the chemical affinity between the mesogen and surface were drastically co

We investigate possible quantum ground states as well as the classical limit of a frustrated ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ Heisenberg model on the three-dimensional (3D) hyperhoneycomb lattice. Our study is inspired by the recent discovery of $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$, where ${\mathrm{Ir}}^{4+}$ ions form a 3D network with each lattice site being connected to three nearest neighbors. We focus on the influence of magnetic frustration caus

Recent experiments point to a variety of intermetallic systems which exhibit exotic quadrupolar orders driven by the Kondo coupling between conduction electrons and localized quadrupolar degrees of freedom. Using a Luttinger $k\ifmmode\cdot\else\textperiodcentered\fi{}p$ Hamiltonian for the conduction electrons, we study the impact of such quadrupolar order on their energies and wave functions. We discover that such quadrupolar orders can induce a nontrivial Berry curvature for the conduction el

We study the fractionalization of space group symmetries in two-dimensional topologically ordered phases. Specifically, we focus on ${Z}_{2}$-fractionalized phases in two dimensions whose deconfined topological excitations transform trivially under translational symmetries but projectively under glide reflections, whose quantum numbers are hence fractionalized. We accomplish this by generalizing the dichotomy between even and odd gauge theories to incorporate additional symmetries inherent to no

Abstract Multipolar physics and their hidden orders have been widely discussed in the context of heavy fermions and frustrated magnets. However, despite extensive research, there are few examples of purely multipolar systems in the absence of magnetic dipoles. Here, we show the magnetic behavior of an icosahedral quasicrystal is generally described by multipoles, and in a specific case by pure magnetic octupoles, resulting from the interplay of spin-orbit coupling and crystal field splitting. Im