# Kyungmin LeeThe National High Magnetic Field Laboratory (National MagLab) · DC Field Facility

Kyungmin Lee

Doctor of Philosophy

## About

30

Publications

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440

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## Publications

Publications (30)

Moiré systems offer an exciting playground to study the many-body effects of strongly correlated electrons in regimes that are not easily accessible in conventional material settings. Motivated by a recent experiment on WSe2/WS2 moiré bilayers [Y. Tang et al., Nature (London) 579, 353 (2020)], which realized a triangular superlattice with a small h...

Moire systems offer an exciting playground to study many-body effects of strongly correlated electrons in regimes that are not easily accessible in conventional material settings. Motivated by a recent experiment on $\text{WSe}_2/\text{WS}_2$ moire bilayers [Y. Tang et al., Nature 579, 353-358 (2020)], which realizes a triangular superlattice with...

Quasiparticles are physically motivated mathematical constructs for simplifying the seemingly complicated many-body description of solids. A complete understanding of their dynamics and the nature of the effective interactions between them provides rich information on real material properties at the microscopic level. In this paper, we explore the...

Metal-to-insulator transitions (MIT) can be driven by a number of different mechanisms, each resulting in a different type of insulator—Change in chemical potential can induce a transition from a metal to a band insulator; strong correlations can drive a metal into a Mott insulator with an energy gap; an Anderson transition, on the other hand, due...

Quasiparticles are physically motivated mathematical constructs for simplifying the seemingly complicated many-body description of solids. A complete understanding of their dynamics and the nature of the effective interactions between them provides rich information on real material properties at the microscopic level. In this work, we explore the d...

Although most quantum systems thermalize locally on short timescales independent of initial conditions, recent developments have shown this is not always the case. Lattice geometry and quantum mechanics can conspire to produce constrained quantum dynamics and associated glassy behavior, a phenomenon that falls outside the rubric of the eigenstate t...

Frustration in interacting systems can constrain dynamics which in turn gives rise to glassy behavior. Although interacting quantum systems tend to thermalize locally on short time scales independent of initial conditions, recent developments have shown that this can be avoided for a large class of disordered and clean systems where the system eith...

Nonequilibrium properties of quantum materials present many intriguing properties, among them athermal behavior, which violates the eigenstate thermalization hypothesis. Such behavior has primarily been observed in disordered systems. More recently, experimental and theoretical evidence for athermal eigenstates, known as “quantum scars,” has emerge...

We elucidate the mechanism by which a Mott insulator transforms into a non-Fermi liquid metal upon increasing disorder at half filling. By correlating maps of the local density of states, the local magnetization, and the local bond conductivity, we find a collapse of the Mott gap toward a V-shaped pseudogapped density of states that occurs concomit...

Non-equilibrium properties of quantum materials present many intriguing properties, among them athermal behavior, which violates the eigenstate thermalization hypothesis. Such behavior has primarily been observed in disordered systems. More recently, experimental and theoretical evidence for athermal eigenstates, known as "quantum scars" has emerge...

Metal-to-insulator transitions (MIT) can be driven by a number of different mechanisms, each resulting in a different type of insulator. Change in chemical potential can induce a transition from a metal to a band insulator; strong correlations can drive a metal into a Mott insulator with an energy gap; an Anderson transition, on the other hand, due...

We elucidate the mechanism by which a Mott insulator transforms into a non-Fermi liquid metal upon increasing disorder at half filling. By correlating maps of the local density of states, the local magnetization and the local bond conductivity, we find a collapse of the Mott gap toward a V-shape pseudogapped density of states that occurs concomitan...

We have investigated many-body renormalizations of the single-particle excitations in 1T−TiSe2 by employing high resolution angle-resolved photoemission spectroscopy (ARPES) measurements. The energy distribution curves (EDCs) of the ARPES data reveal an intrinsic single band peak-dip-hump (PDH) feature. Furthermore, the renormalized electronic disp...

We predict two topological superconducting phases in microscopic models arising from the Berry phase associated with the valley degree of freedom in gapped Dirac honeycomb systems. The first one is a topological helical spin-triplet superconductor with a nonzero center-of-mass momentum that does not break time-reversal symmetry. We also find a topo...

Sharp magnetization switching and large magnetoresistance (MR) were previously discovered in single crystals of 2H-FexTaS2 and attributed to the Fe superstructure and its defects. We report similar sharp switching and large MR in 1T-FexTiS2 (0.086≤x≤0.703) while providing a side-by-side comparison of the only two such ferromagnetic transition-metal...

Sharp magnetization switching and large magnetoresistance were previously discovered in single crystals of 2H-Fe$_x$TaS$_2$ and attributed to the Fe superstructure and its defects. We report similar sharp switching in 1T-Fe$_x$TiS$_2$ ($0.086\;{\leq}\;x\;{\leq}0.703$) and the discovery of large magnetoresistance. The switching field $H_s$ and magne...

We have employed high resolution angle resolved photoemission spectroscopy (ARPES) measurements to investigate many-body renormalizations of the single-particle excitations in $1T$-TiSe$_2$. The energy distribution curves of the ARPES data reveal intrinsic peak-dip-hump feature, while the electronic dispersion derived from the momentum distribution...

We examine superconducting states of gapped Dirac honeycomb systems and outline a novel route to topological superconductivity. We consider the Kane-Mele model and explore the effect of three different interactions - on-site attraction $U$, nearest-neighbor density-density attraction $V$ and nearest-neighbor antiferromagnetic exchange $J$ - within...

Nematicity in quantum Hall systems has been experimentally well established at excited Landau levels. The mechanism of the symmetry breaking, however, is still unknown. Pomeranchuk instability of Fermi liquid parameter $F_{\ell} \le -1$ in the angular momentum $\ell=2$ channel has been argued to be the relevant mechanism, yet there are no definitiv...

One dimensional hybrid systems play an important role in the search for topological superconductivity. Nevertheless, all one dimensional hybrid systems so far have been externally defined. Here we show that one-dimensional domain wall in a nematic superconductor can serve as an emergent hybrid system in the presence of spin-orbit coupling. As a con...

There is now copious direct experimental evidence of various forms of (short-range) charge order in underdoped cuprate high temperature superconductors, and spectroscopic signatures of a nodal-antinodal dichotomy in the structure of the single-particle spectral functions. In this context, we analyze the Bogoliubov quasiparticle spectrum in a superc...

Recent theoretical insights into the possibility of non-Abelian phases in
$\nu=2/3$ fractional quantum Hall (FQH) states revived the interest in the
numerical phase diagram of the problem. In this letter, we investigate the
effect of various kinds of two-body interlayer couplings on the $(330)$ bilayer
state and exactly solve the Hamiltonian for up...

Cooper pairing in the iron-based high-T-c superconductors(1-3) is often conjectured to involve bosonic fluctuations. Among the candidates are antiferromagnetic spin fluctuations(1,4,5) and d-orbital fluctuations amplified by phonons(6,7). Any such electron-boson interaction should alter the electron's 'self-energy', and then become detectable throu...

Cooper pairing in the iron-based high-Tc superconductors is often conjectured
to involve bosonic fluctuations. Among the candidates are antiferromagnetic
spin-fluctuations and d-orbital fluctuations amplified by phonons. Any such
electron-boson interaction should alter the electron's `self-energy', and then
become detectable through consequent modi...

Much interest in the superconducting proximity effect in 3D topological
insulators (TIs) has been driven by the potential to induce exotic pairing
states at the interface. Most candidate materials for 3D TI, however, are bulk
metals, with bulk states at the Fermi level coexisting with well-defined
surface states exhibiting spin-momentum locking. In...

A major question in Fe-based superconductors remains the structure of the
pairing, in particular whether it is of unconventional nature. The electronic
structure near vortices can serve as a platform for phase-sensitive
measurements to answer this question. By solving Bogoliubov-de Gennes equations
for LiFeAs, we calculate the energy-dependent loca...

Tunneling spectroscopy on strong coupling superconductors has been one
of the key experiments confirming the phonon-mediated mechanism of
superconductivity. In the last two decades it has become possible using
STM to access this information in real space with atomic resolution. One
of the most important aspects of these developments is the ability...

The role of bosonic modes has been of great interest in the research of
Fe-pnictides. We aim at identifying fingerprints of specific bosonic
modes in the spectral properties of the multi-orbital superconductor
LiFeAs. For this, we contrast the lowest order contributions to the self
energy of Bogoliubov quasiparticles from two bosonic modes:
antifer...

A major question in Fe-based superconductors is whether the pairing is
of an unconventional nature with a sign change. The electronic structure
in the presence of vortices can serve as a platform for phase sensitive
measurements to answer this question. However as Fe-based
superconductors are in the intermediate regime of correlation strength,
a de...

The recent discovery of intra-unit-cell nematicity in STM studies of cuprate superconductors [1] underscores the importance of the role played by oxygen orbitals in CuO2 plane. Motivated by this observation we study 3-band Hubbard model using exact diagonalization. In particular, we investigate the effects various interaction parameters (Ud, Up, Vp...