Kyungmin Lee

Kyungmin Lee
The National High Magnetic Field Laboratory (National MagLab) · DC Field Facility

Doctor of Philosophy

About

30
Publications
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440
Citations

Publications

Publications (30)
Article
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...
Preprint
Full-text available
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...
Article
Full-text available
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...
Article
Full-text available
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...
Preprint
Full-text available
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...
Article
Full-text available
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...
Preprint
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...
Article
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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...
Article
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...
Preprint
Full-text available
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...
Preprint
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...
Preprint
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...
Article
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...
Article
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...
Article
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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...
Preprint
Full-text available
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...
Preprint
Full-text available
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...
Preprint
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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...
Article
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...
Article
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...
Article
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...
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Full-text available
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...
Article
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...
Article
Full-text available
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...
Article
Full-text available
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...
Article
Full-text available
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...
Article
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...
Article
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...
Article
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...
Article
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...

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