arXiv subjects

Eunseok Oh

Publications and source records attributed to Eunseok Oh.

8 recordsLinked to original sources

arXiv2023

Realizing a Superconducting Square-Lattice Bismuth Monolayer

Interplay of crystal symmetry, strong spin$-$orbit coupling (SOC), and many-body interactions in low dimensional materials provides a fertile ground for the discovery of unconventional electronic and magnetic properties and versatile functionalities. Two-dimensional (2D) allotropes of group 15 elements are appealing due to their structures and controllability over symmetries and topology under strong SOC. Here, we report the heteroepitaxial growth of a proximity-induced superconducting 2D square-lattice bismuth monolayer on superconducting Pb films. The square lattice of monolayer bismuth films in a $C_4$ symmetry together with a stripey moiré structure is clearly resolved by our scanning tunneling microscopy and its atomic structure is revealed by density functional theory (DFT) calculations. A Rashba-type spin-split Dirac band is predicted by DFT calculations to exist at the Fermi level and becomes superconducting through the proximity effect from the Pb substrate. We suggest the possibility of a topological superconducting state in this system with magnetic dopants/field. This work introduces an intriguing material platform with 2D Dirac bands, strong SOC, topological superconductivity, and the moiré superstructure.

cond-mat.mtrl-sci↗

arXiv2021

The emergence of Strange metal and Topological Liquid near Quantum Critical Point in a solvable model

We discuss quantum phase transition by an exactly solvable model in the dual gravity setup. By considering the effect of the scalar condensation on the fermion spectrum near the quantum critical point(QCP), we find that there is a topologically protected fermion zero mode associated with the metal to insulator transition. We also show that the strange metal phase with T-linear resistivity emerges at high enough temperature as far as the gravity has a horizon. The phase boundaries are calculated according to the density of states, giving insights on structures of the phase diagram near the QCP.

hep-th↗

arXiv2020

Ginzberg-Landau-Wilson theory for Flat band, Fermi-arc and surface states of strongly correlated systems

We consider a holographic theory as a Ginzberg-Landau theory working for strongly interacting system near the quantum critical point: we take the bulk matter field $Φ^I(r,x)$, the dual of the fermion bilinear, as the order parameter. We calculate and classify the fermion spectral functions in the presence of such orders. Depending on the symmetry, we found spectral features like the gap, pseudo-gap, flat disk bands and the Fermi-arc connecting the two Dirac cones, which are familiar in Dirac material and Kondo lattice. Many of above features are associated with the zero modes whose presence is tied with a discrete symmetry of the interaction. The interaction induced zero modes either makes the strongly correlated system fermi-liquid like, or creates a disk-like flat band. Some of the order parameters in the bulk theory do not have an interpretation of symmetry breaking in terms of the boundary space, which opens the possibility of 'an order without symmetry breaking'.

hep-th↗

arXiv2020

Tailoring high-TN interlayer antiferromagnetism in a van der Waals itinerant magnet

Antiferromagnetic (AFM) van der Waals (vdW) materials provide a novel platform for synthetic AFM spintronics, in which the spin-related functionalities are derived from manipulating spin configurations between the layers. Metallic vdW antiferromagnets are expected to have several advantages over the widely-studied insulating counterparts in switching and detecting the spin states through electrical currents but have been much less explored due to the lack of suitable materials. Here, utilizing the extreme sensitivity of the vdW interlayer magnetism to material composition, we report the itinerant antiferromagnetism in Co-doped Fe4GeTe2 with TN ~ 210 K, an order of magnitude increased as compared to other known AFM vdW metals. The resulting spin configurations and orientations are sensitively controlled by doping, magnetic field, temperature, and thickness, which are effectively read out by electrical conduction. These findings manifest strong merits of metallic vdW magnets with tunable interlayer exchange interaction and magnetic anisotropy, suitable for AFM spintronic applications.

cond-mat.mtrl-sci↗

arXiv2018

Topological Landscape of Competing Charge Density Waves in 2H-NbSe2

Despite decades of studies on charge density wave (CDW) of 2H-NbSe2, the origin of its incommensurate CDW ground state has not been understood. We discover that CDW of 2H-NbSe2 is composed of two different, energetically competing, structures. The lateral heterostructures of two CDWs are entangled as topological excitations, which give rise to a CDW phase shift and the incommensuration without a conventional domain wall. A partially melt network of the topological excitations and their vertices explain an unusual landscape of domains. The unconventional topological role of competing phases disclosed here can be widely applied to various incommensuration or phase coexistence phenomena in materials.

cond-mat.mtrl-sci↗

arXiv2018

Entanglement String and Spin Liquid with Holographic Duality

We show that the quantum entanglement can be transmuted to a force using the holographic duality. First, we prove that there is an open string in the spectrum of the holographic fermion coupled with scalar. The string ends at two fermions and its tension vanishes in the limit of zero scalar condensation. We associate such string with a dimer and identify the scalar condensation as the degree of the dimerization. Together with divergently large entanglement entropy, the model is expected to describe the Spin Liquid. As a consistency check, we show that there is a Mott transition as the dimerization proceeds. We suggest that the string may be observed in an ARPES experiment of spin liquid or clean Dirac material as a tower of bands.

hep-th↗

arXiv2018

Complete Einstein equation from the generalized First Law of Entanglement

Recently it was observed that the first law of Entanglement leads to the linearized Einstein equation. In this paper, we point out that the gravity dual of an relative entropy expression is equivalent to the full non-linear Einstein equation. We also construct an entanglement vector field $V_{E}$ whose flux is the entanglement entropy. The flow of the vector field looks like sewing two space regions along the interface.

hep-th↗

arXiv2013

Non-spherical collapse in AdS and Early Thermalization in RHIC

In the flat space, non-spherical shells collapse to give globular cluster after many oscillations. We show that in anti de sitter space, they form black holes in one dynamical time. We propose that this is the mechanism of early thermalization in strong quark-gluon plasma in gravity dual. This is traced back to the a remarkable property of AdS : the period in radial motion is amplitude independent in spite of the NON-linearity of the equation of motion. We investigate the interaction effect numerically and observe the same qualitative behavior for the attractive forces. For repulsive interactions, particles halt at a small but finite radius for long time due to the specific structure of the bulk AdS propagator. It helps hair creation in the AdS black hole.

hep-th↗