arXiv subjects

Jae Whan Park

Publications and source records attributed to Jae Whan Park.

13 recordsLinked to original sources

arXiv2024

Emergent Quantum Phenomena of Noncentrosymmetric Charge-Density Wave in 1T-Transition Metal Dichalcogenides

1T-transition metal dichalcogenides (TMD) have been an exciting platform for exploring the intertwinement of charge density waves and strong correlation phenomena. While the David star structure has been conventionally considered as the underlying charge order in the literature, recent scanning tunneling probe experiments on several monolayer 1T-TMD materials have motivated a new, alternative structure, namely the anion-centered David star structure. In this Letter, we show that this novel anion-centered David star structure manifestly breaks inversion symmetry, resulting in flat bands with pronounced Rashba spin-orbit couplings. These distinctive features unlock novel possibilities and functionalities for 1T-TMDs, including the giant spin Hall effect, the emergence of Chern bands, and spin liquid that spontaneously breaks crystalline rotational symmetry. Our findings establish promising avenues for exploring emerging quantum phenomena of monolayer 1T-TMDs with this novel noncentrosymmetric structure.

cond-mat.str-el↗

arXiv2023

Kinkless electronic junction along one dimensional electronic channel

Here we report the formation of type-A and type-B electronic junctions without any structural discontinuity along a well-defined 1-nm-wide one-dimensional electronic channel within a van der Waals layer. We employ scanning tunneling microscopy and spectroscopy techniques to investigate the atomic and electronic structure along peculiar domain walls formed on the charge-density-wave phase of 1T-TaS2. We find distinct kinds of abrupt electronic junctions with discontinuities of the band gap along the domain walls, which do not have any structural kinks and defects. Our density-functional calculations reveal a novel mechanism of the electronic junction formation; they are formed by a kinked domain wall in the layer underneath through substantial electronic interlayer coupling. This work demonstrates that the interlayer electronic coupling can be an effective control knob over several-nanometer-scale electronic property of two-dimensional atomic monolayers.

cond-mat.str-el↗

arXiv2023

Topological soliton molecule in quasi 1D charge density wave

Soliton molecules, bound states of two solitons, can be important for the informatics using solitons and the quest for exotic particles in a wide range of physical systems from unconventional superconductors to nuclear matter and Higgs field, but have been observed only in temporal dimension for classical wave optical systems. Here, we identify a topological soliton molecule formed spatially in an electronic system, a quasi 1D charge density wave of indium atomic wires. This system is composed of two coupled Peierls chains, which are endowed with a Z$_4$ topology and three distinct, right-chiral, left-chiral, and non-chiral, solitons. Our scanning tunneling microscopy measurements identify a bound state of right- and left-chiral solitons with distinct in-gap states and net zero phase shift. Our density functional theory calculations reveal the attractive interaction of these solitons and the hybridization of their electronic states. This result initiates the study of the interaction between solitons in electronic systems, which can provide novel manybody electronic states and extra data-handling capacity beyond the given soliton topology.

cond-mat.mtrl-sci↗

arXiv2023

Mobile Kink Solitons in a Van der Waals Charge-Density-Wave Layer

Kinks, point-like geometrical defects along dislocations, domain walls, and DNA, are stable and mobile, as solutions of a sine-Gordon wave equation. While they are widely investigated for crystal deformations and domain wall motions, electronic properties of individual kinks have received little attention. In this work, electronically and topologically distinct kinks are discovered along electronic domain walls in a correlated van der Waals insulator of 1$T$-TaS$_2$. Mobile kinks and antikinks are identified as trapped by pinning defects and imaged in scanning tunneling microscopy. Their atomic structures and in-gap electronic states are unveiled, which are mapped approximately into Su-Schrieffer-Heeger solitons. The twelve-fold degeneracy of the domain walls in the present system guarantees an extraordinarily large number of distinct kinks and antikinks to emerge. Such large degeneracy together with the robust geometrical nature may be useful for handling multilevel information in van der Waals materials architectures.

cond-mat.mtrl-sci↗

arXiv2022

Z3 Charge Density Wave of Silicon Atomic Chains on a Vicinal Silicon Surface

An ideal one-dimensional electronic system is formed along atomic chains on Au-decorated vicinal silicon surfaces but the nature of its low temperature phases has been puzzled for last two decades. Here, we unambiguously identify the low temperature structural distortion of this surface using high resolution atomic force microscopy and scanning tunneling microscopy. The most important structural ingredient of this surface, the step-edge Si chains are found to be strongly buckled, every third atoms down, forming trimer unitcells. This observation is consistent with the recent model of rehybridized dangling bonds and rules out the antiferromagnetic spin ordering proposed earlier. The spectroscopy and electronic structure calculation indicate a charge density wave insulator with a Z3 topology making it possible to exploit topological phases and excitations. Tunneling current was found to substantially lower the energy barrier between three degenerate CDW states, which induces a dynamically fluctuating CDW at very low temperature.

cond-mat.mtrl-sci↗

arXiv2021

Creation and annihilation of mobile fractional solitons in atomic chains

Localized modes in one dimensional topological systems, such as Majonara modes in topological superconductors, are promising platforms for robust information processing. In one dimensional topological insulators, mobile topological solitons are expected but have not been fully realized yet. We discover fractionalized phase defects moving along trimer silicon atomic chains formed along step edges of a vicinal silicon surface. Tunneling microscopy identifies local defects with phase shifts of 2π/3 and 4π/3 with their electronic states within the band gap and with their motions activated above 100 K. Theoretical calculations reveal the topological soliton origin of the phase defects with fractional charges of {\pm}2e/3 and {\pm}4e/3. An individual soliton can be created and annihilated at a desired location by current pulse from the probe tip. Mobile and manipulatable topological solitons discovered here provide a new platform of robustly-protected informatics with extraordinary functionalities.

cond-mat.mtrl-sci↗

arXiv2020

Atomic structures and electronic correlation of monolayer 1T-TaSe2

We investigate atomic and electronic structures of monolayer 1T-TaSe2 using density functional theory calculations. Monolayers of 1T-TaSe2 were recently grown on graphene substrates and suggested as an intriguing Mott insulator [Nat. Phys. 16, 218 (2020)]. However, the prevailing structural model for the model system of 1T-TaS2, the cation-centered cluster of a David-star shape with strong electron correlation, could not explain the characteristic and unusual orbital splitting observed in scanning tunneling spectroscopy experiments. We suggest an alternative structure model, an anion-centered cluster structure, which can reproduce most of the unusual spectroscopic characteristics with electron doping from the substrate without electron correlation. The unusual spectroscopic features observed, thus, seems to indicate a simple and usual band insulating state. This work indicates the importance of a large structural degree of freedom given for a cluster Mott insulator.

cond-mat.mtrl-sci↗

arXiv2020

Stable Flatbands, Topology, and Superconductivity of Magic Honeycomb Networks

We propose a new principle to realize flatbands which are robust in real materials, based on a network superstructure of one-dimensional segments. This mechanism is naturally realized in the nearly commensurate charge-density wave of 1T-TaS${}_2$ with the honeycomb network of conducting domain walls, and the resulting flatband can naturally explain the enhanced superconductivity. We also show that corner states, which are a hallmark of the higher-order topological insulators, appear in the network superstructure.

cond-mat.str-el↗

arXiv2020

Artificial Relativistic Molecules

We fabricate artificial molecules composed of heavy atom lead on a van der Waals crystal. Pb atoms templated on a honeycomb charge-order superstructure of IrTe2 form clusters ranging from dimers to heptamers including benzene-shaped ring hexamers. Tunneling spectroscopy and electronic structure calculations reveal the formation of unusual relativistic molecular orbitals within the clusters. The spin-orbit coupling is essential both in forming such Dirac electronic states and stabilizing the artificial molecules by reducing the adatom-substrate interaction. Lead atoms are found to be ideally suited for a maximized relativistic effect. This work initiates the use of novel two dimensional orderings to guide the fabrication of artificial molecules of unprecedented properties.

cond-mat.mtrl-sci↗

arXiv2019

Emergent Honeycomb Network of Topological Excitations in Correlated Charge Density Wave

When two periodic potentials compete in materials, one may adopt the other, which straightforwardly generates topological defects. Of particular interest are domain walls in charge-, dipole-, and spin-ordered systems, which govern macroscopic properties and important functionality. However, detailed atomic and electronic structures of domain walls have often been uncertain and the microscopic mechanism of their functionality has been elusive. Here, we clarify the complete atomic and electronic structures of the domain wall network, a honeycomb network connected by Z$_{3}$ vortices, in the nearly commensurate Mott charge-density wave (CDW) phase of 1T-TaS$_{2}$. Scanning tunneling microscopy resolves characteristic charge orders within domain walls and their vortices. Density functional theory calculations disclose their unique atomic relaxations and the metallic in-gap states confined tightly therein. A generic theory is constructed, which connects this emergent honeycomb network of conducting electrons to the enhanced superconductivity.

cond-mat.str-el↗

arXiv2019

Pseudogap and weak multifractality in disordered Mott charge-density-wave insulator

The competition, coexistence and cooperation of various orders in low-dimensional materials like spin, charge, topological orders and charge-density-wave has been one of the most intriguing issues in condensed matter physics. In particular, layered transition metal dichalcogenides provide an ideal platform for studying such an interplay with a notable case of 1${T}$-TaS$_{2}$ featuring Mott-insulating ground state, charge-density-wave, spin frustration and emerging superconductivity together. We investigated local electronic states of Se-substituted 1${T}$-TaS$_{2}$ by scanning tunneling microscopy/spectroscopy (STM/STS), where superconductivity emerges from the unique Mott-CDW state. Spatially resolved STS measurements reveal that an apparent V-shape pseudogap forms at the Fermi Level (E$_{F}$), with the origin of the electronic states splitting and transformation from the Mott states, and the CDW gaps are largely preserved. The formation of the pseudogap has little correlation to the variation of local Se concentration, but appears to be a global characteristics. Furthermore, the correlation length of local density of states (LDOS) diverges at the Fermi energy and decays rapidly at high energies. The spatial correlation shows a power-law decay close to the Fermi energy. Our statistics analysis of the LDOS indicates that our system exhibits weak multifractal behavior of the wave functions. These findings strongly support a correlated metallic state induced by disorder in our system, which provides an new insight into the novel mechanism of emerging superconductivity in the two-dimensional correlated electronic systems.

cond-mat.str-el↗

arXiv2016

Metallic Indium Monolayers on Si(111)

Density-functional calculations are used to identify one-atom-thick metallic In overlayers on the Si(111) surface, which have long been sought in quest of the ultimate two-dimensional (2D) limit of free-electron-like metallic properties. We predict two metastable single-layer In phases, one $\sqrt{7}\times\sqrt{3}$ phase with a coverage of 1.4 monolayer (ML; here 1 ML refers to one In atom per top Si atom) and the other $\sqrt{7}\times\sqrt{7}$ phase with 1.43 ML, which indeed match well with experimental evidences. Both phases reveal quasi-1D arrangements of protruded In atoms, leading to 2D-metallic but anisotropic band structures and Fermi surfaces. This directional feature contrasts with the free-electron-like In-overlayer properties that are known to persist up to the double-layer thickness, implying that we may have achieved the 2D limit of free-electron-like In overlayers in previous studies of double-layer In phases.

cond-mat.mtrl-sci↗

arXiv2015

Hexagonal Indium Double Layer on Si(111)-($\sqrt{7}\times\sqrt{3})$

Density-functional calculations are used to verify the atomic structure of the hexagonal In/Si(111)-($\sqrt{7}\times\sqrt{3}$) surface, which has been considered to represent an ultimate two-dimensional (2D) limit of metallic In overlayers. Contrary to the prevailing assumption, this surface consists of not a single layer but a double layer of In atoms, which corresponds to a hexagonal deformation of the well-established $rectangular$ In double layer formed on Si(111)-($\sqrt{7}\times\sqrt{3}$) [Park $et$ $al$., Phys. Rev. Lett. 109, 166102 (2012)]. The same double-layer thickness accounts well for the typical coexistence of the hexagonal and rectangular phases and their similar 2D electronic structures. It is thus conclusive that, regardless of rectangular or hexagonal, the In/Si(111)-($\sqrt{7}\times\sqrt{3}$) surface does not represent an one-atom-thick In overlayer.

cond-mat.mtrl-sci↗