Shapiro Steps and Surface Acoustic Waves in Charge Density Wave Dynamics

Yu Funami,Kazushi Aoyama 한국물리학회 2023 새물리 Vol.73 No.12

We theoretically investigate effects of a surface acoustic wave (SAW) on charge-density-wave (CDW) sliding dynamics, focusing on the nature of Shapiro steps appearing in the current-voltage characteristics. By numerically analyzing an extended Fukuyama-Lee-Rice model, we find that the SAW can induce the Shapiro steps via vibrations at pinning sites. When the SAW works as a pinning-position vibration, the step width exhibits a damped oscillation as a function of the vibration amplitude similarly to conventional ac-electiric-field-induced one. Effects of an additional pinning-strength vibration are also discussed.

Emergence of a Metal-Insulator Transition and High-Temperature Charge-Density Waves in VSe₂ at the Monolayer Limit

Duvjir, Ganbat,Choi, Byoung Ki,Jang, Iksu,Ulstrup, Søren,Kang, Soonmin,Thi Ly, Trinh,Kim, Sanghwa,Choi, Young Hwan,Jozwiak, Chris,Bostwick, Aaron,Rotenberg, Eli,Park, Je-Geun,Sankar, Raman,Kim, Ki-Seo American Chemical Society 2018 NANO LETTERS Vol.18 No.9

<P>Emergent phenomena driven by electronic reconstructions in oxide heterostructures have been intensively discussed. However, the role of these phenomena in shaping the electronic properties in van der Waals heterointerfaces has hitherto not been established. By reducing the material thickness and forming a heterointerface, we find two types of charge-ordering transitions in monolayer VSe<SUB>2</SUB> on graphene substrates. Angle-resolved photoemission spectroscopy (ARPES) uncovers that Fermi-surface nesting becomes perfect in ML VSe<SUB>2</SUB>. Renormalization-group analysis confirms that imperfect nesting in three dimensions universally flows into perfect nesting in two dimensions. As a result, the charge-density wave-transition temperature is dramatically enhanced to a value of 350 K compared to the 105 K in bulk VSe<SUB>2</SUB>. More interestingly, ARPES and scanning tunneling microscopy measurements confirm an unexpected metal-insulator transition at 135 K that is driven by lattice distortions. The heterointerface plays an important role in driving this novel metal-insulator transition in the family of monolayer transition-metal dichalcogenides.</P> [FIG OMISSION]</BR>

Soft X-ray Synchrotron Radiation Spectroscopy Study of Rare-Earth Chalcogenide Charge-Density Wave Compounds

이은숙,김현우,송승호,J. D. Denlinger,Y. S. Kwon,J.-S. Kang 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.4

The electronic structures of the layered rare-earth chalcogenide compounds of CeTe2, PrTe2, and PrTe3, which have the charge-density wave (CDW) transition and possibly the chiral transition, have been investigated by employing soft X-ray absorption spectroscopy (XAS) and angle-resolved photoemission spectroscopy (ARPES). R 3d XAS measurements show that the valence states of Ce and Pr ions are nearly trivalent in all the compounds. Similar band dispersions are observed in their measured ARPES data, but with the band positions in PrTe3 being shifted up in energy compared to those in CeTe2 and PrTe2. These findings suggest that their Te 5p band structures are determined mainly by the 2D interactions in the Te(2)/Te(3) sheets, but with a larger number of holes in the Te 5p bands in PrTe3 than in CeTe2 and PrTe2. The measured constant energy maps of CeTe2, PrTe2, and PrTe3 for high binding energies are similar to one another, reflecting the Te 5p band structures of the Te(2)/Te(3) square nets. In contrast, the Fermi surfaces (FSs) of CeTe2 and PrTe3 exhibit extra features, different from the FS of the ideal Te(2)/Te(3) square nets, which arise from the CDW-induced FS reconstruction in the Te(2)/Te(3) sheets.

Persistent Charge-Density-Wave Order in Single-Layer TaSe₂

Ryu, Hyejin,Chen, Yi,Kim, Heejung,Tsai, Hsin-Zon,Tang, Shujie,Jiang, Juan,Liou, Franklin,Kahn, Salman,Jia, Caihong,Omrani, Arash A.,Shim, Ji Hoon,Hussain, Zahid,Shen, Zhi-Xun,Kim, Kyoo,Min, Byung Il,H American Chemical Society 2018 NANO LETTERS Vol.18 No.2

<P>We present the electronic characterization of single-layer 1H-TaSe2 grown by molecular beam epitaxy using a combined angle-resolved photoeinission spectroscopy, scanning tunneling microscopy/spectroscopy, and density functional theory calculations. We demonstrate that 3 x 3 charge-density-wave (CDW) order persists despite distinct changes in the low energy electronic. structure highlighted by the reduction in the number of-bands crossing the Fermi energy and the corresponding modification Of Fermi surface topology. Enhanced, spin-orbit coupling and lattice distortion in the single-layer play a crucial role in the formation of CDW order. Our findings provide a deeper understanding of the nature of COW order in the two-dimensional limit.</P>

Thickness dependent charge density wave networks on thin 1T‑TaS2

Yang Wooin,Kim Dowook,Kim Hyoung Kug,Kim Tae-Hwan 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.3

We investigate mechanically exfoliated thin 1T-TaS2 with scanning tunneling microscopy at room temperature. Sample preparation without air exposure enables access to intrinsic charge-density-wave (CDW) phases of thin 1T-TaS2. At room temperature, we can observe the expected nearly commensurate CDW (NCCDW) phase on thin fakes similar to bulk 1TTaS2. Further analysis reveals that CDW domains in the NCCDW phase become smaller and have a more anisotropic shape with decreasing thickness in the range of 8–28 layers. Our fndings demonstrate that the anisotropic CDW nature of thin 1T-TaS2 would be crucial to understand its exotic CDW-related phenomena and demand a systematic study on its correlation between the thickness-driven CDW domain anisotropy and the intermediate CDW states in thin 1T-TaS2.

Factors Affecting the Magnitude of the Metal-Insulator Transition Temperature in AMo₄O₆ (A=K, Sn)

Jung, Dong-Woon,Choi, Kwang-Sik,Kim, Sung-Jin Korean Chemical Society 2004 Bulletin of the Korean Chemical Society Vol.25 No.7

A low-dimensional metal frequently exhibits a metal-insulator transition through a charge-density-wave (CDW) or a spin-density-wave (SDW) which accompany it's structural changes. The transition temperature is thought to be determined by the amount of energy produced during the transition process and the softness of the original structure. $AMo_4O_6$ (A=K, Sn) are known to be quasi-one dimensional metals which exhibit metalinsulator transitions. The difference of the transition temperatures between $KMo_4O_6$ and $SnMo_4O_6$ (A=K, Sn) is examined by investigating their electronic and structural properties. Fermi surface nesting area and the lattice softness are the governing factors to determine the metal-insulator transition temperature in $AMo_4O_6$ compounds.

Novel Anisotropic Superconductivity in Silicides

T. Tamegai,G. J. Li,K. Uozato,T. Nakagawa,Y. Nakajima 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2

The discovery of superconductivity with Tc ∽39 K in MgB2 renewed our interest in intermetalic compounds containing light elements. We have revisited superconductivity in anisotropic silicides, such as CaMSi (M = Al and Ga), R5Ir4Si10 (R: rare-earth elements), and Lu2Fe3Si5. In CaAlSi with the AlB2 structure, an anomalous angular dependence of the upper critical field is found, sugesting the presence of a decoupled superconducting region. An X-ray diffraction study has shown the presence of a pronounced superlatice structure along thec-axis. Magneto-optical observations on the ac-plane of CaAlSi reveal the presence of strong inhomogeneities. Most R5Ir4Si10 (R: Sc, Y, rare-earth elements) compounds show a charge-density wave instability with the ex- ception of Sc5Ir4Si10, which shows the highest Tc among these compounds. We have compared their anisotropic superconductivity in order to get some insight into the exceptional properties of Sc5Ir4Si10. Lu2Fe3Si5 is a superconductor with Tc ∽ 6 K and containing nonmagnetic iron. Previous specific heat measurements show that Lu2Fe3Si5 has a large residual density of state in the superconducting state. We have sucesfuly grown high-quality single crystals of Lu2Fe3Si5 and found a signature of the presence of a second superconducting gap as in MgB2.

Dynamical Metal to Charge-Density-Wave Junctions in an Atomic Wire Array

Song, Sun Kyu,Samad, Abdus,Wippermann, Stefan,Yeom, Han Woong American Chemical Society 2019 NANO LETTERS Vol.19 No.8

<P>We investigated the atomic scale electronic phase separation emerging from a quasi-1D charge-density-wave (CDW) state of the In atomic wire array on a Si(111) surface. Spatial variations of the CDW gap and amplitude are quantified for various interfaces of metallic and insulating CDW domains by scanning tunneling microscopy and spectroscopy (STS). The strong anisotropy in the metal-insulator junctions is revealed with an order of magnitude difference in the interwire and intrawire junction lengths of 0.4 and 7 nm, respectively. The intrawire junction length is reduced dramatically by an atomic scale impurity, indicating the tunability of the metal-insulator junction in an atomic scale. Density functional theory calculations disclose the dynamical nature of the intrawire junction formation and tunability.</P> [FIG OMISSION]</BR>

Electronic structure and charge-density wave transition in monolayer VS2

김혁진,최병기,이인학,김민재,천승현,Jozwiak Chris,Bostwick Aaron,Rotenberg Eli,Chang Young Jun 한국물리학회 2021 Current Applied Physics Vol.30 No.-

Vanadium disulfide (VS2) attracts elevated interests for its charge-density wave (CDW) phase transition, ferromagnetism, and catalytic reactivity, but the electronic structure of monolayer has not been well understood yet. Here we report synthesis of epitaxial 1T VS2 monolayer on bilayer graphene grown by molecular-beam epitaxy (MBE). Angle-resolved photoemission spectroscopy (ARPES) measurements reveal that Fermi surface with six elliptical pockets centered at the M points shows gap opening at low temperature. Temperature-dependence of the gap size suggests existence of CDW phase transition above room temperature. Our observations provide important evidence to understand the strongly correlated electron physics and the related surface catalytic properties in two-dimensional transition-metal dichalcogenides (TMDCs).

Scanning tunneling microscopy study of hidden phases in atomically thin 1T‑TaS2

Yang Wooin,Kim Dowook,Kim Hyoung Kug,Kim Tae-Hwan 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.3

Lower thermal stability due to thinning often leads to unprecedented hidden phases in low-dimensional materials. Such hidden phases can coexist or compete with preexisting electronic phases. We investigate hidden phases observed in atomically thin (6–8 layers) 1T-TaS2 with scanning tunneling microscopy. First, we can electrically induce a hidden stripe phase at room temperature. Such a uniaxial stripe phase has three equivalent orientations by breaking threefold symmetry of 1TTaS 2 . We also reveal that the hidden stripe phase coexists with nearly commensurate charge-density-wave phase. Next, we observe that the emergent stripe phase spontaneously appears without any electric excitation on a tiny flake ( 160 × 80 nm2 ). Our findings may provide a plausible explanation for the previously observed phase transition and twofold optical response in thin 1T-TaS2 devices at room temperature. Furthermore, the hidden stripe phase would be crucial to understand exotic CDW-related phenomena in 1T-TaS2 for potential applications.