Charge Density Wave Research Articles

One-Dimensional Electron Gas Confined along Nanowrinkles in a Unidirectional Charge Density Wave Material.

Two-dimensional (2D) materials inherently exhibit instabilities. Structurally, this may lead to modulations along the third dimension, e.g., wrinkles. Electronically, 2D instabilities can manifest themselves as charge density waves (CDWs). Although wrinkles can alter anisotropic electronic structures susceptible to forming CDWs, less is known about their impact on broken-symmetry ground states. Here, using scanning tunneling microscopy and spectroscopy, we investigate the CDW states on the wrinkled surface of DyTe3. We identify elongated, parallel nanoscale wrinkles stabilized by ribbon-shaped defects. Interestingly, the CDW order persists across the nanowrinkles with a gradual phase shift but is locally suppressed near the defects, where phase windings occur. In addition, these defects induce quantum confinement effects along the nanowrinkles, indicating the presence of one-dimensional metallic states with hole-like dispersion, while angle-resolved photoemission spectroscopy identifies a gap along the wrinkle direction. We ascribe this discrepancy to strain-induced changes in the Fermi surface, which lead to the closure of the gap at the sites of the nanowrinkles. Taken together, our results underscore the complex interplay between structural features and Fermi surface topology, allowing for the deliberate manipulation of quantum states in strongly correlated systems via local crystal deformations.

Fully-gapped superconductivity with rotational symmetry breaking in pressurized kagome metal CsV3Sb5

The discovery of the kagome metal CsV3Sb5 has generated significant interest in its complex physical properties, particularly its superconducting behavior under different pressures, though its nature remains debated. Here, we performed low-temperature, high-pressure 121/123Sb nuclear quadrupole resonance (NQR) measurements to explore the superconducting pairing symmetry in CsV3Sb5. At ambient pressure, we found that the spin-lattice relaxation rate 1/T1 exhibits a kink at T ~ 0.4 Tc within the superconducting state and follows a T3 variation as temperature further decreases. This suggests the presence of two superconducting gaps with line nodes in the smaller one. As pressure increases beyond Pc ~ 1.85 GPa, where the charge-density wave phase is completely suppressed, 1/T1 shows no Hebel-Slichter peak just below Tc, and decreases rapidly, even faster than T5, indicating that the gap is fully opened for pressures above Pc. In this high pressure region, the angular dependence of the in-plane upper critical magnetic field Hc2 breaks the C6 rotational symmetry. We propose the s + id pairing at P > Pc which explains both the 1/T1 and Hc2 behaviors. Our findings indicate that CsV3Sb5 is an unconventional superconductor and its superconducting state is even more exotic at high pressures.

In-plane negative magnetoresistance and quantum oscillations in van der Waals antiferromagnet DyTe3

Abstract Two-dimensional van der Waals (vdW) magnetic materials, characterized by their tunable magnetism, spin transport properties, and remarkable quantum effects, provide significant promise for the development of efficient, low-power spintronic devices. Intriguingly, the Rare earth-Te materials have attracted great attention due to their unique magnetic structure, exotic electronic properties, multiple charge density wave (CDW), and superconductivity under pressure. Here, we report the successful synthesis of high-quality DyTe3 single crystals using a self-flux method. DyTe3 shows an antiferromagnetic transition at 4.5 K and demonstrates the magnetic field-induced ferromagnetism. The high-quality DyTe3 single crystal demonstrates outstanding transport properties, featuring a high carrier mobility of approximately 1.4×104 cm2V-1s-1 and large linear magnetoresistance of 1300%. Furthermore, distinct Shubnikov-de Haas (SdH) oscillations are observed in DyTe3, revealing a small Fermi pocket and an effective mass of 0.24 me. Remarkably, the unconventional in-plane negative magnetoresistances appear along the a-axis below 2 T and c-axis until 9 T from 2 K to 17 K, which are attributed to the complex helimagnetic structures caused by CDW coupling and weak single-ion anisotropy. Our findings offer a significant platform for understanding the complex magnetoresistance behavior and quantum transport effects in RTe3-type materials, holding great promise for advancing applications in electronic and spintronic devices.

Commensurate to incommensurate transition of three-dimensional charge density waves

Commensurate to incommensurate transition of three-dimensional charge density waves

Charge density wave solutions of the Hubbard model in the composite operator formalism

Charge density wave solutions of the Hubbard model in the composite operator formalism

Evidence of spin and charge density waves in Chromium electronic bands

The incommensurate spin density wave (SDW) of Chromium represents the classic example of itinerant antiferromagnetism induced by the nesting of the Fermi surface, which is further enriched by the co-presence of a charge density wave (CDW). Here, we explore its electronic band structure using soft-X-ray angle-resolved photoemission spectroscopy (ARPES) for a proper bulk-sensitive investigation. We find that the long-range magnetic order gives rise to a very rich ARPES signal, which can only be interpreted with a proper first-principles description of the SDW and CDW, combined with a band unfolding procedure, reaching a remarkable agreement with experiments. Additional features of the SDW order are obscured by superimposed effects related to the photoemission process, which, unexpectedly, are not predicted by the free-electron model for the final states. We demonstrate that, even for excitation photon energies up to 1 keV, a multiple scattering description of the photoemission final states is required.

Charge Density Wave and Ferromagnetism in Intercalated CrSBr.

In materials with 1D electronic bands, electron-electron interactions can produce intriguing quantum phenomena, including spin-charge separation and charge density waves (CDW). Most of these systems, however, are non-magnetic, motivating a search for anisotropic materials where the coupling of charge and spin may affect emergent quantum states. Here, chemical intercalation of the van der Waals magnetic semiconductor CrSBr yields Li0.17(2)(tetrahydrofuran)0.26(3)CrSBr, which possesses an electronically driven quasi-1D CDW with an onset temperature above room temperature. Concurrently, electron doping increases the magnetic ordering temperature from 132 to 200 K and switches its interlayer magnetic coupling from antiferromagnetic to ferromagnetic. The spin-polarized nature of the anisotropic bands that give rise to this CDW enforces an intrinsic coupling of charge and spin. The coexistence and interplay of ferromagnetism and charge modulation in this exfoliatable material provide a promising platform for studying tunable quantum phenomena across a range of temperatures and thicknesses.

Evidence for reduced periodic lattice distortion within the Sb-terminated surface layer of the kagome metal CsV3Sb5

The discovery of the kagome metal CsV3Sb5 sparked broad interest, due to the coexistence of a charge density wave (CDW) phase and possible unconventional superconductivity in the material. In this Letter, we use low-energy electron diffraction (LEED) with a µm-sized electron beam to explore the periodic lattice distortion at the antimony-terminated surface in the CDW phase. We recorded high-quality backscattering diffraction patterns in ultrahigh vacuum from multiple cleaved samples. Unexpectedly, we did not find superstructure reflexes at intensity levels predicted from dynamical LEED calculations for the reported 2×2×2 bulk structure. Our results suggest that in CsV3Sb5 the periodic lattice distortion accompanying the CDW is less pronounced at Sb-terminated surfaces than in the bulk. Published by the American Physical Society 2025

Extended Kohler’s scaling and isosbestic point in the charge density wave state of 1T-VSe2

1T-VSe2is a narrow band transition metal chalcogenide that shows charge density wave (CDW) state below TCDW= 110 K. Here, we have explored the relevance of Kohler's rule and the thermal transport properties of VSe2across the CDW state in the presence of magnetic field. The magnetoresistance (MR) follows Kohler's rule above TCDW, while an extended Kohler's rule is employed below TCDW. Interestingly, we observed an anomaly in MR around T ∼ 20 K, below which MR value decreases on lowering temperature. This anomaly is also reflected in the slope (κ) of Kohler's plots and the relative change in the thermal excitation induced carrier density (nT). Despite a strong magnetic field of 14 Tesla, the TCDWremains largely unaffected in both electrical resistivity (ρ(T)) and Seebeck coefficient (S), although the application of magnetic field does enhance the peak intensity of S around T ∼ 60 K. The crossover of S curves measured at different magnetic fields at T ∼ 20 K suggests the existence of a novel feature within the CDW state of VSe2i.e., the presence of a locally exact isosbestic point.

Vacancy-induced suppression of charge density wave order and its impact on magnetic order in kagome antiferromagnet FeGe

Two-dimensional (2D) kagome lattice metals are interesting because their corner sharing triangle structure enables a wide array of electronic and magnetic phenomena. Recently, post-growth annealing is shown to both suppress charge density wave (CDW) order and establish long-range CDW with the ability to cycle between states repeatedly in the kagome antiferromagnet FeGe. Here we perform transport, neutron scattering, scanning transmission electron microscopy (STEM), and muon spin rotation (μSR) experiments to unveil the microscopic mechanism of the annealing process and its impact on magneto-transport, CDW, and magnetism in FeGe. Annealing at 560 °C creates uniformly distributed Ge vacancies, preventing the formation of Ge-Ge dimers and thus CDW, while 320 °C annealing concentrates vacancies into stoichiometric FeGe regions with long-range CDW. The presence of CDW order greatly affects the anomalous Hall effect, incommensurate magnetic order, and spin-lattice coupling in FeGe, placing FeGe as the only kagome lattice material with tunable CDW and magnetic order.

Cascade of pressure-induced competing charge density waves in the kagome metal FeGe

Cascade of pressure-induced competing charge density waves in the kagome metal FeGe

Two-dimensional Janus MoSeH with tunable charge density wave, superconductivity and topological properties

Two-dimensional Janus MoSeH with tunable charge density wave, superconductivity and topological properties

Magnetic and dielectric studies of the charge density wave formation in quasi-one-dimensional material K0.3MoO3

Magnetic and dielectric studies of the charge density wave formation in quasi-one-dimensional material K0.3MoO3

Visualizing the internal structure of the charge-density-wave state in CeSbTe

The collective reorganization of electrons into a charge density wave has long served as a textbook example of an ordered phase in condensed matter physics. Two-dimensional square lattices with p electrons are well-suited to the realization of charge density waves, due to the anisotropy of the p orbitals and the resulting one dimensionality of the electronic structure. In spite of a long history of study of charge density waves in square-lattice systems, few reports have recognized the significance of a hidden orbital degree of freedom. The degeneracy of px and py electrons may give rise to orbital patterns in real space that endow the charge density wave with additional broken symmetries or unusual order parameters. Here, we use scanning tunneling microscopy to visualize the internal structure of the charge-density-wave state of CeSbTe, which contains Sb square lattices with 5p electrons. We image atomic-sized, anisotropic lobes of charge density with periodically modulating anisotropy, which we interpret in terms of a superposition of px and py bond density waves. Our results support the fact that delocalized p orbitals can reorganize into emergent electronic states of matter.

Metal-assisted vacuum transfer enabling in situ visualization of charge density waves in monolayer MoS2.

Recent advancements in quantum materials research have focused on monolayer transition metal dichalcogenides and their heterostructures, known for complex electronic phenomena. While macroscopic electrical and magnetic measurements provide valuable insights, understanding these electronic states requires direct experimental observations. Yet, the extreme two-dimensionality of these materials demands surface-sensitive measurements with exceptionally clean surfaces. Here, we present the metal-assisted vacuum transfer method combined with in situ measurements in ultrahigh vacuum (UHV), enabling pristine monolayer MoS2 with ultraclean surfaces unexposed to ambient conditions. Consequently, in situ scanning tunneling microscopy revealed charge density waves (CDWs) in MoS2/Cu(111), previously unobserved in monolayer MoS2. Additionally, angle-resolved photoelectron spectroscopy identified notable Fermi surface nesting due to substrate interactions, elucidating the mechanisms behind CDW formation. This method is broadly applicable to other monolayer two-dimensional materials, enabling the high-fidelity in situ UHV characterization and advancing the understanding of correlated electronic behaviors in these material systems.

Geminal Mirror Twin Boundaries in H-Phase NbTe2.

Grain boundaries (GBs) in transition metal dichalcogenides (TMDs) significantly influence their physicochemical properties. Mirror twin boundaries (MTBs), a special GB type, reveal one-dimensional quantum features such as topological states and charge density waves. However, the large-scale fabrication of well-aligned MTBs remains challenging. Here, we present a simple solution method to introduce high-density paired MTBs in monolayer 1H-NbTe2. Using atomic-resolution scanning transmission electron microscopy (STEM), we identify two "MTB" types─metastable Nb-oriented 4|4E and Te-oriented 4|4P, forming aligned MTBs with quantized spacings. The formation mechanism of paired MTBs is hypothesized to involve specific intralayer atomic rearrangements within a distorted 1T-phase, followed by H-phase core coalescence, facilitated by strain-induced energy barrier reduction and electron doping stabilization. Density functional theory (DFT) calculations indicate that paired MTBs stabilize metastable H-phase, enabling the coexistence of superconductivity and nontrivial band topology. The approach of our group to fabricating high-density paired MTBs advances boundary engineering in TMDs for designing functional quantum devices.

Light-Induced Phase Transition and Photodetection Application of Nanotube Encapsulated TaS2 Nanoribbon Sensor

Confining molecules in nanotubes is a powerful tool to control the state of guest molecules and tune the properties of host-nanocontainers in host-guest systems. Here, we use carbon nanotube (CNT) encapsulation to achieve large-scale, various-sized, atomically precise TaS2 nanoribbons that exhibit robust phase transitions and reliable photodetection applications. It has been detected that more than 95% of the carbon nanotubes are filled with TaS2, and the total length of the TaS2 nanoribbons ranges from 100 nm to more than 1 μm. Encapsulation improves the stability of TaS2. Interestingly, the TaS2 nanoribbons exhibit Raman activity that is very different from that of the bulk, including frequency, number of peaks, and intensity. This also leads to a single TaS2@CNT exhibiting a robust phase transition due to charge density waves (CDWs). CDWs are one of the most fundamental quantum phenomena in solids, and their application in manipulating this condensed matter has always been a goal in the fields of materials and condensed matter. We found that the CDWs system of the TaS2@CNT sensor is sensitive to light at room temperature. Efficient detection of ultraviolet light (375 nm) can be achieved in the atmospheric environment (8762 A/W). Our research opens up new avenues for realizing sensitive integrated optoelectronics and also provides ideas for studying dimensionality in quantum correlation phase transitions.

RKKY interaction in the presence of a charge density wave order

RKKY interaction in the presence of a charge density wave order

Photoinduced pattern formation and melting of charge density wave order

Photoinduced pattern formation and melting of charge density wave order

Chiral Pseudogap Metal Emerging from a Disordered Van der Waals Mott Insulator 1T-TaS2 - xSex.

The emergence of a pseudogap is a hallmark of anomalous electronic states formed through substantial manybody interaction but the mechanism of the pseudogap formation and its role in related emerging quantum states such as unconventional superconductivity remain largely elusive. Here, the emergence of an unusual pseudogap in a representative van der Waals chiral charge density wave (CDW) materials with strong electron correlation, 1T-TaS2 is reported, through isoelectronic substitute of S. The evolution of electronic band dispersions of 1T-TaS2 - xSex (0 ⩽ x ⩽ 2) is systematically investigated using angle-resolved photoemission spectroscopy (ARPES). The results show that the Se substitution induces a quantum transition from an insulating to a pseudogap metallic phase with the CDW order preserved. Moreover, the asymmetry of the pseudogap spectral function is found, which reflects the chiral nature of CDW structure. The present observation is contrasted with the previous suggestions of a Mott transition driven by band width control or charge transfer. Instead, the pseudogap phase is attributed to a disordered Mott insulator in line with the recent observation of substantial lateral electronic disorder. These findings provide a unique electronic system with chiral pseudogap, where the complex interplay between CDW, chirality, disorder, and electronic correlation may lead to unconventional emergentphysics.