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1. Charge‐Density‐Wave Order And Electronic Phase Transitions in a Dilute D ‐Band Semiconductor

   https://doi.org/10.1002/adma.202303283  

   Chen, Huandong; Zhao, Boyang; Mutch, Josh; Jung, Gwan Yeong; Ren, Guodong; Shabani, Sara; Seewald, Eric; Niu, Shanyuan; Wu, Jiangbin; Wang, Nan; et al (August 2023, Advanced Materials)

   Abstract As one of the most fundamental physical phenomena, charge density wave (CDW) order predominantly occurs in metallic systems such as quasi‐one‐dimensional (quasi‐1D) metals, doped cuprates, and transition metal dichalcogenides, where it is well understood in terms of Fermi surface nesting and electron‐phonon coupling mechanisms. On the other hand, CDW phenomena in semiconducting systems, particularly at the low carrier concentration limit, are less common and feature intricate characteristics, which often necessitate the exploration of novel mechanisms, such as electron‐hole coupling or Mott physics, to explain. In this study, we combined electrical transport, synchrotron X‐ray diffraction and density‐functional theory (DFT) calculations to investigate CDW order and a series of hysteretic phase transitions in a dilute d ‐band semiconductor, BaTiS 3 . Our experimental and theoretical findings suggest that the observed CDW order and phase transitions in BaTiS 3 may be attributed to both electron‐phonon coupling and non‐negligible electron‐electron interactions in the system. Our work highlights BaTiS 3 as a unique platform to explore CDW physics and novel electronic phases in the dilute filling limit and could open new opportunities for developing novel electronic devices. This article is protected by copyright. All rights reserved 

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2. Electronic, vibrational, and electron–phonon coupling properties in SnSe ₂ and SnS ₂ under pressure

   https://doi.org/10.1039/D0TC04356G  

   Kafle, Gyanu Prasad; Heil, Christoph; Paudyal, Hari; Margine, Elena R. (December 2020, Journal of Materials Chemistry C)

   The tin-selenide and tin-sulfide classes of materials undergo multiple structural transitions under high pressure leading to periodic lattice distortions, superconductivity, and topologically non-trivial phases, yet a number of controversies exist regarding the structural transformations in these systems. We perform first-principles calculations within the framework of density functional theory and a careful comparison of our results with available experiments on SnSe 2 reveals that the apparent contradictions among high-pressure results can be attributed to differences in experimental conditions. We further demonstrate that under hydrostatic pressure a superstructure can be stabilized above 20 GPa in SnS 2 via a periodic lattice distortion as found recently in the case of SnSe 2 , and that this pressure-induced phase transition is due to the combined effect of Fermi surface nesting and electron–phonon coupling at a momentum wave vector q = (1/3, 1/3, 0). In addition, we investigate the contribution of nonadiabatic corrections on the calculated phonon frequencies, and show that the quantitative agreement between theory and experiment for the high-energy A 1g phonon mode is improved when these effects are taken into account. Finally, we examine the nature of the superconducting state recently observed in SnSe 2 under nonhydrostatic pressure and predict the emergence of superconductivity with a comparable critical temperature in SnS 2 under similar experimental conditions. Interestingly, in the periodic lattice distorted phases, the critical temperature is found to be reduced by an order of magnitude due to the restructuring of the Fermi surface. 

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3. First-principles study of the electronic structure, Z 2 invariant, and quantum oscillation in the kagome material CsV3Sb5

   https://doi.org/10.1063/5.0232167  

   Bhandari, Shalika R; Zeeshan, Mohd; Gusain, Vivek; Shrestha, Keshav; Rai, D P (December 2024, APL Quantum)

   NA (Ed.)

   This work presents a detailed study of the electronic structure, phonon dispersion, Z2 invariant calculation, and Fermi surface of the newly discovered kagome superconductor CsV3Sb5, using density functional theory. The phonon dispersion in the pristine state reveals two negative modes at the M and L points of the Brillouin zone, indicating lattice instability. CsV3Sb5 transitions into a structurally stable 2 × 2 × 1 charge density wave (CDW) phase, confirmed by positive phonon modes. The electronic band structure shows several Dirac points near the Fermi level, with a narrow gap opening due to spin–orbit coupling (SOC), although the effect of SOC on other bands is minimal. In the pristine phase, this material exhibits a quasi-2D cylindrical Fermi surface, which undergoes reconstruction in the CDW phase. We calculated quantum oscillation frequencies using Onsager’s relation, finding good agreement with experimental results in the CDW phase. To explore the topological properties of CsV3Sb5, we computed the Z2 invariant in both pristine and CDW phases, resulting in a value of (ν0; ν1ν2ν3) = (1; 000), suggesting the strong topological nature of this material. Our detailed analysis of phonon dispersion, electronic bands, Fermi surface mapping, and Z2 invariant provides insights into the topological properties, CDW order, and unconventional superconductivity in AV3Sb5 (A = K, Rb, and Cs). 

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4. Observation of momentum-dependent charge density wave gap in a layered antiferromagnet GdTe3

   https://doi.org/10.1038/s41598-023-44851-8  

   Regmi, Sabin; Bin Elius, Iftakhar; Sakhya, Anup Pradhan; Jeff, Dylan; Sprague, Milo; Mondal, Mazharul Islam; Jarrett, Damani; Valadez, Nathan; Agosto, Alexis; Romanova, Tetiana; et al (December 2023, Scientific Reports)

   Abstract Charge density wave (CDW) ordering has been an important topic of study for a long time owing to its connection with other exotic phases such as superconductivity and magnetism. The$$R{\textrm{Te}}_{3}$$ $R{\text{Te}}_3$(R= rare-earth elements) family of materials provides a fertile ground to study the dynamics of CDW in van der Waals layered materials, and the presence of magnetism in these materials allows to explore the interplay among CDW and long range magnetic ordering. Here, we have carried out a high-resolution angle-resolved photoemission spectroscopy (ARPES) study of a CDW material$${\textrm{Gd}}{\textrm{Te}}_{3}$$ $\text{Gd}{\text{Te}}_3$, which is antiferromagnetic below$$\sim \mathrm {12~K}$$ $\sim 12K$, along with thermodynamic, electrical transport, magnetic, and Raman measurements. Our ARPES data show a two-fold symmetric Fermi surface with both gapped and ungapped regions indicative of the partial nesting. The gap is momentum dependent, maximum along$${\overline{\Gamma }}-\mathrm{\overline{Z}}$$ $\overline{\Gamma }-\overline{Z}$and gradually decreases going towards$${\overline{\Gamma }}-\mathrm{\overline{X}}$$ $\overline{\Gamma }-\overline{X}$. Our study provides a platform to study the dynamics of CDW and its interaction with other physical orders in two- and three-dimensions. 

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5. The phononic and charge density wave behavior of entire rare-earth tritelluride series with chemical pressure and temperature

   https://doi.org/10.1063/5.0110395  

   Yumigeta, Kentaro; Attarde, Yashika; Kopaczek, Jan; Sayyad, Mohammed Y.; Shen, Yuxia; Blei, Mark; Rajaei Moosavy, Seyed Tohid; Qin, Ying; Sailus, Renee; Tongay, Sefaattin (November 2022, APL Materials)

   Here, we present comprehensive phononic and charge density wave properties (CDW) of rare-earth van der Waals tritellurides through temperature dependent angle-resolved Raman spectroscopy measurements. All the possible rare-earth tritellurides (RTe 3 ) ranging from R = La–Nd, Sm, Gd–Tm were synthesized through a chemical vapor transport technique to achieve high quality crystals with excellent CDW characteristics. Raman spectroscopy studies successfully identify the emergence of the CDW state and transition temperature (T CDW ), which offers a non-destructive method to identify their CDW response with micron spatial resolution. Temperature dependent Raman measurements further correlate how the atomic mass of metal cations and the resulting chemical pressure influence its CDW properties and offer detailed insight into the strength of CDW amplitude mode-phonon coupling during the CDW transition. Angle-resolved Raman measurements offer the first insights into the CDW-phonon symmetry interplay by monitoring the change in the symmetry of phonon mode across the CDW transition. Overall results introduce the library of RTe 3 CDW materials and establish their characteristics through the non-destructive angle-resolved Raman spectroscopy technique. 

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