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تسجيل مستخدم جديدKagome superconductors from Pomeranchuk fluctuations in charge density wave metals
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Motivated by the recent experiments on the kagome metals $Atext{V}_3text{Sb}_5$ with $A=text{K}, text{Rb}, text{Cs}$, which see onset of charge density wave (CDW) order at $sim$ $100$ K and superconductivity at $sim$ $1$ K, we explore the onset of superconductivity, taking the perspective that it descends from a parent CDW state. In particular, we propose that the pairing comes from the Pomeranchuk fluctuations of the reconstructed Fermi surface in the CDW phase. This scenario naturally explains the large separation of energy scale from the parent CDW. Remarkably, the phase diagram hosts the double-dome superconductivity near two reconstructed Van Hove singularities. These singularities occur at the Lifshitz transition and the quantum critical point of the parent CDW. The first dome is occupied by the $d_{xy}$-wave nematic spin-singlet superconductivity. Meanwhile, the $(s+d_{x^2-y^2})$-wave nematic spin-singlet superconductivity develops in the second dome. Our work sheds light on an unconventional pairing mechanism with strong evidences in the kagome metals $Atext{V}_3text{Sb}_5$.
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As a foundation of condensed matter physics, the normal states of most metals are successfully described by Landau Fermi liquid theory with quasi-particles and their Fermi surfaces (FSs). The FSs sometimes become deformed or gapped at low temperature
s owing to quasi-particle interactions, known as FS instabilities. A notable example of a FS deformation that breaks only the rotation symmetry, namely Pomeranchuk instability, is the d-wave FS distortion, which is also proposed as one possible origin of electron nematicity in iron-based superconductors. However, no clear evidence has been made for its existence, mostly owing to the mixture of multiple orders. Here we report an unequivocally observation of the Pomeranchuk nematic order in floating monolayer (ML) FeSe on 1 ML-FeSe/SrTiO3 substrate. By using angle-resolve photoemission spectroscopy, we find remarkably that the dxz and dyz bands are degenerate at the Brillouin zone center (Gamma point), while their splitting is even larger at zone corner (M point), in stark contrast to that in bulk FeSe. Our detailed analysis show that the momentum-dependent nematic order in floating monolayer FeSe is coming from the d-wave Pomeranchuk instability at M point, shedding light on the origin of the ubiquitous nematicity in iron-based superconductors. Our results establish the single-layer high-Tc superconductors as an excellent material platform for investigating emergent quantum physics under complex intertwinement.
The recently discovered family of AV$_3$Sb$_5$ (A: K, Rb Cs) kagome metals possess a unique combination of nontrivial band topology, superconducting ground states, and signatures of electron correlations manifest via competing charge density wave ord
er. Little is understood regarding the nature of the charge density wave (CDW) instability inherent to these compounds and the potential correlation with the accompanying onset of a large anomalous Hall response. To understand the impact of the CDW order on the electronic structure in these systems, we present quantum oscillation measurements on single crystals of CsV$_3$Sb$_5$. Our data provides direct evidence that the CDW invokes a substantial reconstruction of the Fermi surface pockets associated with the vanadium orbitals and the kagome lattice framework. In conjunction with density functional theory modeling, we are able to identify split oscillation frequencies originating from reconstructed pockets built from vanadium orbitals and Dirac-like bands. Complementary diffraction measurements are further able to demonstrate that the CDW instability has a correlated phasing between neighboring V$_3$Sb$_5$ planes. These results provide critical insights into the underlying CDW instability in AV$_3$Sb$_5$ kagome metals and support minimal models of CDW order arising from within the vanadium-based kagome lattice.
The transition metal dichalcogenide (TMD) $1T$-TaS$_{2}$ exhibits a rich set of charge density wave (CDW) orders. Recent investigations suggested that using light or electric field can manipulate the commensurate (C) CDW ground state. Such manipulati
ons are considered to be determined by the charge carrier doping. Here we simulate by first-principles calculations the carrier doping effect on CCDW in $1T$-TaS$_{2}$. We investigate the charge doping effects on the electronic structures and phonon instabilities of $1T$ structure and analyze the doping induced energy and distortion ratio variations in CCDW structure. We found that both in bulk and monolayer $1T$-TaS$_{2}$, CCDW is stable upon electron doping, while hole doping can significantly suppress the CCDW, implying different mechanisms of such reported manipulations. Light or positive perpendicular electric field induced hole doping increases the energy of CCDW, so that the system transforms to NCCDW or similar metastable state. On the other hand, even the CCDW distortion is more stable upon in-plain electric field induced electron injection, some accompanied effects can drive the system to cross over the energy barrier from CCDW to nearly commensurate (NC) CDW or similar metastable state. We also estimate that hole doping can introduce potential superconductivity with $T_{c}$ of $6sim7$ K. Controllable switching of different states such as CCDW/Mott insulating state, metallic state, and even the superconducting state can be realized in $1T$-TaS$_{2}$, which makes the novel material have very promising applications in the future electronic devices.
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