اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدOrbital ordering and fluctuations in a kagome superconductor CsV3Sb5
485
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Recently, competing electronic instabilities, including superconductivity and density-wave-like order, have been discovered in vanadium-based kagome metals AV3Sb5 (A = K, Rb, Cs) with a nontrivial band topology. This finding stimulates wide interests to study the interplay of these competing electronic orders and possible exotic excitations in the superconducting state. Here, in order to further clarify the nature of density-wave-like transition in these kagome superconductors, we performed 51V and 133Cs nuclear magnetic resonance (NMR) measurements on the CsV3Sb5 single crystal. A first-order phase transition associated with orbital ordering is revealed by observing a sudden splitting of orbital shift in 51V NMR spectrum at the structural transition temperature Ts ~ 94 K. In contrast, the quadrupole splitting from a charge-density-wave (CDW) order on 51V NMR spectrum only appears gradually below Ts with a typical second-order transition behavior, suggesting that the CDW order is a secondary electronic order. Moreover, combined with 133Cs NMR spectrum, the present result also confirms a three-dimensional structural modulation with a 2ax2ax2c period. Above Ts, the temperature-dependent Knight shift and nuclear spin-lattice relaxation rate (1/T1) further indicate the existence of remarkable magnetic fluctuations from vanadium 3d orbitals, which are suppressed due to orbital ordering below Ts. The present results strongly support that, besides CDW order, the previously claimed density-wave-like transition also involves a dominant orbital order, suggesting a rich orbital physics in these kagome superconductors.
قيم البحث
اقرأ أيضاً
The kagome lattice of transition metal atoms provides an exciting platform to study electronic correlations in the presence of geometric frustration and nontrivial band topology, which continues to bear surprises. In this work, using spectroscopic im
aging scanning tunneling microscopy, we discover a cascade of different symmetry-broken electronic states as a function of temperature in a new kagome superconductor, CsV3Sb5. At a temperature far above the superconducting transition Tc ~ 2.5 K, we reveal a tri-directional charge order with a 2a0 period that breaks the translation symmetry of the lattice. As the system is cooled down towards Tc, we observe a prominent V-shape spectral gap opening at the Fermi level and an additional breaking of the six-fold rotation symmetry, which persists through the superconducting transition. This rotation symmetry breaking is observed as the emergence of an additional 4a0 unidirectional charge order and strongly anisotropic scattering in differential conductance maps. The latter can be directly attributed to the orbital-selective renormalization of the V kagome bands. Our experiments reveal a complex landscape of electronic states that can co-exist on a kagome lattice, and provide intriguing parallels to high-Tc superconductors and twisted bilayer graphene.
We report the transport properties of kagome superconductor CsV3Sb5 single crystals at magnetic field up to 32 T. The Shubnikov de Haas (SdH) oscillations emerge at low temperature and four frequencies of $F_{alpha}=$ 27 T, F_beta = 73 T, F_epsilon =
727 T, and F_eta = 786 T with relative small cyclotron masses are observed. For F_beta and F_epsilon, the Berry phases are close to pi, providing a clear evidence of nontrivial topological band structures of CsV3Sb5. Furthermore, combined with the angular dependence of SdH oscillations and theoretical calculations based on the undistorted structure, we have demonstrated that the Fermi surface related to F_beta is quasi-two-dimensional and can be assigned to the Dirac cone along the Gamma-K direction of Brillouin zone (BZ). The F_epsilon could be related to the Fermi surface centering at the H point of BZ. The absence of F_alpha and F_eta in theoretical calculations suggests that charge density wave transition could have an important influence on the shapes of Fermi surfaces, especially near the M and L points of BZ. These results will shed light on the nature of correlated topological physics in kagome material CsV3Sb5.
The superconductivity of a kagome superconductor CsV3Sb5 is studied by scanning tunneling microscopy / spectroscopy at an ultralow temperature with high resolution. Two kinds of superconducting gaps with multiple sets of coherent peaks and residual z
ero-energy density of states are observed on both half-Cs and Sb surfaces, implying multiband superconductivity with gap nodes. Sixfold star-shaped magnetic vortex is observed with conventional Caroli-de Gennes-Matricon bound states inside. Magnetic impurities suppress the superconductivity, while nonmagnetic impurities do not, suggesting the absence of sign-change in the superconducting order parameter. Moreover, the interplay between charge density waves and superconductivity differs on various bands, resulting in different density of state distributions. Our study provides critical clues for further understanding the superconductivity and its relation to charge density waves in CsV3Sb5.
We present a systematic study of the nematic fluctuations in the iron chalcogenide superconductor Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ ($0 leq x leq 0.53$) using the elastoresistivity technique. Near $x = 0$, in proximity to the double-stripe magnetic order
of Fe$_{1+y}$Te, a diverging $B_{1g}$ nematic susceptibility is observed. Upon increasing $x$, despite the absence of magnetic order, the $B_{2g}$ nematic susceptibility increases and becomes dominant, closely following the strength of the $(pi, pi)$ spin fluctuations. Over a wide range of compositions ($0.17 leq x leq 0.53$), while the $B_{2g}$ nematic susceptibility follows a Curie temperature dependence (with zero Weiss temperature) at low temperatures, it shows deviations from Curie-Weiss behavior for temperatures higher than $50K$. This is the opposite of what is observed in typical iron pnictides, where Curie-Weiss deviations are seen at low temperatures. We attribute this unusual temperature dependence to a loss of coherence of the $d_{xy}$ orbital, which is supported by our theoretical calculations. Our results highlight the importance of orbital differentiation on the nematic properties of iron-based materials.
Kagome metals AV3Sb5 (A = K, Rb, and Cs) exhibit superconductivity at 0.9-2.5 K and charge-density wave (CDW) at 78-103 K. Key electronic states associated with the CDW and superconductivity remain elusive. Here, we investigate low-energy excitations
of CsV3Sb5 by angle-resolved photoemission spectroscopy. We found an energy gap of 70-100 meV at the Dirac-crossing points of linearly dispersive bands, pointing to an importance of spin-orbit coupling. We also found a signature of strongly Fermi-surface and momentum-dependent CDW gap characterized by the larger energy gap of maximally 70 meV for a band forming a saddle point around the M point, the smaller (0-18 meV) gap for a band forming massive Dirac cones, and a zero gap at the Gamma-centered electron pocket. The observed highly anisotropic CDW gap which is enhanced around the M point signifies an importance of scattering channel connecting the saddle points, laying foundation for understanding the nature of CDW and superconductivity in AV3Sb5.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
