Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session G61: Superconductivity: Kagomes & Other SC Materials -IIRecordings Available
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Sponsoring Units: DCMP Chair: Rongying Jin, University of South Carolina Room: Hyatt Regency Hotel -Field |
Tuesday, March 15, 2022 11:30AM - 11:42AM |
G61.00001: Coexistence of superconductivity and magnetic order in a kagome lattice material Liangzi Deng, Melissa J Gooch, Trevor Bontke, Jiaxin Yin, Youguo Shi, Qimiao Si, Guoqing Chang, Zheng Wu, Ching-Wu Chu The intertwining of superconductivity, magnetism, and non-trivial topology is at the frontier of condensed matter physics. Kagome lattices have attracted research interest due to their potential for hosting a quantum spin liquid. Recently, it was demonstrated that they can possibly host both topologically protected bands and non-dispersing or flat bands. Ru atoms form a kagome lattice perpendicular to the [111] direction in CeRu2. Our density-functional theory (DFT) calculations also revealed a kagome flat band near the Fermi surface. At ambient pressure, CeRu2 shows a sharp superconducting transition at ~ 5 K based on resistivity measurements, as well as a weak magnetic order at temperatures up to ~ 40 K. A systematic investigation was performed to study the superconductivity and magnetic order in CeRu2 under pressure via both magnetic and resistivity measurements. An unusual magnetic phase diagram that suggests an intriguing interplay between its superconducting order parameters has been constructed. A Tc resurgence was detected under pressure above ~ 30 GPa. Detailed results will be presented and discussed. |
Tuesday, March 15, 2022 11:42AM - 11:54AM |
G61.00002: Revealing the competition between charge density wave and superconductivity in CsV3Sb5 through uniaxial strain Tiema Qian In this talk, I will discuss the effect of uniaxial strain ε applied on the newly discovered Kagome superconductor CsV3Sb5 [1]. At ambient conditions, CsV3Sb5 shows a charge-density-wave (CDW) transition at TCDW=94.5K and superconducts below Tc = 3.34 K. We revealed that when the uniaxial strain ε is varied from -0.90% to 0.90%, Tc monotonically increases by ~ 33%. On the other hand, for ε changing from -0.76% to 1.26%, TCDW decreases monotonically by ~10%. The opposite response of Tc and TCDW to the uniaxial strain suggests strong competition between these two orders. Comparison with hydrostatic pressure measurements indicates that it is the change in the c-axis that is responsible for these behaviors of the CDW and superconducting transitions, and that the explicit breaking of the sixfold rotational symmetry by strain has a negligible effect. Together with the theoretical studies, we propose that the trilinear coupling between the M+1 and L-2 phonon modes plays an important role in the CDW. |
Tuesday, March 15, 2022 11:54AM - 12:06PM |
G61.00003: A New Superconductor with Ir Kagome Lattice Xin Gui, Robert J Cava Novel materials consisting of Kagome lattice are recently strongly desired and thought to host exotic quantum physics such as quantum spin liquid state, topological quantum state and superconductivity. Flat bands, Dirac cones and topologically nontrivial surface states are also supposed to be favored in Kagome compounds. Here in this work, we present the synthesis and characterization of a new layered ternary material with heavy-metal Kagome lattice. Small crystals can be found in as-cast samples after arc melting. Physical properties measurements performed on the crystals show bulk superconducting behavior with Tc ~ 5.2 K. The magnetization results indicate a small lower critical field ~ 5.5 mT while the upper critical field ~ 4.7 T is determined by electrical resistivity measurements. The normalized superconducting heat capacity jump is calculated to be 2.45, which significantly exceeds the value for weak coupling BCS superconductor (1.43), suggesting strongly coupled nature in the new material. Moreover, the short Ginzburg-Landau coherence length implies strong electron-electron correlation in our material. Electronic structures were calculated with and without consideration of spin-orbit coupling (SOC) effect to further interpret the physical properties. Semimetallic behavior is suggested by band structure calculated with SOC effect. The d states of heavy atoms were found to be dominant near the Fermi energy (EF) while a nearly flat band was observed around 100 meV below EF as well. Two Dirac points found close to EF without consideration of SOC effect suggest potentially topological interests in the newly discovered system. |
Tuesday, March 15, 2022 12:06PM - 12:18PM |
G61.00004: Discovery of chiral charge order in kagome superconductors AV3Sb5 (A=K, Rb, Cs) and beyond Jiaxin Yin, Yuxiao Jiang, Nana Shumiya, Shafayat Hossain, M Zahid Hasan Quantum orders featuring magnetic and electronic duality are rare in nature. A chiral charge order with orbital currents has been proposed for achieving the quantum anomalous Hall effect in topological materials and for the hidden phase in cuprate high-temperature superconductors. However, the experimental realization of such an order is challenging. I will discuss our discovery of a 2x2 chiral charge order in kagome superconductors AV3Sb5 (A=K, Rb, Cs) and beyond. In these materials, we use magnetic field perturbed scanning tunneling microscopy to observe the 2x2 modulations in both topography and spectroscopy imaging. The 2x2 electronic order exhibits chirality, which can couple with an external magnetic field or intrinsic magnetic order. I will further discuss the implications of the chiral charge order in the kagome lattice. |
Tuesday, March 15, 2022 12:18PM - 12:30PM |
G61.00005: Van Hove charge density waves on hexagonal lattices: Haldane-model phase diagram, higher-order topology, and kagome superconductors Yu-Ping Lin, Rahul Nandkishore I show that the charge density waves can realize a host of unconventional phenomena at the Van Hove singularity on the hexagonal lattices, including the triangular, honeycomb, and kagome lattices. Under the interplay of real and imaginary orders, a Haldane-model phase diagram arises from the 3Q complex orders at three nesting momenta. The Chern insulators explain transparently the recent experiments on the kagome metals AV3Sb5 with A = K, Rb, Cs. Meanwhile, the 3Q charge bond orders can realize the higher-order topological insulators, where in-gap corner states arise and manifest fractional corner charges. I further propose that the superconductivity can develop from the reconstructed Pomeranchuk fluctuations in the parent charge density waves, which acquires strong evidences in the kagome metals AV3Sb5. Our theoretical model unprecedently explains the double-dome superconductivity under pressure, which is attributed to two reconstructed Van Hove singularities. More intriguing phenomena are expected for future explorations. |
Tuesday, March 15, 2022 12:30PM - 12:42PM |
G61.00006: Mechanisms for superconductivity, density wave, and excitonic order in kagome metals Julian P Ingham The recent discovery of superconducting kagome metals AV3Sb5 (A= K, Rb, Cs) have provided an exciting example of quasi-two-dimensional materials exhibiting unconventional superconductivity, a topologically non-trivial normal state, and novel competing ground states - with density wave order and signatures of time-reversal symmetry breaking above Tc. Inspired by these developments, this talk will describe theoretical approaches to superconductivity in kagome metals. First, we describe a theory reliant on approximately nested portions of the Fermi surface. Considering a stack of weakly-coupled two-dimensional layers at slightly displaced carrier densities, we find weak interlayer coupling gives rise to a chiral excitonic instability alongside density wave order and superconductivity. The perturbative RG method is used to analyze the interplay between superconductivity and competing orders. Second, we describe an approach which relies on the unnested Dirac pockets. The Berry phase of the Dirac points leads to a destructive interference effect, whereby a paired state of electrons with momenta k and -k partially cancels the Coulomb repulsion, making it energetically preferable to form Cooper pairs. The resulting superconducting state is spatially modulated, and possesses higher-order topology with Majorana corner modes. Connections with experiments on AV3Sb5 are discussed. |
Tuesday, March 15, 2022 12:42PM - 12:54PM |
G61.00007: Novel relation between superconductivity and CDW phase in kagome metal AV3Sb5 Rina Tazai, Hiroshi Kontani, Youichi Yamakawa, Seiichiro Onari Recent experiments have revealed unconventional charge density-wave (CDW) and superconductivity in frustrated kagome metal AV3Sb5 and their interplay attracts increasing attention. Here, we study microscopic origin of the CDW and superconductivity based on the simple Hubbard model with on-site Coulomb interaction U. We reveal that the David-Star-type bond order originates from the nonlocal backward and umklapp scattering due to the novel paramagnon interference among different van Hove singular points. In addition, the bond-order fluctuations give sizable beyond-Migdal pairing interaction for superconductivity. For this reason, both the triplet p-wave pairing and the singlet s-wave pairing states are expected to emerge as bond-fluctuation mediated exotic superconducting phase. |
Tuesday, March 15, 2022 12:54PM - 1:06PM |
G61.00008: Muon spin resonance charaterization of a CsV3Sb5 single cystal superconductor. Jonah Gautreau, Graeme M Luke, Stephen D Wilson, Brenden Ortiz, Kenji M Kojima, Sudarshan Sharma, James W Beare, Mathew Pula, Yipeng Cai, Sungwon Yoon CsV3Sb5 a member of the recently discovered class of Kagome superconductors AV3Sb5 (A=K, Rb, Cs), which provide a rich environment to study topological band structure and charge density wave (CDW) order in an ideal vanadium Kagome lattice. In this work we performed muon spin rotation/relaxation (uSR) measurements on high-quality single crystal samples in the normal and superconducting states. In our measurement of we find no evidence of broken time reversal symmetry behavior associated with the superconducting state. Our measurements of the magnetic field penetration are well described by a two-gap model. Measurements of the normal state reveal changes to the internal field distribution at the muon site below approximately 60K and 30K, indicating the presence of several changes in the electrodynamics of CsV3Sb5 in addition to its charge density wave and superconducting order. |
Tuesday, March 15, 2022 1:06PM - 1:18PM |
G61.00009: Anisotropic energy gap induced by charge density wave in kagome superconductors AV3Sb5 Takemi Kato, Yongkai Li, Tappei Kawakami, Min Liu, Kosuke Nakayama, Zhiwei Wang, Ayumi Moriya, Kiyohisa Tanaka, Takashi Takahashi, Yugui Yao, Takafumi Sato We have investigated the electronic structure of kagome superconductor AV3Sb5 by high-resolution angle-resolved photoemission spectroscopy (ARPES) [1,2], and observed multi-orbital nature of the valence-band structure in AV3Sb5. Our high-resolution measurements also revealed a drastic electronic reconstruction and an energy gap opening triggered by the charge-density-wave (CDW) transition. In this talk, we will show temperature and hν dependence of band structure across TCDW, and discuss the origin of CDW in terms of the electronic structure. |
Tuesday, March 15, 2022 1:18PM - 1:30PM |
G61.00010: Competition of superconductivity and charge density wave in selective oxidized CsV3Sb5 thin akes Tianping Ying, Yanpeng Song, Xu Chen, Xu Han, Andreas P Schnyder, Yuan Huang, Jiangang Guo, Xiaolong Chen The recently discovered layered kagome metals AV3Sb5 (A = K, Rb, and Cs) with vanadium kagome networks provide a novel platform to explore correlated quantum states intertwined with topological band structures. In the firt part, we report the prominent eect of hole doping on both superconductivity and charge density wave (CDW) order, achieved by selective oxidation of exfoliated thin akes. A superconducting dome is revealed as a function of the effective doping content. The superconducting transition temperature (Tc) and upper critical eld in thin akes are significantly enhanced compared with the bulk, which are accompanied by the suppression of CDW. Our detailed analyses establish the pivotal role of van Hove singularities (VHSs) in promoting correlated quantum orders in these kagome metals. Our experiment not only demonstrates the intriguing nature of superconducting and CDW orders, but also provides a novel route to tune the carrier concentration through both selective oxidation and electric gating. In the second part, we report our discovery of two new families of A-V-Sb system, namely AV6Sb6 and AV8Sb12. |
Tuesday, March 15, 2022 1:30PM - 1:42PM |
G61.00011: Electronic Nature of Charge Density Wave and Electron-Phonon Coupling in Kagome Superconductor KV3Sb5 Hailan Luo, Xingjiang Zhou, Kun Jiang, Qiang Gao, Yuhao Gu, Youguo Shi The Kagome superconductors AV3Sb5 (A=K, Rb, Cs) have received enormous attention due to their nontrivial topological electronic structure, anomalous physical properties and superconductivity. Unconventional charge density wave (CDW) has been detected in AV3Sb5 that is found to be intimately intertwined with the anomalous Hall effect and superconductivity. High-precision electronic structure determination is essential to understand the origin of the CDW transition and its interplay with electron correlation, topology and superconductivity, yet, little evidence has been found about the impact of the CDW state on the electronic structure in AV3Sb5. Here we unveil electronic nature of the CDW phase in our high-resolution angle-resolved photoemission (ARPES) measurements on KV3Sb5. We have observed CDW-induced Fermi surface reconstruction and the associated band structure folding. The CDW induced band splitting and the associated gap opening have been revealed at the boundary of the pristine and reconstructed Brillouin zone. The Fermi surface and momentum-dependent CDW gap is measured for the first time and the strongly anisotropic CDW gap is observed for all the V-derived Fermi surface sheets. In particular, we have observed signatures of the electron-phonon coupling for all the V-derived bands. These results provide key insights in understanding the nature of the CDW state and its interplay with superconductivity in AV3Sb5 superconductors. |
Tuesday, March 15, 2022 1:42PM - 1:54PM |
G61.00012: Evolution of three-dimensional electronic structure in kagome superconductor CsV3Sb5 Yang Luo The effect of out-of-plane dimensionality on correlated quasi-two-dimensional (2D) materials has become increasingly evident. Recently, CsV3Sb5 has attracted much attention as the first quasi-2D kagome superconductor. While the kagome layers are 2D in nature, interlayer-interaction has been considered crucial in this system, and 3D charge density wave (CDW) has been observed. Here, we reveal the 3D electronic structure in CsV3Sb5, using angle-resolved photoemission spectroscopy (ARPES), complemented by scanning tunneling microscope (STM) and core level measurements. The complete 3D electronic structure of CsV3Sb5 in high temperature normal state are revealed, which agree well with density functional theory (DFT) calculations. New electron energy bands are observed in low temperature state, which exhibit clearly periodicities along the out-of-plane momentum (KZ). STM and core level measurements further indicate that the low temperature band reconstruction mainly appears on regions where the 3D CDW is most clearly identified. Our results reveal a direct response to the three-dimensionality of CDW in single-particle spectral function, and establish an electronic platform to examine the exotic phenomena beyond 2D limit in kagome superconductors. |
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