1Orbitalhybridization-drivenchargedensitywavetransition inCsV3Sb5Kagomesuperconductor ShulunHan1ChiSinTang12LinyangLi3YiLiu4HuiminLiu1JianGou56JingWu7

2025-04-30 0 0 2MB 16 页 10玖币

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Orbital hybridization-driven charge density wave transition

in CsV3Sb5Kagome superconductor

Shulun Han1#, Chi Sin Tang1,2,#, Linyang Li3,#, Yi Liu4,#, Huimin Liu1, Jian Gou5,6, Jing Wu7,

Difan Zhou1, Ping Yang2, Caozheng Diao2, Jiacheng Ji1, Jinke Bao1, Lingfeng Zhang1,*,

Mingwen Zhao8, M. V. Milošević9, Yanqun Guo1, Lijun Tian1, Mark B. H. Breese2,5,

Guanghan Cao10, Chuanbing Cai1, Andrew T. S. Wee5,6,*, Xinmao Yin1,*

1Shanghai Key Laboratory of High Temperature Superconductors, Shanghai Frontiers Science

Center of Quantum and Superconducting Matter States, Physics Department, Shanghai

University, Shanghai 200444, China

2The Singapore Synchrotron Light Source (SSLS), National University of Singapore,

Singapore 117603

3School of Science, Hebei University of Technology, Tianjin 300401, China

4Department of Applied Physics, Zhejiang University of Technology, Hangzhou 310023,

China.

5Department of Physics, Faculty of Science, National University of Singapore, Singapore

117542

6Centre for Advanced 2D Materials and Graphene Research, National University of Singapore,

Singapore 117546

7Institute of Materials Research and Engineering, Agency for Science, Technology and

Research (A∗STAR), 2 Fusionopolis Way, Singapore, 138634 Singapore

8School of Physics, Shandong University, Jinan 250100, China

9Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen,

Belgium

10Department of Physics, Zhejiang University, Hangzhou 310027, China

*Correspondence to: yinxinmao@shu.edu.cn (X.Y.); lingfeng_zhang@shu.edu.cn (L.Z.);

phyweets@nus.edu.sg (A.T.S.W.).

#These authors contributed equally to this work.

Abstract: Owing to its inherent non-trivial geometry, the unique structural motif of the

recently discovered Kagome topological superconductor AV3Sb5(A = K, Rb, Cs) is an

ideal host of diverse topologically non-trivial phenomena, including giant anomalous

Hall conductivity, topological charge order, charge density wave (CDW), and

unconventional superconductivity. Despite possessing a normal-state CDW order in the

form of topological chiral charge order and diverse superconducting gaps structures, it

remains unclear how fundamental atomic-level properties and many-body effects

including Fermi surface nesting, electron-phonon coupling, and orbital hybridization

contribute to these symmetry-breaking phenomena. Here, we report the direct

participation of the V3d—Sb5porbital hybridization in mediating the CDW phase

transition in CsV3Sb5. The combination of temperature-dependent X-ray absorption and

first-principles studies clearly indicate the Inverse Star of David structure as the

preferred reconstruction in the low-temperature CDW phase. Our results highlight the

critical role that Sb orbitals plays and establish orbital hybridization as the direct

mediator of the CDW states and structural transition dynamics in Kagome

unconventional superconductors. This is a significant step towards the fundamental

understanding and control of the emerging correlated phases from the Kagome lattice

through the orbital interactions and provide promising approaches to novel regimes in

unconventional orders and topology.

1. Introduction

Spontaneous symmetry breaking is a quintessential concept in condensed matter physics.

Landau's theory of phase transition emphasizes the importance of symmetry and links phase

transitions to symmetry-breaking phenomena such as superconductivity,[1, 2] superfluidity and

Bose-Einstein condensation,[3, 4] long-range charge-density wave (CDW)[5, 6] and magnetic

transition.[7] Symmetry-breaking phenomena are often found in quantum systems where the

complex interplay of charge, spin, lattice, and orbital degrees of freedom takes place.[8, 9]

Among other macroscopic quantum phenomena, the periodic distortion of the long-range

CDW is well recognized for the role it plays at the atomistic level. Yet the mechanism that

underlies its competitive or complementary relationship with unconventional

superconductivity[10, 11] remains unresolved. Recent reports of exotic chiral orders in the

layered Kagome Dirac metals, AV3Sb5(A = K, Rb or Cs),[12] are tantalizingly appealing to the

research community. With their unique lattice geometry, Kagome Dirac metals host a diverse

range of exotic properties and topologically-nontrivial states, exhibiting giant anomalous Hall

conductivity,[13] magneto-quantum oscillations,[14] topological charge order,[12, 15] and

superconductivity.[16, 17] Although there are reports of normal-state CDW of the topological

chiral charge order [12] and diverse superconducting gaps structures in Kagome materials,[18]

the roles of fundamental properties such as Fermi surface nesting,[19] electron-phonon

coupling,[20] and orbital hybridization play in these symmetry-breaking phenomena remain

largely unclear. Notably, this interest is further catalyzed by the effects of hybridization

between different constituent atomic orbitals and their close association with various quantum

phase transition processes.[21-25]

Here we report the direct participation of the V3d—Sb5porbital hybridization in mediating

the CDW transition dynamics in CsV3Sb5. The combination of temperature-dependent X-ray

absorption spectroscopy and first-principles studies in this comprehensive study further

reveals the Inverse Star of David (ISD) as the preferred structure in the CDW phase. Contrary

to conventional view where long-range charge order is mediated solely by the vanadium

atoms,[20, 26, 27] this study unambiguously highlights the pivotal role that the constituent

antimony orbitals play on the formation of van Hove singularity structures and the stability of

the CDW states in AV3Sb5systems, through their extensive interaction and the complementary

effects between the V- and Sb-atoms on the electronic structures (Figure 1a).[28-30] Our study

additionally gains importance in light of the recent report where Sb–oxygen covalency

contributes to the emergence of superconductivity in antimonates.[31] Unraveling the

mechanism that governs the CDW states in CsV3Sb5Kagome systems provides essential hints

to identify the key ingredients of Kagome unconventional superconductors and further serves

as a platform to uncover the interplay between the symmetry-breaking orders[19, 32] and other

unconventional orders and topologies.

2. Results and Discussion

2.1. Validation of Sample Quality

Layered CsV3Sb5single crystals were synthesized via a self-flux growth method.[16] This class

of AV3Sb5materials exists in both the conventional 1×1 hexagonal crystal structure,[13] and the

√3×√3R30° reconstruction.[32] Figure 1b displays the Scanning tunneling microscopy (STM)

topographic image of the Cs-terminated surface which indicates the typical single-unit-cell

terrace of ~ 9.4 Å (Figure 1c).[13, 33] The two unique cleaved Cs surface morphologies along

the red dotted lines (Figure 1d) are plotted in Figure 1e where they correspond to the 1×1

hexagonal and √3×√3R30° structures, respectively.

The very high crystallinity and quality of the CsV3Sb5sample is further confirmed via

high-resolution X-ray Diffraction (HR-XRD), in its diffraction pattern and its regular

hexagonal structure (Figure 2a).[34] Reciprocal space mappings (RSMs) along the (004)HL and

05)HL orientations (Figure 2b and c, respectively) further confirmed the good crystalline

property of the single-crystal sample via the weakly diffusing features B and C from the main

peak A.

The presence of the CDW states in the CsV3Sb5sample is confirmed through the magnetic

susceptibility, χ(T), where it exhibits a sharp decline at ~94 K for µ0H=1 T and H//ab (Figure

2d).[13, 16] Temperature-dependent magnetic susceptibility 4πχ(T) under zero-field-cooling

(ZFC) and field-cooling (FC) modes at 1 mT for H//ab (Figure 2e) also confirms the

superconductive state in this sample at TC~2.6 K.[16]

2.2. Temperature-dependent X-ray Absorption Spectroscopy Characterization

To investigate the evolving electronic structures and orbital-coupling properties of CsV3Sb5in

temperature ranges near TCDW, the temperature-dependent X-ray absorption spectroscopy

(XAS) is conducted to examine how the V3dorbital evolve in this temperature range. The

characteristic peaks registered by the XAS measurements correspond to the unoccupied band

above the Fermi surface, which is strongly sensitive to lattice symmetry, crystal field splitting

and orbital hybridization.[35, 36] Figure 3a displays the temperature-dependent V L-edge XAS

spectra of the CsV3Sb5sample over a wide temperature range around TCDW. In the XAS

spectra, where shoulders A* (~517.0 eV), B* (~518.2 eV) and the characteristic peaks C* and

D* (~519.2 and ~525.6 eV, respectively) are observed. Feature A* is attributed to the slight

hybridization between atomic orbitals while C* and D* are the L2,3-edges representing the

V2p3/2/p1/2→3delectronic transitions,[37] all displaying very weak temperature variation that

falls within the experimental error range between 40 and 300 K. While feature C* registers a

slight temperature variation, there is no clear temperature-dependent trend that is noticeable.

Conversely, we noticed a prominent shoulder B* (denoted by black solid arrow) before the

L3-edge displaying very strong and clear temperature-dependent unlike the other

aforementioned features in the XAS spectra. To better distinguish the temperature-dependent

intensity of the respective features, an intensity differential map, ∆μ=μ(T)-μ(TCDW=94 K), is

plotted for the entire temperature range between 40 and 300 K (Figure 3b) with the XAS

spectrum at TCDW=94 K taken as reference. The intensity differential, ∆μ, displays very strong

temperature-dependent fluctuation at ~518.2 eV where feature B* is located, while remaining

largely unchanged in the other spectral regions, especially where the V-L2,3 absorption edges

are located. These are indications that the V3dorbital do not mediate or participate in the

formation of the CDW states alone. Instead, the strong temperature-dependence of shoulder

B* particularly near TCDW provides strong suggestion to investigate in detail the interaction

and hybridization of the V3dorbital with their neighbouring electronic bands.[38] Notably, the

roles of orbital hybridization in mediating the CDW phase transition are not merely restricted

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1Orbitalhybridization-drivenchargedensitywavetransitioninCsV3Sb5KagomesuperconductorShulunHan1#,ChiSinTang1,2,#,LinyangLi3,#,YiLiu4,#,HuiminLiu1,JianGou5,6,JingWu7,DifanZhou1,PingYang2,CaozhengDiao2,JiachengJi1,JinkeBao1,LingfengZhang1,*,MingwenZhao8,M.V.Milošević9,YanqunGuo1,LijunTian1,MarkB.H.Bree...

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1Orbitalhybridization-drivenchargedensitywavetransition inCsV3Sb5Kagomesuperconductor ShulunHan1ChiSinTang12LinyangLi3YiLiu4HuiminLiu1JianGou56JingWu7

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