Enhanced Charge-Density-Wave Order and Suppressed Superconductivity in Intercalated Bulk $\mathrm{Nb}{\mathrm{Se}}_{2}$
Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院）；Institut Néel CNRS/UGA（格勒诺布尔国家科学研究中心/格勒诺布尔大学尼尔研究所）
Huanhuan Shi, Qili Li, Antoine M. T. Baron, Marie-Aude Méasson, Sangjun Kang, Dirk Fuchs, Fabian Henssler, Alexander Haas, Paolo Battistoni, Nour Maraytta, Mich… 展开作者
Huanhuan Shi, Qili Li, Antoine M. T. Baron, Marie-Aude Méasson, Sangjun Kang, Dirk Fuchs, Fabian Henssler, Alexander Haas, Paolo Battistoni, Nour Maraytta, Michael Merz, Amir-Abbas Haghighirad, Wulf Wulfhekel, Christian Kübel, Matthieu Le Tacon
The electronic ground states of transition-metal dichalcogenides are strongly shaped by reduced dimensionality, yet the properties of atomically thin layers remain difficult to probe due to their small size and environmental sensitivity. Here we demonstrate that controlled electrochemical intercalation of organic cations provides a robust bulk platform for accessing monolayer-like physics in NbSe$_2$. Intercalation of tetrapropylammonium and tetrabutylammonium expands the interlayer spacing by nearly a factor of two, electronically decoupling the NbSe$_2$ layers while simultaneously introducing well-defined charge doping. Using a combination of Raman spectroscopy, scanning tunneling microscopy, X-ray diffraction, and photoemission, we uncover a pronounced enhancement of the charge-density-wave transition temperature to $\sim 130$ K together with a strong suppression of superconductivity, reproducing the phase diagram observed in exfoliated monolayers. The enhanced charge-density-wave order and reduced $T_c$ arise from the combined effects of dimensionality reduction and electron injection, and are accompanied by distinct dip-hump anomalies in the tunneling spectra suggestive of collective mode excitations. Our results establish molecular intercalation as a powerful and scalable route for engineering competing orders in layered quantum materials.
We systematically investigated the superconducting properties and the interplay between charge-density-waves (CDW) and superconductivity in lithium-intercalated 2H-TaS2. By gradually increasing the lithium content x, the CDW formation temperature is continuously suppressed, and the onset temperature of superconductivity is increased with a maximum transition temperature Tc = 3.5 K for x = 0.096. The bulk nature of superconductivity is confirmed by a superconducting shielding fraction of the order of unity for this composition. The electronic contribution to the specific heat and Hall resistivi…
We present a theoretical investigation on electron-phonon superconductivity of honeycomb MX$_2$ layered structures. Where X is one element of the group-IV (C, Si or Ge) and M an alkali or an alkaline-earth metal. Among the studied composition we predict a $T_c$ of 7 K in RbGe$_2$, 9 K in RbSi$_2$ and 11 K in SrC$_2$. All these compounds feature a strongly anisotropic superconducting gap. Our results show that despite the different doping and structural properties, the three families of materials fall into a similar description of its superconducting behavior. This allows us to estimate an uppe…
We report the superconductivity in Ca-intercalated bilayer graphene C$_6$CaC$_6$, the thinnest limit of Ca graphite intercalation compound. We performed \textit{in situ} electrical transport measurements on pristine bilayer graphene, C$_6$LiC$_6$ and C$_6$CaC$_6$ fabricated on SiC substrate under zero and non-zero magnetic field. While both bilayer graphene and C$_6$LiC$_6$ show non-superconducting behavior, C$_6$CaC$_6$ exhibits the superconductivity with transition temperature ($T_{\rm c}$) of 4.0 K. The observed $T_{\rm c}$ in C$_6$CaC$_6$ and the absence of superconductivity in C$_6$LiC$_6…
We report comprehensive high pressure studies on correlation between intercalated magnetic layers and superconductivity in EuFe2(As0.81P0.19)2 single crystal through in-situ high pressure resistance, specific heat, X-ray diffraction and X-ray absorption measurements. We find that an unconfirmed magnetic order of the intercalated layers coexists with superconductivity in a narrow pressure range 0-0.5GPa, and then it converts to a ferromagnetic (FM) order at pressure above 0.5 GPa, where its superconductivity is absent. The obtained temperature-pressure phase diagram clearly demonstrates that th…
Pd-intercalated ErTe$_3$ is studied as a model system to explore the effect of "intertwined" superconducting and charge density wave (CDW) orders. Despite the common wisdom that superconductivity emerges only when CDW is suppressed, we present data from STM and AC susceptibility measurements that show no direct competition between CDW order and superconductivity. Both coexist over most of the intercalation range, with uniform superconductivity over length scales that exceed the superconducting coherence length. This is despite persisting short-range CDW order and increased scattering from the …
The weak van der Waals interlayer interactions in the transition metal dichalcogenide (TMD) materials have created a rich platform to study their exotic electronic properties through chemical doping or physical gating techniques. We reported bulk superconductivity up to 7.6 K through careful manipulation of the charge carrier density and interlayer spacing d in the chemically intercalated two dimensional 1T-SnSe2 phase. We found, for the first time in the two dimensional SnSe2, that polar organic molecules cointercalated with the alkali metal Li into the basal layers, thus significantly enhanc…
Bulk FeSe becomes superconducting below 9\,K, but the critical temperature (T$_{c}$) is enhanced almost universally by a factor of $\sim$4-5 when it is intercalated with alkali elements. How intercalation modifies the structure is known from in-situ X-ray and neutron scattering techniques, but why T$_{c}$ changes so dramatically is not known. Here we show that there is one-to-one correspondence between the enhancement in magnetic instabilities at certain $\bf q$ vectors and superconducting pairing vertex, even while the nuclear spin relaxation rate ${1}/{(T_{1}T)}$ may not reflect this enhance…
The parent compound of an unconventional superconductor must contain unusual correlated electronic and magnetic properties of its own. In the high-Tc potassium intercalated FeSe, there has been significant debate regarding what the exact parent compound is. Our studies unambiguously show that the Fe-vacancy ordered K2Fe4Se5 is the magnetic, Mott insulating parent compound of the superconducting state. Non-superconducting K2Fe4Se5 becomes a superconductor after high temperature annealing, and the overall picture indicates that superconductivity in K2-xFe4+ySe5 originates from the Fe-vacancy ord…
TaSe$_2$ has several different polytypes and abundant physical properties such as superconductivity and charge density waves (CDW), which had been investigated in the past few decades. However, there is no report on the physical properties of 4$Ha$ polytype up to now. Here we report the crystal growth and discovery of superconductivity in the tantalum self-intercalated 4$Ha$-Ta$_{1.03}$Se$_2$ single crystal with a superconducting transition onset temperature $T_{\rm c}$ $\approx$ 2.7 K, which is the first observation of superconductivity in 4$Ha$ polytype of TaSe$_2$. A slightly suppressed CDW…
The superconductivity and intercalation statein the lithium-and hexamethylenediamine (HMDA)-intercalated superconductor Li$_x$(C$_6$H$_{16}$N$_2$)$_y$Fe$_{2-z}$Se$_2$ have been investigated from powder x-ray diffraction, thermogravimetric and magnetic susceptibility measurements, changing the intercalation temperature, $T_i$, and the Li content, $x$. Both Li and HMDA have been co-intercalated stably up to $x$ = 2 roughly in the molar ratio of $x : y = 2 : 1$. In the case of $T_i$ = 45$^\circ$C, it has been found that both Li and HMDA are co-intercalated locally at the edge of FeSe crystals, in…
Inspired by naturally occurring sulfide minerals, we present a new family of iron-based superconductors. A metastable form of FeS known as the mineral mackinawite forms two-dimensional sheets that can be readily intercalated by various cationic guest species. Under hydrothermal conditions using alkali metal hydroxides, we prepare three different cation and metal hydroxide-intercalated FeS phases including (Li$_{1-x}$Fe$_x$OH)FeS, [(Na$_{1-x}$Fe$_x$)(OH)$_2$]FeS, and K$_x$Fe$_{2-y}$S$_2$. Upon successful intercalation of the FeS layer, the superconducting critical temperature $T_c$ of mackinawi…
Superconductivity intrinsic to the intercalated black phosphorus (BP) with a transition temperature Tc of 3.8 K, independent of the intercalant, whether an alkali or an alkaline earth element, has been reported recently by R. Zhang et al. (2017). However, the reported Tc and the field effect on the superconducting (SC) transition both bear great similarities to those for the pure Sn, which is commonly used for BP synthesis under the vapor transport method. We have therefore decided to determine whether a minute amount of Sn is present in the starting high purity BP crystals and whether it is t…
Though the superconducting phase of the type-II Dirac semimetal PdTe$_2$ was shown to be conventional in nature, the phase continued to be interesting in terms of its magnetic properties. While certain experiments indicated an unexpected type-I superconducting phase, other experiments revealed formation of vortices under the application of magnetic fields. Recently, scanning tunneling spectroscopy (STS) experiments revealed the existence of a mixed phase where type-I and type-II behaviours coexist. Here, based on our temperature and magnetic field dependent STS experiments on Cu-intercalated P…
Bulk Ising superconductivity in an intercalated TaSe2 bilayer structure
Hangzhou Normal University（杭州师范大学）；Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；Zhejiang University（浙江大学）；University of Chinese Academy of Sciences（中国科学院大学）
To realize topological superconductor is one of the most attracting topics because of its great potential in quantum computation. In this study, we successfully intercalate potassium (K) into the van der Waals gap of type II Weyl semimetal WTe2, and discover the superconducting state in KxWTe2 through both electrical transport and scanning tunneling spectroscopy measurements. The superconductivity exhibits an evident anisotropic behavior. Moreover, we also uncover the coexistence of superconductivity and the positive magneto-resistance state. Structural analysis substantiates the negligible la…
In the case of Li-intercalated hexagonal boron nitride bilayer (Li-hBN), the vertex corrections of electron-phonon interaction cannot be omitted. This is evidenced by the very high value of the ratio $λω_{D}/\varepsilon_{F}\sim 0.46$, where $λ$ is the electron-phonon coupling constant, $ω_{D}$ is the Debye frequency, and the symbol $\varepsilon_{F}$ represents the Fermi energy. Due to the nonadiabatic effects, the phonon-induced superconducting state in Li-hBN is characterized by the much lower value of critical temperature ($T^{\rm LOVC}_{C}\in\{ 19.1, 15.5, 11.8\}$ K, for $μ^{\star}\in \{0.1…
Superconductivity in the Intercalated Graphite Compounds C6Yb and C6Ca
本文报道了在等结构石墨层间化合物C_6Yb和C_6Ca中发现的超导电性，其转变温度分别为6.5K和11.5K。这些化合物的结构表征表明，它们是六方层状系统在同一类的其他石墨插层。如果我们假设所有的外层s-电子都从嵌入物转移到石墨片上，那么这些化合物中的电荷转移与其他超导石墨嵌入物如C8 K 1，2相当。然而，C6 Yb和C6 Ca的超导转变温度高达两个数量级。有趣的是，超导上临界场的研究和电阻率测量表明，这些化合物是显着更各向同性比纯石墨。这是出乎意料的，因为引入插层剂的效果是使石墨层进一步分开。
The discovery of superconductivity in alkali-ammonia co-intercalated FeSe has generated intensive interest because of their highest Tc (~ 45 K) among iron-chalcogenide superconductors with bulk form. Here, we report the phase diagrams of two series of Li/Na-ammonia co-intercalated FeSe1-zTez. When superconductivity is suppressed by Te doping, the magnetic ordering states are emergent. Moreover, a novel phase Lix(NH3)yFe2-δTe2 with possible antiferromagnetism is discovered. This strongly indicates the intimate relation between superconductivity and magnetism in these materials, like in other ir…
Superconductivity at 22.3 K in Compressed Sodium-intercalated Graphite
Center for High Pressure Science, State Key Laboratory of Metastable Materials Science and Technology, Yanshan University（燕山大学亚稳材料科学与国家重点实验室高压科学中心）；Hebei Key Laboratory of Microstructural Material Physics, School of Science, Yanshan University（燕山大学理学院河北省微观结构材料物理重点实验室）；Key Laboratory of Weak-Light Nonlinear Photonics, School of Physics, Nankai University（南开大学物理学院弱光非线性光子学重点实验室）
The discovery of the high temperature superconducting state in compounds of hydrogen, carbon and sulfur with the critical temperature (Tc) of 288 K at high pressure is an important milestone towards room-temperature superconductors. Here, we have extensively investigated the high-pressure phases of CS2H10, and found four phases Cmc21, P3m1, P-3m1 and Pm. Among them, P3m1 can be dynamically stable at pressure as low as 50 GPa, and Cmc21 has high Tc of 155 K at 150 GPa. Both of Cmc21 and P3m1 are host-guest hydrides, in which CH4 molecules are inserted into Im-3m-H3S and R3m-H3S sublattices, res…
Topological superconductivity is an exotic phase of matter in which the fully gapped superconducting bulk hosts gapless Majorana surface states protected by topology. Intercalation of copper, strontium or niobium between the quintuple layers of the topological insulator Bi$_2$Se$_3$ increases the carrier density and leads to superconductivity that is suggested to be topological. Here we study the electronic structure of strontium-intercalated Bi$_2$Se$_3$ using angle resolved photoemission spectroscopy (ARPES) and Shubnikov-de Haas (SdH) oscillations. Despite the apparent low Hall number of $\…
Ca-intercalation has opened a way for superconductivity in graphene on SiC. However, the atomic and electronic structures being critical for superconductivity are still under discussion. We find the essential role of the interface between monolayer graphene and the SiC substrate for superconductivity. In the Ca-intercalation process, at the interface a carbon layer terminating SiC changes to graphene by Ca-termination of SiC (monolayer graphene becomes bilayer) with inducing more carriers than a free-standing model. Then, Ca is intercalated in-between graphene layers, which shows superconducti…
Creating carrier reservoirs in layered compounds can effectively tune the carrier density, which often induces a variety of emergent properties. Based on solid-ion-conductor gating technique, we successfully induce superconductivity of 4.8 K in ultrathin Li-intercalated SnSe2 samples. The Li+ ions are driven in between interspacing of SnSe2 layers and form a single reservoir layer to provide electrons. In addition, a dome-like T c is found through substituting of S for Se, where the optimal T c is 6.2 K for SnSe1.8S0.2. Density functional theory calculations confirm that the intercalated LiSnS…
Built on a realistic multiband tight-binding model, mirror symmetry is used to map a calcium-intercalated bilayer graphene Hamiltonian into two independent single layer graphene-like Hamiltonians with renormalized hopping. The quasiparticles exhibit two types of chirality. Here a quasi-particle consists of two electrons from opposing layers where possess an additional quantum number called "cone index" which can be regarded as the eigenvalue of mirror symmetry operations. To obtain tight-binding parameters, both effective monolayer Schrodinger equations are solved analytically and fitted to fi…
Behavior consistent with Coulomb-mediated high-T$_C$ superconductivity is shown to be present in the intercalated group-4-metal nitride halides A$_x$(S)$_y$MNX, where the MNX host (M = Ti, Zr, Hf; X = Cl, Br) is partially intercalated with cations A$_x$ and optionally molecular species (S)$_y$ in the van der Waals gap between the halide X layers, expanding the basal-plane spacing d. The optimal transition temperature is modeled by T$_{C0}$ ${\propto}$ ζ$^{-1}$(σ/$A$)$^{1/2}$, where the participating fractional charge per area per formula unit σ/$A$ and the distance ζ, given by the transverse A…
This study examines the potential of superconductivity in transition metal (TM) intercalated bilayer graphene through a systematic study of the electronic and magnetic properties. We determine the electronic structure for all first row TM elements in the stable honeycomb configuration between two layers of graphene using density functional theory (DFT). Through an analysis of the electron density, we assess the induction of the magnetic moment in each case, where a comparison of the ferromagnetic and antiferromagnetic configurations allow us to ascertain an estimated exchange coupling between …
When certain elemental metals like Cu, Sr and Nb are intercalated between the layers of Bi$_2$Se$_3$, a topological insulator, the intercalated systems superconduct with critical temperatures around 3 K. Naturally, in all these cases, the possibility of topological superconductivity was suggested and explored. However, in cases of Cu and Sr intercalated systems, the low-temperature scanning tunneling microscopy (STM) experiments revealed fully formed gaps where no signature of low-energy states, a requisite for topological superconductivity, was found. Here, through STM spectroscopy down to 40…
Chiral superconductors, a unique class of unconventional superconductors in which the complex superconducting order parameter winds clockwise or counter-clockwise in the momentum space, represent a topologically non-trivial system with direct implications for topological quantum computing. Intrinsic chiral superconductors are extremely rare, with only a few arguable examples including heavy fermion metals (UTe$_2$, UPt$_3$) and perovskite superconductor Sr$_2$RuO$_4$. Chiral molecules with neither mirror nor inversion symmetry have been widely investigated, in which the spin degeneracy may be …
Graphene holds promises for exploring exotic superconductivity with Dirac-like fermions. Making graphene a superconductor at large scales is however a long-lasting challenge. A possible solution relies on epitaxially-grown graphene, using a superconducting substrate. Such substrates are scarce, and usually destroy the Dirac character of the electronic band structure. Using electron diffraction (reflection high-energy, and low-energy), scanning tunneling microscopy and spectroscopy, atomic force microscopy, angle-resolved photoemission spectroscopy, Raman spectroscopy, and density functional th…
We have succeeded in synthesizing new intercalation superconductors Lix(C2H8N2)yMoSe2 and Lix(C6H16N2)yMoSe2 with Tc = 4.2 and 3.8-6.0 K, respectively, via the co-intercalation of lithium and ethylenediamine or hexamethylenediamine into semiconducting 2H-MoSe2. It has been found that the Tc values are related not to the interlayer spacing between MoSe2 layers so much but to the electronic density of states (EDOS) at the Fermi level. Moreover, only Li-intercalated LixMoSe2 with a small interlayer spacing has been found to be non-superconducting. Accordingly, it has been concluded that not only …
Charge density waves (CDWs) with superconductivity, competing Fermi surface instabilities and collective orders, have captured much interest in two-dimensional van der Waals (vdW) materials. Understanding of CDW suppression mechanism, its connection to emerging superconducting state and electronic correlations provides opportunities for engineering the electronic properties of vdW heterostructures and thin film devices. Using combination of the thermal transport, X-ray photoemission spectroscopy, Raman measurements, and first-principle calculations, we observe an increase in electronic correla…
Novel quasi two dimensional typically layered semimetals offer a unique opportunity to control the density and even the topology of the electronic matter. In intercalated MoTe2 type II Weyl semimetal the tilt of the dispersion relation cones is so large that topologically of the Fermi surface is distinct from a more conventional type I. Superconductivity observed recently in this compound [Zhang et al, 2D Materials 9, 045027 (2022)] demonstrated two puzzling phenomena: the gate voltage has no impact on critical temperature, Tc, in wide range of density, while it is very sensitive to the interl…
New intercalation superconductors of Li$_x$(C$_2$H$_8$N$_2$)$_y$TiSe$_2$ and Li$_x$(C$_6$H$_{16}$N$_2$)$_y$TiSe$_2$ with $T_{\rm c}$ = 4.2 K have successfully been synthesized via the co-intercalation of lithium and ethylenediamine or hexamethylenediamine into 1T-TiSe$_2$. Moreover, it has been found that both intercalation compounds of Li$_x$TiSe$_2$ and (C$_2$H$_8$N$_2$)$_y$TiSe$_2$ also show superconductivity with $T_{\rm c}$ = 2.4 K and 2.8 K, respectively. These results indicate that both the electron doping due to the intercalation of lithium and the expansion of the interlayer spacing b…
We present a new way to enhance the electron-phonon coupling constant and the critical superconducting temperature of graphene, significantly beyond all reported values. Using density functional theory, we explore the application effects of the tensile biaxial strain on the lithium intercalated graphene. Both effects together, the presence of adatom and the strain, trigger enhancement of critical temperature, up to 300\%, compared to non-strained lithium intercalated graphene.
The discovery of ThCr2Si2-type AxFe2-ySe2 (A = K, Rb, Cs and Tl) with Tc ~ 30K make much progress in iron-based superconducting field, but their multiple-phase separations are disadvantageous for understanding the origin. On the other hand, for small alkali metals, studies on (Li,Na)FeCu(S,Se)2 and NaFe2-δS2 shows that these compounds possess CaAl2Si2-type structure, implying that ThCr2Si2-type structure is unstable for small alkali-metal intercalated FeSe under high-temperature. Here we report a new intercalate Na0.65(1)Fe1.93(1)Se2 with Tc ~ 37 K, synthesized by low-temperature ammonothermal…
Superconductivity and charge density wave (CDW) appear in the phase diagram of a variety of materials including the high - $T$$_c$ cuprate family and many transition metal dichalcogenides (TMDs). Their interplay may give rise to exotic quantum phenomena. Here, we show that superconducting arrays can spontaneously form in TiSe$_2$ - a TMD with coexisting superconductivity and CDW - after lithium ion intercalation. We induce a superconducting dome in the phase diagram of Li$_x$TiSe$_2$ by using the ionic solid-state gating technique. Around optimal doping, we observe magnetoresistance oscillatio…
Molecule-intercalated van der Waals Josephson junctions uncover complex multiband superconductivity
CIC nanoGUNE（CIC纳米技术研究中心）；Centro de Física de Materiales – Materials Physics Center (CFM-MPC) CSIC-EHU（材料物理中心（CFM-MPC）西班牙国家研究委员会-巴斯克大学）；Departamento de Polímeros y Materiales Avanzados: Física, Química y Tecnología, Facultad de Químicas (EHU)（巴斯克大学化学学院先进聚合物与材料系：物理、化学与技术）；Instituto de Nanociencia y Materiales de Aragón (INMA) CSIC-Universidad de Zaragoza（阿拉贡纳米科学与材料研究所（INMA）西班牙国家研究委员会-萨拉戈萨大学）；Laboratorio de Microscopías Avanzadas (LMA), Universidad de Zaragoza（萨拉戈萨大学高级显微镜实验室）；Ikerbasque, Basque Foundation for Science（伊克尔巴斯科科学基金会）
