Electronic structure study of the charge-density-wave Kondo lattice CeTe_(3)

The behaviors of f electrons are crucial for understanding the rich phase diagrams and ground-state properties of heavy fermion(HF)systems.The complicated interactions between f electrons and conduction electrons largely enrich the basic properties of HF compounds.Here the electronic structure,especially the f-electron character,of the charge-density-wave(CDW)Kondo lattice compound CeTe_(3)has been studied by high-resolution angle-resolved photoemission spectroscopy.A weakly dispersive quasiparticle band near the Fermi level has been observed directly,indicating hybridization between f electrons and conduction electrons.Temperature-dependent measurements confirm the localized to itinerant transition of f electrons as the temperature decreases.Furthermore,an energy gap formed by one conduction band at low temperature is gradually closed with increasing temperature,which probably originates from the CDW transition at extremely high temperature.Additionally,orbital information of different electrons has also been acquired with different photon energies and polarizations,which indicates the anisotropy and diverse symmetries of the orbitals.Our results may help understand the complicated f-electron behaviors when considering its interaction with other electrons/photons in CeTe_(3)and other related compounds.

Two-coupled structural modulations in charge-density-wave state of SrPt_2As_2 superconductor

Transmission electron microscopy （TEM） study of SrPt2As2 reveals two incommensurate modulations appearing in the charge-density-wave （CDW） state below TCDW ≈ 470 K. These two structural modulations can be well explained in terms of condensations of two-coupled phonon modes with wave vectors of q1=0.62a＊ on the a＊-b＊ plane and q2 = 0.23a＊ on the a＊-c＊ plane. The atomic displacements occur along the b-axis direction for q1 and along the c-axis direction for q2, respectively. Moreover, the correlation between ql and q2 can be generally written as q1 = （q2 ＋ a＊）/2 in the CDW state, suggesting the presence of essential coupling between q1 and q2. A small fraction of Ir doping on the Pt site in Sr（Pt1-xIrx）2As2 （x ≤ 0.06） could moderately change these CDW modulations and also affect their superconductivities.

Anisotropic Transport and Magnetic Properties of Charge-Density-Wave Materials RSeTe2（R=La,Ce,Pr,Nd）

Single crystals of RSeTe2 （R =La, Ce, Pr, Nd） are synthesized using LiC1/RbCI flux. Transport and magnetic properties in the directions parallel and perpendicular to the a-c plane are investigated. We find that the resistivity anisotropy P⊥/P∥ lies in the range 486-615 for different compounds at 2K, indicating the highly two-dimensional character. In both the orientations, the charge-density-wave transitions start near Tcow = 284（3）K, 316（3）K, 359（3）K for NdSeTe2, PrSeTe2, CeSeTe2, respectively, with a considerable increase in dc resistivity. While for LaSeTe2, no obvious resistivity anomaly is observed up to 380K. The value of TCDW increases monotonically with the increasing lattice parameters. Below TCDW, slight anomalies can be observed in NdSeTe2, PrSeTe2 and CeSeTe2 with onset temperature at 193（3）K, 161（3）K, 108（3）K, respectively, decreasing as lattice parameters increase. Magnetic susceptibility measurements show that the valence state of rare earth ions are trivalenee in these compounds. Antiferromagnetie-type magnetic order is formed in CeSeTe2 at 2.1 K, while no magnetic transition is observed in PrSeTe2 and NdSeTe2 down to 1.8 K.

31P Nuclear Magnetic Resonance of Charge-Density-Wave Transition in a Single Crystal of RuP

We perform 31p nuclear magnetic resonance （NMR） measurements on a single crystal of RuP. The anomalies in resistivity at about TA = 270 K and TB = 330 K indicate that two phase transitions occur. The line shape of alp NMR spectra in different temperature ranges is attributed to the charge density distribution. The Knight shift and spin-lattice relaxation rate 1/T1T are measured from 1OK to 30OK. At about TA = 270K, they both decrease abruptly with the temperature reduction, which reveals the gap-opening behavior. Well below TA, they act like the case of normal metal. Charge-density-wave phase transition is proposed to interpret the transition occurring at about TA.

Multiband nodeless superconductivity near the charge-density-wave quantum critical point in ZrTe(3-x)Sex

It was found that selenium doping can suppress the charge-density-wave（CDW） order and induce bulk superconductivity in ZrTe3. The observed superconducting dome suggests the existence of a CDW quantum critical point（QCP） in ZrTe3-xSex near x ≈ 0.04. To elucidate the superconducting state near the CDW QCP, we measure the thermal conductivity of two ZrTe（3-x）Sex single crystals（x = 0.044 and 0.051） down to 80 m K. For both samples, the residual linear term κ0/T at zero field is negligible, which is a clear evidence for nodeless superconducting gap. Furthermore, the field dependence of κ0/T manifests a multigap behavior. These results demonstrate multiple nodeless superconducting gaps in ZrTe（3-x）Sex,which indicates conventional superconductivity despite of the existence of a CDW QCP.

Preparation of Polycrystalline Singe-phase K0.3MoO3 by Hot Isostatic Pressing Sintering

Nearly single-phase and polycrystalline charge-density-wave compound K0.3MoO3 have been prepared by using a simple method. In this work, K2CO3 and MoOs were used as starting materials and reacted by hot isostatic pressing （HIP） sintering. The product is nearly single phase K0.3MoO3 determined by X-ray powder diffraction （XRD） and energy dispersive spectroscopy （EDS）. Measurement of temperature dependence of resistivity reveals that the transport property of polycrystalline K0.3MoO3 obviously differs from that of single crystal due to the grain boundaries and the anisotropic structure in this kind of compound.

Pressure tuning of the anomalous Hall effect in the kagome superconductor CsV_(3)Sb_(5)

Controlling the anomalous Hall effect(AHE)inspires potential applications of quantum materials in the next generation of electronics.The recently discovered quasi-2D kagome superconductor CsV_(3)Sb_(5) exhibits large AHE accompanying with the charge-density-wave(CDW)order which provides us an ideal platform to study the interplay among nontrivial band topology,CDW,and unconventional superconductivity.Here,we systematically investigated the pressure effect of the AHE in CsV_(3)Sb_(5).Our high-pressure transport measurements confirm the concurrence of AHE and CDW in the compressed CsV_(3)Sb_(5).Remarkably,distinct from the negative AHE at ambient pressure,a positive anomalous Hall resistivity sets in below 35 K with pressure around 0.75 GPa,which can be attributed to the Fermi surface reconstruction and/or Fermi energy shift in the new CDW phase under pressure.Our work indicates that the anomalous Hall effect in CsV_(3)Sb_(5) is tunable and highly related to the band structure.

Superconductivity in CuIr_(2-x)Al_(x)Te_(4) telluride chalcogenides

The relationship between charge-density-wave(CDW) and superconductivity(SC), two vital physical phases in condensed matter physics, has always been the focus of scientists’ research over the past decades. Motivated by this research hotspot, we systematically studied the physical properties of the layered telluride chalcogenide superconductors CuIr_(2-x)Al_(x)Te_(4)(0 ≤x≤ 0.2). Through the resistance and magnetization measurements, we found that the CDW order was destroyed by a small amount of Al doping. Meanwhile, the superconducting transition temperature(T_(c)) kept changing with the change of doping amount and rose towards the maximum value of 2.75 K when x = 0.075. The value of normalized specific heat jump(△C/γT_(c)) for the highest T_(c) sample CuIr_(2-x)Al_(x)Te_(4)was 1.53, which was larger than the BCS value of 1.43 and showed the bulk superconducting nature. In order to clearly show the relationship between SC and CDW states,we propose a phase diagram of T_(c) vs. doping content.

Tri-hexagonal charge order in kagome metal CsV_(3)Sb_(5) revealed by (121)Sb nuclear quadrupole resonance

We report ^(121)Sb nuclear quadrupole resonance(NQR)measurements on kagome superconductor CsV_(3)Sb_(5) with Tc=2.5 K.^(121)Sb NQR spectra split after a charge density wave(CDW)transition at 94 K,which demonstrates a commensurate CDW state.The coexistence of the high temperature phase and the CDW phase between 91 K and 94 K manifests that it is a first order phase transition.The CDW order exhibits tri-hexagonal deformation with a lateral shift between the adjacent kagome layers,which is consistent with 2×2×2 superlattice modulation.The superconducting state coexists with CDW order and shows a conventional s-wave behavior in the bulk state.

Evidence for charge and spin density waves in single crystals of La_(3)Ni_(2)O_(7) and La_(3)Ni_(2)O_(6)

Charge and spin orders are intimately related to superconductivity in copper oxide superconductors.Elucidation of the competing orders in various nickel oxide compounds is crucial,given the fact that superconductivity has been discovered in Nd_(0.8)Sr_(0.2)NiO_(2)films.Herein,we report structural,electronic transport,magnetic,and thermodynamic characterizations of single crystals of La_(3)Ni_(2)O_(7)and La_(3)Ni_(2)O_(6).La_(3)Ni_(2)O_(7)is metallic with mixed Ni^(2+)and Ni^(3+)valent states.Resistivity measurements yield two transition-like kinks at~110 and 153 K.The kink at 153 K is further revealed from magnetization and specific heat measurements,indicative of the formation of charge and spin density waves.La_(3)Ni_(2)O_(6)single crystals obtained from the topochemical reduction of La_(3)Ni_(2)O_(7)are insulating and show an anomaly at~176 K on magnetic susceptibility.The transition-like behaviors of La_(3)Ni_(2)O_(7)and La_(3)Ni_(2)O_(6)are analogous to those observed in La_(4)Ni_(3)O_(10) and La_(4)Ni_(3)O_(8),suggesting that charge and spin density waves are a common feature in the ternary La-Ni-O system with mixed-valent states of nickel.

Charge density wave transition in Na_2Ti_2Sb_2O probed by^(23)Na NMR

Herein we investigated the electronic properties of layered transition-metal oxides NazTi2Sb2O by 23Na nuclear magnetic reso- nance （NMR） measurement. The resistivity, susceptibility and specific heat measurements show a phase transition at approxi- mately 114 K （TA）. No splitting or broadening in the central line of 23Na NMR spectra is observed below and above the transi- tion temperature indicating no internal field being detected. The spin-lattice relaxation rate divided by T （I/T1T） shows a sharp drop at about 110 K which suggests a gap opening behavior. Below the phase transition temperature zone, I/T1T shows Fermi liquid behavior but with much smaller value indicating the loss of large part of electronic density of states （DOS） because of the gap. No signature of the enhancement of spin fluctuations or magnetic order is found with the decreasing temperature. These results suggest a commensurate charge-density-wave （CDW） phase transition occurring.